Shiv had mentioned in the "Isn't that lean" thread that while doing a pull your AFR readings may lag:

https://www.evolutionm.net/forums/sh...=210281&page=2

Instead of digging through the post above I thought I would start a new one. Can someone explain why this happens? Why aren't AFR readings realtime when you are doing a pull?

 

^^^^ i want to also know this??
he said something about the load on the dyno being diff of that on the street!

 

https://www.evolutionm.net/forums/sh...d.php?t=205121

This thread should help shed some light on this.

 

It's due to the placement of the wideband O2 sensor in the exhaust stream; hence the farther downstream it is placed for readings the more lagtime there is.

 

Damn, I just remembered this. I have a 4th gear dyno chart with AFR and several 3rd gear dyno charts with AFR. I did these back in March of 06. Check out the difference in AFR/gear. There is a 1.38 difference in AFR at 6500 rpm The AFR really richens up per gear.

I am begining to get what Shiv is trying to do. I believe the maps on his web site are tuned with 4th gear in mind. That is why when we do our runs in 3rd gear we get the lean reading. If I can do a 4th gear pull to redline I bet that I will see a full point drop in Shiv's maps. The 12.5:1 that we are seeing in 3rd gear becomes 11.5:1 in 4th gear. Problem solved.

The next time I go dyno tuning, I will request two maps one with the AFR tuned in 3rd gear and one with the AFR tuned in 4th gear. I will add these maps to my ever growing collection of map

 

We are tlaking about palcing the WBO2 in the SAME location and getting different results in 3rd gear, than in 4th gear. You are talking about something totally different.

 

I've read what Creamo3 said but I'm still having a hard time following that logic. At what speed do exhaust gases move out of the engine and through the exhaust? I would think pretty damn quick!

My wide band is mounted near the end of the down pipe mounted at 2 o'clock. So for gases to move approx 30 inches ...what is the sampling rate in a wideband?

Edit: I read the post that NJ referenced above -- that clears up a few other questions I had but the questions above still remain...

 

Here is the answer from Klaus as to why the AFR changes per gear:

Hi,

You can post the .log files in this forum. Leaner conditions in 1st and 2nd are very common with many ECUs. I've seen it more pronounced on MAF based systems. Different to a carb, that reacts instantly, a ECU calculates the next injector duty cycle on the previous engine cycle(s). When RPM is fast rising, it is behind. Some higher end aftermarked ECUs and some OEM ECUs try to compensate either by looking at the current gear or trying to predict from RPM rise rate. That's why tuning should be done in higher gears.

Regards,
Klaus
http://www.innovatemotorsports.com/f...ead.php?t=4109

 

wow so klause says to tune in higher gears thats a totally diff opinion of many people in this site which almost all of them tune in 3erd gear!
hope shiv gives his opinion on this???

 

You should really tune all of your gears and all of your driving scenarios. Realistically a 3rd gear pull suffices for 90+% of all driving situations ... I mean how many times do you find yourself going for redline in 4th gear?

The whole AFR thing is very difficult to nail down without logging and comparing your logs to your timing and fuel maps to determine which cells were being hit by the ECU. The AFR difference in the log shown above could have been something as simple as the ECU hitting a different load cell, giving it a different fuel target to shoot for. Impossible to know without logging.

l8r)

 

Yep, he sure does. I asked him which gear to tune in and this is what he said:

"The highest gear you can without endangering yourself and others. On a load dyno you also tune at steady state. High gear approximates that best.

Regards,
Klaus"

Shiv tunes on a DD dyno that has the ability to approximate the load of the highest gear. So even though he might tune in 3rd gear, he can set-up the dyno load to approximate the highest gear. Mustang dynos do the same thing. That leave a Dynojet dyno out in the cold. Or you can dyno your car in 4th gear on a dynojet and get the same effect as a DD or a Mustang dyno.

Most people who get custom tunes from certain vendors do so with street tuning, ie, w/o a dyno. Tuning on the street in 4th gear will be downright dangerous. The Evo 8 maximum speed in 4th gear till cutoff is 122 mph. Imagine trying to tune at these speeds and making multiple runs

3rd gear is much better for a street tune since the maximum speed in that gear is 85 mph.

Next time I go to the dyno I will tell my tuner to tune my 93 octane map in 4th gear.

 

Have you ever driven on a fast road course like Willow Springs? On that track you are in third only once, the rest of the time you are in 4th or maybe fifth.

In my SE-R (have not taken my Evo yet), I am in 4th gear only and I hit 120 mph at the end of the front and rear straights with the rpm pegged at 7500. The redline on the car is 7800 rpm and the gear ratios are longish just like the Evo's.

I do not know if I can do the same in the Evo w/o blowing it up because of it being FI, but my point is tuning for 4th gear is worth under certain track conditions.

 

without understanding how you are logging:

I know with standalone logging systems you are able to tune out weakness on acceleration. You don't factor in log delay() I don't believe Mitsu would tune their cars to act like that either. Fairly certain Mitsu would use a throttle map to augment fueling.

Nevertheless I am willing to bet that there is an element to these logs or their management that explains why you are getting faulty readings. If they are actual readings then I would be unhappy with them.
On the other hand if the tune was developed to be lean in acceleration that is your choice.

 

You are correct, which is why I said 90+%, because unless you have a dedicated racecar, it still spends the majority of its time on the street. I'd also be running racegas at the track, so there'd be inherently more flexibility in regards to AFR.

l8r)

 

Not all cars behave the same with their ECU. As Klaus mentioned, there are differences. I just looked at my inventory of logs for our Spec V project car and I happend to have a 3rd gear and 4th gear AFR logs. I exported the logs to excel and plotted them per 100 rpm. In the Spec V, there is not much difference n the AFR between 3rd and 4th gear under load in the high rpm. This is unlike the EVO.