I was just reading David Buschur's clarification that AFRs are much leaner on the street than on the dyno. I found this to be a big surprise, especially given his experience of seeing almost 1 full point difference.

Al, what has been your experience on the difference?

It seems that you target mid 11s on your posted dyno charts. Are you targeting something leaner on street tunes?

I have a mail-in tune and an SAFC/wideband and am wondering what I should be shooting for. Since I'm in the very low 11s/high 10s now as measured on the street (with the SAFC zeroed out), would I be in the mid-10s on the dyno? Maybe I should be shooting for upper 11s on the street at WOT to have comparable AFRs to your custom tunes? I assume that your timing in a mail-in flash is no more aggressive than what you would use in a custom tune.

 

I read Buschur's post and had the same question.

Knowing you big Al, you are taking into account the lean tendency for road use when you custom dyno tune (vs. mail in) for low 11s. If so, what is the street/real world target for AFRs?

Also what is the AFR that you usually find in the stock ECU program?

Thanks Bro

 

The answer is going to depend on the quality and type of fuel you use. I use 93 octane during my street tune and he kept it at a low 11.xx/1 A/F.

 

What he's saying is that more load is generated on the street than on a 2WD dynojet, so if your tuning does not account for that higher load, it is going to inject the same amount of fuel it did for the lower-load dyno tune, causing you to run lean.

Reason being, to the ECU, 22psi looks the same as 23psi looks the same as 24psi looks the same as 25psi. If you tune 11.8:1 for 22psi on a dyno you are going to have issues if in fact your car might see 24psi in colder weather on the street.

This is not a problem with all dynos or with all dyno tuning, but specifically with dynos that can't generate street-like loads and/or tuning computers (like the stock ECU) that can't be finely mapped above 21psi.

 

My own vague interpretation of the concept when tuning on the dyno is that assuming somewhat normal ambient temperatures in the dyno room (through the use of fans simulating real world airflow) the car is tuned with a margin of safety where the degree of variances in temperature and load in real world conditions are taken into account. Hence, a car more aggressively tuned, especially in the realm of fueling, i.e leaner afrs at load points on the dyno, are more prone to inconsistent performance on the street. A turbo car paired with your average MBC/open loop boost controller is subject to slight boost spikes in colder temperatures that can cause the mixture to enlean, furthermore colder denser air enleans the mixture on its own, beyond its possible adverse affects on open loop boost controllers set in varying temperature and load settings. That is where the true danger to a car comes in.

No matter what condition a car is tuned in in, either on the dyno, the street, in the colder weather or in the warmest weather a tuner must have solid knowledge of the platform in question and experience as to the limits of the application in all condtions to maximize safety and assure consistent performance.

 

Every car needs a different unique a/f target and most dynos load differently so the answr to the question varys on which dyno and which car.

Genreally - I personally tune on the very rich and safe side - finding that a leaner a/f usually only nets slight gains and runs a much greater risk of engine damage.

I have over 1500 evo tunes out there and zero issues with blown motors

I laugh when ever I see storys of blown engines from people trying to push the last 10 whp.

 

Can you give any more specific advice? With your mail-in tune, my car's AFRs were in the 10.9-11.0 range for the most part. By leaning it out to 11.4-11.6 using an onboard wideband the car is noticeably stronger, especially up top around 6000-6600 rpm. An OBD-II log shows that the car is not pulling timing. Am I okay?

 

If its not pulling any timing you will make usually a few whp more at the leaner a/f ratio - (10 or so) - the marginal gains do not justify the inhanced risk on through the mail tuning where car to car variance can create up to a half point variation one way or the other. Aiming slightly rich means that I am never too lean and too dangerous. Of course the additional margin of saftey comes at a price of a few whp. However, I would prefer to maintain my reputation as a very relaible tuner who has a great durability record. I will leave the dyno bragging claims to those who don't mind leaving a few toasted motors in their wake every so often.


Keep in mind that the stock car goes so rich off the scale at 5500 rpms that you can not even measure it with a conventional wide band 02 sesnor so a 11.0 a/f target is not that radical a concept.

 

You don't need to convince me that a margin of error makes sense on a mail-in tune. And as far as fine tuning with the wideband and datalogger, it's fun for me to feel like I'm actually doing something constructive on the tuning front without going off the deepend with an expensive standalone or UTEC. Between the new base tune and the new cams/FMIC/injectors (I just upgraded from Buschur Stage 2), my car is worlds faster than before