Ok, I think I have finally done enough of my own research, and I need some thoughts from people who have had more experience than I have. Here is what is going to stay in the car:

327 .03" over, stock bottom end, th350 shift kit, 3.73 gears and posi, street tires, engine accessories on pulleys are flex fan and alternator, HEI ignition, headers & exhaust, slapper bars

I am only looking to do a shortblock buildup from what I have, so here are the parts:

*Vortec 060 heads from Scoggin Dickey, assembled with .55" lift upgrades already (1.5 rockers)

*EDELBROCK rpm air gap manifold
*COMP XE274H
*2200-2600 B&M stall converter
*Edelbrock 600CFM carb
This totals out to (minus the carb) 1440 dollars, including all gaskets, lubricants, bolts, spark plugs etc.

If I forgo the vortec heads and go with pro-topline aluminum or trick flow, (64cc 180cc) the price jumps to 1860, because the vortecs come as a package deal (much cheaper). Would there be much benefit in running either one of these heads over the vortecs?

All in all, my goal is to be ASSURED(ASSURED ASSURED) 12 second timeslips on street tires, but I really am trying to avoid the 2000 dollar barrier. I have thought of things I could do like 1.6 rockers (250 bucks) or running an electric fan, but would those be necessesary or beneficial? I just dont want to spend money where I dont have to, if you get my drift. Am I in over my head or am I close and within budget? Well thanks a lot in advance, I hope I find some answers. Thanks

I wouldn't bet money on twelves especially with street tires. Sounds more like solid thirteens.

sounds more like a mid to low 13 second car, which usually means high 13 car with street tires. IMO a 327 won't cut it even though many will disagree, I would maybe go with the vortecs since the trickflows have a much larger port volume which aint' gonna help much with that small engine. definetly woulnd't go with the protoplines, every professional head person i have talked with said their flow numbers were totally bogus, have heard good things about the trickflows. if you plan on building a bigger engine in the future go with the trickflows, otherwise get the vortecs! that combo seems pretty mild, don't think you will be in the twelves but it will be fun to drive. just to let you know my friend has a 2000WS6, with gears, chip, exhaust, blah, blah, blah, his car seems pretty fast, doesn't get beat a whole lot, even beats stock new vettes, his car only runs a 13 flat.
p.s.
not to sound like an ***, but i hate to say, who in the world can guarantee you that your car will run a certain time???? I wouldn't count on your car going a certain speed based on peoples opinions. Hope the best for you though graemlins/beers.gif

I have to agree with Codi and Jim. I really don't think anyone can GUARANTEE a particular time slip unless you have unlimited funds and in my opinion, $1,500 won't do it. I would guess mid to high 13's with the set-up you outlined.

check my signature it is very close to your planned combo. Same heads, had local shop clearance the guides. Same carb but an rpm not air gap. I only made two passes so that i would have a point of reference for the new 383 going in. I ran a 13.6 @ 103 with a 1.77 60 ft and a 13.7 @101 with a 1.69 60 ft. I hit the rev limiter(6000) the second time, guess i got a little more confident :eek: . This was on 40 series Z rated tires with no warm up burnout. Looks like everybody here is pretty darn accurate with their guesses. I don't think you will be able to hit 12's without some major 0-60 foot times and slicks, but i am no expert good luck. Cody i am surprised to hear about the toplines not flowing as advertised i think another member here found they actually outflowed their advertised numbers.

Here's what I dont get then, if this combo was on a 350, people would say that Id be knocking at the door of 12.99, but with a 327, everything just seems to get so much more impossible...is it really that much harder to do with a 327, or what? Why is it that supposedly a 350 block can do everything? :350envy: It just seems a little weird to me that an engine with only 23ci more can do "so many amazing things."

Steve, maybe I just have a little more faith than other people, but IMO with a little adj. to your combo it can be done....but I wouldn't bet on STREET tires i.e. regular radials.

I would back off the cam to the 268 IMO. The 274 is going to be a pretty stout cam in a 327. The Vortec idea is right on the money. The rest will depend on the efficiency of your exhaust and most importantly your patience and tuning skills. IMO

I've heard nothing but good things about the Pro Toplines myself. I was very impressed with the fit and finish of them when I got mine. The only independent flow bench test I know of showed that they beat their advertized numbers across the board.

Hey ratmotr! Hows the bb coming?
Thanks for the advice, and support ;) .

Is there anyone out there who has done what I want to do?

Well, theres no point in arguing with years of experience. I guess Ill just have to see what this thing can do, and shoot for 13's on street tires. Its not so much that I can't afford slicks, but I want a 12 second car because of horsepower, and not because of traction.

Originally posted by sik68:
Here's what I dont get then, if this combo was on a 350, people would say that Id be knocking at the door of 12.99, but with a 327, everything just seems to get so much more impossible...is it really that much harder to do with a 327, or what? Why is it that supposedly a 350 block can do everything? :350envy: It just seems a little weird to me that an engine with only 23ci more can do "so many amazing things." That is a good point you raise. IMO 23 cubes is worth another 30 HP and 30 FT/LBS in a stout combo like yours. 30HP & 30 FT/LBS is definately worth some ET. You have to really use some gear and stall with a 327 to "make up" for it being a smaller engine --- and that doesn't appear to be what you are doing.

I wouldn't necessarily think that this exact combo with a 355 would be 12's either. A 383 yes, but a 355 no. I ran a very similar combo (Sportsman II heads and Comp 280H cam) in a 355 before and I could only get 13.3's @ 104 MPH on street tires. I MIGHT have squeeked out a 12.99999 with slicks and a tail wind. Maybe.

I'm not dogging your combo at all, it looks really streetable and well thought out. Especially so considering your budget - speed is expensive, ain't it ;) Just don't set your expectations too high and enjoy your ride - honest 13's for a street car are fast no matter what anyone says.

I agree with most here, your combo, being street drivable, is worthy of 13 sec. times. As Eric68 suggested, maybe with a tailwind, slicks, and a heavy cam, it'd be a 12.9XX ride. Doing some figuring, your est weight, 3100#, and 95 mph, your rwhp is estimated 207. Gong the same weight, you would need 300-325 rwhp to acquire 12.6XX.

But, as mentioned, it is expensive. Rule of Thumb: For every second to go faster will cost $2K each, maybe, if not more.

