Hi folks! I'm curious as to what the compression might be in my 327. Its bored .30 over with forged TRW flat tops(four valve relief), 461 camel humps (not milled), and the head gasket came with a fel-pro kit. I know theres some kind of equation for calculating this but I think it includes the head gasket thickness (which I don't know). Ive been told 10.5:1 but Ive also heard it might be lower. Any ideas?
Thanks, Dave

I have the same set-up,but with 462's.I was told by a few Tech guys,while searching for a cam,that the 10:1 factory ratio was actually closer to 9.2-9.3:1.I don't know how true this is.I would like to know for sure myself.

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67 RS RAGTOP # matching
4X4 Chevy truck
4X4 Suburban

I computed my 350 with the same specs as your engine and came up with 9.7 to 1. With a 327 it would be slightly lower, say 9.5 to 1 or so.

Try www.prestage.com (http://www.prestage.com) they have some good formulas under "car math". The Fel-Pro composite gaskets are usually between .039 and .041 depending on which one you use.
Stephen

Thanks for the response guys. This is one awesome site! I guess the lower comp. numbers are probably better for the fuel today but I was looking forward to the extra HP with the higher compression. Not sure but if I was to somehow get 10.5:1 I might still be OK. I was kinda hoping my cam would bleed off a bit of the squeez at lower RPM. The stick I'm running is an ISKY 280 mega cam (232 @ .50, .485 lift, 108 deg. lobe centers). Any body else running this cam? If so whats it like? ( haven't fired the mill yet).

I just put a Comp 268H in my 327,and it "rocks".All I can say is that Isky's gonna thump in a 327 http://www.camaros.net/forum/biggrin.gif .
I hope you have a manual trans,or a high stall converter in your auto,the bottom end torque is going to be non-existant.
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67 RS RAGTOP # matching
4X4 Chevy truck
4X4 Suburban

[This message has been edited by 67drake (edited 07-26-2000).]

Im running a B/G T-10 with a 3.73 10 bolt posi. I had the bottom end balanced so winding the motor up isn't going to be a problem (if it stays together!!). I've heard the Isky 280 is a pretty good cam my other choice would have been something from comp though, possibly a split pattern.

Same here,mine was balanced,blueprinted,ARP bolts,forged pistons,ect.My little 268H spins my 327 to nearly 7000RPM.I have heard nothing but good things about Isky.I was considering a few Isky grinds myself.The ones I had run on the "dyno 2000" program were going to make power at an even higher RPM then my 268,so I went with Comp.You should have a nice lopy idle with that one!Good luck.

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67 RS RAGTOP # matching
4X4 Chevy truck
4X4 Suburban

I am building a 327 with a retro-fit roller cam. I want to drive it on the street but want performance as well. What pistons do I want to use? - flat top to 9.5:1? Aslo do you have a suggestion on a roller cam grind from Comp Cams?

31 Model A coupe - 4 speed car

Hi folks! I'm curious as to what the compression might be in my 327. Its bored .30 over with forged TRW flat tops(four valve relief), 461 camel humps (not milled), and the head gasket came with a fel-pro kit. I know theres some kind of equation for calculating this but I think it includes the head gasket thickness (which I don't know). Ive been told 10.5:1 but Ive also heard it might be lower. Any ideas?
Thanks, Dave


I am building something similar, .040 over with 492 DH heads. A lot depends on the head gasket. If you run a .015 I think you get close to 9.7.

Whitey

The 4 valve relief pistons are right at -6cc volume. Using 64cc head chamber volume and .025 in the hole you're static compression is 9.1:1 with the standard .039 rebuilder head gaskets and almost 9.6:1 with .018 thickness shim gaskets.

Using Pat Kelly's calculator your dynamic compression ratio is a little over 7.0:1 with the .039 gaskets and a little over 7.4:1 with the .018 gaskets, which is basically saying your cam is too big for your combo, or your compression is too low for that cam. You want to shoot for around 8.0 dynamic compression for a street car.

