There's no standard solution. First you need to know how much boost you're supposed to have and what the acceptable variation is among properly installed systems. If you're off by an unreasonable amount, then search for the cause and fix it Too much boost is most likely caused by a leak in the wastegate boost sensing line. Too little boost is most likely a boost leak in the intake system between the turbo and the throttle body.

NOLA's problem was easy to diagnose just from looking at the shape of his boost curve in his data log. Incorrect wastegate setup.

We still don't have a straight answer for what the normal amount of boost is yet. Snarf and I are off by 1 psi from each other, which seems like more than an acceptable variance to me. I'm interested in seeing how much boost NOLA has after correcting his wastegate setup.

If NOLA gets about 9 psi like Snarf, then I will suspect I have a boost leak, and I'll have to perform a boost leak check: fabricate a way to hook an air compressor to the turbo inlet so I can pressurize the full intake system and search for leaks at all the connections with soapy water.

If NOLA gets 8 psi like me, then there's a few possibilities:

1) Maybe there's a 1 psi pressure drop across the throttle body. Snarf's wastegate boost source is downstream of the throttle body. Mine is upstream of the throttle body, and NOLA will be duplicating my setup. If there's a pressure drop across the throttle body, then the downstream boost source will result in more boost in the intake manifold. I could test this easily by temporarily rearranging things so that my wastegate is hooked up similar to Snarf's.

2) Maybe Snarf has too much boost. I had about 1 psi extra boost with stage one, which I suspect was caused by a mangled o-ring on one of the fittings for the boost sensing line for the wastegate. If the test for option 1 above fails, then I would as Snarf to double check that all his wastegate boost sensing line connections are tight.

3) Maybe NOLA and I BOTH have boost leaks. If tests for option 1 and 2 both fail, then I'll work on a boost leak test.


If everything checks out and it turns out there really is a wide normal variation in boost across different installs, then a simple manual boost controller could be used to get a lower boost system up to 9 psi. They basically introduce a controlled leak into the wastegate boost sensing line to trick the wastegate into "seeing" less boost so that it opens later and at a higher actual intake manifold boost level.