2ktransam

iTrader: (12)

I asked this question over on Performance truck and I wanted to get some more opinions.

What AFR are you STS guys shooting for on you wideband. I have my wideband after the turbo in the back of the truck like PLX recommends but I don't know how accurate that is. I would imagine that being that far back on the truck and being after the cats would throw off the reading by up to a full point from what the engine is actually seeing. I have been tuning for 11.5 to 1 on all boost levels but it's all by the butt-o-meter. Today I leaned it out 12.5 to 1 with 16.5 degrees of timing at 10psi and the truck felt a lot stronger. I didn't have any KR and I am spraying a ton of meth for safety. What do you guys think? Could my wideband be off by quite a bit due to the cats burning off some of the left over fuel in the exhaust? I know the cats have to affect the reading some. On my TA which is NA, I have the wideband pre-cat and it reads about .6 to .7 richer than the sniffer does on the dyno. Theoreticly the cats heat up to burn off left over fuel that is in the spent exhaust coming from the engine. If the cats burn off some of the extra fuel before the wideband reads it then the fuel mixture should be leaner at that point and would give you a false reading. I don't think a lot of the front mount guys have this issue due to there wideband sensor being in the downpipe before the cats so they get a better reading. Am I making any sense or am I crazy?

CamaroSS19

iTrader: (24)

I am thinking about doing the wideband in the same spot but with no cats . Dont think it will be a problem cause most tunners use a tailpipe wideband and under WOT they should flow free past the cats (from what I was told).

It feels better cause its leanned and with FI you can run 12.5 and be good . but the 11.5 target is safer cause with boost it wount take much to melt stuff . That point is your buffer zone with the FI NA cars can get away with it cause if it happens to go lean its less devistating .

I would back it down to the 11.5

nuclearxp

Alot depends on your compression and boost level, but I'd shoot for 12.5 if I were you. 12.5 may run knock free (with meth) but you run two risks: a - if you ever see knock it'll do much more damage at a leaner AFR and b - the leaner AFR runs higher combusion temps which will stress the motor (pistons) alot more.

As far as the wideband location, I don't think it really matters much. Being post-cat shouldn't matter as a wideband just measures ambient o2.. the cat just cleans out pollutants. And, like camaro said, a dyno shop uses a tail sniffer anyway.

OUTLAWZ RACING

iTrader: (9)

I moved mine from after the turbo to befor the turbo. There was no change in the reading. I put it as close to the stock manifolds as possible.

koolaid_kid

iTrader: (21)

I shoot for 12.5, pre-turbo and after the cats. 11.5 is quite rich, IMO.

MY99TAWS6

iTrader: (3)

Its normal to run bit different at max hp and max torque. I don't think 12.5 is very good in a fi car. If something does go wrong with meth or whatever it could be bad. I think 11.5 is better idea. In various places like my dsm forums they have shown that in order of power production in FI that boost produces biggest gains,then timing and lastly afr. There was not much to be gained by leaning it out much so running safer but not pig rich is a good idea. Just keep the afr a bit lower and run more boost first choice and bit more timing second choice keeping a close eye on knock readings.
Some guys also go for huge boost and very low timing and we have other guys going for lower boost but higher timing. The timing increases seem to give a car more torque which is not always best for the drivetrain.
I believe in being pretty conservative. But like to keep my cars running not broken.Don't enjoy taking them apart much anymore.

Someone should do a reading pre and post cat with their wideband. I always thought pre cat was best. But as said many dyno shops do take tailpipe readings.
Maybe a dyno shop can chime in on this subject..

2ktransam

iTrader: (12)

This whole idea started when I had my TA on the dyno the other weekend. My car is tuned to about 13.2 to 1 and my first pull on dyno showed 13.8 so it freaked me out. I asked the dyno operator what the deal was and he said that was normal when you are pulling the AFR from tailpipe and they always tune for about .5 leaner to compensate which is still safe. The next pull we made we watched the wideband which is pre-cat in the header collector instead of the dyno and it was a steady 13.2. I deffinitely want to stay safe but it makes me wonder if I should tune for around 12.0 to actually be at the 11.5 goal.

MY99TAWS6

iTrader: (3)

Hmm that was a bit confusing..13.8 is leaner than 13.2 . So you are saying its leaner out the tailpipe after cats? But its 13.2 on your wideband pre cat? So would think that means they are tuning richer not leaner??
Safe NA is usually considered 12.8 to 13.2 type range. Safe FI is usually more like 11.0 to mabye 11.5. I guess a bit leaners on meth injection or race gas.

2ktransam

iTrader: (12)

I didn't know if that made sence when I was typing it. What I meant was they tune about .5 leaner on there dyno AFR knowing that it is actually about .5 richer at the the motor where it counts. So they would tune my car a little leaner say 13.8 on there dyno readout knowing that it is still safe and probably closer to 13.2 at the motor. My wideband was showing a richer AFR close to the motor which they tell me is normal and is what they base there tuning theory on.

MY99TAWS6

iTrader: (3)

Ok..think follow that .
I found this for aps dyno with meth injection

13) AFR 11.1 at peak torque, 12:1 at peak power,

14) Ignition timing 14 - 16 degrees,

I think might try to stay more like 11.5 max at peak power.

koolaid_kid

iTrader: (21)

Dyno shops have to use the tailpipe clamp, there is no way around it.
Your ideal AFR is also dependent on variables such as your boost level (higher boost should run richer), methanol injection, etc.
In my low boost environment, 12.5 is good. I monitor my EGTs, so I can keep a watch on whether it is too lean.

2ktransam

iTrader: (12)

What do you consider low boost? I am going to be running 11-12psi on high boost.

geeteego

iTrader: (1)

Low boost for me. That's off the WG spring pressure. But boost #'s are irrelevant by themselves anyway.

koolaid_kid

iTrader: (21)

I currently run at 4 & 7 p.s.i. (methanol but no intercooler). You are in the next range up from me, so you most likely want to run richer than I do. Sounds like geeteego is in at least the 20 p.s.i. range, although they did not say.

98catfish

iTrader: (13)

My tuner removes the rear o2 and puts the W/B in there.

Doug

koolaid_kid

iTrader: (21)

That is awesome. It should be more accurate there. I have been to several tuners around here and all have used the tailpipe clamp.

Schantin

iTrader: (6)

My $0.02 is to reduce the AFR to 11.1 to 11.5 and set timing 16-20*. 12.5 is too lean for FI at WOT.