[torsen] Turbo theory

[Brian Devlin]

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OK, so lets say you set up the wastegate to open whenever the
throttle closes. Is that feasible in a purely mechanical setup? Then,
hopefully, the turbo would maintain more-or-less the same speed while
you shift, instead of grenading.
The problems that occured to me had more to do with engine control.
By putting the throttle so far upstream you would have the huge
volume of all the tubing and intercooler between the throttle and
cylinders. First problem: you'd need to fill it up when you step on
it, which might be a noticable delay (or maybe not, if the turbo is
going fast). If you were using CIS, would it go rich while all this
plumbing is filling up?
Second, when you let off the gas all this pressurized air needs to go
somewhere. So if you push in the clutch while releasing the gas, the
rpms would jump sharply. It seems that either a blow off valve or
fuel cut off would be needed to control this.
This is about the time that Javad should suggest EFI, which would be
a good idea anyway.
-Brian

>In a message dated 11/20/2001 6:43:28 PM Eastern Standard Time,
>bdevlin at stanford.edu writes:
>
>>Why is the turbo on my Audi upstream of the throttle? It seems to me
>>that it would keep spinning faster and longer if it was in vacuum.
>>-Brian
>>
>
>
>Because then the throttle would act as a choke to the turbo and
>could cause some real spin problems. If the turbo was spinning hard
>and the throttle is closed to shift, the turbo would be trying to
>suck thru a closed pipe and the results to the turbo and whatever
>entered the engine after breakup wouldnt be funny at all. To keep
>the turbo spinning faster and have it spool quicker you should
>reduce any intake restrictions and reduce exhaust backpressure to as
>near zero as possible (10lb range is excellent and I would love to
>have it) I run a K&N cone where the oil cooler used to be and gutted
>cats w/3" exhaust and have more work to get maximized. Reducing
>restriction in and out is the key, just like in an engine. More air
>in and out: more power for an engine, with a turbo, minimize the
>energy required to suck air in and reduce restrictions to pushing
>air out and you increase spool-up speed increase bearing
>effectiveness, reduce blade instability and decrease heat generated!
>by internal friction, all really good things.
>If you decide to try the throttle first trick, let me know what
>happens but be on guard in regards to personal risk (dont stand too
>close).
>Rod