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Sr20det Compression Test Question???
What is the ideal compression for a s13 Redtop with cp 8:5:1 cr pistons, and 264 cams... I read an article saying that cams are a factor... Also what is the cause if cylinders read 190 psi across the board??? Info would be much appreciated...
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im not sure but 190 across the board looks good for 8.5:1
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haha 190? All of my 8.5-9.0 motors made 165.
The bigger the cams, the lower the compression, depending on the valve overlap of the cams. 190psi sounds like a 10.5-11.0 motor to me. Were those CP's flat-tops? Otherwise, the machine shop probably decked your block/head a crapton. |
wow 190 . . isnt stock 150?
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or your cam timing is off.
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Originally Posted by miataspeed
(Post 7413486)
or your cam timing is off.
Block/head decked, different pistons, bad compression gauge. |
Ya, i think it is a bad compression gauge. The guy i am possible trading my car for his motor said he is going to try it again... and after doing some research the readings are a lot higher than they should be... one cylinder he says read 197 psi, and another 194... Thanks for all the input btw
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You sure it isn't a ka..? lmao
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The cam timing can effect the compression. As you probably alread know most cams are ground with +4 advance based on TDC. This is to make the cam more drivable, Idleable.... If you retard the cam to true zero, it can increase the "Static" compression and take some drivability out of it. It's all based on the intake valve closing position and how much intake charge is allowed to excape. It's call the Volume/pressure index and requires a large slide ruler to calculate. Good Luck , and thank you. zack
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Originally Posted by miataspeed
(Post 7413957)
The cam timing can effect the compression. As you probably alread know most cams are ground with +4 advance based on TDC. This is to make the cam more drivable, Idleable.... If you retard the cam to true zero, it can increase the "Static" compression and take some drivability out of it. It's all based on the intake valve closing position and how much intake charge is allowed to excape. It's call the Volume/pressure index and requires a large slide ruler to calculate. Good Luck , and thank you. zack
You're talking 1-2psi of compression... if that. At cranking speeds, there's 100mS of time for the cylinder fill event. This is more than enough to ensure that cylinder pressure is equal to the manifold pressure. The flowrate for that situation is just 5 Liters/sec. You're passing that through two holes that are an inch across... thats really not a whole lot of flow restriction. comparatively, at 9,000RPM, you need a flowrate of 150 liters/sec. yikes. |
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