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Thierry25 Thierry25 is offline
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Join Date: Feb 2009
Location: FRANCE (Besanšon)
Posts: 310
Originally Posted by 911nut View Post
Keith, if this were true, all of our turbo engines would go rich at max rpm, not lean.
Also, the compressor is sucking double the air across the metering plate than a n/a engine does.

Your sentence allow me to explain my idea about the full behaviour.

Actually, I think it is wrong to think the intake air flow increase considerably at high RPM.
Actually past the max TQ band , we can see the torque is dropping dramatically. This drop tell us directly that barrel filling becomes very poor. ( due to the cams, turbo, intake and exhaust limit...). Somewhere step by step, air can not go in and exhaust gas can not go out.

So past the max TQ band, the flow is mathematically increased by RPM but is decrease by filling efficiency. So I think the air flow doesn't increase so much .

Then be back to the so called Kjet behaviour (stock), I think the max fuel capacity of the Kjet is already achieved at little above max TQ band. Past this point the air flow increase slowly but as the flowed fuel is already at it max, the AFR is increasing step by step either.

Then when we switch to more agressive cams, we never get any problem with mid RPM ( since the kjet is self tuning ) but past it fuel capacity we hit the limit in sharper way. No matter higher or a bit lower RPM is ....

Dropping the pressure control doesn't change anything... the metering plate is fully moved ( or very nearly).

Acting the lambda freq valve doesn't change anything either...For max capacity it is even much better to turn it off and to increase the valves adjs. screws. ( Remember this FV returns an important amount of fuel to the tank)

Increase the fuel system pressure ( by shimming the head) bring almost nothing it self.

965 C2T / 1991 3.3 TURBO
Old 01-06-2010, 04:13 PM
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