Re: Indy pop-off valves

[PDQSHIP@aol.com]

In a message dated 96-02-29 21:39:36 EST, you write:

>will produce substantially less mass (read exhaust gasses) to push the 
>turbine side of the turbo.  So am I wrong in thinking that the turbo will 
>progressively spin DOWN with operation of the pop-off valve?  Of course 
>as soon as the valve shuts, boost has to build again.  I think this is 
>what Graydon was talking about.
>
>Jere

Turbo map theory Jeremy.... Nerd cap on......  We are talking about a turbo
with no wastegate first off.....  Sooooo, the turbo cannot slow down fast
enough on a full throttle run, and in fact it will explode on the first full
throttle run AND the pop off valve will activate too, prolly right before the
schrapnel......   The wastegate slows the turbo down, without it, any boost
condition would be MAX boost immediately....  To map a turbo to conform to
just the requirements of an engine is not the practice....  Most builders
exceed the demand of an engine by at least 10% more like 20, to adapt for
various conditions of load/throttle......   In theory the turbo will spin
down with the activation of the pop off valve, yes, but if you have no
wastegate, the initial reaction of the pop off valve (assuming spring loaded
mechanical similar to a wg) would be for the turbo to spin faster, not
slower, to overcome the air loss of the bleed.....   Again, I'm not sure this
needs too much discussion, just about EVERY turbo car I've seen, Race or
Street, has a Wastegate, so this discussion is tangentile as far as I'm
concerned....  With a pop off valve, you are not controlling the boost with
it, just the boost threshold, and given the design of turbos, you will pop it
on every throttle on condition....  Hardly the intent of CART.....  Their
intent is to prevent wastegate manipulation with a: you exceed this level of
boost, you loose....

Scott