If money is no object, there is a guy in Kansas, runs a Super Stock, SS/NA '56 Chev wagon. That means, it's a 265 CID. He has a 5.13 gear and a 8K convertor. He currently runs 11.50's on 9 inch slicks. Definitely has my respect. graemlins/thumbsup.gif

I was able to run real close to your goals with almost nothing, in the way of money, when my car was in SB trim. Here's how it was set up;

350+.060
STOCK 441 casting heads
9.8 comp.
CC xe 284
750 DP
Team G intake
1.5 roller tips
1.75 pri. headers
2.5 in. american thunder system
TCI street fighter 3000+
TH400
3.73 posi
slapper bars
26-10.5 et streets

My car was all steel, full tail pipes etc. My best times were, 13.01@104.3 with a best of 1.78 60 ft. 1.80 being my average. I only took it to Sac Raceway 3 times.

Looking at my combo it is obvious that it was mismatched. The intake, headers, cam, and carb were all too big. I was trying to get the car going and threw together a used, wornout, junkyard motor and went and had some fun! I only had $500 in this motor! :D All used parts. I could have gotten it to go 12.90's but tore it apart and began the BB swap.

I think if you stay conservative and focus on building torque you might be suprised what you will accomplish.

Here is a table of how heads flow! You might want to bookmark this page if you are going to buy heads soon. Makes me want to skip the vortecs and go with something that will breathe a little better. Enjoy!

http://users.erols.com/srweiss/tablehdc.htm#Chevy

IMO, since you're on a tight budget, I would go with the vortecs, and take the extra money, and put it into some slicks, or drag radials or something. If you want a 12sec ET, street tires arent going to do it for you. I have a 350 with more cam, more stall, and 4.11s, blah blah blah...and I don't think I'll ever get into the 12s on street tires, desite tuning. If you want a lot of bang for your buck, then go the nitrous route. But you'll definatly need slicks. Like the other guys said a 13sec car is fast, and respectable on the street, especially with a 327 and a friendly gear.
And if you've never driven a 13sec car, trust me you'll love it. ;)

If you want a 327 to run your gonna have to spin it cause there isnt gobs of torque with a 3.25 stroke crank. A 327 is a legitimate 10,000 rpm motor with good internals. But thats really the only way to make a 327 run its best is to buzz it. You can do it but its going to take more cam more gear and its gonna have to see some rpm {not 10,000 but more than these 383's and 400's usually doo} Dont build a motor for what its not. I doubt anyone would build the long stroke 496 to spin 10,000 so why build a 327 for torque. Just my opinion though

I dont believe that to meet the goal of a 12 second combo that you have to really spin it, more so then a 350 or 383, yes, but 10,000 rpms no way.
the effect of "10,000rpms" varies becuase of piston speed/stroke lenght, but 10,000rpms on a valvetrain is still 10,000rpms.

DO YOU DRIVE THE CAR EVERYDAY??

If not consider a solid flat tappet cam, such as the comp xe solid line.

Why are you spending the extra money for an "Air gap" intake when an RPM will do the same and cost less?
If your goals are as said build a solid combo and tweak from there, things like 1.6 rockers, and "air-gap" intakes, and such are something for tweaking every thousand out of the combo, and in many cases net NOTHING.
What my point is, buy what you need.

I know the air gap is a waste of money by itself, but scoggin dickey offers it as part of a package deal that comes with the vortecs. As for the 1.6 rockers, Ive seen/read that just a swap to a 1.6 ratio will net anywhere from 10-20hp. I cant say whether it's true for certain, but there have been plenty of tests that all show about the same results.

Sik68,


As a fellow 327 owner, I'm rootin' for ya! As you have seen, the general consensus is that your combo won't make it into the 12's.

However, all is not lost IMO. Your combo should be solidly into the 13's and be a blast to drive on the street.

With your combo, you may be able to suprise :eek: a few people with what a "little 327" can do! :D

Good luck with your combo.

Mark P.

IMO If you are going to run Vortec heads a swap to 1.6 rockers is the last thing you need. Vortecs are limited to how much lift you can run. Stock they are at about .460" max, if you use +.050" retainer locks and then shim the springs up .050" to maintain correct installed height you can get away with a .500" lift cam. Definately check retainer to guide clearance if you are going to push the limits.

Here's an idea for a cam that I've always thought would work real nice in a 327 with camel hump or Vortec heads. Crower #00321 - 274SF. Advertised duration 274*I/282*E, duration @ 050 242*I/248*E, lift .482"I/.504"E, LSA 114*. This cam would make a wide power band like 2400 - 6400 RPM.

I think everything looks well thought out except for the convertor. Speaking from experience, my 350 w/vortec heads and a XE268 cam would be a better match for the convertor you selected. With the shorter stroke and larger XE274, I think something around 3000 stall would be a better match. The XE268 comes on hard around 2500 rpms in a 350.

FWIW, I think 12.99's are possible with the right convertor. I know of a nova similar to mine that runs a 327 w/1.94 441 heads, an old tech 350hp 327 hydraulic cam, 2800 stall, and 3.90's...with 26x10.5 et streets it runs 13.3's. With your better heads, lighter weight, and some traction, I think very high 12's are possible.

Did I miss the compression you are running? :confused:

My freeway rpm is 3400@65mph on a 26" tire. This car is only a twice a week cruiser, but it does see freeway miles. Do you think I can get away with more stall, like a 3000 stall?

No problem at all.

Did I miss something here? The first car I ever owned was a 67 SS/RS 350 4speed 295 HP stock with 3:73 gears and I could get the low 13's on BS street tires(G-60-15 Road Huggers for those that remember that numbering system) back in the early 70's.

OK, Im coming at you guys again with a more radical setup this time, albeit a little more money

327 .030" over, 9.5:1 (with camel humps)
Pro Topline 180cc 64cc iron heads
Comp Magnum 282S (yes solid) (1.52 roller rockers)
Edelbrock Torker II intake
600cfm carb

TH350 shift kit
3000B&M stall
3.73 gears and posi
BFG radial tires
Car is 3200 pounds

Important: Will my cast bottom end hold up?

What do you think guys, 12's on street tires?

Here are the numbers I got from desktop dyno:
www.geocities.com/capitolstrokers/327singleplane (http://www.geocities.com/capitolstrokers/327singleplane.jpg)

Here are my current numbers on my car (just for comparison purposes) (If the links dont work, copy and paste into your brower)
www.geocities.com/capitolstrokers/327original (http://www.geocities.com/capitolstrokers/327original)

Now I know I shouldn't depend on Desktop Dyno for all the answers, but it sure has seemed accurate on all of the testing I have done in the last couple days. I cant believe all the power!! Torque isnt lacking too much either, as I only lose 26ft lbs at 2500 rpm from my setup right now!

