Thread: boost bleed off
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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,744
My motor with stock '78 RoW headers, open dump pipe, open "muffler", factory wastegate and 3DLZ would momentarily swing past 13, 13.5 PSI on the VDO mech gauge and then regulate perfectly at 12.5 PSI exactly.

With GHLs, (another, without melted studs) factory wastegate and a K27/HF and a factory muffler (but still an open dump pipe), it does precisely the same thing.

Transient (1/4 of a second, tops) overswing and slight (1 PSI) overboost, followed by rock-solid boost until I get scared/need to watch the road/redline. It might even simply be gauge overswing in my case.


Alan, glad you're driving the car!

Note that boost level is dependant on load as well.

In other words, you will see the boost drop as load drops off - like if the throttle isn't flat on the floor - e.g. if you kick it to 1/3 or 1/2 throttle, watch the boost build and then don't give it any more throttle, the boost will drop off as the RPM's rise. Completely normal.

I'd suggest that to be sure you might want an accurate gauge and a full-throttle 2nd gear run up to 6,000 or so - ideally up a steep hill, preferably with someone else watching the boost.

These cars do change your idea of what a "long, straight stretch of road" actually is...
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'77 S with '78 930 power and a few other things.
Old 12-17-2007, 04:06 AM
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