Where'd my boost go?

Pudge

Pudge

New member
Joined
Aug 23, 2007
Messages
421
I seem to have lost about 20lbs of boost somewhere, and can't find it. We are running the same charger from last year, but we changed everything else. Last year was an all stock motor, this year we have a cam and greatly increased headflow as well as a "big" pump. We've pressure tested the system and only found 3lbs difference from the turbo inlet to the intake manifold. (53-50lbs) So it's not leaking, much anyway. We currently have 35lbs boost and 57 drive pressure. We've changed and checked boost gauges and moved the boost sensors on our data logger. The turbo seems fine (s400), no excessive shaft play, some side to side but none in and out, and the wheels haven't been damaged. Any ideas? Is there any way that the head work and cam would cause it to drop 20lbs of boost? It's been consistent in the boost and drive for the past 10 pulls or so that we have logged, not getting any worse but we should have more boost, I feel anyway. Any ideas will help greatly. Thanks guys. 12v motor by the way
 
I agree, but I don't think anyone only makes 35lbs of boost with a 2.6" charger in a s400 frame, or are they? lol
 
does she still spin out at the top of the track and pull just as hard as before?
 
Last year it wouldn't spin out at all, now it does. It's definitely got more power with less boost than it had
 
I know of some 2.6 trucks in the midwest that are easily over 1000hp and make just under 40psi boost.
 
It's your headwork. I'm running a charger that my buddy ran last year and I'm maken 55psi when he was making 37psi only difference was his headwork and a cam.$.02
 
sometimes less boost mean more power. when i put a 3pc manifold on and ported the head a little i lost 8psi
 
I agree with above. We changed heads this year and our 2.6 S400 only makes around 30psi at 4k. This is down from 45psi last year with a head that had less port work.
 
Thanks guys, it puts my mind at ease somewhat. There's no one else around here to talk to about it.:Cheer:
 
Where'd your boost go? Into your engine :D As long as you don't have any boost leaks, thats a good sign you've got 'er flowin some air.
 
Pudge said:
We've pressure tested the system and only found 3lbs difference from the turbo inlet to the intake manifold. (53-50lbs) So it's not leaking, much anyway.
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ANY boost leak is very bad for performance! I dont know how you are checking it, but I anyways performed a leak down test on a closed system.
$.02
 
Closed system. I've got a plug for the front of the turbo and we pressurize it from there with a regulator on the air hose, checking the pressure vs the boost gauge.
 
I have one for you guys ZERO boost! Just rebuilt engine, P Pumped, turbo rebuilt Pro66, spins like crazy, pressure the intake of turbo and found no leaks, checking waste gate tomorrow but there is no boost at all and you can hear turbo screaming!, hoping its waste gate, if not what else!, Thanks, Rick
 
Pudge said:
Closed system. I've got a plug for the front of the turbo and we pressurize it from there with a regulator on the air hose, checking the pressure vs the boost gauge.
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Are you taking the slack out of the exhaust valves to make sure all are closed???
 
Its driving me CRAZY, wired waste gate closed, you can hear Turbo scream, digital gauge reads Zero, and of course no power, no leaks, have not pulled valve cover yet, but adjusted as always, can't seem to find problem, welcome any help, thanks, Rick
PS: no one local to brain storm!
 
If you are compressing intake tract. And turbo is spinning your wastegate won't have shying to do with it.
Loosen intake rockers to make sure valves are closed, if there is no boost leaks before engine its your valves.
 
I am a few hours away...

Have you loaded the engine at all on the street or in a pull?
 
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