Geeze:
I was 24 digests behind this list due to obscene work-load. It has taken
two weeks to wade through all of them and catch-up. Man! ... it is
frustrating to be about two weeks behind everybody reading the list and
then see something that you want to reply to. However, you realize it
would be so totally out of sink with the current list that it would just
totally confuse everything. . . maybe even get flamed to boot :-)
The GM roots blower numbering system stands for the number of cylinders
times their volume. For example, a 6 cylinder (2 cycle) diesel with 71
cubic inch cylinders would use a 671 blower. The ROOTS is a positive
displacement device and it was sized by GM to produce 3 psi pressure in the
exhaust (i.e., crankcase ) of the 2 cycle diesels. Since a two cycle has a
power stroke (or intake stroke) EVERY revolution you would DOUBLE the 3 psi
or 6 psi for a 4 cycle engine. So... 6 x 71 = 426 cu. in. On a 426 (4
cycle) motor you would get 6 psi of boost by using a 671 blower if it was
geared 1:1. Put it on top of a 350 cu inch motor and 426 /350 = 1.21. 6
psi x 1.21 = 7.26 "theoretical" boost. I say "theoretical" because the
numbers assume a perfect set-up. I.e., no rotor leakage, no adiabatic heat
of compression, 100% volumetric efficiency, etc. Since, a ROOTS is
positive displacement pump, a "ballpark" starting point is to just make a
ratio out of the over (or under) drive you want and multiply that times
your existing pressure. Your mileage may vary.
-Elon
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