max compression
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
It actually has a lot to do with the cam you are running and it's duration/overlap but for something with a mild cam with a aluminum heads
I agree with the post above 11:1 CR is a good limit to impose on yourself when building a motor. Mine runs on 91 but I have a fairly big cam
I agree with the post above 11:1 CR is a good limit to impose on yourself when building a motor. Mine runs on 91 but I have a fairly big cam
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
Originally Posted by MotorHead
It actually has a lot to do with the cam you are running and it's duration/overlap but for something with a mild cam with a aluminum heads
I agree with the post above 11:1 CR is a good limit to impose on yourself when building a motor. Mine runs on 91 but I have a fairly big cam
I agree with the post above 11:1 CR is a good limit to impose on yourself when building a motor. Mine runs on 91 but I have a fairly big cam
Mine has 11:1 CR with aluminum heads & is OK with 93,(barely) & 230 deg. @ 0.50" hyd. roller cam.
Drifting
Joined: Sep 2003
Posts: 1,325
Likes: 6
From: FRANKLIN GA
Motorheads right, compression is only one component of an engine. A well thought out engine can handle a lot of compression on pump gas or visa versa one that is randomly thrown together by picking stuff out of a cataloge can ping at 10:1
Cam overlap, piston head shape and material, combustion chamber shape of the heads and head material, piston to head quench, timing and timing curve, and carb. jetting all have a very definate impact on how much compression you can get away with on pump gas.
I'm running 11.94:1 and it will run on 93. I have to richen the carb and turn the timing back a little but it runs fine on 93. You just have to think about how everything works together.
Cam overlap, piston head shape and material, combustion chamber shape of the heads and head material, piston to head quench, timing and timing curve, and carb. jetting all have a very definate impact on how much compression you can get away with on pump gas.
I'm running 11.94:1 and it will run on 93. I have to richen the carb and turn the timing back a little but it runs fine on 93. You just have to think about how everything works together.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Another thing that is overlooked alot is the vacuum advance. That can advance you timing into the 50 -55 and more degress. I have never run one and never had any pinging problems. My last 355ci had 10:1 CR with iron heads and the crankiing compression was 230psi across the board and I ran 40deg advance on 93 octane no problem.
Also when I first put my 406 motor in I set the timing but with all the crap going on the distributor must have got bumped a little because when Lars looked at it a few days later he said it was set at 45deg advance at 3000RPM, that's with 11:1 CR and aluminum heads. If I was running a vacuum advance I bet there would have been alot of pinging
Also when I first put my 406 motor in I set the timing but with all the crap going on the distributor must have got bumped a little because when Lars looked at it a few days later he said it was set at 45deg advance at 3000RPM, that's with 11:1 CR and aluminum heads. If I was running a vacuum advance I bet there would have been alot of pinging
Melting Slicks
Joined: Dec 2004
Posts: 2,161
Likes: 0
From: pr, frederick md.
Originally Posted by EDDIEJ82
Motorheads right, compression is only one component of an engine. A well thought out engine can handle a lot of compression on pump gas or visa versa one that is randomly thrown together by picking stuff out of a cataloge can ping at 10:1
Cam overlap, piston head shape and material, combustion chamber shape of the heads and head material, piston to head quench, timing and timing curve, and carb. jetting all have a very definate impact on how much compression you can get away with on pump gas.
I'm running 11.94:1 and it will run on 93. I have to richen the carb and turn the timing back a little but it runs fine on 93. You just have to think about how everything works together.
Cam overlap, piston head shape and material, combustion chamber shape of the heads and head material, piston to head quench, timing and timing curve, and carb. jetting all have a very definate impact on how much compression you can get away with on pump gas.
I'm running 11.94:1 and it will run on 93. I have to richen the carb and turn the timing back a little but it runs fine on 93. You just have to think about how everything works together.
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