2003 Dyno Results AFR question

[StrongIsland45]

Just got back from the Mustang Dyno today, and the numbers for my 03 Vert seem respectable...However would like to get some comments on the AFR they logged...

Max Rwhp = 463
Max Torq = 491
AFR: 11.9

Note, the car has a few bolt on mods, K&N CAI, Corsa Cat Backs exhaust, BBK Throttle Body, and tune from Specialty Performance.
Do you think the AFR @ 11.9 is normal for this set up on a 2003??

would like to hear the forums thoughts before I look to change anything..

2003 Viper Dyno results.PNG

[345s-bspinnin]

My A/F was slightly richer when stock, but stayed flat at 12:1 after a tune. That looks a little fat on the high end, but probably done to protect engine.

[Steve M]

There are too many variables to give you a solid answer on what may or may not be going on here. Yes, you started out around 11.9, but it looks like it dips down into the 10s in the upper RPMs, which is way rich. Unfortunately, wideband readings on a dyno can vary widely, so I wouldn't put much stock in them.

Do you still have catalytic converters?

Was the wideband shoved in the tail pipe?

What brand/model was it?

If you do some poking around on the internet, you'll find people with wildly varying results when it comes to measuring the AFR on a dyno vs. on the street. Some show lean on the dyno, some show rich - usually up to about a half point either way. If you really want to know what's going on, the sensor needs to be after the collector but before the cats, and you need to log the data on the street so you can see what's going on under actual loading conditions with air flowing around (and into) the car.

FWIW, I aim for about 12.6:1 on the street...mine seems to like that AFR the best.

As long as the car runs fine on the street and pulls hard, I wouldn't worry about it too much. Dynos are nothing more than a tool to help with tuning, and are subject to operator error/manipulation just like any other tool.

[StrongIsland45]

Thanks guys for your input....in response to Steve, Yes I still have the Cat Converters..... the W/B sensor was put in the side pipes, however, I am not sure of the brand/model.
I agree the AFR will post a different read out on this set up, but would the range be off by 2 basis points at the upper end? meaning, 10.6 to 12.1 (avg) I am seeing for others if I were to check it from right after the collector?

For these Viper motors, what is a safe AFR I can adjust to without pushing the limits, but getting the added HP I may be missing due the rich AFR??
thanks for all your help... this forum is great!!!

[Steve M]

Because of the cats and wideband sensor location, it definitely could be way off. How does it feel on the street when making a WOT pull? If it is way rich, it will feel sluggish and won't pull clean to the top of the RPM range.

12.6-12.8 is a perfectly safe AFR to shoot for in my opinion, and should net you the most power.

[StrongIsland45]

She pulls pretty damn good at WOT, so I will chalk it up to the placement of the sensor at the tailpipe during the Dyno runs.... question though, would adding HFC help improve things a bit??? any gains there using HFC with stock headers and Corsa Cat backs?

[Steve M]

They'll improve things (maybe +5-10HP), but for the price (assuming Gen 3 HFCs are about the same price as Gen 4), it's a bit tough to justify. The only reason why I went with them on my car was because it was the easiest way to be able to add an additional pre-cat O2 sensor bung so I could run a wideband for tuning. I couldn't do that due to the location of the flex section on the OEM setup.

[WDW MKR]

The tailpipe sniffer widebands (if properly maintained and calibrated) will typically read leaner than actual... up to half a point. The gap will often close at higher RPM. Either way, you are definitely rich and that can rob power or even wash fuel past the rings in extreme cases.

[kirkinsb]

My 2003 with no cats, 3.55 gears, and SCT Tune at 4700 feet altitude did:

HP 448
Tq 488
AFR 11.48

I would say you are right on target. Mine runs solid.... Pulls clean and hard with zero hesitation or quirks.

IMG_3469.jpg

[StrongIsland45]

Thanks Man... Nice Car... like the rims... Who did your tune?

[kirkinsb]

Thanks Man... Nice Car... like the rims... Who did your tune?

Roe Racing did mine about 3 years ago. I gave him my mods on the order form and over the phone, and they built a tune, loaded it onto the SCT and shipped it out.

Thanks man, I love the 6-spoke wheels. Only available on 08-10 vipers I think. They are forged and much lighter than stock 10-spokes.

[Dan Cragin]

One note, on motors with catalytic converters and production cast pistons its better to keep the AF on the fat side to protect the engine from piston scuffing and the catalyst from damaging itself.

On the track, we found that production engines tuned for best power (12.5 to 12.8) had reduced engine life and catalyst plugging issues.

Performance engines built with forged pistons, optimized clearances and no catalyst, can be tuned to the "lean edge" for best power.

My 2 cents.

[StrongIsland45]

Big Thumbs up to Dan and his team @ Specialty Performance... one of the best Viper Tuners around!!! Thanks Dan!