S197GT07

Ok guys, heres the story.

I went to a Dyno a month or so ago to get some base numbers. I ran the stock tune, and then 2 custom tunes from American Muscle/Bama. Turned out the stock tune made more power w/ a 13:1 A/F, and each custom tune was around 14.5 A/F measured at the muffler with cats.

I called AM to discuss the results, which were posted in the AM section of this forum. After speaking with the tuning people, it was found that the 87 octane timing tables were loaded, when I had asked for 93. Got sent the new tunes, and they felt a little better.

Now, yesterday, the same Dyno had a $20/pull dyno day, so I went down to see if the new tunes did in fact change things. On the 93 race tune, the car did make more power, but the A/F was around 15:1 at the muffler, with NO cats. I was told by the tuner (Pete) that having no cats should make the A/F more rich.

Does this seem right? Should the A/F be that high with no cats? I only netted 9hp & 12tq with the custom tune, which sounds low. So I don't know if it's the loss of cats or the 25 degree temp drop that makes up for that. I imagine it would be more with the A/F being more correct.

I just want to make sure im not going crazy, and worrying about something silly. Thanks

Here is the dyno PDF chart:

BruceH

15:1 isn't bad if you weren't under wot. What was the af during a wot pull? Can you post up a dyno sheet?

Simon1

Thru the tail pipe sniffer is usually off by .3 to a full point. People who own and operate their dyno's should know exactly what a car should read while being tuned on their dyno, to correlate into street driving. The tuner should have been able to tel you what your car would read on the street. Theoretically.

The most accurate way to do it is thru an O2 sensor location (Wideband), upstream of the cats.

Your HP should not be affected by the weather if you are quoting SAE numbers, which factors in specific weather conditions that are uniform for all applications. It will read higher on the dyno with uncorrected HP, so the car actually does make more power, but corrected, it should bring it close to equal.

15-1 is seems too lean.

S197GT07

Bruce - It peaked at 14.7 and this was during the WOT dyno run. Its a little crazy around here since I'm having an engagement party for a cousin, so i'll prob post up the graph tomorrow.

Simon - The SAE thing makes sense, i completely forgot about that. He did say it wasn't a very good tune due to it being so lean. I have an intake I'm waiting to put on, but if i cant get a decent base tune, i don't wanna try the intake one yet.

SpartaPerformance

Agreed 15:1 is way to lean when stoich. is 14.7:1. Also I agree with Simon that sniffer is not that accurate, especially when you don't know how old and clogged and gunked up the sniffer is. It's the same part used to do sniffer emissions tests here in NY on OBD 1 cars. They require cleaning and replacement every so often.

BruceH

That's too high for wot. I read part of your thread in the AM section. IIRC CR said they command a 12.8 af in the tune. That would give you 13-13.5 with a sniffer. More than likely you have a mechanical issue or the sniffer wasn't giving correct readings. Did you see any other cars do pulls and if so how were their af's?

VistaGT

The taiipipe is usually off around .3

And 15@WOT is definitely too lean, but timing comes into play too. Where even something that lean is not detrimental unless there's detonation. 13 - 13.5 with the correct amount of timing for your car is nice for N.A.

I run 13.4/13.5 @ peak and the car pulls nice and has put down great #s

S197GT07

Bruce - When i had the stock tune dynoed there a month ago it was spot on at 13.5 A/F mix. Also all of the cars there that day were fine, if anything on the rich side.

Also, because the stock tune was spot on, i think that takes out the possibility of the sniffer itself.

Vista - The thing is its on the "race" tune, which Chris told me they run 30 degrees of timing, compared to the stock 22. So that much timing, and 15:1 got me worried.

Also the graph has been added to the original post

BruceH

Stock tunes I've seen on the dyno are usually pretty fat, like 11-12. 13.5 is about the leanest a "safe" performance tune will be.

Edit: I just noticed the pdf file in your first post. Looks like you are at 14 towards the end of the pull which is probably about 13.5. Still leaner than I'd want to be but I'm fairly conservative when it comes to the motor. You should probably get on a different dyno. Ask around at a local Mustang meet and see where people are have tuning done.

AMChrisRose

Okay, so it looks like you're mid-high 13's at WOT, some points 14.0. Being that you don't have cats, I imagine they used the dynojet sniffer at the tailpipes which reads about .25 too lean.

With that being said, you're probably between 13.2-13.75 during the pull. This is between 1-5% off. I have already sent out tune updates. It's the tunable induction/demolet intake... sometimes, that same exact MAF calibration on another car will dyno at 12.2. I don't know if there was a difference at production at some time? Who knows...

Your car should now dyno between 13.1-13.4 from the tailpipe which will be just below 13 to right at 13 closer to the motor.