A/F question

[Mark Brokaw]

Went to the track last night with the DS, ran a 12.8 at 106.My A/F ratio dropped down into the 8's even dipping into the 6's for a very short time.Does this mean im rich??Also my fuel injector PW stayed in the 90%'s even going as high as 120%.I know i typed this but can somebody tell me what all this means??

 

[Mark Brokaw]

Went again tonight,Ran 3 times first run fuel press at 44 (vac off)
2nd run 42 (vac off) 3rd run same press bumped boost up 2 pounds to 23.Did not get any knock what so ever all 3 runs.
My blm chart stayed on the number 16 block (with 131 showing in block) .MY inj. duty cycle were in the 90's and hitting the 120's all 3 runs. I run the 009's with Red's 108 chip with 114 oct.anybody have any ideas??maybe bad burn on chip??IF i need to give more info please let me know.

 

[BoostKillsStres]

That low of an A/F ratio simply means the chip burner expects you to run additional boost and since you'll be pegging the MAF then he has to guess at the additional fuel you'll need in the PE vs. RPM table and the Time in PE table for that extra boost thus you end up with a lower reported A/F ratio number than the car is actually running and isn't a useable reference to any actual A/F ratio such as a wideband. You didn't mention if you had any knock but I'd guess you may be a bit on the rich side with 110 MPH and %90+ DC on 009's but it all depends on what the individual car likes and can run with.

HTH

 

[JDEstill]

The A/F ratio shown in DS is that *commanded* by the ecm, NOT the A/F ratio you actually have. So ease your mind!

The reason that is done is because the MAF gets pegged pretty quick. Once the MAF gets up to 255 gm/s, it doesn't read any higher.

Suppose the chip maker thinks you are going to run about 350 gm/s of air, and he wants you to have an 11:1 A/F ratio. Then the A/F ratio that has to be commanded by the ecm, taking into account the 255 gm/s MAF limit, is (255/350) x 11 = 8.0:1

So in that case 8.0:1 would be displayed by DS. But in real life you would be running at 11:1. Or you would be if you were actually moving the 350 gm/s that the chip maker assumed. If you were moving more or less air then you'd be accordingly leaner or richer.

Comprende?

John

 

[Mark Brokaw]

OK sorta understand.

here is some more info from the 1340' all numbers at the the 1/4 mile mark

rpm 4750
tps 4.60
maf 255...but during run it did drop to 234 while shifting into 3rd
inj.PW 27.82 (110%) that seems a little high
spark advance 25*
knock 0.0
A/F 7.5 :1
O2's 796
O2 X-cnt 109

blm 16th box at 131
the above run was with 22# OF BOOST 42# FUEL PRESS(vac off)
was reading 64# at WOT.
hope this helps,please let me know.
Look in my sig for combo