<VV> Question about stock '63 turbo boost

Jim Simpson simpsonj at verizon.net
Wed Oct 30 20:44:02 EDT 2013

The turbo Corvair is a very primitive system compared to your Porche 944 --
no waste gate, no intercooler, no fuel injection, no knock sensors...  When
Chevrolet designed the system, they were trying for simplicity (and low
cost).  They had to build an engine that could manage without any of the
controls we consider standard on a modern turbo.  Their approach was to use
a restrictive carb, pressure retard and -- depending upon who you talk to
-- a somewhat restrictive muffler all to control boost and preserve the

By comparison to your Porche, the stock Corvair turbo is "peaky", has major
turbo lag and does not produce significant boost in the lower gears.

I doubt you would ever see any boost in first; the exhaust is still heating
up and you aren't normally in first long enough to get significant boost.
Sometimes you'll see some in second.  Third and fourth are different story,
but again the turbo doesn't produce anything below 2500 rpm and even at
3000 it's still just coming on.  Think of the Corvair turbo as more of a
passing gear.  Floor it in third or fourth, give it a second or so to wind
up, and it will perform.

As others have pointed out, Chevrolet claimed about 10 psi boost.  I have a
'66 turbo (larger turbo and carb) and have instrumented it just to satisfy
my own curiosity.  I've seen 10.9 psi boost in test runs.  (I do run a
Safeguard knock sensor to protect the engine.)

The stock system responds well to modifications.  Wrapping the exhaust
system to retain heat works, but dramatically shortens the exhaust
crossover pipe's life.  It will burn out in a few months.  Larger carbs
allow much more flow plus higher boost.

Similarly, relatively minor problems will greatly reduce boost.  For
instance, a very minor exhaust leak will just about kill any boost.

Jim Simpson
'66 Corsa turbo

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