phlanigan

I just dynoed yesterday and had a couple of notes to share:

1) 285 whp at 12.5 psi. Intake, IC, DP. Temp around 40F. No torque reading as the rpm pickup wasn't reading correctly.

2) I did three runs, the first of which was the best due to heat soak later on. By adjusting the timing split on the last run to 8 degrees throughout higher boost cells, the last run was generally 8-10 hp higher than the second run throughout the curve, even though it had the highest air temps. Quick way to gain power. At very high rpm, the split changes didn't seem to make much difference though.

3) My Oz WB reading was WAAAY too rich. I was logging AFRs of between 10.4-11.1 during the run, and the Superflo wideband read between 11.5-11.9. I'd been hesitant to lean out the boost cells until I could confirm the readings on dyno. The Oz WB and the dyno WB read exactly the same at idle, but there is an obvious problem at the non-stoich AFR areas. The tech said they just replaced the sensor about 4 months ago and didn't have many runs on it. I was shooting for 11.4 AFRs, so I'm not necessarily unhappy about my map, but I no longer trust my WB readings.

es

Wait a sec. You're saying the TEWB reads richer then the dyno sniffer up the tailpipe. And you don't list a MP in your mods which leads me to believe you're running the stock cat...

If the TEWB NTK sensor is in the downpipe, or anywhere before the cat the two sensors readings are going to be way off when compared to each other, & you will get faster & more accurate readings out of the sensor before the cat.

Let me know if my Main-cat assumption was wrong.

phlanigan

No, you're right--I still have the stock cat. But I swear that I've read posts that say the AFRs should still be pretty close pre- and post-cat, although there is plenty of incorrect info on the board. Maybe I misread the posts, or the guy posting had a MP. I'll see if I can find them...

es

Everybody I've ever talked to about tailpipe probes say cats drop ~.5 or more A/F points & as much as one full point. I'll admit though, I've never personally tried it.

There's a shop here that wont even try sticking the probe in the tail pipe. They actually make you weld a bung in 3' from the head or 1' from the turbo! His reason is that the tailpipe probes are easier but not accurate enough. His background is in emissions testing though & he's probably never tried to compare the tailpipe to the bung on a car with no cats...

phlanigan

That would certainly mesh with what I saw.

I've checked out the DIY board a little more and a number of people had the same experience I did when comparing the TEWB to a tailpipe sensor. There is another dyno shop near me that uses a bung sensor like the one in your area, so I think I'm going to go there before I lean out my map anymore. I would have gone there first, but the place I went to was closer.

As much as my gas mileage sucks, I think I believe the TEWB over the dyno, but I'm not willing to bet a rebuild on it until I get a second opinion...

Jason

iTrader: (5)

I would think that the O2 after the cat is going to read leaner based on the fact the airpump is diluting the mixture with air.

Jason

rynberg

Ah, but the air pump does not pump air to the cat after 3200 rpm....

I had these same concerns when I dynoed last fall. The techs at the dyno place I went to (ATP in Fremont, CA, a pretty respected place) stated that the tail-pipe location didn't matter with the sensor. FWIW, my A/F readings on the stock ecu looked realistic to me, with readings of 12-13 under 3000 rpm and then going below 10:1 after the transition. I seriously doubt it was reading significantly leaner than the actual A/F. JUst my 2 cents.

phlanigan

The AFR measured at the tailpipe is markedly leaner pre-3000 rpm than post, but I believe this is due to the fuel map and not the airpump as I also saw this on my wideband.

The stock O2 narrowband sensor was reading up to 1.0V during the runs. I know you can't get a direct AFR from this, but the high voltage reading makes me think that my downpipe sensor readings in the 10s were probably closer to the real AFR than the tailpipe sensor readings.

I'm going to a dyno next Friday that has a sensor I can put in the stock 02 sensor location. I'll post back with the results.

twokrx7

iTrader: (1)

Tailpipe probe works flawlessly without a cat, I tried both the downpipe and tailpipe and got equivalent readings with the Uego WB.

The only time I have experienced a problem is during high tail wind while parked. The readings would go full lean, 20 afr, at idle. Had me fooled for a bit until I snapped to the wind.

Wargasm

The wideband measures the partial pressure of the oxygen gas in the exhaust stream. Even if the airpump is not pumping in air, the catalytic converter is still converting or trying to convert CO to CO2 and so on...