I wont be driving the car everyday either, like twice a week, but with it being not so radical, I could couldn't I? Any suggestions or wrong paths I have taken. Again, the bottom end on my car is worrying me. Will it be OK or should I tone it down somewhere?

[ 04-17-2003, 12:24 AM: Message edited by: sik68 ]

Help? I guess people are graemlins/boring.gif

Well that is a good combo, I think you need better cylinder heads to make a solid 12 sec. combo. Of the 4 independent tests I have seen for the Pro Topline heads not one has even come close to their 'claims.' I had a set of 200cc that I eventually returned that only got 237/165cfms @.500 Lift, thats no better then a set of vortecs. I've also seen another test that got a little more then me(these were assembled with actualy Pro Topline valves, mine were assembled probably with cheapo take offs from Powerhouse). I believe this guy got 247/170cfms @.500 Lift but again the lower lift #s were off 20-30cfms from Pro Toplines 'claims.' I emailed a rep. from Pro Topline about this and he just ignored me.

I'd think you would be better off with the proven vortecs, I'm just not sold on these Pro Toplines yet. But againg I'm not sure if the vortecs would get you a solid 12 sec. run....I'd be looking into a set of 180cc AFR Heads...expensive yes, but they will flow what they say and I believe it will be a 12 sec. car no problem then.

I think that would work. The cast bottom end would probably be OK for a while, but keep in mind that the higher you rev it and the more power you put to it the more likely you are to break a piston, spin a bearing, etc. A stock 327 bottom is pretty solid for a few extra RPM, just be aware your pushing it a little. I think you'll be fine personally.

We put this same combo together in my friends 327. It used to run 13.2's @ 102-103 MPH with the old XE 284 cam and 200cc Dart Iron Eagle heads. It "feels" faster with the ProTopline 200cc heads and 282s cam, we just haven't had it to the track yet this season. He has small domed forged pistons that make about 10.3:1 compression.

More compression would be nice for your combo - you might consider milling your heads if the stock pistons are flat tops. Flat tops make about 9.5:1 with 64cc heads in a 327, with aluminum heads and the 282s a little over 10:1 would be nice --- 10.5:1 ideal IMO.

Allgo, thanks for the Topline warning. I am concerned about the legitimacy of their flow numbers as well. Ill try to find some more info on them. If it turns out to be an overwhelming "dont buy em", I might buy a set of sportsmanII's and have some port work done on them.

Thanks Eric for the info on your friends car! Im sure you must have some idea about the Pro Topline numbers as well, do you think they are legit?

Anyone else have any Pro Topline Hurrah's or Nay's? Maybe Ill do a search.

Edit: How will milling the heads affect engine assembly geometry? Different pushrods, etc? Also, what is a typical milling height?

When we bought those 200cc ProToplines I visually compared them to Dart Pro1's and Edelbrock Performer RPM's. All bare castings. the ProToplines had the best looking ports by far.

They came out of the box with blended bowls - looked almost like CNC work to me. The valve guide area is nice and narrow (tear drop shaped like it should look after being ported). The intake ports are tall and narrow which helps with flow past the pushrods. The port floor is raised and the short turn radius is a long gentle curve. All these things points toward a good flowing port --- on top of that a member here had them flowed out of the box and they BEAT advertised numbers on the exhaust side.

I assembled these 200cc heads from bare castings. There was some variation in pocket deptht so I had to use a few different thickness shims to get the exact installed height I wanted. The spark plugs are relocated slightly which is a PITA when using Hooker Competition headers for 1st gen Camaro. The taller and narrower intake ports require a taller gasket or they won't seal - we used a medium race port Felpro # 1206. Other than that the fit and quality appears to be very good.

I personally believe the ProTopline flow numbers are legit. All the bad-mouthing I've heard about them has been from builders or speed shops that aren't making as much money selling low priced ProToplines as they do on other overpriced heads. They pull the same crap with trick Flows too - heard lots of bs from builders about valve guides etc --- I've run the TF's for 2-1/2 years and have been very satified.

ps. Milling heads significantly will probably require shorter pushrods. Go to the ProTopline site to find out exactly how much cutting the head chamges the volume. I think they give you cc's per .010" or something like that.

Eric68,

WOW! Thanks for spending your time answering my "measly" questions smile.gif . I think its real cool of you to spend time sharing your experience with everyone here. You made my day! Thanks again.


Steven graemlins/hurray.gif

While the visual inspections of the Pro Topline heads look good, the #s just don't back them up. I flow tested these heads and the #s were way off, Chevy High Performance flow tested these heads(235ccs) and again, numbers way off. A member at chevytalk.com forums who owns a shop flow tested the 200cc and 235cc and both tests were 20-25cfms off. After seeing my bad results a member at nastyz28.com toke the 235ccs off his car, tested them and got really low numbers(like 245cfms @.500 Lift-Similiar to what chevy high performance got). This is the first time I have ever heard of anyone actually getting the #s that they claim for their heads.

I don't want it to sound like I am saying these heads suck, they are just not in the AFR 'league' that Pro would have you believe. I would compare them more to Dart Iron Eagles.

Think of it this way...have you heard of anyone ever questioned the legitamacy of AFR's flow numbers? I haven't and thats for a reason; their #s are legite. If Pro Topline's flowed as good as they claimed do you really think there would be soo many people that have flow tested these heads and gotten way off from their numbers? Just something to think about.

I don't think these heads would be a bad choice, just don't think by buying them your getting AFRs for $300 less. It may even be possible to squeeze out a 12 sec. run with the Pro Toplines(maybe, with a finely tuned combo) but I bet ya money it will be a whole, whole lot easier with the AFRs.

PS-I know this is probably not something that you want to hear but I just want you to have all the information possibly before putting your cash down....I didn't and ended up making a poor decision but luckily I was able to return the heads and get my cash back.

Allshow, I definately appreciate your experience with these heads. I thought at first maybe it was just heresay that you were getting your information from, but now that you tell me your personal experience, I will definately take it more to heart. Now I dont know what to think. I guess it is a gamble for me to go with the toplines, and I will proably be happier with the AFR heads anyways (once I get over the price difference). Thanks a lot. I still have some financial barriers to get over, but this will hopefully be a summer project that will be worth it.

