Help....I've purchased an old Chevy and it runs a GM 4-71 blower(on top of a 400 Pontiac which is supposed to have been rebuilt to suit the blower).The car runs o.k. but lacks the grunt I thought it would have.
I fitted a 'sport comp' boost/vacuum gauge to the intake manifold (under the blower).at idle I get about 20in.hg of vacuum and flat out the gauges reads about 0psi boost/vacuum.
Why am I not getting any boost?(everything looks o.k. ie no leaks,pulleys are both about the same size.)The rotors do not have any teflon strips and look to be in resonable condition apart from one that has a small mark on it.
What can I do to sort this problem without sending the blower to an 'expert'?
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tbucketdom

Hopefully, others with experience will respond, but in the meantime, here's a few thoughts.
------The 4-71 may be too small for your 400. A 6-71 may be more suitable.
------The 4-71 may need to be overdriven (turn faster than the crankshaft) to pump more air.
------If your carburetion is too restrictive, you can lose boost.
------Check to see if any pop-off valve is fully seating, and not leaking. (A friend's would not leak under vacuum, but would leak under boost.) Also, if equipped with a pop-off, be certain that it is adjusted to allow boost, yet still function as planned. ------Check websites of the various blower builders. Many have tech info which may help.

What does a blower have to do with a "Shiny, puffy thing?" .........OH, I get it!
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MrWillys aka HRB
Member: Dipstick Street Rod Association
Paint don't make 'em any faster!

sorry,it must be my 'warped Kiwi' sense of humour!
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tbucketdom

http://www.project33.com/search.cfm
Project 33

Click the "view engine build" links. He give a lot of info about rebuilding a blower.
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Damn, I wish I had more time.
35 Ford Pick-Up

All the sugestions are very good. sometimes a light car needs to pull a long hill in intrmediate gear to show true boost.