i have hks 280s, 102k miles at 155psi across all 4 cylinders

 

Factory service manual says Min. is 138 psi.

 

All of your info is correct. Except number 2. Which could not be more wrong. Cams, and pistons are the two things that create your static compression number.

Larger cams have overlap, and thus less compression. Higher or lower CR pistons will also take this in to account.

An stock piston evo 8 with good rings, and hks272's made 155 on my compression tester. My completely stock evo 8, made 175 psi on the very same tester, 2 mins later. All readings were taken AT WOT and with the motor at or close to operating temp. With my new motor - I will take a reading after about 500 miles and see. This will be 9.0 wiseco pistons and kelford 272 cams. I expect to see numbers in the mid to high 150's.




See post above.


138 is very low - only extreme milage, or a lost of hg, or broken ring land will lead to this..

 

for reference, evo 8's should have around 160 which is a strong motor and evo 9's with around 140 for a strong motor

Rob

 

My low mileage evo8 def had 175 on the tester when hot.

 

I was getting 170psi across the board with GSC S2's and stock block.

 

my evo with 50 k miles stock block and cams tested at 155 psi cold

 

engine is big air pump , so everything you do intake , cams , exhaust ,valve job , intake manifold will impact the compression in some way , highly overlaping cams will lower compression readings , also it makes difference if engine is cold or hot

 

The service limit for EVO 9 IX compression test is 650 kpa which is about 95psi. Normal is 1000 kpa or 145psi. I have put together an evo 9 engine with fp5r cams twice. On a fresh build after a few hundred miles of driving both times I have numbers right around 100psi. No variance between cylinders. Also performed a leak down test and the leak down numbers were good. So everything was sealed up tight.

I would not get too concerned with a used cammed evo 9 engine compression unless it was in the 70s, and or if there was a substantial difference in cylinders. You have to remember that not only do larger cams have more overlap so less air gets trapped during the test, but mivec cams gear is at full retard when there is no oil psi. I believe with the stock cam that this would actually be about 7* retarded compared to an evo 8 intake cam. I dont know off hand what most aftermarket mivec cams are ground on.

Also on "built" engines, you will have to take in affect the material removed in the combustion chamber to unshroud the valve, as well as larger valve reliefs/different dish cc of the piston.


If you have consistent low numbers on a compression test in any evo 9 I would do a leak down test before freaking out. Mainly, if the car runs as good as you like and its not smoking/using a lot of oil, dont worry about it.