KA24DE-T Overboosting

[RobbyMcDonald]

I am having trouble holding boost with my ISIS RS3871. If I go WOT it will hold boost at 11psi, when I have it set to 7psi. I have tried setting the actuator arm lower but it still holds at 11psi. I have checked for leaks and found none. I though it might be the actuator, so I swapped on another new ISIS 3871 I had, but I still had the same problem. I was hoping you guys could throw me some ideas to try out, cause I'm stumped atm. Thanks for any help.

[AzS13hatch]

I know nothing about that turbo specifically, but are you sure the spring in the wastegate isn't an 11psi spring? If it is, you will only be able to go as low as spring pressure unless you have the ability to adjust the actuator to have the wastegate permanently open some, in which case your spool time will be slower and would be very inefficient for the turbo. Better off just running 11psi and going with it

[RobbyMcDonald]

It's internal and you adjust it through the arm on the side. I had it set to around 8 psi on my last motor, but swapped to another ka recently. It was holding 7 psi fine, but I had a leak with the intake manifold. After getting that fixed it would not hold boost properly.

[Koukiii]

Maybe it was holding 7psi fine only because there was a leak not letting it creep up. Internal gates on quality turbos are already not that great so on an isis...

[RobbyMcDonald]

It could be, but I don't think that is the issue. I was using this turbo on my last motor until my 4th cylinder went bad. It had no issues on that motor and none on this motor until I had the gasket changed on the intake manifold. But I don't understand how fixing the air leak in the manifold would cause this issue unless my gauge is reading wrong for some reason after the change.

[AzS13hatch]

If you had a leak on the intake and fixed it, saw more boost.... You just solved your own issue. Vacuum leak fixed and you now see the correct amount of boost.

[RobbyMcDonald]

But my problem is that no matter what I set the boost to it always pulls at 11psi full throttle. Im pretty sure its not the acuator or turbo cause i changed to new ones and adjusted it around on those also and only read 11psi.

[jr_ss]

Try a different gauge.

[mewantkouki]

Probably the fact that a quarter sized internal wastegate port can't effectively bleed off boost from a turbo that large.

[RobbyMcDonald]

SOLVED
I got confused on what to set the timing at. Had it at 17* when it needed to be at 20*. After fixing that it pulls hard and keeps boost pressure steady at what I set it at.