New 402, 135-145psi on compression test?
Thread Starter
On The Tree
Joined: Jan 2005
Posts: 112
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From: Boulder, CO
New 402, 135-145psi on compression test? The cam is a comp XER, 238/244 .605/.612, 112LSA, 2 degrees advanced. Duration at 0.006" is 287/293. The intake valve closes 73.5deg after bottom dead center.
The static compression ratio is 10.9:1, dynamic compression ratio is 8.1:1. I found an online calculator (http://www.rbracing-rsr.com/comprAdvHD.htm) that says my "dynamic cranking pressure" is 162psi.
Next Level Performance (who's tuning it) did a compression test, and got 135-145psi, across the board. That's with the engine cold, and no mileage on it yet, besides the dyno runs.
NLP thinks the compression test is low. FFHP (who built the motor) thinks it's nothing to worry about.
I know the cam overlap and late closing of the intake valve will bleed some pressure off, so I shouldn't expect as high of compression test results as a stock LS1. I also know compression tests give lower results on a cold engine. I do not know if the rings are fully seated, or if perhaps compression will go up after the rings are done seating.
Thoughts?
The static compression ratio is 10.9:1, dynamic compression ratio is 8.1:1. I found an online calculator (http://www.rbracing-rsr.com/comprAdvHD.htm) that says my "dynamic cranking pressure" is 162psi.
Next Level Performance (who's tuning it) did a compression test, and got 135-145psi, across the board. That's with the engine cold, and no mileage on it yet, besides the dyno runs.
NLP thinks the compression test is low. FFHP (who built the motor) thinks it's nothing to worry about.
I know the cam overlap and late closing of the intake valve will bleed some pressure off, so I shouldn't expect as high of compression test results as a stock LS1. I also know compression tests give lower results on a cold engine. I do not know if the rings are fully seated, or if perhaps compression will go up after the rings are done seating.
Thoughts?
Thread Starter
On The Tree
Joined: Jan 2005
Posts: 112
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From: Boulder, CO
Originally Posted by Patrick B
check your abdc, sounds wrong.
With the cam that's in there, if it's installed straight up (with the 2 degrees of advance that are ground in), the intake valve closes 73.5 degrees ABDC.
Sounds low to me unless the rings aren't seated yet. Squirt some oil in the cylinder and check it again. I'm putting out 250-260 psi with about the same DCR as you and 11.0 SCR. I also checked mine cold which may read a little lower. How many cycles did you turn the motor over when you checked it? Good cylinder pressure = good HP. How did it do on the dyno?
Dan
Dan
Thread Starter
On The Tree
Joined: Jan 2005
Posts: 112
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From: Boulder, CO
Originally Posted by DanZ28
Sounds low to me unless the rings aren't seated yet. Squirt some oil in the cylinder and check it again. I'm putting out 250-260 psi with about the same DCR as you and 11.0 SCR. I also checked mine cold which may read a little lower. How many cycles did you turn the motor over when you checked it? Good cylinder pressure = good HP.
Originally Posted by DanZ28
How did it do on the dyno?
