Author Topic: accell and boost  (Read 6615 times)

Offline Arthur

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accell and boost
« on: September 16, 2009, 01:50:24 am »
Hi all.

When I open throttle on 2000rmp my lump turbo doesn't do much. When I do the same on 4000 the requiered accell needs to be a lot more because there's a big turbo pushing in more air.

Does vems multipy accell enrichment on boost?

Do I need to use pressure based accell enrichment to solve this problem?

Offline Jorgen

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Re: accell and boost
« Reply #1 on: September 16, 2009, 04:30:05 am »
Hi,

When going from a small or no throttle opening to a high throttle opening the turbo will not be able to spool up during the interval when you normally need acc enrichment. This means that the boost will not affect how much acc  enrichment you need.

When dropping the hammer after throttling the engine enough that you only get maybe ATM pressure in the plenum even if the turbo is pushing hard on the throttle blades you will not need much acc enrich as the fuel film in the intake is mostly stabilized (most of the reason you need acc enrich at all). In these cases it's common to have too much acc enrich if the engine is tuned to have the right acc enrich when starting from lower initial intake pressure. So at the end we have a small problem but it is the opposite of what you fear.

There is something else that may cause the acc enrich demand to seem larger at higher engine speeds and at higher boost levels. That is if you accelerate hard and then shift slowly while releasing the throttle enough to activate the overrun fuel cut during the shifts, just to slam on the throttle very hard after the shift. During the overrun fuel cut event the fuel film in the intake will be vented out and the car will need several times the normal acc enrich after the shift. So this kind of driving will not only be slow and make your passengers sick. It will also require very wierd acc enrichent settings. We are working on a way to solve this but just like most other systems we haven't currently found a way to solve this, at least not one that will be possible for an end user to tune or one that he can afford to have a tuner set up for him. In the very recent firmwares that are under testing now we have forced a delay in the overrun fuelcut that will minimize this problem. We also have some fuel film compensations that further help minimize the problems related to this kind of driving.

We hope to find a new and more powerful way to set up the acceleration enrichment over a wide range of conditions without making it very time consuming to tune.

I hope my answer was helpful.

Jörgen Karlsson

Offline Arthur

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Re: accell and boost
« Reply #2 on: September 16, 2009, 10:50:36 pm »
Oke

Sound logic. Fuelcut has something to do with it. It gets better when turned off.