I have a 5.3L with a 67 turbo, one of the old QMP kits. The spring that is in teh wastegate when not hooked up to a boost controller runs at 8psi. With the boost controller hooked up I had the boost turned up when i had it tuned, and it would initially spike around 18psi and settle down to 14ish. I was thinking the reason for the boost falling off was becuase the spring was too weak to keep the boost pressure, so i got a heavier spring. However, now with the boost controller not hooked up, the boost will go up to 12 psi and then slowly trail off to about 9psi. I obviously know the turbo can hold 12 psi, but for some reason appears to want to drop 3-4 psi at the top end. Any ideas as to what the problem could be here.
Thanks
Justin

 

High Back pressure? Wastegate not big enough?


When running a boost controller, i would think you want the lightest spring possible,

also, what controller are you using?

 

The car has a eboost on it, but it stopped working for some reason. So I put a hallman manual boost controller on it. I was under the impression that if I put a heavier spring in my wastegate, it would be able to hold the boost better in the higher rpm's.

 

check for leaks on the cold side.

 

I checked for leaks today on the cold side and found 2 spots where there was a decent leak. I hooked up my eboost controller and took the manual controller off. It seems to be able to hold boost around 10psi now, but once I go above that, the boost still drops a few psi. I would obviously like for the boost to stay steady up to redline. I even hooked up my eboost controller with the high boost setting that is supposed to apply pressure to the top of the wastegate to help it stay closed to reach a higher boost, and it still trails off. Any suggestions as to what I can do to keep the boost even up top?
Justin

 

Is the wastegate boost referenced at the turbo or manifold ?
I think the turbo is just running out of steam up top.