Turbo Bypass

[Greg Hermann]

>Does anyone have any thoughts or references to info on the type and
>positioning of Turbocharger bypass valves?
>
>Things I'm wondering about...
>
>- bypass to compressor inlet vs. dump to atmosphere
>- pre-intercooler vs, post-I/C dump point
>- effects on A/F Ratio
        My first and best thought is AVOID USING BLOW OFF VALVEs IF YOU
POSSIBLY CAN! How? Draw through a throttle body(s) into the compressor(s),
and run the compressor(s) in vacuum at part throttle. No restriction points
between compressor(s) and intake ports. Yep, you need to have the best
compressor seal to do it this way, but it's well worth it. It becomes
virtually impossible to put a properly selected compressor into surge, You
will have much shorter spool up time (because the compressor will be
spinning far faster as part throttle). You will have much lower exhaust
back-pressure on the engine at part throttle, and consequently longer life
and lower cruising BSFC (better mileage).
        As far as I'm concerned a throttle between compressor and intake
only happened because factories wanted to add turbos with a minimum number
of part revisions and cheap seals. Yes, some of the early porsche race
turbo cars did it to get better throttle response with relatively primitive
design turbos. This is just not that much of a factor any more, and those p
cars were pretty much an efficiency be damned design. If you really want to
chat about efficiency and turbos, get hold of me off list (this is a bit
off mission) and we'll talk about using long tube headers with turbos.
                                        Regards :), Greg