Here's the deal...

I got tuned for alky, but I could not hold more than 22psi. Tried a different boost controller same thing. Tried a different boost gauge same thing. Did a boost leak test and found the stock bov leaking at 22. I bought an APS bov and now I can hold up to 26 but I should be at 28. The guy I bought it from had a short screw in it so I bought a longer screw, tightened it, and it got up to ~27/28 but with a lot of compression surge. Played with the setting and lost the compression surge, but now its at 26 again. And its also tapering off all the way to 18, which of course is way too much.

For another test, I pulled the wastegate vacuum line from the boost controller, did a 2nd gear pull but it only held to 26, didn't get up to 28-30.

I have a knowledgable friend who believes its the wastegate and I'm leaning in that direction also. Does anyone have any ideas? What else can I check??

 

You are trying too hard to get to that "magical number". That is actually OUT of the turbos effective range! You are fine where you have it!

 

i think 28psi on pump is too much to be running. id stick with ~26psi

 

He's not on pump - he's on alky with pump. He can run any boost the turbo can give him as long as it's tuned properly with enough alky.

However, worrying so much about 28 just makes no sense. The turbo is not efficient beyond 25psi. Higher than 25 can be sustained only at lower rpms, and you can make more torque, but it just generates heat up top. For reference, and this is not the end-all for every Evo, but it illustrates a good point:

- 26psi peak tapering to 22.5psi by 7k on a Dynojet with bolt-ons, stock cams, alky, and custom flash, I made 341whp/361wtq
- 28psi peak tapering to 23.5psi by 7k on a Dynojet with same mods, I made 347whp/383wtq.

I got the big 20wtq peak gain, which is right for 2more psi, but I only gained 6 peak whp. Additionally, after this peak whp figure, which was in the low 6000rpm range, my 28psi curve dropped BELOW my 26psi due to blowing too much hot air. I found 26psi to be a good, reliable boost level for daily driving that didn't cause heat at higher rpm.

 

Ok...so far the consenses is that I'm maxing out the turbo. Then tapering all the way to 18psi in 3rd should point to a leak. But, I did a boost leak test up to 24 and everything was fine. Could it still be the wastegate?