Hi all, I've recently installed (well...installing) a twin turbo setup on my car. It's a 2006 mercedes slk 55 amg. 5.4l v8. Sts kit with 2 - sts200 model (.36a/r, 48mm s-trim ...if it helps they're the ones in the 5.0-6.0l corvett kit). I have 2.5" exhaust all the way, x-pipe pre-turbos. 2-38mm wastegates with factory spring (5lb). 550cc injectors, haltech elite 2500 ecu. No BOV installed at the time(I have one just don't need it on there yet...1 more potential leak). 2" charge pipe coming up each side to a 3" y to the throttle body.

The problem I'm having is this:
When I rev up to the rev limiter (4k rpm) it starts to build up boost around the 2500 rpm range. Gets the vac/boost gauge up to almost 0(within 1 or so in/hg on the vac side)then drops mack to full vacuum. No matter how long I hold on 4k rpm it won't build again.
I've checked all the charge pipes for leaks, pulled both wastegates and put 3/4" silicone/rubber fuel hose inside the spring to hold them shut, and still does the same thing.
I pulled the charge pipes and ran them out the side so I could put my hand over them while I rev, just to see if it was really blowing(thinking it might be a gauge issue) but it does exactly what the gauge says. Starts to push air and then drops off to what feels like a hairdryer in the cold/low setting... Watching the turbo impeller wheel as i rev, I can see it is spinning, just can't figure out why no boost.. These are small turbos...really small, but the vette guys are getting 500-ish RWHP out of these same turbos on their setups...I'm stumped.
I know a lot of people don't like sts, and that's fine. To each their own, bash sts if you must, but please help with the issue.

 

You are testing this loaded ? In gear with load or are you free reving the engine?

 

Revving. The car is on stands, so no load.

 

that might be part of your problem. Free revving with no load may not build boost but driving it should.

 

Oh, ok. This will be my first turbo experience other than just driving cars with factory turbos.. never worked on any before. Wouldnt have thought the carvwpuld know the difference between revving and loaded, but the rev limiter seems to know., so I guess the turbos/exhaust/intake could too. Lol. Thanks!

 

test drive the car, you need load like 91turboterror said.

 

No load , no boost

 

Like others have said, with a turbo you can't typically build boost just free revving the engine in neutral. The exception is if you have a two step and retard the timing and/or cut spark, which is what drag cars do before launching