AIR/FUEL Readings

[FREAK_SHO]

Did a search to try and find this info, but came up short.

Had the car dynoed, and the air/fuel reading was taken at the end of the exhaust (typical). However, I am running a catted Y-pipe, and the readings were in the 14.5 to 15:1 level up to about 7500 rpm where it dropped to 13.4:1.

Qusetions are, with no way of checking the ratio before the cats, does this seam to be ok? Or do I need to fatten up the ratio a bit? And will the cats cause this type of reading?

I realize the with a tuner and wideband O2, I could solve this myself. But I don't have that oppertunity.

 

[NotSoSlowSHO]

I cant see how any readings POST cat will be of any use.

There is a reason that the stock O2s are before the cats.

 

[yamahaSHO]

The readings are not perfect, but they are very close and you'll be fine. As long as their equipment is up to par, be comfortable in your readings.

 

[SHOZ123]

I don't trust their readings. I got 16:1 on my first pull. Don't think they had the numbers fudged up right at the start.

 

[FREAK_SHO]

I agree with all this.

I guess I am trying to figure out if, say, 16:1 or 15:1 after cat could actually be 13.5:1 pre cat?

Thought someone may have had the oppertunity to see the effect use the wideband and the sniffer at the end of the ehaust at the same time. Might be able to find some ~ sort of ratio of change from this.

I know the cats have an effect on the readings, I quess I am trying to figure out how drastic the effect is. But in thinking about it, there are to many variables, car, mods, exhaust system type, ect...

 

[yamahaSHO]

WB02 here... Dyno'd with the 'sniffer'. As I said before, they were not far off at all.

 

[FREAK_SHO]

Thanks for the added info yamahasho...That is what i was looking for. More of a confirmation of the numbers...More tuning is in the works.

 

[SHOZ123]

Well there is no way I would have gotten the 193 HP that I did with a 16:1 A/F ratio. Then 187 at 15:1 and 185 at 14.5:1....

This was on the an OBDII car though.

 

[FREAK_SHO]

SHOZ123

That does seam a bit strange, I was with in 2-3hp thru the 3 pulls. All with the same A/F readings across the band.

Wonder in your O2's are going screwy?

 

[yamahaSHO]

Well there is no way I would have gotten the 193 HP that I did with a 16:1 A/F ratio. Then 187 at 15:1 and 185 at 14.5:1....

This was on the an OBDII car though.

Make sure their equipment is up to par...

 

[gospeedgo]

Our local dyno with a fresh wideband will read a full point leaner after the cat than before. I have a standalone on my Turbo ****** and have monitored it while dynoing. This will change with a less new wideband...a few pulls on a dirty car and they are off for good. Our dyno changes about once a month.

If possible, have a bung welded in before the cat and you will be much happier than guessing.

 

[SHOZ123]

SHOZ123

That does seam a bit strange, I was with in 2-3hp thru the 3 pulls. All with the same A/F readings across the band.

Wonder in your O2's are going screwy?

I wondered that too seeing as they are the original ones. So I did some data logging last night. Good smooth cycling from 0 to 850 mV. At least I think that is good. They did not stay at any point long except at WOT (850mV) or closed throttle (0 mV).