I was using the specs from this cam card.

http://www.iskycams.com/timingchart.php?product_number=201281&timing_chart_id=98

That cam would run better with 10.25-10.5:1 static compression.

Here's Pat Kelley's article.

http://www.empirenet.com/pkelley2/DynamicCR.html

Mark

I am building a 327 with a retro-fit roller cam. I want to drive it on the street but want performance as well. What pistons do I want to use? - flat top to 9.5:1? Aslo do you have a suggestion on a roller cam grind from Comp Cams?

31 Model A coupe - 4 speed car

We need a lot more info Justin to make any kind of suggestions. Heads, cam choice, auto, manual, rear gears etc.

Mark

The 108° LSA is going to make it a 'lumpy' idle engine. Might have to idle around 900-1100 rpm just to keep it running, low vacuum.

I ran the 280 mega in a 327 years ago and i loved it. it sounded great and ran really good. I didn`t have a tach at the time so I don`t know what the idle was but it wasn`t too high.

Should be right at 9.77 to 1 w/ Fel-pro's #1094, .015" thick shim headgaskets.

Perfect for CC's old 268HE, Crane/Cam Dynamic's old 272/272 Energizer and Isky's 270 HL.

I like a solid lifter cam tho.

pdq67

I have undercammed a small block before, and it is not fun. I ran a .447 lift Erson in my 350 and it sucked. It was around 9.5 to 1. I put the General Kinetics .480 lift and 288 duration in it and it would scream. Be sure you have it "right".

Should be right at 9.77 to 1 w/ Fel-pro's #1094, .015" thick shim headgaskets.

Perfect for CC's old 268HE, Crane/Cam Dynamic's old 272/272 Energizer and Isky's 270 HL.

I like a solid lifter cam tho.

pdq67

A solid runs TOTALLY different. I like it, but its maintenance free.

Right, lash it and as long as you have at least valve springs like the old Z-28, (-142) jobbers and a decent STREET solid lifter cam up to an Isky Z-30, she will rpm to the moon!

pdq67

Sorry it has been so long getting back on the subject.
I am building a 327 for a 31 model a coupe- 4 speed, 370 gears. Heads being used are 62cc double hump. I am wanting to run on pump gas nothing extreme. The car only weight 2000lbs. I also have decided not to run the roller camshaft. I want to run a hyd flat tappet. 268 comp??

What will the compression ratio be???

If it started out life as a 210hp/327 and you install a 275 or 300hp/327 topend on it, it will be right at 9.77 to 1 w/ .015" shims! Just about dead-nuts on for the good old CC 268HE, imho.

pdq67

The topend will be a set of 3782461 62cc heads with flattop pistons. Yes, I plan to use the 268HE cam. I have great results with other 350's

pdq67 - I was wondering how you calculated the 9.77:1?? Do you have a handbook or internet site?

Also will this be too much compression for 87 pump gas?

The topend will be a set of 3782461 62cc heads with flattop pistons. Yes, I plan to use the 268HE cam. I have great results with other 350's

pdq67 - I was wondering how you calculated the 9.77:1?? Do you have a handbook or internet site?

Also will this be too much compression for 87 pump gas?

Justin

You can try this.

http://www.kb-silvolite.com/calc.php?action=comp

Or, go back to post #11 and read Pat Kelley's article and download his dynamic compression ratio calculator.

Mark

Guys, I've got a 327 210 original that's never been apart. What "tweaks" (on a budget) can I do to spice her up a bit.

THNX

Guys, I've got a 327 210 original that's never been apart. What "tweaks" (on a budget) can I do to spice her up a bit.

THNX

Not much in the way of tweaks if you want to keep everything numbers matching. If numbers don't matter, a head swap, 4-barrel carb and headers would wake it up. Throw in a cam change with everything else and it'll really wake up.

Mark

Which cam? What estimated hp would she wake up to?

