Re: [DML] Re: Turbo PRV.

[Martin Gutkowski <martin@xxxxxxxxxxxxxx>]

Hi David

I'm afraid you're barking up the wrong tree here. Either that, or I've 
misunderstood how my engine works :-) What you're describing is a safety 
device to control overpressure. Not sure what it'd be called but I know 
that the one on my Turbo-diesel everyday car is also controlled by the ECU.

A "proper" turbo'd engine blows -through- the throttle(s). This means 
that when the throttles are closed, the turbo is suddenly pushing 
against an enclosed space. At the same time the throttles are closed, 
you get vacuum in the manifold, and this is connected to the dump valve 
(blow-off valve) which uses the vacuum to open a port on the turbo 
outlet and either lets the air excape in to the air, making that typical 
"Pshhhhh!" or the better way of doing it  (and more correct especially 
on an air-mass metered engine) is to plumb the dump valve outlet back to 
the inlet of the turbo. This is called a recirculating dump valve.

In the case of both the BAE and Island turbo kits, they suck from the 
throttles, so when the throttles close, the turbo is evacuated rather 
than pressurised which is not how they are designed and will eventually 
blow seals.

Hope this makes sense!

Martin

David Teitelbaum wrote:

>
>Dump valves (over here we call them blow-off valves) would seem to be
>a necessary part of any complete turbo system. There is a thing called
>turbo overboost, sort of the opposite of turbo lag where if you
>release the throttle at high speeds quickly you can overshoot the
>limit on your boost momentaraly and overboost the motor. The blow-off
>valve is basically a pressure relief valve set slightly higher than
>the boost controller so if the boost should exceed the control's limit
>the blow-off valve releases the excess boost pressure. I am guessing
>it has not been offered because of cost. IMHO it may be good
>insurance, especially if a boost control or a wastegate should stick.
>Boost valves can be either a simple pressure relief valve or it can be
>controled by a line monitoring the boost pressure.
>David Teitelbaum
>vin 10757
>  
>






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