With everyone's help on this site, I feel much more confident that this summer's project will be great, full of burnouts, and full of 12 second passes smile.gif .

Steven

Heard the same thing about the toplines graemlins/sad.gif from more than one source, as i stated earlier, I wouldn't use them, although a couple of people on this site have them and like them, i just have heard the same exact things about them many times, plus if they were so good i think more people would recongnize them, especially with their low prices, remember most manufactures do exagerate their flow numbers a little, or just give the best possible numbers, i.e. using better than stock valves and so on. but who is keeping them from posting fake numbers??? I think the old saying takes affect here " if it sounds too good to be true, it probably is". I have also heard bad things about the trickflows but I have seen many proven combos with them and believe they are decent heads, haven't seen many people with the toplines that have proven combos.

go with what you feel is right for you as far as heads. that said, my machinist builds a buttload of roundy round motors and has had excellent results w/ pro topline cast heads. i am running aluminum 220cc pro's on my 406 and they work killer. i actually went with them on his suggestion that they might be worth a look. he is actually a racing buddy as well, so when he got them, he flowed them on his superflow flowbench, for me and his own personal data, and the intake was as good low and better up high than advertised, and the exhaust outflowed the advertised numbers all the way, and by 15 cfm peak. this was a totally unbiased test, and had they sucked, he would have sent them back for me. they also, as eric stated are thier own design port wise, and are very nice as cast, and they seem to be cnc bowl blended from factory. in fact he built another motor using the same heads as mine, after the excellent results, and once again repeated the excellent flow numbers as mine had. as an example, on this same bench, my buddy's 215 dart pro 1's were flowed and were down 15 to 20 cfm from mine, basically across the board. of course these heads (my 220's) likely flow thier best over 250-300 cfm, mine flowed the same at 600 (mine were only flowed to 600, thats all the cam i have) as they advertised at 700, on the intake, and outflowed the 700 exhaust numbers by 15cfm, again at 600. in fact, my machinist buddy said the only other heads he's seen repeat numbers like the pro heads are the afr's, which he does think are one the best heads, and also highly reccomends them. but, if you can find a comparable set afr's for a scant 300$ more than the pro heads, i'd be surprised, and jump on them immediately. for my set up, the similar afr set up would have been 500+ more than what i paid. and as eric said (i agree 100% with his comments on this, btw) they seem to be somewhat finnicky to set up spring installed height, and seem to be best suited to thier own intake gasket. the chambers also seem best suited to a flattop piston (or dished). again, this is my experience with them, and they work absoluteley killer on my 406, and i would not even hesitate to buy another set. good luck with your choice graemlins/thumbsup.gif

I think there's a trend in the posts here:

1 Anti Topline
1 Pro Topline (pun intended)
1 Anti Topline
1 Pro Topline

etc... smile.gif

Why dont magazines test these things? I wanna go see a flow test myself now. Well thanks for the continued help guys. I cant say I feel any better, but it is clear that there must be some inconsistency on Pro Topline's end as to the flow numbers. I wouldn't mind if they were a couple digits off, but some are saying 15 under some are saying 10 over.

Assembled Iron Topline $843
Assembled AFR $1250 (wait time 6 weeks)

what to do what to do.

Edit: for the sake of argument, if I went with the AFR's and with the combo I listed on page 2, will I be in the 12's on street tires?

For those that say they have got bad numbers from the ProToplines, could you please post your numbers. I would be interested in seeing lift vs. cfm --- good or bad. and also the test spec - 25 or 28" water --- and whether a test pipe was used on the exhaust. I've seen enough heads to be able to tell when a port is decent or not, the Pro Toplines look pretty darn good.

If you are sure you don't ever want slicks, you need to under stall your combo. Otherwise you will not even come close to hooking at the track. I think this will get you 12's on street tires on a perfect day:

Xtreme solid 274, 274/280 236/240 @ .050 .501/.510 lift. 110 ls
Heads, see below.
Performer RPM intake.
Holley 650, ditch the Edelbrock carb.
If you need rockers, buy 1.6's, if you have 1.5's use em.
1 5/8 headers, 2.5" exhaust.
Rev to 6500, might go to 10,000... not.

Head flow numbers don't tell the whole story, take em with a grain of salt.

My 1st choice in heads would be Edelbrock performer RPM's. I run these heads now and I know they would be a great 327 head. A lot of people bash these heads cause of flow numbers and small runners, but I just waive as I pass.

As long as the Pro Topline 180's have a good bowl blend, I would use them instead of Vortecs, only because they need work for bigger cams. Studs, springs. If that Vortec package deal comes with upgraded springs and screw in studs, I would buy that on a budget.

If you don't do anything else, loose the flex fan. It costs .15-.2. Use a regular duty clutch fan or an electric.

I agree this combo will work best with a 3000 or more converter with slicks. With regular street radials I would run 25-2600 stall.

Eric- Heres a link to the results of my test: #s shown are 28" and no pipe on exhaust.
http://www.nastyz28.com/ubb/Forum8/HTML/004939.html

Again I think a small problem with these heads is the big valves(2.08s) that I believe were shrouded in the chamber....I know of someone who flowed these 200cc heads with 2.02 valves(if you search at the chevytalk.com forums in the Performance section you will find it...his username is sryplates or something like that)and got nearly the same #s of me under .500 lift but got 247/170 at .500 Lift.

Heres another link to a member who got his 235ccs tested:
http://www.nastyz28.com/ubb/Forum5/HTML/006424.html

Here's another thought: If you are like me and like Iron heads, why not buy the Pro Toplines, take them to your local head porter and give him the $407 difference to make you a killer set of heads that would probably be better than the AFR's? Or better yet, buy them bare and have your local head porter customize the valves/springs/retainer assembly in addition to the port work.

Allgonoshow. thanks for the link - it explains a lot. You bought your heads from a company that you bash the crap out of in your post, including the 2.08 / 1.6 valves you bought from pro-engine kits.com.

1. The Pro Topline 200cc heads do not use a 2.08 intake valve. They use a 2.02 valve. If you put a 2.08 valve on a seat cut for 2.02 and you have problems --- flow and otherwise.

2. All valves are not created equal. Good valves flow WAY more than cheap valves. Things like a 30* backcut and tuliped heads can make a 25 cfm difference.

