What Should My Afr Be?

[Fujiwara]

Forgot to ask this before.

When i got by car dynoed it showed an AFR of between 12-13

Is this ok?

I thought it was running a bit rich, but the workshop said that this is fine

Excuse the quality...taken with phone

Edited July 9, 2007 by Fujiwara

[Beer Baron]

that all depends on where in the rev range and load you are talking about. if we are talking light throttle, cruise then yeah 13 is too rich. if we are talking full throttle, high load and rpm then 13 is too lean.

[RANDY]

It's slightly rich, if you're talking about the perfect ratio... but otherwise it's "safer" to have it a little rich. (rather than a little lean)

[djr81]

The Baron is spot on.

On full throttle most people pick an AFR in the 11.5 to 12 range. Or thereabouts. 13 is too lean.

On light throttle you can go for a stoichiometric ratio (Look it up) which is 14.7 from memory.

In between should be, um in between.

[Devils_Advocate21]

11.8 to 12.2 are better ranges but as said slightly richer on higher load is safer

[180bfj20det]

Depends on boost!!!!!!!

I aim for:

Cruise/light throttle can see stochiometric (14.7) to 16

1-6psi 13 afr

7-14psi 12afr

14-23psi 11-11.5afr

30 psi 10-10.5afr

All depends on compression ratio and head design. On my higher compression engine, I drop AFRS earlier.

My afrs are always fatest where max torque/VE occurs

So your afr of 12-13 is mostly fine. Hard to say without dyno sheet and boost used and other impt factors (fuel, CR etc).

Edited July 9, 2007 by 180bfj20det

[T04GTR]

yeah but where abouts is this ratio? if its on boost its to lean. if its off boost its to rich

[T04GTR]

oh yeah what ^^^^^^^^^^^ said lol

[Fujiwara]

Graphs now attached.

Can the gurus please guide me?

[Beer Baron]

it's borderline. personally I'd say that's a little too lean. not much margain for safety being that lean.

[mad082]

you may pick up a bit of power going a touch richer. my mate had his 33 on the dyno and i had 2 maps saved on his emanage and we changed between the 2 and picked up hp by adding in 4% more fuel. and his afr was around 12.1. there was no adjusting of the car other than flicking the switch on the emanage to change between the 2 maps. the runs were done about 20 seconds apart and the run with the extra fuel was done second so it would've had more heat in the cooler etc.

[Adriano]

Mate, that looks perfect, 12:1 at full recs, and a little dip at peak torque. At that power level you wont gain anything from adding more fuel, you would probably gain some by leaning it out but at the expense of high EGT't and combustion temps. I would leave it exactly as it is.

[Fujiwara]

ok..

Let's say it is running lean.

How do i fix this?

Can i fix it with PFC/injectors/fuel pump?

[mad082]

it depends on what is causing it to run lean. i highly doubt it will be the injectors maxing out. they may need cleaning though. your fuel pump may be dying, or you could get an aftermarket ecu. if the problem is the pump or injectors the ecu won't really help much and the problem will just get worse.