Rocc and Rado
Legacy Member
wouldn't oversixing the exhaust slow down the exhaust thus making the turbo spool at a higher RPM?
The way I see it is this: the amount of ''air'' that comes out of the exhaust is independent from the size of the xhaust. So, smaller exhaust = faster ''air'' speed through to the exhaust = faster/earlier spool... :dunno:
I'm just curious as to know the ''mechanics'' of it..
And to answer the question, Any n/a with high displacement, take a pic! V10TDI probably or W16!!
what you fail to see is that the exhaust gas is expanding once it leaves the turbine, so the more room it has to expand, the quicker it can go across the turbine... this is why a k03 on 3" DP tends to overspool and makes boost control difficult throwing CEL's and whatnot, this is what affects the spool directly, not really the velocity of the exhaust as this is a function of volume AFTER it has crossed the turbine
your theory that the "amount of air" being independant from the exhaust volume is not totally incorrect as this statement implies mass air flow, but the velocity of the air is not an abolute indicator of efficiency, allow me to explain
you want the pressure differential between the manifold and the exhaust to be as great as it can be, this is accomplished by increasing the exhaust system volume, thus the velocity of the exiting air is directly affected by its volume, but you are not looking to increase said velocity thru the tailpipe, but across the turbine wheel...
if the exhaust volume is too small, it will increase the exhaust velocity at the tailpipe but also increase the pressure making it harder to pass from the manifold (under great pressure) to the exhaust (the smaller one having more pressure). this means the turbine wheel does not get all the energy from the gases due to increased temps and pressure in the manifold, rather it is lost in the form of heat thru the manifold piping, making a less efficient system with overall less power, this can also lead to reversion if the exhaust pressure is so great as to impede the passing of the exhaust thru the turbine forcing the gas back into the combustion chamber
it is only desirable to keep the exhaust velocity greater in the exhaust manifold so it will transfer more energy to the turbine wheel, as long as there is not so much heat, pressure, and/or ultimately reversion as to harm performance
i hope this helps you out freddyboy, fabio... danther is abolutely correct
and to answer the Q, G60 and 16v's ftw, the shittiest motors that require the most love are my fav's, heh, maybe this is why i can put up with high-maintenance woman, or not, lol