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Compression question

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Old Oct 22, 2008 | 12:10 AM
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Default Compression question
I am underway of installing a new 347 longblock that I bought off a forum member. I have an A&A D1SC and looking to make in the 700+rwhp on pump gas. My question is 10.1:1 compression going to limit me on reaching my goal? I have some ported/polished 317 heads with 72cc chambers that should lower the compression to 9.3:1, should I swap the AFR heads for the 317s?

Here is the build sheet.

General Description - 347 Aluminum LS1 Long Block
Short / Long Block - Long Block
Block Type - 5.7L Aluminum Gen III
Displacement (CI) - 347
Bore - 3.905"
Stroke - 3.662"
Application - Forced Induction
Desired Compression Ratio - 10.1:1
Core Provided? - No
Crank - OEM - Magnaflux and Balanced
Rods - Scat H Beam 6.100" x 0.927"
Pistons - Diamond with -2cc Valve Reliefs
Rings - Diamond
Cam Bearings - Durabond
Rod Bearings - FM
Main Bearings - FM
Main Studs - ARP
Main Caps - OEM
Rod Bolts - ARP
Heads - AFR 205cc
Head Fasteners - ARP studs
Head Gaskets - GM MLS
Camshaft - MTI "R1" hydraulic 232/236 115 LSA
Timing Chain - Rollmaster Dual
Oil Pump - None
Lifters - Comp Cams 850-16
Pushrods - Chrome-moly
Rocker Arms - None
Last edited by EVLZ06; Oct 22, 2008 at 12:13 AM.
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Old Oct 22, 2008 | 06:00 AM
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No, I don't see it being a problem. Add a methanol injection kit to it and you can even put some timing in there. Bob
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Old Oct 22, 2008 | 08:02 AM
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I wouldn't trade AFR's for 317's
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Old Oct 22, 2008 | 09:04 AM
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Originally Posted by BLOWNBLUEZ06
I wouldn't trade AFR's for 317's
Been running the AFR's on my stock bottom setup and the only problem I have is wheelspin
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Old Oct 22, 2008 | 10:03 AM
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You shouldn't have any problem....maybe get a better set of Heads and defently add Methanol! !
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Old Oct 22, 2008 | 10:11 AM
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Originally Posted by MIKE-C5
You shouldn't have any problem....maybe get a better set of Heads and defently add Methanol! !
Better set than the AFR's? Forgot to mention up top I have a methanol kit.
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Old Oct 22, 2008 | 10:15 AM
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I'm just worried that with 10:1 compression its going to hold me back from running bigger boost safely!
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Old Oct 22, 2008 | 10:19 AM
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My compression is 9.5:1 and I will be going to the dyno to get some new #'s this weekend hopefully, but I'm expecting over 900. With 1/2 point higher compression and a few less cubes, you still should easily be able to reach your goal and safely I might add.
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Old Oct 22, 2008 | 11:16 AM
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I know there are more variables but how much boost could I safely run on pump gas?
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Old Oct 22, 2008 | 03:00 PM
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Originally Posted by EVLZ06
I'm just worried that with 10:1 compression its going to hold me back from running bigger boost safely!
The AFR's will generate higher power numbers and provide more torque throught the curve....10.1:1 is not high compression for boost by todays standards. If given a choice of 500rwhp with 9psi at 9.5:i CR OR 500rwhp with 7psi at 10.1:1 CR I would pick the lower boost version EVERY TIME Better throttle response and less chance of belt issues
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Old Oct 22, 2008 | 03:06 PM
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Originally Posted by NemesisC5
The AFR's will generate higher power numbers and provide more torque throught the curve....10.1:1 is not high compression for boost by todays standards. If given a choice of 500rwhp with 9psi at 9.5:i CR OR 500rwhp with 7psi at 10.1:1 CR I would pick the lower boost version EVERY TIME Better throttle response and less chance of belt issues
Very well said The more efficient your combo is the less boost required to hit your goal.
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Old Oct 22, 2008 | 03:53 PM
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Originally Posted by 95vettski
Very well said The more efficient your combo is the less boost required to hit your goal.
Thank you sir You touched on a key word, "efficient". Generally speaking, the higher CR's make the most of the combustion stroke yielding more power & fuel economy...although I know that nobody in the FI section is interested in MPG
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Old Oct 22, 2008 | 04:10 PM
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Thanks guys for all of the great responses I'm going to stick with the AFR's and let her rip!!
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