Waste Gate control sampling port
07-14-2002, 06:53 AM
#1
Track Day
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Location: Oregon
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Waste Gate control sampling port
Hello Boost Addicts,
I have a '77 turbo (U.S. specs) modified with B&B exhaust, Elgin SC330 cams and TIAL wastegate. At 80K the motor was rebuilt by Porsche here in Germany due to oil leaks. Big no-no over here.
For 6 months the car ran sluggish at lower speeds. It would build boost very slowly reaching max boost (.70 - .75 bar) at 4500 RPM as read by my big 2" VDO boost gauge plumbed into the brake booster hose.
The waste gate control line is a 7/16" unit that was sampling boost pressure from a port on the throttle body located above the butterfly valve.
Out of frustration, I re-routed the waste gate control hose to another port located beneath the butterfly valve. My thinking is that the wastegate and the boost gauge will now read real manifold boost pressure instead of pre-throttle pressure. Anyway, since I made this change the car is MUCH more responsive to throttle input. Small changes in throttle pressure increases boost pressure nicely. Full throttle runs on the autobahn are still limited to 0.75 bar pressure. The funny thing is that at 1/3 to 1/2 throttle the boost pressure will creep up to 0.9 bar.
Did I booger something up by changing the sampling port, or will this setup fly.
Thank you, Turbo wizards, for your input.
SlowTurbo
(But I still drive faster than most of you, eh eh eh!!)
I have a '77 turbo (U.S. specs) modified with B&B exhaust, Elgin SC330 cams and TIAL wastegate. At 80K the motor was rebuilt by Porsche here in Germany due to oil leaks. Big no-no over here.
For 6 months the car ran sluggish at lower speeds. It would build boost very slowly reaching max boost (.70 - .75 bar) at 4500 RPM as read by my big 2" VDO boost gauge plumbed into the brake booster hose.
The waste gate control line is a 7/16" unit that was sampling boost pressure from a port on the throttle body located above the butterfly valve.
Out of frustration, I re-routed the waste gate control hose to another port located beneath the butterfly valve. My thinking is that the wastegate and the boost gauge will now read real manifold boost pressure instead of pre-throttle pressure. Anyway, since I made this change the car is MUCH more responsive to throttle input. Small changes in throttle pressure increases boost pressure nicely. Full throttle runs on the autobahn are still limited to 0.75 bar pressure. The funny thing is that at 1/3 to 1/2 throttle the boost pressure will creep up to 0.9 bar.
Did I booger something up by changing the sampling port, or will this setup fly.
Thank you, Turbo wizards, for your input.
SlowTurbo
(But I still drive faster than most of you, eh eh eh!!)
07-14-2002, 10:42 AM
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Join Date: Jun 2001
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The only thing I can think might be a problem is subjecting the wastegate to vacume. I also didn't think the difference in port would make that much difference. The throttle doesn't make a big restriction. If you had a inefficient intercooler and plumbed the wastegate too before the intercooler. Then I could see a big difference. I think I would make sure that there is no boost leak.
Dean
Dean
07-15-2002, 11:16 AM
#3
Nordschleife Master
Everything is fine. The boost gauge in your dash probably isn't that accurate. My VDO boost gauge sometimes will spike to 1.5bar eventhough I know the MoTec computer will shut the car off at 1.2bar. I also take my pressure reading from the brake booster and my car is set for 1.0bar.
