351 Compression Ratio Piston Choices

[351carlo]

Ok guys, so the motor's in the shop getting built. The machinist told me to stick with the 9.5 flat tops and I agreed. He said with the open chambers it'd be 9.5 to 1 (Speed Pro Hypo's), and would be the highest he would go streeting the motor.

I know plenty of guys running 10.5 in their stangs, how adverse will this be for my performance?

Just as a sidenote, any idea how this new motor will fair?
Current buildup is:

351 Cleveland .030 over
Speed Pro Hypo 9.5 pistons
Balanced rotating assembly
2.05 Manley swirled stainless valves
1.71 exhaust valves
3A valve job
Springs matched for cam
270H cam .519 .519 with 110 LSA and .224 .224 at .050
Performer RPM
625 Demon (hopefully replaced with 780 DP Holley)
1 3/4 Headers
Dual 2.5 flowmaster 40 series
Fresh FMX transmission
2000 stall converter
B&M Stage 2 shift kit
Pertronix Ignitor II

 

[bapford]

comp ratio

Just opinion, but he's right with the 9.5 for a street motor.
No use in going any more if your going to drive it on the street and don't want the problems of having to use better that pump grade gas all the time.
I went that route once, 10.15:1. It was great if I ran race gas and hit the track, but stunk on the street. Oh well.
Brian

 

[SadbutTrue]

Are the heads on that cleveland 4vs? Looks like you have 4v sized valves in it anyway, so with a portjob it might not matter. But it'd still be good to know i guess.

 

[351carlo]

Are the heads on that cleveland 4vs? Looks like you have 4v sized valves in it anyway, so with a portjob it might not matter. But it'd still be good to know i guess.

No, while my valves are oversized, they are a planned oversize. While the exhaust is from the 4v Cleveland, the intake is much smaller, yet still .015 over stock. Stock size is 2.04 mine will be 2.055. These are actually SBC valves with a .300 extension which will allow them to work in my heads. Apparently this is a good combination to use to make the 2V heads work up to their full potential.

Any thoughts on this topic?

 

[nosaj122081]

With a mild cam, 9.5 will run fine. I'd clean up the ports a little also. No such animal as a Performer RPM for the 351C, only 2 choices for a a 2V Cleveland that aren't real expensive or hard to come by are the Performer or the X-CELerator. Also, for that motor your 625 Demon should be perfect; you don't wanna run a DP with an auto tranny. I figure that combo will make around 300 or so flywheel horsepower.

 

[351carlo]

Truthfully, I'd be pretty pissed with only 300 FWHP. My machinist estimated 375+.

 

[nosaj122081]

Truthfully, I'd be pretty pissed with only 300 FWHP. My machinist estimated 375+.

I had a similar setup with my old motor; except my cam was a little stouter. In a lightened 72 it was probably a high 13 second setup with 3.89's. No way was it almost making 400HP though, at max it was 350 flywheel, which even that is probably a bit optimisitic. My friend had a built 5.0 that dyno'd at ~300 RWHP through a Tremec, which would put it around 350 flywheel, and that car woulda romped mine. 300-350 is a realistic number.

 

[351carlo]

My eventual goal is low 13's. For now I'd be satisfied with a high 13 timeslip in my 70.