What is the process to determine the pulley ratio to run with a regular
roots type blower? . . . Would a simple 2:1 ratio be a good place to start?
- Aron
As usual I'm 3 days behind the list but I have had a good time reading all
the comments regarding blower issues. A lot of good experience and wisdom
behind those words. But the question was how to establish pulley ratios.
Here is my stab at it.
600cc blower x 2:1 ratio = 1200cc output. 1200/1000 = 1.2 pressure ratio.
1.2 x 14.7 (one atmosphere) = 17.6 psi, which is only 3 psi boost. These
numbers are only theoretical because in practice, as boost increases, your
pressure looses increase and a host of other issues develop that lower boost
pressure from the theoretical ideal. So even though you want to limit the
amount of pulleys you have to fabricate, in reality, you will need a few
ratios on both sides of your calculations. But remember, blower RPM is the
product of engine rpm times blower ratio. If the engine sees 7,000 rpm x
3:1 blower ratio you get 21,000 RPM at the blower and a lot of shrapnel :-)
-Elon
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