throttle before or after turbo

Van Setten, Tim (AZ75) Tim.Van.Setten at CAS.honeywell.com
Mon Mar 8 15:43:50 GMT 1999


On our off-road cars, we have done it both ways.  I have to tell you from
experience, go BLOW thru!  On the suck-thru you have to have the carbon seal
behind the compressor to keep engine oil out of the manifold.  Good luck!  I
have seen the best and no matter what you do, you will have manifolds full
of oil.  When oil gets into the air / fuel mix, it lowers your octane
immediately, and pinging will start at lower boost pressures. 

On blow thru turbo's, the carbon seal (which adds drag) is replaced with a
steel ring.  Bosch makes a vacuum operated "Pop-off" valve for about $
30.00.  Bosch PN  0 280 142 102.  These work beautiful and keep the turbo
spooled up.

One more thing to consider:  I have a friend that works for Garret designing
turbo's and the statement made is that you do not want to restrict the air
intake to the turbo or you will lose compressor efficiency.  To be safe,
figure about a 110 degree angle immediately off of the intake hole into the
biggest air filter you can find.  Case in point, look at any big diesel rig,
they have about a 10" air hose going to the side of the turbo which has a
little 1.5" opening.  They do this for a reason.
If you need help finding these pop off valves, let me know.  Glad to help.
Tim.



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