correct a/f setting

[kent menges]

does any one know what the correct air fuel setting sould be, after putting flps with no cats car is running richer

[WA 2 FST]

I would set it ~12.5:1. I know some guys run it ~13.0:1. Some cars make more power there. Mine didn't. It will run a bit leaner in the heat of the summer anyway, so this is safe, but not as rich as I'm sure you're running now. What is the A/F ratio now?

[kent menges]

thanks wa 2 fst, don,t know the setting now, just know that when i start it up in the garage the fumes start burning your eyes didn,t do it before the headers, down the street has a way to check the a/f but not the wide band, so i will have to waite till all the snow goes away to get it to the dyno shop, they give you two pulls for $90 and about half hour to do adjustments, do you think that a predator will adjust it ok, thanks kent

[Reboot]

My car seems to run best at a 12.8 - 13.0 A/F ratio.

[Inferno]

Every car is a bit diffrent, but after watching over the shoulders of many dyno tunes12.4-12.5 seems to be the sweet spot. Some cars seem to get nock around the 13.0 point for some reason (don't think this is too normal though), but I have not seen much gained from going from 12.5 to 13.0. Just my 2 penny's

Brian

[JWSchmidt3]

Originally posted by WA 2 FST
It will run a bit leaner in the heat of the summer anyway, so this is safe,

I thought cold air made the A/F ratio leaner, hence why they make more HP in cold air. I just had mine tuned at 21st CMC, and we leaned it out because it was 30~ degrees, and figured we'd be safe for Summer time that way.

[Inferno]

I think Wes prolly had a stiff cup of joe and miss typed. You will be leaner a/f wise in the winter. Because of they diffrent ways Wes tunes (used to use MAFT and now LS Edit) these two things are used in diffrent ways and my have gotten them backwards.

[WA 2 FST]

Makes more power in cold air b/c you are cramming more oxygen-rich air into the motor. Cold air has more oxygen content than hot air. Also, typically colder air comes with high barometric pressure and less humidity (not talking relative humidity here...that may be the same on a cold day as on a hot day, but the colder air cannot have as much water vapor as warm air).

It will run leaner in the heat of the summer. Granted, there are things programmed into these sophisticated PCM's that can compensate somewhat. That's why we have IAT sensors.

You have to be careful with either extreme, though. On a really cold day, you can actually be getting too much oxygen into the engine...and that can make it run lean, too. However, this is typically the result of someone getting too greedy with the tune. More efficient combustion (due to the extra oxygen present) likes more timing very often.

But on a hot day you have to worry more about heat soak of the engine.

Take two supercharged motors and tune them aggressively and run one on a cold day and one on a hot day...the one being raced in the heat is going to die first. Seen it firsthand...more than once.

Chances are good that an aggressive N/A tune isn't going to be affected too much (not harmfully, anyway) by change in ambient temps...even large swings.

[WA 2 FST]

No, I didn't mis-type. However, I'm more accustomed to tuning forced-induction motors... which are much more susceptible to hot climates than a typical N/A one.

Assuming the fuel delivery is the same no matter what, less oxygen present (hot day) would mean a richer mixture. I understand that. However, you also typically have elevated engine coolant temps (not talking 220^, but 195-200 vs. 175-180^ in the winter... assuming a car with a fan controller and t-stat).

I've seen too many heat soaked engines run leaner, not richer.

Just my experience.

Again, I will say that a N/A motor isn't going to be nearly as affected by the heat as a FI engine.

[JWSchmidt3]

Okay, I'm still confused, so please answer my question: We dyno tuned my car with LS Edit, in 30~ degree weather, and had a final A/F ratio between 12.7-12.8, and raised my timing to 25-27. Is this optimum?? safe?? and will the car run okay in the hot Texas heat?? Thanks.

[WA 2 FST]

JW,

I have yet to meet John P over at 21st Century yet, but from the few e-mail discussions I had with him, the guy is sharp. If they tuned your car, then I wouldn't worry about it.

Also, 12.7-12.8 now is going to be fine in July when its 100^ out. What's cool about these sophisticated PCMs is that they will pull out timing if you encounter serious knock (some knock sensors are more sensitive than others... after all its a $5 part), so you are not going to hurt anything.

If it was a nitrous/turbo/blower application it would be much more sensitive to weather changes as far as safety of tune is concerned.

It would be interesting (if only for fun) to run a scan with EASE or AutoTap in the summer when its really hot, your engine temps are up to normal, and you are running the car hard repeatedly. I'd be curious as to whether you get any knock present or not.

[SilverStateZ06]

12.8 to 12.9 on a wideband

[kent menges]

thanks to all, looks like i will be looking for around 12.5 to 12.9 to1 next question is will the predator get me there, and how about the right timeing? thanks kent

[SilverStateZ06]

Didn't touch my timing to get near 400 rwhp.

[Reboot]

I got to 407 with stock timing.