3. Yours were flowed at 25" and you "compensated" using a thumbrule - its not that simple. I cannot tell you exactly how to change 25" numbers to 28" numbers but I think there is more to it if you want to be accurate.

4. No test pipe on exhaust when you had yours flowed. A test pipe makes a huge difference on the exhaust and represents how the head would behave with headers on it.

So I stand behind my previous comments about their numbers most likely being good and will add this - if you want to claim the company isn't selling what they say they are, you need to have your act together -------- using THEIR valves, assembled at THEIR factory and test using the SAME jigs and test criteria they do.

ps. Sik68, you are very welcome :D

2 questions I have just come up with, hopefully this thread still gets enough attention...

1) I want to measure my volume between my deck and my pistons. When "filling it up" with the chemistry lab thing, what medium should I use, water? And what do I do with the piston and block afterwards, sponge it out and WD-40 then sponge that out?

2) Here is the casting mark off my heads that I have right now, do you know what they are?
(you may have to copy and paste the link into a brower window if clicking doesnt work)
www.geocities.com/capitolstrokers/headcast.jpg (http://www.geocities.com/capitolstrokers/headcast.jpg)

Sik68,

The easiest way to measure deck volume IMO is to use a feeler gauge --- no liquids necessary. Just rotate the engine so the piston is at TDC, make sure it is ALL the way up. Then lay a straight edge across the cylinder and use your feeler gauge to measure the distance between the top of the piston and your straight edge. That measurement is your deck height.

Then if you want to convert deck height to deck volume use the following formula: (1/2 bore)^2 x deck height = deck volume. Convert to cc by multiplying times 16.39

Example:

(.5 x 4.030)^2 x .025 =

2.015^2 x .025 =

4.060 x .025 = .412 cu in

.412 x 16.39 = 6.75 cc

I've seen a 350 with the same heads and cam run 12.1 on radial tires. 3400lb car. He goes by the name "Pony Killer" on www.thirdgen.org (http://www.thirdgen.org)

Chris88z, whoa thanks a lot! That seriously gets my juices flowing! I guess Ill still keep my expectations to high 12's for purposes of not being dissapointed, but it does inspire me. Ill check the car out.

Eric, thanks for the info. I just thought maybe if I had a rather poor piston depth or didn't have flattops(for whatever reason) I might have to go with using a fluid measurement.

Eric- Did you read the other post too from the other member who bought the 235ccs from Summit with the Pro Topline valves(the same ones that are used in Pro Topline claims) and he got really, really bad results...only 245cfms@.500 Lift. And as I said before there was a member at chevytalk.com forums that flow tested the 200cc as assembled by Pro Topline(2.02/1.6 valves) and he got nearly the exact same #s(within 5 cfms) that I did under .500 Lift but at .500 Lift he got a little better...247/170cfms. While these max #s were pretty good, the lower lifts #s are not much better then mildly worked over stock heads.

sik98- If you buy these heads pay the $30 bucks or so to get them flowed, I am willing to bet money you get, at the least, 15-20cfms off their claims.

Of the now 7 flow tests(other then Pro Toplines) I have seen of these heads, 6 have gotten considerably(20cfms+ off) worse numbers....theres got to be something there...its hard to refute 6 different tests from 4 different people(myself, member at chevytalk, chevy high performance, and the other member at nastyz28.com i linked too).

PS-Eric-I also used the correct method to convert the #s to 28". To get the new flow rating you just use the square root of the division of the new pressure drop(28") to the old pressure drop(25"). Since the sqaure root of 28/25 is 1.0583005, I just rounded it to 1.06 and timed the 25" numbers to get 28". Actually the #s in my post are probably 2-3cfms inflated cuase I rounded up. And Powerhouse also cut the valves for the 2.08s (they didn't just put em in the 2.02 seat)-I had the heads checked at the local machine shop to verify this.

I scanned them quickly. The other example I looked at was about 10cfm off which I thought was pretty reasonable. Temperature differences and equipment differences could easily account for that. There were several people that posted in your message that seemed to be more than satisfied with their ProToplines. Keep in mind I DO NOT entirely trust ANYONE'S advertised flow numbers, they tend to be optimistic. ALL of them.

Anyway, regarding your test. You clearly modified your heads and then blamed ProTopline for YOUR poor results. Your fault - not ProTopline's fault.

Larger valves do not always increase flow --- in fact in an SBC larger valves tend to hurt low lift numbers but CAN make up the low lift loss at high lifts if the chamber does not shroud.

I reviewed a LOT of data with my friend at his machine shop where he does porting and flows heads on about every kind of car you can imagine - from Fords to Chevy's to rice burners. He actually graphed a lot of his results and showed me the trends with various heads, porting techniques and valve sizes. He consistently gets better low lift numbers on 64cc Chevy heads with 1.94 intakes, but 2.02's usually make up for it and beat the 2.02's around .300 lift and up. Comparing 2.055's to 2.02's did the same thing with my TFS 23* heads - the 2.055's beat the 2.02 only above .500" lift --- and that was with a top quality back-cut valve with necked down stem.

I'm sure you will get different results with different valve sizes on different heads, but often with very big valves like 2.08's in a small chamber head like the 64cc ProToplines you are going to SERIOUSLY hurt flow unless you do some carefull de-shrouding work in the chamber. I have no doubt that your attempt at going to a large 2.08 valve in a head designed for a 2.02 valve (whether you cut the seats and throat back or not) is the cause of your heads less-than-advertised flow.

I'm not trying to argue, just point out that you are jumping the gun beating on ProTopline for poor flow that resulted from something YOU did.

I did not modify the heads, Powerhouse did and I just had my shop check the heads over to make sure the seats were correctly cut for the 2.08 valve and cleareances were correct, etc. etc.. If you go back to my original posts I even admit that the 2.08s probably hurt flow more then helped(hind sight is 20/20). Again I refer you to the other posts where the heads were assembled with Pro Topline components directly from Pro Topline with the same bad results(mine were a little worse probably due to 2.08s).

