User 52121

I'm with blown944... I've never heard of this being a problem before. The 951 is the first turbo car I've owned that DIDN'T tap the intake manifold for a WG pressure/vac source.

Dave W.

A good ball and spring type MBC will not let vacuum get to the wastegate. The ball/spring will close off the line under vacuum. Not all MBC's are ball/spring type, some are just simple bleeder valves.

This is a good discussion. I automatically hooked up my MBC to the turbo outlet pipe just like stock and never thought about it. Now I may change things around and get the pressure source from the manifold.

User 52121

Ok did a little experimenting - swapped the boost source from the banjo to one of the manifold ports. I closed my MBC for both tests (so minimum boost.)

End result: Banjo bolt - ~12psi, falls to 10. Manifold source, 13psi, falls to ~11 eventually - but DOES hold on longer, it takes a bit longer to fall down to 11.

So it made a difference.

refresh951

I appreciate all the input I received in this thread. Ran some more tests at the dyno last night. I made a few changes; added a spring (small yellow) to my Tial 38 that made the spring effectively 1.15 Bar. I also moved the WG supply line to the output side of the IC and ran a bigger WG supply line (3/16" ID) as shown below. I was able to to hold boost better with about 0.5 psi drop (rather than 1.5 psi) between peek and redline. Even though I held boost better I did not see any real difference in power on top. I was expecting to see 10-15 more horsepower but just did not happen. I really think 350 is the max I am going to see out of this current setup. Therefore this spring/summer I am planning 3 projects:

1) Full 3" Exhaust (2.75" downpipe)
2) Head work (not sure exactly what path I will take yet)
3) Rogue EBC

Results...TBD

zerMATT951

Hell yeah!



...and thanks for documenting all of this, it's great info.