Compression question

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Oct 22, 2008 | 12:10 AM

EVLZ06

Thread Starter

Burning Brakes

Joined: Sep 2005

Posts: 1,218

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From: Temple TX

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.

Oct 22, 2008 | 06:00 AM

0EPP

Former Vendor

Joined: Dec 2006

Posts: 2,239

Likes: 1

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

Oct 22, 2008 | 08:02 AM

BLOWNBLUEZ06

Tech Contributor

Joined: Apr 2007

Posts: 10,924

Likes: 78

From: Forney Texas

I wouldn't trade AFR's for 317's

Oct 22, 2008 | 09:04 AM

NemesisC5

Le Mans Master

Joined: Dec 2005

Posts: 8,475

Likes: 332

From: Port Arthur, Texas 77642

Quote:

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

Oct 22, 2008 | 10:03 AM

MIKE-C5

Race Director

Joined: Jan 2003

Posts: 19,802

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From: San Antonio Texas

St. Jude Donor '05-'06-'08

You shouldn't have any problem....maybe get a better set of Heads and defently add Methanol! !

Oct 22, 2008 | 10:11 AM

EVLZ06

Thread Starter

Burning Brakes

Joined: Sep 2005

Posts: 1,218

Likes: 0

From: Temple TX

Quote:

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.

Oct 22, 2008 | 10:15 AM

EVLZ06

Thread Starter

Burning Brakes

Joined: Sep 2005

Posts: 1,218

Likes: 0

From: Temple TX

I'm just worried that with 10:1 compression its going to hold me back from running bigger boost safely!

Oct 22, 2008 | 10:19 AM

BLOWNBLUEZ06

Tech Contributor

Joined: Apr 2007

Posts: 10,924

Likes: 78

From: Forney Texas

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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Oct 22, 2008 | 11:16 AM

EVLZ06

Thread Starter

Burning Brakes

Joined: Sep 2005

Posts: 1,218

Likes: 0

From: Temple TX

I know there are more variables but how much boost could I safely run on pump gas?

Oct 22, 2008 | 03:00 PM

#10

NemesisC5

Le Mans Master

Joined: Dec 2005

Posts: 8,475

Likes: 332

From: Port Arthur, Texas 77642

Quote:

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

Oct 22, 2008 | 03:06 PM

#11

95vettski

Safety Car

Joined: Mar 1999

Posts: 3,600

Likes: 170

From: Toronto, Canada

Quote:

Originally Posted by NemesisC5

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.

Oct 22, 2008 | 03:53 PM

#12

NemesisC5

Le Mans Master

Joined: Dec 2005

Posts: 8,475

Likes: 332

From: Port Arthur, Texas 77642

Quote:

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