I finally got my mechanical boost gauge installed, drawing the vacuum line from below the throttle plate. (ran a line through the firewall under the rear seat)
So I have some questions about what to expect;
I get very little boost in first gear even if I push the rpms to 4000rpm it only gets about .2 bar.
The boost drops completely changing to 2nd gear then builds again to about .5 bar at 4000rpm. If I stop accelerating (close the throttle) and hold it at 4000rpm the boost then drops off and becomes vacuum.

If the throttle is barely open should the boost be maintained based on RPM alone?

Is my wastegate malfunctioning?

My setup is K26, stock waste gate, Kokeln intercooler.

 

RPM alone will not sustain boost as boost is built according to engine load. Say you are crusing at 4500 RPMs in third on th freeway and holding steady. You will likely have no boost at all. If you start to go up a hill, however, and want to maintain 4500 RPMs, you will build boost to hold that speed.

When my car was mostly stock (like yours), the boost was very much an all or nothing proposition. Once boost started it would come on all at once. If you want full boost in first gear, you may have to go past 4000 RPMs. Try pushing the throttle to the floor and holding it to 6000 RPMs or so - I bet you see .8 bar.

 

At steady state you should have vac after the throtle plate. The closed/restricted plate keeps the motor from accelerating. You might actualy still have boost before the throtle plate based on the quanity of exaust gasses.

Any time you are under load (accel) the vacum will go to zero. If you are turbo'd or suppercharged you will achive boost, if you have it.

If you change to a GLH header system & a K27-7200 you will see much more boost in first gear and easly full boost in second much earlyer.

You have the old style "Compressor Bypass Valve" which I'm not very fimillar with. If you shift quickely you should not see to much loss of boost between gears at higher rpm's. Might have yours checked or ask others on the board how well theres works.

I have a C2T style CBV and you can hear it working between quick shifts. My boost comes back much quicker now that I have it working right.

K

 

Thanks for the info Bill and K.

On a Kokeln I assume the CBV is the black plastic valve which is connected to to the short hose on the drivers side of the intercooler. Does any one know how to test the Compressor Bypass Valve?

 

Correct about Kokeln.

Not sure but on a formal test procedure but:

If you tried to blow into the side that attaches to the I/C and at the same time into the small tube that attaches at the throtle plate - no air should pass.

If you then add vachum to the small tube, the valved should open and you will be able to blow air into the I/C supply oppening. You could use a hand vackunm pump to do this but don't add to much vac or you might rupture the dipharm.

Or for $45 you can just replace it.

The two supprizes I had on my car was a bad CBV and injectors that had a poor spray pattern. Both changes reduced my turbo lag so some degree.

K