Here's my combo

Small journal 327 bored 0.030”/ decked 0.015”
Original GM Steel crank turned 0.010/0.010
TRW L2166NF Forged Pistons
Comp Cams Magnum 270H 0.470” lift
Edelbrock Performer RPM intake
Dart S/R Torquer heads 67cc 2.02/1.60”
Comp Cams Guide Plates
Magnum Roller tip rocker arms
Holley 650 double pumper
1” phenolic 4 hole carb spacer
Mallory Unilite Vacuum Advance
Jet HOT-ed Hooker Competition Headers #2451 1 5/8” primaries
2 ½” Aluminized Exhaust
TH350 with a B&M shift improver kit
TCI Break away 11” 2400rpm? Stall
3.31 Posi 10 bolt 8.2”
275-60-15s on 15 X 8” in the rear


I have built the engine and the rest of the car is there, just needs to be assembled.

I calculated the compression ratio to be about 10.3 to 10.5:1, does that look right?

Do the rear end gears or the rear tire size seems out of place to anyone?

Any other comments or criticisms are welcome.

Thanks, Scott

Might need a little more gear like 3.73 with the cam. The pistons must have a small dome?

I think the 327 would probably like 4.10 gears or better to get it up in it's powerband faster and keep her there, the 4hole carb spacer might not add anything and I'd try it without first. The compression matches the cam well. No professional here just expressing my opinions. Overall I think she'll rip. graemlins/beers.gif Bob

So how does that gentically engineered corn taste btw... :D

With a 28" tire like you have, your gears are more like 3.10 with a stock 25.5" tire. A little tall for a 2400 stall. I cruise at 2450ish at 55 with my 275/50's & 3.08's & 2k stall.
If possible, switch to a 275/50 at least, or go to 3.50/3.73's.
You'll probably need a 2400 stall or better too.

I would run a smaller collector than the 3" stocker that comes with the 2541's. On our road race motors I cut off the collector and add 8-10" of primary length and a 2-1/2" merge collector. Makes a big difference in the midrange performance of the motor.

Tire size is big,gears are tall.Motor seems ok.Try 3.73 with 2:55 60's

Would need to know which head gasket you're running to calc static and dynamic compression ratio. Are you trying to run on pump gas? If so with iron heads you're probably going to need 94 or so octane.

I had a 327 with 2166 pistons, comp XE274, iron 64 cc heads, and was having to boost 92 octane to get it to run right. The DCR calc'd out to about 8.3 on it. It was in a '60 vette with 3.55 gears with 26" tires so the car was much lighter (i.e. 2900lbs) which would be more forgiving than in a Chevelle with 3.31s and taller tires. The 270H has an intake closing event at 61*abdc vs the XE274 was at 63*abdc. The 67cc heads will help out some. If your static is at 10.3, with a 61*ABDC intake valve closing your DCR would calculate out to about 8.4 which is ok for aluminum heads but high for iron heads.

You may want to retard the cam 4* to help bleed off some compression (the 270H has 4* advance built into it so retarding 4* would set it straight up) or get a bigger cam. Again this is if you're intending to run on readily available pump gas. My $.02

Wow! Thanks for the response. I suspected the rear end gears were a little off. You guys are awesome.

As far as the head gasket, I used a Fel-pro Fpp-1003 Nominal thickness-0.041" Compression Volume 9.1cc.

So ,rpol78, how exactly do you calculate dynamic and static compression ratio? My method was incredibily crude(so bad I wont explain it). But I would love to learn how to. I understand that A=(r)2 * Pi would give you cylinder volume, but how do calculate compression ratio without knowing exactly what the deck height is? Am I missing something?

Scott, I have an excel sheet that I use. I don't remember which site I got it off of. It calculates static and dynamic compression ratio (aka DCR). It uses bore dia, stroke, head gasket dia and thickness, deck height, top ring land height, rod length, piston dome volume, intake valve closing, etc to come up with the calcs.

Static compression assumes the intake valve closes at bottom dead center verses in reality the intake valve doesn't close until some point after bottom dead. So the DCR calc takes this into account. By using the 270H cam in a 327, with the intake closing at 61* ABDC you only get 79.8% of the cylinder volume rather than the 100% that the static calc gives you.

In order to run higher static compression ratios on pump gas you have to run a cam with a later intake closing to "bleed off" some of the compression. The numbers that typically float around are a DCR of 8.0 for iron head and 8.5 for aluminum heads. The other factor to look at is quench. Most folks say the target is .040 to help prevent detonation.

GM generally had a .020 deck and a .022 shim gasket, so you go from there. Hope this helps, Ted

Motor combo looks good. I agree withe rest go for a set of 3.90's and 275/50/15's. Also on the converter...I would skip over the 2400 and go right to a 3000. You will love it !

Originally posted by red68chevL:


So ,rpol78, how exactly do you calculate dynamic and static compression ratio? My method was incredibily crude(so bad I wont explain it). But I would love to learn how to. I understand that A=(r)2 * Pi would give you cylinder volume, but how do calculate compression ratio without knowing exactly what the deck height is? Am I missing something? http://members.uia.net/pkelley2/DynamicCR.html

That site has the best dynamic and static compression ratio calculator ever! Use it and know your motor! Woot!

So i downloaded a compression ratio calculator and have been meesing with it for a couple of days. After reading a ton of posts hear on quench, dynamic compression ratio, valve timing. It seems I would be better off with a bigger cam!?? Like a Comp cams 280H or a XE274. With a 280H ,this will drop my DCR to 8.18. Does that mean that I could run a lower octane gas with a bigger cam?

Scott, that's correct. It bleeds off cylinder pressure by having a later intake closing event which allows it to run on lower octane fuel. Both the 280H and the XE274 have 4* advance built into their grinds. If it were my choice I'd probably opt for the XE274 and retard it 4* (which actually has it installed straight up due to the 4* advance ground in). The 280H has a 66* ABDC intake close verses the XE274 at 4* retard would have a 67* ABDC intake close (the XE274 normally has a 63* ABDC intake close).

In hind sight that's what I should have done with the 327 in the vette. The engine ran great, I just had to bump the octane to get it up around 94 to keep it from pinging. If I would have retarded the cam 4* I probably wouldn't have had to.

Again just my .02

dcr does not account for the engines ability to fill the cylinder, overfill the cylinder, or lack there of.

dcr does not account for the engines ability to fill the cylinder, overfill the cylinder, or lack there of. Agreed, VE plays a key role also, but it's alot better predictor of octane requirements than static compression ratio. It at least takes cam timing into account.