347, 9.6:1, 5-6lbs boost, stock block

[NicD]

If my stroked 302 combo ends up around 320-350 rwhp, i'd like to be able to add a little boost (5-6 lbs.) to up the hp to around 400-420rwhp...

My 347 is being assembled in a stock block, and the compression ratio with my AFR 185's (611cc combustion chamber) and dish top pistons is going to be around 9.6:1...

Would adding boost be feasible or would i be better off (and safer in terms of what the stock block could handle) going with say 11:1 with flat top pistons and no boost?

Opinions please...

Oh, daily driver, pump gas (CA 91 octane), custom cam, RMP II manifold, 70mm TB & EGR, 75mm MAF...

Thanks...

 

[TheUser]

9.6:1 seems a little high to me for boost. Lets see what the others say.

 

[mustangmarks]

9.6:1 seems a little high to me for boost. Lets see what the others say.

I have 10.1 with 7lbs of boost on a stock block with p&p stock heads and no problems here.

 

[mustangmarks]

I have 10.1 with 7lbs of boost on a stock block with p&p stock heads and no problems here.

Yet!!!

 

[TheUser]

I have 10.1 with 7lbs of boost on a stock block with p&p stock heads and no problems here.

Have you had it dyno tuned?

I'd definately recommend a dyno tune if planning to run boost on a 10:1 engine. The tune could make or break you or NicD really.

Good Luck. Others will chime in w/ more experience-based answers. I'm just really basing my opinion on the little that I've read on here about higher than stock compression and boost.

 

[Sicarius428]

You are going to be pushing the limits of the block. Some get away with it some don't. Nobody will know for sure but definately get a good tune. It might make the difference.
Kevin

 

[NicD]

You are going to be pushing the limits of the block. Some get away with it some don't. Nobody will know for sure but definately get a good tune. It might make the difference.
Kevin

Is there a general consensus of what the rwhp a stock block will take? I've heard 400rwhp - 450rwhp?

Another general question, if i decided to add a supercharger, how much could i lower the compression by going with a larger head gasket?

 

[TheUser]

have you considered domed pistons instead of dished?

 

[NicD]

have you considered domed pistons instead of dished?

I was told i'd be about 9.6:1 with dish top, 11:1 with flat top...Never really considered dome top...

 

[TheUser]

ha ha, I had things twisted in my mind; I was thinking domed=less compression and dished created more compression...my badamnit:

 

[88_GT_5_oh]

9.6:1 should be ok with some low boost.

 

[304billet]

Stock 302 roller block, CAT 4340 forged crank and CAT 4340 H beam rods, Dart Windsor Sr ported heads, ported Downs lower, Comp cam XE282HR, 9.75:1 comp flat tops, C116 race gas, 611rwhp and 630rwtq on 15 lbs of boost from a S-trim, custom burned chip. This was scary and probably should not have done it. Limits of stock block 500-520rwhp.

Backed off the C116 went to 100 octane and hit 550/560 @ the RW.

This same 347 stroker w/ AFR 185's ported heads, same cam and intake, 30lbers and 10.3:1 comp put down 400/400 @ the RW, NA on 93 octane. He flycut the pistons to reduce it to 9.75:1 in the above combo.

331 stroker drag motor w/ 11:1 comp pistons running 25 lbs of YSi boost, 780rwhp. Owner is an engine builder, drag racer and dyno tuner. It's all in the tune.

Bottom line is 9.6:1 will be fine for a boosted app. Don't go beyond 500rwhp.