Vintage Mustang Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
647 Posts
Discussion Starter #1
The title says it all. With aluminum heads, this gives an effective CR of about 10.8:1.

I want to finish ordering my stroker kit today, and this question is holding me up.

Thanks,
rk
 

·
Registered
Joined
·
19,949 Posts
You can't just go by static ratio. Cam timing and combustion efficiency are going to have an awful lot to do with it running on pump gas. BTW, you didn't mention what octane pump you want to use. By me, it's 93 and other parts premium is 91. Also how do you know it's 11.3? You must measure all the parts to determine actual compression, do not assume or take some one's claim!

Good news though. Aluminum heads conduct heat better and usually allow a little higher ratio. Also most heads on the market are combustion efficient too. I read of a 351W build up years ago that ran a very similar ratio running 87 octane!

Read this site for more info on combustion efficiency. This guy has built engines with over 20:1 for gas. www.theoldone.com
 

·
Registered
Joined
·
647 Posts
Discussion Starter #4
A little more info


393w
roller cam: 232/240 duration at .050, 566/576 lift, 112 LSA
Edelbrock performer heads - aluminum, 60cc
Octane: 93

Number used to caculate CR
Bore - 4.03
Stroke - 3.85
Gasket thickness - 0.039
Gasket bore - 4.1
Deck height - 0.02
chamber volume - 60cc
Piston volume: either -5CC or -14.5CC

The pistons are what I have to choose from. the -5cc gives the 11.3CR and -14.5cc gives the 10.2 CR. Which would you go with?

rk
 

·
Registered
Joined
·
19,949 Posts
The new Edelbrocks are suppose to be more efficient. In the latest issue of Muscle Mustang & Fast Fords, they tested 13 aftermarket heads on a 302. I forget the cam used but with stock E7 heads the motor made 300 hp. With GT40P, 337 hp. Edelbrocks made 384 hp! And that was more then any other aluminum head stested, such as Canfields! I'd recomend getting that issue and reading up.

Good luck.
 

·
Registered
Joined
·
38 Posts
I'm running a 351W with cast iron world heads and a 10.3 static CR. I do use some octance booster but to tell you the truth, I've never tried leaving it out. Car runs great and doesn't make any wierd CR related noises. Why do you want to go over 11? Seems like overkill that will just cause problems down the road. Now if you were going to a computer controlled fuel injection and ignition system that could compensate, well maybe but even then you'd be spending thousands of dollars without getting your monies worth.
 

·
Registered
Joined
·
560 Posts
I your slug .002 or .02 in or out of the hole. If it is
.002 in or out of the hole your math is incorrect. The 14cc heads will get ya to 11.
The 5 cc heads will get ya closeer to 12:1.
Have you 4 squared your block yet?
I just got finished going thru all this with my just completed 393. I ended up at 11:1
 

·
Registered
Joined
·
647 Posts
Discussion Starter #9
Horeseplay

The piston clearance is 0.02 in the hole, and that is how I made my calculations.


edit: 0.02, not 0.2
 

·
Registered
Joined
·
560 Posts
If it is .02 in the hole it ain't probably gonna matter what compression you run, you will have detonation with that large of a quench ::. Shave & 4 corner the deck
I think moking up your stroker is in order before you actually have a clue :: of where the slug is gonna be.
 

·
Registered
Joined
·
647 Posts
Discussion Starter #11
First off, thanks everyone for their input. I am a relative newbie here, so I don't deserve good answers to question's that demand "quick response"

My choice is the 14.5cc dished piston. That was the real question I needed to answer, not just a vague CR question.

Basically, I decided to be conservative. The CR calculation is only accurate once you know the exact measurements you feed in. The big unknown is the piston-to-deck height, which can only be determined with everything installed. The 0.02 measurement came from SCAT, which is where I am getting the stroker kit. 0.02 may not be exact, but I bet it is pretty close.

My decision is also based on observations of my 351w before I decided to stroke it. It dynoed over 400hp, and I never had a problem with detonation with 37 degrees of timing. When I tore it down (spun bearing), the piston-to-deck height was about 0.2 (not 0.02). I also had flat-top, butterfly-cut pistons. So dead reckoning leads me to think that the 14.5cc dished pistons, combined with the 0.02 piston-to-deck height will give me close to the same CR I had before.

That may all be rationalization on my part, but that is how I made my decision.

Finally, I don't usually make quick decisions, but today I wanted to get my stroker kit ordered from SCAT. I went through this process before with CHP, but I was not in a hurry. When I changed my mind about the stroker kits, it put me behind, and has made me hurry this decision.


My next big topic will be "cam choice". I have the cam that I mentioned previously, but I may swap.
thanks again,
rk
 
1 - 11 of 11 Posts
Top