Turbo Bypass-reading turbo speed

Greg Hermann bearbvd at sni.net
Thu Aug 13 08:47:41 GMT 1998


>Chris
>U'm thinking it's not a problem. Durn! this one kept me awake. Mass flow
>thru compressor must always be equal to or greater than mass flow through
>turbine (Not counting fuel mass) (greater than when waste gate is open.)
>Or else sumthin is badly sick in the engine. If compressor intake is
>throttled, pressure ratio across compressor will always be higher relative
>to pressure ratio across turbine, and turbine will not make as much power
>relative to compressor load, therefore, shaft speed will be lower.

This is not a lot different from what a dirty air cleaner will do to a blow
through set-up, or from the way an aero engine behaves with increasing
altitude.
The aero engine doesn't even have to contend with increasing backpressure
against the turbine, and the waste-gate opens less and less, and finally
not at all with increasing altitude, and then power begins to drop as you
go higher still. All of which indicates that shaft speed falls off with
increasing compressor vacuum.

May still run through some calcs.

                                        Regards, Greg




>Chris,
>
>
>
>>
>> Sounds like this setup needs a way to read the turbine's RPM, and make
>> that an input into the wastegate/boost control. Something as simple
>> as an audio pickup with some filtering might even do, if the turbo
>> has a clear enough note to it. Though something that reads shaft
>> speed a bit more directly would be nice, of course. Any comments?
>>
>
>I'm going to watch turbo speed on my turbo kit that I'm building for
>my car. I think a good setup is a flush mounted optical
>sender/reciever mounted on the compressor side of the turbo. Then
>paint one leading edge of a compressor vane with some black paint. So
>as the compressor rotates the signal changes frequency. Then all you
>have to do is setup the electronics to count the pulses, have'nt
>worked this part out yet.
>If the sensor gets dirty of course your readings will be skewed...
>
>Later,
>Andre
>
>==
>
>Andre
>_________________________________________________________
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