how much will my A/F ratio change?

[98COBRA281]

right now my a/f ratio is 11.7 at max power (225hp) with the mods in my sig, i will be doing my P&P npi heads, ss swirl polished valves, (that are supposed to be under cut to improve flow) and long tube headers, but i dont know how much my a/f ratio will change, and will i need a tune? hopefully not cause the only guy that dyno tunes around me is 600$

 

[DBMSTNG]

it all depends on how well the heads flow and how well your ECU can compensate. get a canned tune from a respectable tuner if you don't want to pay for a dynotune, or buy some tuning software.

 

[BennyBlown2v]

Why are you shooting for 11.7afr? That's sort of rich for an NA car.

 

[98COBRA281]

Why are you shooting for 11.7afr? That's sort of rich for an NA car.

no im not shooting for that, that is what it is right now with the current mods i have, i know thats rich for a N/A car, i was hoping it would lean up a little

 

[98COBRA281]

it all depends on how well the heads flow and how well your ECU can compensate. get a canned tune from a respectable tuner if you don't want to pay for a dynotune, or buy some tuning software.

i think they flow a little better then a stock npi

 

[CobraRed_96_GT]

No, you wont need a tune.

 

[BurningRubber]

I dunno, how much wood can a woodchuck chuck...?





Really though, if your at 11.8 now I wouldnt sweat it leaning out to a dangerous level.

 

[SaleenGT2001]

it should be fine. it needs to be leaned out anyways


maybe you should unplug a couple of injectors?

 

[98COBRA281]

i was kinda worried that it would lean it out to much, and then i would have to get a tune, but i hope it will lean it out a little.

btw, i just ordered my ss swirl polished valves

 

[oxfordgt]

Installing P&P heads will barely move your a/f ratio. You really need to get a tuner and lean that out. You are over a point to rich.

 

[98COBRA281]

Installing P&P heads will barely move your a/f ratio. You really need to get a tuner and lean that out. You are over a point to rich.

yeah every one says i could get another 5-10hp if i leaned it up

 

[oxfordgt]

If you get it to 13:1 and, depending on your cooling system and intake temps. run enough timing you could gain close to 20hp.

 

[98COBRA281]

If you get it to 13:1 and, depending on your cooling system and intake temps. run enough timing you could gain close to 20hp.

is 13.1 where it should be? my T/A is at 15*, my cooling system is good, but i have the stock t-stat in it.

 

[urban96]

theoretically the a/f shouldnt change as long as your injectors/maf dont get maxed out


the MAF measures the amount of air passing by it and dumps in the correct amount of fuel. so if its just flowing more air past it its just gonna dump in more fuel. the ECU already has a fuel curve all mapped out for the OEM maf, only way to adjust it safely is with a tune

 

[DBMSTNG]

theoretically the a/f shouldnt change as long as your injectors/maf dont get maxed out


the MAF measures the amount of air passing by it and dumps in the correct amount of fuel. so if its just flowing more air past it its just gonna dump in more fuel. the ECU already has a fuel curve all mapped out for the OEM maf, only way to adjust it safely is with a tune

the problem is that the adaptive learning has it's limits. i think stock it's set to +/-10%. meaning it's programmed only to adjust the tune by 10% from the original tune. he has PI cams as well.

 

[98COBRA281]

i dont think i anywhere near the max on the stock maf and injectors, but i hope it will lean it up a little, is it normal that my car is that rich?

 

[bhuff30]

I don't believe these engines are programed to keep the same AF ratio when you increase the flow. I've noticed, with each mod you do to increase airflow, the AF gets a bit richer. I really think ford programed the computer to do that on purpose. It'd make sense for Ford to do something like that, because rich is safer, not just for the buyer but for any attempted warrenty claims as well.
My point is, you SHOULD get a tune either way. An AF of 11.7:1 is perfect safe and acceptable on a car you are feeding 15psi of boost to, but doesn't make ideal power when you are NA. Even my stock 97GT had poor AF ratios that I could gain a lot by changing... It runs 13.4:1 in the low and mid range and then fattens to 12.0:1 by 5000. And that's about what nearly every stock 4.6 will do.