And again, as I explained in my other posts, I am not saying these heads suck, and I agree that other people are very satisfied with them, but they are not as good as AFRs. I don't see how you can discredit all these bad results, while I can understand 10-15cfms differences according to the variables in flow testing that you discuss, we are talking nearly 30cfms and more. Have you ever seen anyone with AFRs that got 30cfms off what they claim? I've seen maybe 5 different tests by different people with different operators and different flow benchs and the biggest variance in the #s to what AFR claims was only 7cfms. They gurantee their numbers within 5% for a reason, cause they are confident that the #s you see will be very close to what they say, regardless of the variables you outlined(within reason). Same deal with Dart Iron Eagles....people are very happy with them but they don't flow as good as they claim(but I think they even state that their #s are reflective of a mild bowl work, Pro Topline doesn't).

I emailed technical reps. from Pro Topline about the numbers I got and I also linked to the other people who have gotten the bad numbers. I also emailed as many reps. from Pro Topline as I could find. Suprise, none emailed me back. I made sure they were getting my emails by emailing the same reps from a different address and asking some easy question(ie- why should i buy your heads) and they responded. If they actually think their #s are 100% true why would they not even attempt to defend themselves??

I don't think thier #s are made up, I just think they are reflective of a clean up and some porting(I again emailed a rep. to ask this question but again got no reply). Again I urge you to look at the other link I posted and if you have time go to chevytalk.com and search for flow #s from the user sryplates or soemthing like that and you will see they used the correct components by Pro Topline heads and got the low numbers. Even if you could completly discredit my flow test there are many more that support the results that I got....its hard to discredit them all.

Not trying to attack you or argue just stating what I saw and what many others have too. This is a good post it provides a lot of good information!

PS- What example are you referring to that only got 10cfms off?

You DID modify your heads --- whether it was you personally or Powerhouse that did the work is a matter of symantics. My point is that your heads were modified and that resulted in the flow loss.

I read all those posts and frankly the people who were complaining weren't very convincing to me. They seemed to be the ones who screwed around with their heads and were disappointed with the results or they bought them from some third party builder who stuck their own cheap parts in the heads. Maybe I missed something, I don't know.

Here's a couple more links to threads with independent Flow Bench results on the ProTopline heads. Notice that in neither of these threads have the heads been altered from their designed configuration.

http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=4;t=005700#000003

Here's another one. read the part by Boodlefoof.

http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=4;t=005821#000006

AFR is pretty much the gold standard - I wouldn't doubt for a minute that they make good stuff. But all of us cannot afford to spend $1500 for a set of heads when there are $800 heads out there that flow as good. The $500-$700 difference is money I could spend on a lot of other go-fast parts that will more than make up for 10 or 20 cfm - even pay for porting that will put you way ahead flow wise with cash to spare.

I think I've said my peace ;)

I wouldn't buy the protoplines, have heard WAY too many complaints, from gurus in the actual industry, not local guys! One thing to remember, if you are in CA remember sales tax! about $130 for some small block heads, and they are taking about 5-6 weeks! Eric68 i didn't look at the links but is seems that he is saying that they had stock protoplines from summit not "altered" heads, but you actually looked, so i can't say much on that.

We'll just agree to disagree smile.gif

We need someone with a lot of money to do back to back comparision on an actual dyno!

That was a great example of how two people on this site can disagree without being jerks! I think that there are other that could learn from this post as it was very informative and civil.

Originally posted by AllGoNoShow:
and I agree that other people are very satisfied with them, but they are not as good as AFRs. Who said they are as good as the AFR's?

The real question is are the Toplines a good head for the money.

Comparing them to AFR's doesn't seem like an apples to apples comparison give the cost difference.

There are those of us on a bugdet that would love to have a set of AFR's but just don't have the cash.

What other heads in the same $$$ ballpark would be comparable to the Toplines? Sort of a "budget head shootout" type category.

Originally posted by CFunK:
</font><blockquote>quote:</font><hr />Originally posted by AllGoNoShow:
and I agree that other people are very satisfied with them, but they are not as good as AFRs. Who said they are as good as the AFR's?

The real question is are the Toplines a good head for the money.

Comparing them to AFR's doesn't seem like an apples to apples comparison give the cost difference.
</font>[/QUOTE]I think that if you consider the price difference, and the flow similarity, that there would be no competition and the ProToplines would leave the AFR's in the dust, however, I think that somewhere in the automotive world there has been a discrepancy as to what the actual flow nubmers of the heads are.

Here's what Im gunna do guys:

No matter what 64cc heads I buy, I will have to have them milled by ~3cc to get the compression where I want it on my combo.

I am going with a copper gasket; I wouldnt feel comfortable with running a steel gasket on an unprepped deck to bring the compression up.

So since they will be milled anyways, I figure I will have the heads I buy flow tested, and then pocket ported to bring them up to AFR standards (most likely the toplines if need be). Also, the machine shop I will be working with (I dont know if you have heard of Rex Hutchinson Racing) is a dealer of Pro Toplines as well as AFR's, so I figure that he will be more honest, since there will be a sale either way.

I am actually going to call him tomorrow and discuss some preliminary/general things with him like the Topline/AFR debate. Hopefully I will get a hold of him and Ill fill you all in on the details tomorrow. Im getting thoroughly pumped up, ready to make some serious HP graemlins/hurray.gif

why would you buy some heads and spend extra money to pocket port them? might as well buy the better heads the first time, after spending money to pocket port them,they still might not flow as good and you would have almost as much money in them, have seen way to many people go down that road and wish they had done it right the first time!

OK Sik68, here is another twist to this head debate. Pro now has an even smaller chamber head out. I dont have the catalog in front of me, but I think it was 56cc, so they would not have to be milled, and I believe the AFRs smallest chamber is 68cc(i have not looked at the 180s though) which = alot of milling to get the compression up on your 327, which would make the AFRs even more expensive when you add in the cost of the milling.

This thread has been of intrest to me because I am concidering new heads for my car also, and I can buy the pros VERY cheep at wholesale from my warehouse. I too, like the AFRs, but my warehouae is not a ditributor for ARF and the cost differance is very large when you compair the wholesale cost of the Pros to the over the counter cost of the AFRs.

I also want to throw one more log into the fire. Dont flame me too bad if I am off a little on the following numbers because I am pulling this from memory. Too break into the 12s in a reasonably well set up car in the 3200# range with good traction will take around 380HP minumum.
I think it is pretty well accepted that it takes somewhere it the range of 195cfm of intake flow to support 400HP. Of course you have to have the cam, intake, exhaust, etc that will allow your heads to reach that level of flow. Knowing this, just about any SBC head will work. Even the old double hump heads flow around 200cfm, and the 186s are around 190cfm.

