Danno

"if I don't have some sort of absolute system that measures the mass of the air going in, I may end up with boost+ambient and not get sea level performance"

Once the ambient air gets compressed by the turbo, it's irrelevant what its initial pressure/density was. Boost in the intake-manifold is measured in absolute pressure like the gauge on the dash. It may just happen to be that the turbo has to spin faster to generate that same boost at 5300' as at sea-level, but that's what the boost-controller and its adjutability is for; to regulate the boost-level.

Also since the bottom of the wastegate-diaphragm is vented to the atmosphere, lower ambient pressure will cause the wasteate to open at a lower boost-pressure. Again, requiring a boost-controller with adjustability. An electronic controller would be best here as it will maintain the same boost-level regardless of altitude and ambient pressure (within mechanical capabilities of turbo and wastegate).

Jfrahm

That's what I thought, but that means I would need to move more CFMs than a sea level car, so I might need to go with a bigger turbo to achieve the same levels of performance (total air molecules in.) That or overspeed the turbo... but does lower ambient air pressure skew the efficient operating range of the turbo? Then I'm just revving it to death sooner but perhpas still in an efficient range?

-Joel.

toddk911

Andy, thanks for the info. I know I desparately need to get the cat out and wastegate shimmed.

Danno, didn't you mention GURU was working on some kind of wastegate upgrade or spring change for the stock wastegate???

Do any of the 930 wastegates fit or can you use the spring of the 930 for 951???