Ive been messing with Desktop Dyno, and with the combo I plan on building, Im trying to squeeze every amount of theoretical power everywhere I can. When I retard the cam by 4 degrees, it gives me 15HP at the top end, while only sacrifing 5 ft lbs at 3000 rpm. Why then does comp recommend to install the cam at 106 (on a 110 lobe center) instead of 110, where its obviously going to have more aread under the power curve? Are there any downsides to it other then mild torque loss?

Heres the combo Ive been working with:

327 .030" over
Pro Topline 180cc 64cc (to be milled to 59-60)
10.8:1 compression (8.2 DCR)
.056 quench (I will be using octane booster)
Comp 282S cam
Single Plane manifold (most likely Weiand Excellerator, opinions?)
1.52 rockers
Edelbrock 600cfm


Heres what DDyno says: (you may have to copy and paste the link)
www.geocities.com/capitolstrokers/327_Lightning.jpg (http://www.geocities.com/capitolstrokers/327_Lightning.jpg)

Does this kind of power seem reasonable? Seems kinda high for a 327 doesnt it? PS I do all my Ddynos with open headers, so subtract 22 from the top end according to Ddyno for mufflers. Judging from similar combos that have been run at the track, nearly 500 HP seems high.

You are opening a real can of worms with your question b/c it has to do with where you want your power to be in the rpm band and how you like your car to drive!!

Looking at a single pattern cam where both lobes are the same as well as the cam having straight up or single numbered LCA/ICA numbers like 111/111 vs 110/106.

You will find that it is where your intake valve ACTUALLY closes as the point that governs power production moreso then anything else. THIS is b/c the engine can't build compression until the intake valve is closed, assuming the exhaust valve is closed, too...

The LCA is ground into the cam but you can move the ICA by just playing with the installation point with respect to the crank keyway or use offset bushings in the cam sprocket or even an adjustable cam sprocket thing.

My own thoughts on this is to use a single pattern cam that is made so that the LCA is where you want the cam to be ran AND then use placement of the ICA to fine tune my engine. But I also have been chatting with UDHArold about his line of dual pattern cams and his reasons why he likes them so I am trying to continue to learn on this all the time...

When I was searching for a small hydraulic for my 454 engine before I went 496, I ran almost all of them through D2K and I found out that Erson's Hi Flow AH cam which is an older design single pattern cam made on 111/111 installed put the power just exactly where I wanted it, FOR MY PARTICULAR COMBINATION!!!

I even called Erson and asked one of their Tech. guy's about it and he said they liked the idle quality as well as where the power was produced in the rpm range when a cam was made and installed straight up at 111/111 for this cam.

He said LCA is really an overlap/idle qualilty thing as well as a max. torque number placement range in the powerband so you really have to pick where you want it and how you like your idle lope for your own combination!!!

I called Isky one time and got this from them.. Their Mega cams are 108/108 but they said to install them on an ICA of 106 so go figure???

GM used both types of cams. Just look at the old 30-30 and the -178 solids and both ran very well so take your pick..

I'm sorry, I feel like I am just beating around the bush and have not given you a definative answer b/c I really don't think there is one.

I do know that the roundy-round guy's try to set their cars up so that they get max. torque (or accelleration) coming out of the turns so they use cams that are ground on tight LCA's and install them on tight ICA's so the power comes on down low in the rpm range! This gives them a peaky cam that comes on down lower in the rpm range b/c this is where their engines rpm is at coming out of a turn...

Hope I haven't just confused you more..... pdq67

How did you get 10.8:1 static compression? With a .056 quench and 64cc heads you would need a 7cc dome piston. Is that what you are running? If so which dome piston? A small .120" dome piston makes about 10.3:1 compression in a 327 with 64cc heads.

You are very likely to have interference problems between the dome and the quench area under the spark plug on the ProToplines --- we had to "work" my friends heads to get adequate clearance.

I would also consider trying to optimize your quench area a little better. Even though the compression ratio will increase with a tighter quench, the engine will be MORE detonation resistant than at a lower compresison ratio with looser quench.

If I assume your static compression ratio is exactly correct with the 282s cam installed 4* advanced your DCR is 8.4:1. That is fine with a modern chamber design aluminum head and pump premium gas. My point is only that it is OK to run the cam advanced 4 degrees without causing detonation.

As for the power band you are expecting I would not rely too heavily on Desktop Dyno. the tendency for me is to stare at the program and make very minor changes that result in the most HP and TQ possible, but in reality the program is not that accurate to begine with. Its like measuring your cylinder bore with a ruler - comes close but don't use it to pick your piston size.

The Comp 282s will run hard in a 327 from 2500 - to 6000+ RPM when advanced 4 degrees like Comp recommends. If you retard the cam from its recommended install ICL you will shift the power band upwards in a 327 - not really what you want IMO you need all the TQ you can get especially if you are not using a big stall and big gears to make up for it. I think in REALITY the TQ loss at lower RPM will be more significant than DD2k is telling you.

I would also consider using the Performer RPM dual plane instead of a single plane. If you plan on running a big stall and big gears a single plane would be good, but don't push your luck with anything smaller than a 3500 stall and 3.73 gears.

Just my opinion.

ps. even though you install a cam 4* advanced don't forget that the timing chain may stretch and wear a little retarding the cam from its installed postion. That's why IMO most cam companies grind advance into their cams.

PDQ, thanks for the info. I understood what you wrote, but I will need to reread it to get all of the specifics you said. smile.gif Thanks a lot though


Eric, the 10.8 came after milling my heads to 59cc. The 10.8 figure is only a rough estimate because I actually don't know how far my piston is in the hole. I know I cant get an accurate reading that way so all the information is basically useless, but depending on how far it is from the deck, I am planning my setup accordingly to try to reach my desired comp ratio. (both SCR and DCR).

I am trying not to look at the actual power numbers that DD says (although its hard to ignore 500hp), but rather the changes that each little thing gives me, like you said. Its given me a better under standing of how each component matters to the engine. Thanks a lot, you've basically kept me afloat with your own 327 experience these last few weeks. Once I get my engine to the track (hopefully mid july) I'll let you know how everything goes.

--Steven

Steven, your welcome smile.gif

You know its usually safe to assume (for planning purposes only) that factory SBC pistons are usually right about .025" down the hole --- that is if you have never decked the block. If you have flat tops with 6cc valve reliefs your compression ratio should be 10.2:1 if you use a steel shim head gasket that is .015 thick. felpro makes a real nice rubber coated steel shim that is .018" thick, I think. That would also make your quench right about .040" which IMO is perfect.

Good luck with your project, I apreciate you letting me know how it runs.

Ditto the .025" down in the hole as a starting point for using a sim. program to get you going... pdq67