So, in your case, I would not sweat too much that the Pros only flow 235cfm(475hp) and that the AFRs flow 275cfm(550hp). Unless you plan on later going to big single plane intake, huge roller cam, 4.56 gears and 3500 or more stall. Then you will need the extra flow from the best flowing head you can find.

The point I'm trying to make is you only need as much flow as the rest of the combination needs, and a head that flows 300cfm wont make any more power than a head that flows 250cfm if the cam only opens the valve far enough and long enough to flow 200cfm. And usually heads that have huge high end flow numbers dont have all that great of lower lift flow. I'm not saying stock heads would work as good for you as aftermarkets. Its just that there are many heads out there that would meet you disired performance levels and would flow more than enough even for a pretty nasty 327 buildup.

What I would look for in a mild street combination is the head that flowed the best at the max lift of my cam and below, and does it with the smallest port.

Now, back to my engine. I have a 400sb "beater" engine I threw together to get the car running at the end of its restoration. It has stock heads(pocket ported) making around 420hp and running 12.75s. From the flow charts I cant help but feel I,ve reached the limits of my heads potential and they are holding back the rest of the combo. So I am looking at the Pros because I can buy them so cheep. I want to stay cheep because I also have a stroker 505 BBC that I am building up for the car and dont want to get to much into the 400sb before it comes out next winter, but I would also like to see if I could sneek into the 11s this season with the 400.

So, to make a long story longer, I got some Pro 220s from my warehouse last week and took them to get flowed. If they suck I'll send them back and go with AFRs, or just blow it all off and wait for the BB. But, if anyone is interested I'll have yet another set of flow numbers for thr Pros in a few days.

Kamero68, thanks for the tip on the 56cc heads, that may make my life a lot easier! (56 maybe kinda small) Please le us know how the flow test goes... although it would not be directly befeficial to me, I think it would be a good indication of how well Pro-Topline handles their products, and probably how well I will take them seriously. PS, you have mail graemlins/waving.gif

As for the minimum CFM theory:

Ill trry to take this more from a physical perspective:
The largest amount of air that 1 cylinder can hold in its cylinder is the total displacement of one cylinder (normally aspirated). In my case, the maximum amount of air you can put in will be 327/8~40ci (plus combustion chamber etc). However, given an engines rapid cycle and limited flow potential, an engine cannot fill its entire cylinder within that short time. However, for all intensive purposes we can dump as much fuel into the cylinder as we want, so we are of course limited by how much air we can force into a cylinder.

Air is taken in by the use of the piston creating a vacuum above it, and the environment seeking to get to euqilibrium, reacts by trying to fill the void above the cylinder, so air travels into it. The air must travel and make its way through all of these passages including the intake port on your head. All of these things inhibit flow directly into the engine. What we seek to do when we buy heads that move more cfm is to minimize the restriction that is given by the head. However, there is another aspect to it.

If we have too large of a port, we actually taking away some of the vacuum potential that the piston brings (try sucking water through a 2.5 inch diameter pipe, you wont get anywhere). So the objective is to move as much cfm as we can while actaully trying to MINIMIZE the port that we use. Thats why better flowing heads create more horsepower, so I think the target should be to find the highest cfm flow possible, while trying to keep the actual port small.

I would actually like to attain maxium Torque and HP numbers within reason, so altough theoretically it may only take 235cfm to , I wouldnt mind if it flowed 445 cfm if it gave me 560HP smile.gif .

a side thought:
(I bet straw designers did tests on how fast people wanted to suck fluid into their mouths, and adjusted the diameter accordingly...interesting smile.gif )

sik68, I think I understand your point, but wanted to point out that you CAN force more air into a cylinder than the cylinder's volume. You said,


Ill trry to take this more from a physical perspective:
The largest amount of air that 1 cylinder can hold in its cylinder is the total displacement of one cylinder (normally aspirated). In my case, the maximum amount of air you can put in will be 327/8~40ci (plus combustion chamber etc). However, given an engines rapid cycle and limited flow potential, an engine cannot fill its entire cylinder within that short time. However, for all intensive purposes we can dump as much fuel into the cylinder as we want, so we are of course limited by how much air we can force into a cylinder.


I just wanted to point out that your statement would be true if we were talking about a liquid - because you cannot compress a liquid. But with a gas, like air, we can compress it to get more into the cylinder. true it will still only be 327 cubes in volume but you could pressurize it to get twice the air molecules into the engine if you wanted. AND you do not need a blower to do it --- you just need to take advantage of scavenging so that volumetric efficiency exceeds 100%. If you have a 327 with a VE of 110% (pretty hard to do in an N/A engine but entirely possible BTW) you have the equivalent of roughly 360 cubic inches of air at atmospheric pressure COMPRESSED into a 327" engine.

So you CAN fill a cylinder beyond its "liquid volume" capacity. Most N/A engines do not but with the correct valve timing events and effecient induction and exhaust systems, scavenging will cause VE in excess of 100%.

kamero68, well said and good point.

Well I just got off the phone with my machine shop, heres the prices they quoted me for the machining work:

In this order:
flow test 50 (for the internet's sake)
dissassemble
flat mill 3-4cc 75
pocket port (if numbers are too low) 300 including dis/assembly
reassemble
flow test 50
$475

I think it seems like a fair/good deal for all I am asking for (with a very reputable company), but then again puts it right there in line with AFR's, which I wouldnt flow test or port, just mill. With the pocket port, my expectations would be to have them flow significantly better than the AFR's, otherwise I wont be too happy graemlins/sad.gif .
I know it seems like I am getting too wrapped up with the "flow", but I think at this stage I really need to find out before I start writing the checks. In a perfect world (nearly perfect) the Pro's would flow a few CFM under what they say (no biggie), I would have them milled and be done with it. Like Cody said, I am taking a gamble with the heads, to the tune of about 400 bucks and they may not flow better. Risky

You know I planned on pocket porting my friend's 200cc Pro Toplines and honestly they didn't need it. You might just get them flowed first and see what you've got.

The transition between the seat insert and the bowl had already been cleaned up to about 1" deep at the factory and the ports looked perfect. the only thing I did was smoothed a couple little spots (and I mean tiny) of casting flash off the valve guides where the bronze insert meets the aluminum casting.

I was going to say the same thing about the Pros but Eric beat me to it, There is vertually nothing to pocket port on the Pros, and what little there is you could do in 15 minutes with an 1/8 Dremel. Those heads are that close. If they dont flow out of the box, there is not much to work with to improve them.