Which cam? What estimated hp would she wake up to?

Frank

There's a whole lot of options. Some old school double hump heads, a 4-barrel and headers will get you in the 275 hp range. Add a little bit bigger cam like a Comp 268H and it'll be closer to 300hp. Or, you can go a whole lot wilder.

If your car has a powerglide transmission, putting in a T-350 will help. A gear swap in the rearend will also help. It all depends on how much you want to spend and where you want to start. Just be warned, once you start, there is no end. ;)

Mark

Mark, My 327 is about the same as yours will be and I MUST run 93 octane fuel, or it pings something awful. Also, there is an end with those heads ! They don't breath that well. Too small of a runner. As PDQ67 always says, "The factory had it right !" Do not go much larger on the cam than they did. A 268 cam is all you need or will want. If you port the heads or replace them, sure get a bigger cam. Otherwise stay where you are at. The XE-268h is a flat tappet, hydraulic lifter cam. It is not a roller cam. Maybe they have a similar roller, I'm not sure. Good Luck ! and Merry Christmas !

Update: Yes, they do make a roller in about that size. I would look at something smaller in a roller, like the 260HR to get your RPM range down in the 1200 - 4500 RPM range. This should make around 350 HP and 420 TQ.

Mark, My 327 is about the same as yours will be and I MUST run 93 octane fuel, or it pings something awful. Also, there is an end with those heads ! They don't breath that well. Too small of a runner. As PDQ67 always says, "The factory had it right !" Do not go much larger on the cam than they did. A 268 cam is all you need or will want. If you port the heads or replace them, sure get a bigger cam. Otherwise stay where you are at. The XE-268h is a flat tappet, hydraulic lifter cam. It is not a roller cam. Maybe they have a similar roller, I'm not sure. Good Luck ! and Merry Christmas !

Update: Yes, they do make a roller in about that size. I would look at something smaller in a roller, like the 260HR to get your RPM range down in the 1200 - 4500 RPM range. This should make around 350 HP and 420 TQ.

Tom,

This is what mine has. It'll run on 91 octane but prefers 93.

327 .060 over, about 10.5:1 comp.
.125 dome forged TRW pistons (+5.3cc dome)
Summit brand (Dart Iron Eagle S/S) heads, 67cc chamber, 165cc runners
2.02/1.6 valves, 3 angle seats
Isky Z-25 solid lifter cam with 1.6 rockers
Edel. RPM intake with Q-Jet
1 5/8 headers
stock ignition
8.5 3.42 posi rear

.125" domes and you still run pump gas !? My TRWs are flat tops. My cranking compression is 200 psi, so I figure it is real close to a 10:1 engine. Yours must be pushing 12:1.

.125" domes and you still run pump gas !? My TRWs are flat tops. My cranking compression is 200 psi, so I figure it is real close to a 10:1 engine. Yours must be pushing 12:1.

Actually my static compression ratio is less than 10.5:1. The domes only have a +5.3cc volume and the heads have 67cc chambers. With that cam, the dynamic compression ratio works out to right at 8.0. Pump gas friendly. :thumbsup:

Mark

With the engine being .060 over should help your numbers also. My engine has the 62cc, 461 heads, which also tightens it up. The block has not been decked either, which actually lowers my compression !

Actually my static compression ratio is less than 10.5:1. The domes only have a +5.3cc volume and the heads have 67cc chambers. With that cam, the dynamic compression ratio works out to right at 8.0. Pump gas friendly. :thumbsup:

Mark


Does it run 13.25 with street tires?

Does it run 13.25 with street tires?

Yep, with a 2.0ish 60ft. With some decent traction it would run high 12's. We'll see what it'll do this coming spring. Probably blow the stock clutch out of it if it hooks up. It seems to be the weakest link right now. Starts to stink after a few runs. :D

Mark

I'm figuring Mark's 327 will do a 12.7 to .5 or so, easy!

pdq67