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

N

NicD

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Mar 4, 2004

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Oct 28, 2005

#1

• Oct 28, 2005

• #1

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...

 

T

TheUser

Active Member

Jul 25, 2003

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Springfield, MO

Oct 28, 2005

#2

• Oct 28, 2005

• #2

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

 

M

mustangmarks

New Member

Dec 14, 2004

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Oct 28, 2005

#3

• Oct 28, 2005

• #3

TheUser said:

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

Click to expand...

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

 

M

mustangmarks

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Dec 14, 2004

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Oct 28, 2005

#4

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• #4

mustangmarks said:

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

Click to expand...

Yet!!!

 

T

TheUser

Active Member

Jul 25, 2003

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Springfield, MO

Oct 28, 2005

#5

• Oct 28, 2005

• #5

mustangmarks said:

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

Click to expand...

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.

 

S

Sicarius428

Active Member

Jan 6, 2004

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Oct 28, 2005

#6

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• #6

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

 

N

NicD

Member

Mar 4, 2004

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Oct 28, 2005

#7

• Oct 28, 2005

• #7

Sicarius428 said:

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

Click to expand...

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?

 

T

TheUser

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Jul 25, 2003

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Oct 28, 2005

#8

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have you considered domed pistons instead of dished?

 

N

NicD

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Oct 28, 2005

#9

• Oct 28, 2005

• #9

TheUser said:

have you considered domed pistons instead of dished?

Click to expand...

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

 

T

TheUser

Active Member

Jul 25, 2003

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Oct 28, 2005

#10

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• #10

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

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

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WPG/MB/CA

Oct 28, 2005

#11

• Oct 28, 2005

• #11

9.6:1 should be ok with some low boost.

 

3

304billet

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Sep 16, 2005

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#12

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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.