HP /TQ / CR questions
 

Everybody,
What do you guys think the CR of a 454 with a standard FelPro head gasket, flat top pistons, & vortec heads with a 100cc would be?? I have seen the online calculators, but I do not know the answers to all the variables. Here are the specs on the engine: 454 bored .040 over, flat top pistons, vortec heads with the stock valves (2.06 / 1.72), 280 comp cam, (specs link below), roller tip rockers, Edelbrock RPM Air Gap intake & Holley 750cfm carb. Below are the links for the cam & CR.
Thanks,
Chris

http://www.compcams.com/Cam_Specs/Ca...?csid=388&sb=2
http://www.race-cars.net/calculators...alculator.html

Re: HP /TQ / CR questions
 

If you don't know all the variables then how can we figure out the CR? Why don't you know the specs? What don't you know?

Re: HP /TQ / CR questions
 

Ok, alot of the variables automatically filled out when I hit compute. So it says that I have about a 9.6 CR with a 454 .040 (462) over & flat top pistons with 100 CC chambers on the Vortec heads & a .039 head gasket. That's good. Any idea on the HP & TQ & what RPM they would be at??

Re: HP /TQ / CR questions
 

Do you know your piston depth? CR seems a bit high with 100cc heads. Although I'm not all that familiar with the BBC.

Re: HP /TQ / CR questions
 

Nope, sorry, I do not know the piston depth.

Re: HP /TQ / CR questions
 

I believe the piston volume would be 947.47. The rocker arm ratio is 1.7. I forgot to put that in the specs earlier.

Re: HP /TQ / CR questions
 

OK, here is the things you MUST have to calculate the compression ratio. Leave anything to guess and you have the potential; for a total erronious answer.

Bore
stroke
EXACT deck clearance
Gasket bore diameter
Gasket thickness
cc of chamber
dome / valve relief volume

Re: HP /TQ / CR questions
 

if you don't know the piston depth (deck clearance) then you can't come up with a CR. A .05 difference in deck clearance make it a 9:1 or 10:1 motor. That's a big difference.

Re: HP /TQ / CR questions
 

oh, I did not know it made that much of a difference. I assume it's the stock height. Wouldn't it be stock if the heads have never been shaved??

Re: HP /TQ / CR questions
 

If the motor has ever been apart or rebuilt, heads refurbished, a valve job...... Heads could have been milled, AND/OR the block could have been decked. That diminsion is criticle to compression ratio. The combination of deck clearance (pistons at TDC typically sit below the block deck,, unless the block has been decked) and gasket thickness makes up your 'quench'. A motor with a large quench is typically more detonation prone, and a motor with a tighter quench is typically more detonation resistant. In that you can play with compression ratios a little. If the motor is detonation prone because of a large quench, you would want to error on the conservative side of compression ratio suitable for the fuel available. Inversly if the motor is quite detonation resistant because of messaged piston domes and chambers smoothed for sharp edges, a tight quench,,,, you can bump static compression up a 1/2 a point generally and still not detonate. But it's a FINE line and something you really don't want to guess at. As is most every measurement in calculating compression.

Re: HP /TQ / CR questions
 

Thanks for the explanation Marv D. The block has been rebuilt & the heads have been pocket ported. Either way, I don't think the block has been decked or the heads milled. If they were, wouldn't that increase the CR from 9.5? A 9.5 CR is what a 454 bored .040 over (4.29 x 4.0) with flat top pistons & 100cc chamber heads & a gasket thickness of .039 calculates to. Can we base the HP & TQ calcultions off of that estimate??

Re: HP /TQ / CR questions
 

Hey, it isn't in and running yet?? It was decked and the heads were shaved to true them, not zero decked, just squared. The machinist told me to figure on the 9.6-9.8 static, but the rest of the info is needed to do the actual compression ratio. I figured that engine should be close to 450-500hp and about 500lb/ft of tq. Again the machinist said he had built quite a few 462-8's along the same lines as this, but they didn't have the Vortec head, and those numbers were about right for them, so this should be at least that and then some as the Vortec heads are a way better casting then the early gm ovals.

Re: HP /TQ / CR questions
 

Hey Mike,
Nope, I'm ashamed & embarrassed to say that I haven't goty it in yet. I thought I would have done it by now. I used to have money & no time, now I have the time & no money. Now I am just trying to figure out the specifics on it to waste time i guess.