Best afr to tune for on a s/c Cavalier

[c24s/c]

Hey guys,
well, been tuning my VE tables and its going pretty good. Now i've read different things about what the afr at wot should be for our cars. I'm hitting max 10psi but mostly 8-9.5 psi. Would something like 11.8 be too rich, vs the ideal 12:1 most guys talk about. Also, would it be bette to lean it up at the redline or keep it constant.

Interested in some experienced tuner input.

Thanks
Nate

[spyhunter]

Hey guys,
well, been tuning my VE tables and its going pretty good. Now i've read different things about what the afr at wot should be for our cars. I'm hitting max 10psi but mostly 8-9.5 psi. Would something like 11.8 be too rich, vs the ideal 12:1 most guys talk about. Also, would it be bette to lean it up at the redline or keep it constant.

Interested in some experienced tuner input.

Thanks
Nate

Personally, over here with our lil circle of tuner geeks, we dig the 12:1 ratio as the goal. Outstanding circumstances aside.

[killerjuice]

12.1 is good, 11.8 can be better if you wanna advance timing a little more, or are trying to fight KR

[IanB]

Also, would it be bette to lean it up at the redline or keep it constant.
Nate

I've read in other sections on these forums (V8, etc), that it's best to richen towards redline, after hitting HP peak. Each car will be different though, and you can get close tuning on the street, but perfection will only come with dyno time to see how the engine reacts to fine tuning changes.

[97cavie24ls]

my cav runs pretty good with a 11.5 or so afr

[JANNETTYRACING]

I tune a lot of cars and I will tell you there is no magic number for all cars,

I use only ECM wide band O2 (1500.00 dollar wide band) in the head pipe for accuracy on all cars I tune.

I have seen some cars make peak power as rich as 10.0:1 and as lean as 12.5:1 boosted applications.

Every engine has a personality and only trial and error will find what it wants.

Just yesterday I was tuning a Mustang with a blower and it made 460 at 15 psi at 11.8:1

I threw some fuel at it just as a test and it made 515 at 15 psi at 10.4:1 and I am not just talking peak numbers it was better from 2200 rpm to 5500 rpm.

Now on the other hand, if you find an engine makes peak power at say 12:1 that would be fine in a drag race application where your only at full throttle for a few seconds.

If you are tuning for long top end runs like in road racing or top speed events you have to continue to richen as time goes on, some computers have this option some do not so you must tune for say as much as a 1.5:1 richer than peak power A/F. for piston protection.

Just food for thought.

[c24s/c]

I tune a lot of cars and I will tell you there is no magic number for all cars,

I use only ECM wide band O2 (1500.00 dollar wide band) in the head pipe for accuracy on all cars I tune.

I have seen some cars make peak power as rich as 10.0:1 and as lean as 12.5:1 boosted applications.

Every engine has a personality and only trial and error will find what it wants.

Just yesterday I was tuning a Mustang with a blower and it made 460 at 15 psi at 11.8:1

I threw some fuel at it just as a test and it made 515 at 15 psi at 10.4:1 and I am not just talking peak numbers it was better from 2200 rpm to 5500 rpm.

Now on the other hand, if you find an engine makes peak power at say 12:1 that would be fine in a drag race application where your only at full throttle for a few seconds.

If you are tuning for long top end runs like in road racing or top speed events you have to continue to richen as time goes on, some computers have this option some do not so you must tune for say as much as a 1.5:1 richer than peak power A/F. for piston protection.

Just food for thought.

Thats some good info.Well, having my a/f around 11.7-12.0 at the track last night netted me a best of [email protected]. 2mph slower then usual, and very iinconsistant. Ranged from 14.4 and dropped a 1oth each run. Mind you, didnt have any stellar 60 fts. However, when she was in the low-mid 12s with 2.2-2.1 60fts i was 14.1-14.0 @98-99mph all day. Then hit 2.0 6ofts for 13.9s.

Going to try to lean it up for the track next friday. However, other then throwing my HO table (-4) into my low table i haven't touched the timing. Not getting any knock, other then off the line. HOWEVER, if i say on the road, step on it at a lower rpm in the right gear, it gets a little rich off the bat and shows knock till the rpms get going. How do u fix that??

Nate

[JANNETTYRACING]

I would return your Low Octane map to stock and work with the high octane map.

[c24s/c]

I would return your Low Octane map to stock and work with the high octane map.

I have a good question for you

What controls the commanded afr when i look my logs?Now below my set PE what controls the commanded afr, and while in PE, is it strickly the base afr in pe vs engine coolant temp? Cause i noticed in my logs that that commanded line seems to be getting lower and lower. Or does it go by settings in the VE tables as well? And to reassure myself, the timing will be pulled if the afr is too far (lean or rich) off that commanded line. right?

Nate

[JANNETTYRACING]

I have a good question for you

What controls the commanded afr when i look my logs?Now below my set PE what controls the commanded afr, and while in PE, is it strickly the base afr in pe vs engine coolant temp? Cause i noticed in my logs that that commanded line seems to be getting lower and lower. Or does it go by settings in the VE tables as well? And to reassure myself, the timing will be pulled if the afr is too far (lean or rich) off that commanded line. right?

Nate

Your Stoich (spelling) air fuel ratio is the base, multiplied by the PE ratio is your commanded at WOT.

There is a delay timer from closed to open loop.

Some cars have an Open loop map also but I think this is only during warm up.

I have not seen a timing retard for lean conditions but that doesn't mean it doesn't exist.

[Sp00ner]

Good info Jannety, just started working on the A/F ratio on my Ion Redline, Supercharged Ecotec as well, and I want to get a few tunes ready for the dyno. One at 12.5:1, 12:1, 11.5:1. I've got it around 12.5:1 now, it was all over the place before, but down to around 11:1 near redline, and I think it was running stronger at that 11.x:1...

Is there a 'rule of thumb' with a smaller, higher revving, boosted powerplant like these in anyway? Seems the more I ask, the more people are getting better results with richer (11.x:1) A/F's and adding in as much timing as possible.

I guess you sorta answered that already with "each car is different", but curious if you feel that there are any things common.