Twin Turbos (Massive snippage safe to read)

[Greg Hermann]

>>or 1500 rpm, and WAY more efficient than even a screw compressor type
>
>That's exactly why I want one... just don't have quite that much cash.  They
>spool up to full boost much earlier, like you said.  Matches everything I've
>read.
>
>>supercharger (such as a Whipple).
>
>
>I never considered the Whipple all that efficient... you're talking the
>intake mounted unit, like the Weilands, right?

A Whipple-charger (which is a true screw compressor, actually made by
Auto-Rotor, in Scandinavia) is easily 50% more efficient than a good old
Roots type blower. (As in all the various size variants of the Jimmy
"Screamin' Demon" 2 stroke diesel blowers.) (Remember--the Jimmy diesels
never meant their blower to generate any boost--these type blowers are only
really properly applied as a positive displacement, very low pressure fan!)
I got a copy of the volumetric efficiency--adiabatic efficiency curves for
the various size Autorotor compressors from Whipple a while back.

Most of the screw compressors have an AE that peaks at about 55 or 60%--as
compared to a 68 to 76% peak AE (in the center of the "island") for most
decent centrifugal compressors. Another interesting point with the screws
is that you have to spin them at a pretty good clip before their VE comes
up to a decent level (due to blow back being a significant percentage of
their displacement at low speeds). So--a properly matched Whipple unit
(matched so as not to overspeed it at the top end) probably does not get
the boost up at any lower engine speed than a VATN turbo will. Likewise for
a properly matched Roots blower.

Be EXTREMELY interesting to see what happens when the AA/F dragster boys
figure out what VATN turbos could do for THEM!!! (One per cylinder??? With
acetone/dry ice cooled intercoolers???? 4's anyone??) :-) Yeeee
Hawwwww!!!--Whole new kind of skiin' for Grumpy!!

Regards, Greg
>
>Frederic