New crate motor
Thread Starter
7th Gear
Joined: Dec 2011
Posts: 7
Likes: 0
From: Whiteford Maryland
New crate motor
I put a new GM 350 crate motor #12520270 4-bolt main 8.75:1 compression ratio (rated as 190 hp with stock heads and cam) in my 1991 Coupe. My GM tech removed my cam and alm heads from my L98 motor (all in very good shape). I am breaking in the motor now with 700 miles so far. Any ideas on what this motor will produce HP wise with the corvette FI, cam and heads from the L98? Any other ideas or tips? Car runs great, will change the oil and have tech go over it at 1000 miles.
Appreciate your thoughts.
Jim
Appreciate your thoughts.
Jim
Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
Thread Starter
7th Gear
Joined: Dec 2011
Posts: 7
Likes: 0
From: Whiteford Maryland
I pulled the cast iron heads off, and the cam out of the crate motor, and put my still good L98 fuel, injection, cam from the L98 and the heads from the L98 onto this new crate motor.
Jim
Jim
Race Director
Joined: Apr 2003
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From: moraga ca
Your original L98 had 10:1 compression, the crate 8.75 as you stated. I'm not sure if the difference was in the heads or in the pistons. If your current pistons are dished, you will be down on compression and down on horses. Over one point of compression is a lot.
Race Director
Joined: Feb 2004
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Going from a 76cc combustion chamber down to a 58cc chamber will take that crappy compression ratio up to near 10.5 to 1.
Should run a pinch better than stock.
Should run a pinch better than stock.
Last edited by Pete K; Dec 19, 2011 at 06:50 PM.
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Safety Car
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I don;t think the stock motor was ever 10:1....9.5:1 is all I ever read about.
After mine was bored and used thin gaskets all I ended up with was 10.5:1 with stock style pistons, same cut outs same dish.
I agree that the change from iron to alum heads alone will hopefully get his compression up...at <9:1 he could run brandy in the thing and not knock...E85....low compression motors are for junk fuels..
After mine was bored and used thin gaskets all I ended up with was 10.5:1 with stock style pistons, same cut outs same dish.
I agree that the change from iron to alum heads alone will hopefully get his compression up...at <9:1 he could run brandy in the thing and not knock...E85....low compression motors are for junk fuels..
Race Director
Joined: Apr 2003
Posts: 17,699
Likes: 1,667
From: moraga ca
I don;t think the stock motor was ever 10:1....9.5:1 is all I ever read about.
After mine was bored and used thin gaskets all I ended up with was 10.5:1 with stock style pistons, same cut outs same dish.
I agree that the change from iron to alum heads alone will hopefully get his compression up...at <9:1 he could run brandy in the thing and not knock...E85....low compression motors are for junk fuels..
After mine was bored and used thin gaskets all I ended up with was 10.5:1 with stock style pistons, same cut outs same dish.
I agree that the change from iron to alum heads alone will hopefully get his compression up...at <9:1 he could run brandy in the thing and not knock...E85....low compression motors are for junk fuels..
Le Mans Master
Joined: Jun 2006
Posts: 5,642
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From: One day you're a Comet...the next day you're dust... Arkansas
This is from memory but I believe the 1991 pistons were flat tops and compression was @ 10.2:1 They may have tinkered with the cam profile or just stated a low HP rating to make the LT1 look better in 1992. Either way the 113 heads didn't change.
