I had a compression test done recently.

It seems my car is not holding boost the way it should.

I just had comp 272 cams installed. The car boosts fine - spikes @ 21psi holds 19ish to 7k rpm then drops off to about 17 psi.

I've done some research and some posts have stated that since my VE has changed the turbo can't keep up some boost drops off. But, I see posts were others have cams and seem to hold 20 ~ 21 psi to redline.

We checked and found no boost leaks. I changed out my TurboSmart BOV to a Evo IX BOV.

The compression test was done as a last resort.

Here are the numbers:

cylinder 1: 180
cylinder 2: 180
cylinder 3: 180
cylinder 4: 165

That is less than 10% difference, but it still seems a little troubling to me.

What do you guys think?

I may change my stock WGA to the Forge unit thinking maybe it will fix the boost drop off.

 

Head studs done?

Have you done a boost leak test? Seems a little soon to jump to a compression test.

 

You know what, I just installed the exact same cams 3 days ago, and my boost is the same as it was before I installed cams. 20psi all the way to redline.

 

Headstuds - yes.

Boost leak test done and no boost leaks.

We are thinking that I may have a faulty WGA. The compression test was done because we were changing the spark plugs so decided to do it.

I think the numbers are withing spec. Just curious what others think.

 

When you mean redline - do you mean all he way to your rev limit i.e. 7800 rpm or there abouts?

Or, do you mean when it just starts hitting redline - 7000 rpm?

Thanks.

 

hmm number four is a little suspect!

 

i dont like number 4 either.

 

My compression was 170-175 across the board with 35,000 miles...I guess that is good...I haven't looked up the exact numbers and what the service limits and what not are supposed to be...I don know that if you install cams and don't degree them, compression checks can look funny.

 

That might be your answer right there. Comp cams have a lot more lift then most streetable aftermarket cams for the evo.

 

What would be the next step?

What causes compression numbers to change?

What's the best case AND worst case scenario?

 

I used to have a similar problem as this too. My comp numbers are 150/150/150/150. Based on my experience, I would either readjust or replace the wastegate actuator.


After I put the Forge one on there, my problem was gone.

 

I have seen dozens of evos with a low cylinder

Its usually 3 or 4

Often there is some corelation between this and a probem with boost falling off

HAVE YOU PRSSURE TESTED THE SYSTEM TO 26 PSI ?????

If so - the next step is a leak down test and see if the air is leaking down the bottom or the top

Intesreting observation, I have seen several cars lately with 272 cams from HKS which appera to have issues with exhuast valves closing all the way - don't know if its just a few cars needing exhuast valves or what

BTW - feel free to bring the car by when I am in DC this comming week and I will be happy to give it a free look over at VIP

Al

 

the stock WGA is adjustable, so shorten up the rod by a full turn. i think the forge WGA will allow a min of 22-23 psi.

 

Well I shift at 7200rpm right now

 

150 is kinda low is that with car fully warm or cold?