If there is some confusion on the CFM required to support X amount of horse power, let me try to clear it up a little. As I understand it.....The example Of 195cfm to support 400HP is not thretical, it is relativly actual. Meaning it has been observed that 195cfm is the air flow requirement at that HP level. It should stay close the the same flow demands if the engine peaks at 400hp or if it is an 800hp engine using 195cfm as it passes the 400hp mark on its way up to 800hp mark.
Now the 380hp to run high 12s is subject to many varables and can be way off. The example assumes a V-8 engine like what we have been talking about. But if you took a 1.0 liter Indy engine that also makes 400hp, but it does it at 10,000 rpm, the sample 3200# car and gears would run a much slower time because the power curve is not matched to that combination and would run well out of its power band.

One more thing about head flow, In an example where you have two heads that flow 250cfm at .500 lift you should focus on the lower lift numbers to see which should make more power. assuming the port cc is the same and max lift flow is the same, the head flowing more at lower lifts will make more power because it adds up to more total flow under the lift curve. And dont discount that the valve is only at maxumim lift once in a cycle, but it passes through the lower lift zones twice, as the valve opens and as the valve closes. That is also part of why a roller cam will make more power than a flat tappet, the roller lobe profile opens and closes the valve faster and thus can hold it open longer at higer lift allowing more time under the curve for flow to enter the combustion chamber.

Sik68, I could not find your email. ?

[ 04-21-2003, 09:48 PM: Message edited by: kamero68 ]

I like my Pro Toplines. :D

Hopefully I'll get the car to the track sometime and put them to the test.

I didn't wanna start a new topic since I am still talking about the same combo here, but hopefully people will still respond to this, so here it goes:

Here is what is staying in the car:
327 .03" over, stock bottom end, th350 shift kit, 3.73 gears and posi, engine accessories on pulleys are flex fan and alternator, HEI ignition, headers & exhaust th350 shift kit


What do people think about this combo:

200cc Pro Topline heads 50cc chambers (I will explain why in a second)
COMP 282Solid (ret 4*, will explain)
Comp 1.52 roller rockers
Weiand 7546 Xcellerator manifold (already bought)
Edel. 600cfm carb
B&M Holeshot 3000 converter
BFG drag radials

What my focus has been is on top end power, and I am not concerned about pump gas issues, meaning I wouldnt mind adding 15 bucks of octane boost in my gas tank every fill up, because the car is only a twice a week street machine. I found myself in a dilemma between the 200cc Toplines and the 180cc's, because I know 180 is better matched for a small engine, but on the other hand, the 200's have their advantages:

1. 50cc chambers for upped compression (versus 64 with the 180 toplines)

2. No Milling to get the compression where I want it $$$

3. They will work better on a bigger motor if I ever build another (or if the 327 breaks)

So I hope that explains the head situation. As for retarding the cam 4*, This is only necessary to get my DCR down a little lower.

With a .031 gasket (assuming 6cc reliefs and .025 deck height):
Static Comp= 11.01 .052 quench (hence hi octane)
DCR with cam at 106= 8.5*
DCR with cam at 110= 8.3*

With the current specs in DDyno through mufflers, I get
361lbft at 3000rpm
411lbft at 4000rpm

462HP at 6500rpm


The purpose of this vehicle is to be able to handle the streets without constant worries, but the car is by no means a daily driver. It is a 19 year old's hot rod that people will stare at when they hear the cam at idle, and will get up out of their seats when I take it to the 1/4 mile. I am not so much a torque guy; I like the higher rpm's, (even though this engine makes more torque than my current combo above 2000rpm smile.gif )

Are there any changes people would make, or have I struck gold for my particular situation? Also, I think my race track goals are fairly reasonable, I am thinking mid to high twelves in a fairly light camaro (~3200).

If you get 200cc ports because you may build a bigger engine later, get the 64cc chambers too. The compression ratio will go real high real quick with 50cc chambers on a 383 or even 350.

. . . and if you aren't worried about adding octane booster why retard the cam? The 4* advance Comp grinds in is there for a reason.

Just my opinion.

Heck if you want to wind her a little go with a bigger cam. The way i see it if you have to reatard the cam for bleeding off compression you may as well just get a bigger one. And remember there are alot more companies out there than "comp" check out Howard, Erson, Doug Herbert, Isky, Etc. You may find a better suited cam than somthing "comp" makes. Since were winding it, id go 200cc heads, get the 64cc chambers like Eric said and leave them alone if your going to build a bigger engine down the line. Now im no 327 guru but wouldnt the car benifit from a little more than a 600cfm edelbrock? Octane booster is a joke, its not going to stop you from detonation or give you more power. Race gas will, but who wants to spend 4.00 a gallon on there gas when 1 point of compression is only worth roughly 4% power. Also Im willing to bet once you get it going youll be driving it more than you think. graemlins/thumbsup.gif Just my opinion.

I see I see Eric...I guess I'm turning into a compression junkie. tongue.gif

I actually just stumbled upon the Xtreme Solid lineup, and I started comparing stats:

The Magnum282S I was considering makes the same peak power (using DDyno) as the XS274S, but at 2500rpm the XS274S makes nearly 20 ft lbs more, thats pretty impressive, and something I will consider.

Novaguy, I guess I am stuck on the whole Comp thing because Comp seems to make it easy on the buyer with their kits. Ill look at the others you mentioned, as I am sure they do something similar. Thanks graemlins/thumbsup.gif

There ARE some good cam companies out there besides Comp . . . Isky, Ultradyne, Crane, and Crower all have some nice solid FT grinds too. I do realy like the looks of teh Comp XS line though, maybe the next motor I build will have one . . .

BTW 4% per point of compression isn't everything like Novaguy said, but on a 400 HP motor 4% = 16HP which is nothing to sneeze at. That could be a couple tenths in the 1/4. You DO have to be careful though - detonation is an expensive problem top fix so you better be right on the money with your static ratio and cam choice. That's why I like Pat Kelley's DCR calculator so much :D

I agree with Novaguy on the advance/retard issue - if you have to retard the cam you might as well step up a size and run it a few degrees advanced. IMO engines typically DO NOT run well with retarded cams. IMO a cam installed straight up will in reality wind up retarded a couple degrees because of timing chain stretch/wear, stack up tolerances in the valve train, etc.

Best of luck with your build graemlins/thumbsup.gif