To make that conversion it requires O2. Either from the exhaust stream or injected as "air" via the airpump.

So wouldn't it be reasonable to assume that the cat is removing oxygen gas from the exhaust which would make it look leaner due to less partial pressure of O2?

Brian

SPOautos

I've heard from 2 dyno shops that they dont waist thier time tuning a car with cats and a tail pipe sensor. They get the customer to pay for a bung installation mounted before the cat or either use thier stock bung. But they never tune with a tail pipe sensor on a car with cats.

It sounds right to me, thats the entire purpose of a cat

Also, as far as the Tech Edge wb accuracy, I checked mine out on a brand new dyno, I was only the 3rd person to run on it so the sensor was brand new. I have my bung welded in the bottom of the dp about 3 " from the mp. My wb and thier wb was always within .1 or so. For a total investment of $400 I'd say its extremely accurate. I do believe placement is very important though and that it should be mounted in the bottom of the dp. BTW - thier wb monitor cost $5000. Sounds like a waist to me haha

STEPHEN

newRX7fan

iTrader: (1)

The A/F should read richer after a cat, if everything is working correctly. The cat tries to take fuel and O2 and convert it into water and CO2. So it uses up O2. Since the WB sensor measures O2 concentration, it will read as if there is less O2 than before the cat. Lower O2 concentration = richer.

I think your results make sense, and for the Oz WB sensor to get the same readings it would have to be installed in the same position as the big $$ WB sensor.

phlanigan

Thanks for the info NewRx7, but I don't think the AFR should necessarily change after the cat. It is, by definition, the ratio of fuel to oxygen, and if both fuel and oxygen are being used to produce water and carbon dioxide in the cat, then the ratio should stay approximately the same. I agree that if you are using an OXYGEN sensor, that oxygen levels pre- and post-cat should be different. However, I guess the question I have is whether typical dyno tailpipe sensors measure AFRs or whether they measure oxygen partial pressure to extrapolate an AFR. I know that the NTK sensor used by my wideband measures oxygen partial pressure, and I'm guessing that a typical tailpipe sensor just measures O2.

BTW, the measurements at the tailpipe were leaner, not richer.

I've seen and read so many different explanations for what is going on that I'm not going to be satisfied with my wideband until I can verify my readings with another sensor. I'm checking this weekend, and I have more dyno time next Thursday,

SPOautos

Where is your TE located? Is it in the stock bung? I've heard that is to close to the engine and you get better readings with it in the bottom of the dp close to the mp. The sensor is heated to the temp it needs to be but your exhaust right out of the turbo can exceed that temp causing your sensor to become more hot than its supposed to be which will throw off the calculations.

That is something else to consider depending on where you mounted it.

Like I said, mine is around 3-4" up from the mp and with no cats I was spot on with the dyno wideband which was located in the tail pipe.

STEPHEN
STEPHEN

phlanigan

I have the sensor in a second bung located on the downpipe just before the DP junction with the cat, so I shouldn't be having heat issues. I'm going to a dyno on Thursday next week that uses a screw-in sensor that I'll put in the stock O2 location and read in parallel with my WB. Hopefully this will resolve the conflicting AFR readings I got from the last dyno run.

Badog

I've been suggesting 4 inchs ahead of the flange, or about 8 inchs after the flange in the MP after the curve since I started tuning. Works great with the TEWB and compares within a tenth with tail pipe sniffers (without cats).

The stock location works, but it shortens the life of the sensor. Our exhaust is too hot. Ideal is something within the heat range of the heat pump of the TEWB.

Get an extra (your 2nd extra) bung put in before the cat and stop sniffing.

phlanigan

OK, I just got back from my second dyno run, this time using a sensor placed in the same bung I use for the TE wideband. This is placed just before the DP/cat flange.

I had exactly the same AFRs I measured with a tailpipe sniffer. I measured 11.5-12 last time and this time it was even slightly leaner 11-7-12.3. MY wideband is still reading 9.9-10.7 over the full throttle range.

Conclusions:

1) The cat has a minimal effect, if any on measured AFRs at the tailpipe compared to those measured at the DP.

2) My wideband is not calibrated correctly and I'm going to get in touch with the Techedge people for some troubleshooting.

BTW, while I was on the dyno, I richened everything up and am now running 11.2-11.7 at WOT cells. Lost a little power, but still making 265 whp on a dynojet.