Flowmaster BP

[Dave Williams]

-> Was afraid to turn up the boost more than 18 with all that BP.

 7psi back pressure doesn't sound bad at full throttle.  I have an SAE
report of 15psi on the stock Mustang II V8.  My 302 RX7 with single
exhaust and stock Mazda muffler runs 0 unless at full throttle, where it
runs about 10.  My '71 Capri 2000 runs 0, with 1-1/2 to 2 at full
throttle.

 Back pressure is not good, but how bad it is seems to vary according to
the motor.  A friend with a Galant VR4 (turbo) had read about the
wondrous power increases available with expensive exhaust systems.  We
tried back to back runs at the drag strip, stock and disconnecting the
entire exhaust system past the turbo downpipe.  There was lots of noise,
but the ET didn't change a bit.  We therefore inferred that if zero back
pressure gained us nothing, a $400 HKS exhaust pipe and muffler was
unlikely to do any better.

 My '68 F100 has dual exhausts - about four feet of 2-1/2" pipe coming
off each manifold, with an H-pipe.  No mufflers.  Exit under the
passenger side of the cab.  You'd expect back pressure to be low, and it
should be, but the high pressure pulses are still formidable.  Enough
that it has blown a manifold gasket and an exhaust donut.  Compared to
that, a few PSI from a muffler is probably close to irrelevant.

==dave.williams at chaos.lrk.ar.us======================================
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