Question about Req_Fuel

Jon k · Post by **Jon k** » Mon Aug 21, 2006 7:50 pm

I put my engine size etc in to MT and it came up with req fuel of 6.3 but while tuning I found I had numbers approaching over 100 VE while not even on full boost.

Engine:

2.5L inline 6 cyl
42# injectors

So, can I just set my req_fuel upward to like 10 so that my VE numbers are lower? I know it shouldn't matter having the numbers over 100, but I just don't think well like that.

PSIG · Post by **PSIG** » Mon Aug 21, 2006 8:20 pm

Well, your MAP pressure goes over 100 on boost - so why not your VE?

Perhaps you can think of it as over-filling the cylinders on boost - which you are. You're just stuck thinking from a naturally aspirated viewpoint. I would not recommend changing your RF rather than changing your viewpoint.

It's all relative...

David

Jon k · Post by **Jon k** » Mon Aug 21, 2006 8:24 pm

PSIG wrote:Well, your MAP pressure goes over 100 on boost - so why not your VE? Perhaps you can think of it as over-filling the cylinders on boost - which you are. You're just stuck thinking from a naturally aspirated viewpoint. I would not recommend changing your RF rather than changing your viewpoint.

It's all relative...

David

Yeah but to get a like 13.0:1 afr below 100 KPA im hitting like 94 VE...

PSIG · Post by **PSIG** » Mon Aug 21, 2006 8:29 pm

Jon k · Post by **Jon k** » Mon Aug 21, 2006 8:41 pm

PSIG wrote:So?

Ok but THEORETICALLY can I just move my req_fuel higher?

eliotmansfield · Post by **eliotmansfield** » Tue Aug 22, 2006 12:16 am

yes, there's a scale function that will scale your bins down if you up the req_fuel.

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eliotmansfield · Post by **eliotmansfield** » Tue Aug 22, 2006 12:16 am

yes, there's a scale function that will scale your bins down if you up the req_fuel.

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Fastest95PGT · Post by **Fastest95PGT** » Tue Aug 22, 2006 4:23 am

But increasing the Req. Fuel for the sake of decreasing your VE bins will also change your DC. I'd suggest leaving your Req. Fuel at whatever value matches your injectors/displacement for a more accurate duty cycle reading.

Jon k · Post by **Jon k** » Fri Aug 25, 2006 1:27 pm

Fastest95PGT wrote:But increasing the Req. Fuel for the sake of decreasing your VE bins will also change your DC. I'd suggest leaving your Req. Fuel at whatever value matches your injectors/displacement for a more accurate duty cycle reading.

Ok i'll leave it but then what is the highest value I can put in for VE?

Fastest95PGT · Post by **Fastest95PGT** » Fri Aug 25, 2006 1:58 pm

On an NA vehicle in my car group who has a non-stock intake manifold and agressive cams I dyno'd to need 110 in the VE at the best air flow of the intake manifold. That's at about 97kpa.

That was for a 13.5 AFR.

IMO, just set your req fuel to what it should be and tune based on it. Don't worry about what the VE value is except knowing it is what you want for an AFR.