Dyno'ing & A/F
 

When dyno'ing, can A/F ratios be measured?, if yes:

• Does it require the car in question to have a Wide Band O2 sensor?

Thanks for any responses!

Edit, I've seen some comments of measurements being taken from the exhaust tailpipes...how accurate is it? as accurate as the instrument?

Yes and yes!

I don't like sensor probes in the tailpipe of the car at the rear. They work but aren't as accurate as a good lambda sensor near the beginning of the system. A conventional O2 sensor does not have the accuracy to show proper a/f ratios.

In other words: should I dyno the 8, I won't be able to get accurate A/F readings.
RG, you rock!

Thanks!

You'll probably be OK if you just want to see basic a/f ratios when you dyno the car. I wouldn't try to tune an ecu off of this probe though. It is too far away and would be too slow to respond to changes.

okay. I know so little about the goings-on of the ECU that its pathetic... But, I'm pretty sure that I saw an A/F ratio output from a CANScan unit not long ago. This guy's 8 had no WB 02 sensor and there was nothing up his tailpipe (haha). So, if my memory is correct, wouldn't this existing sensor give you the needed accuracy? Afterall, its accurate enough for the ECU to use. The CANScan costs about ~$200 - - I think....

The 8 does have a wideband O2 sensor.

I am just curious about current health status of my motor, and wanted to do it for the heck of it. I originally wanted to get a compression test first...but -don't laugh- certain shops compression tester is out of order :rolleyes:

Back to A/F: in theory, with the probe, I should be able to get an idea of how the A/F curve behaves, right? That should be good enough for now.

It would be great if I had the CANScan tool for tomorrow...but, that ain' t gonna happen. But like I said before, the probe should get me an idea of how the a/f curve behaves.

Alright, I just got back from Rotary Performance. Got the car base lined @
178.4 whp @ 8000
134.4 wtq @ 5700

Ambient temp: 77ºF - Pressure: ?? - Humidity: low?
All numbers are SAE corrected.

In other words, another average dyno, for an average Joe (me!)
Did not get A/F -I didn't specifically ask, and Chris pulled it off in less than 35 minutes because I had to get back to the office.

Comments on the HP curve:
1. Remember the pre-L (or M) flash dips? Well, they are still there. I don't know if they look so pronounced because of the scale or what. Anyways, the dips happened @~6200rpm & ~7400rpm.

Next step is getting a compression test. Once I have all the base numbers...well, we'll see.
I will take a pic of the sheet once I get home. And sorry, but I made the move to the 21st century....no scanner.

And here we go: https://www.rx8club.com/vbgarage.php...type=im&id=227

A baseline w A/F
 

Attached (if I figure out how to do this) is a baseline run I made for my Rx8 with A/F taken by the dyno's meter done with a long probe place deep in the exhaust ~ Unfortunately the dyno printout doesn't indicate exact rpms where peak bhp & torque figures were taken, but it looks like peak bhp of 187 (SAE adjusted) occured somewhere @ 8,500 rpm, with peak torque of 134 ft/lbs @ 6,000 or so.

The car, build date Aug., '03 had the "M" flash done mid August '04

[/IMG]https://www.rx8club.com/attachment.php?attachmentid=29431&stc=1https://www.rx8club.com/attachment.php?attachmentid=29431&stc=1

HTH

the dips are the SDIAS system flipping from low to medium to high rev configurations, they'll always be there.

also, as we can all see the car is running rich on an open-loop run to redline. that's probably not a good thing.

where is that 02 reading taken from? is that the compter in the dyno's interpretation of the voltage signal from the sensor itself, or is that the reading the dyno is getting from the RX-8's computer interpretation of the sensor reading?? it would be very interesting to find out which, as if that's from the 8, it means the car itself thinks it's running rich (it did make it that way) and it's suppost to be. that's... well, the reason you can gain so much power from a good tune.

Roger that! I figured...but that was not my point. My point was, I cannot feel them anymore (w/my butt dyno that is) eventhough they don't look any less steep than the original dips on the "K" or "L" car dyno sheet.

BTW, in case I didn't specify these things:

The car has got the M calibration & 18K miles on it

He said they used "a probe" on the exhaust to get those readings. Like RG said, that method is not completely accurate, since it is sor far back in the entire system.

The probe has its own sensor, which picks up oxygen levels and translates them in to voltage singal. No different, I think, from a bread & butter O2 sensor.

There are people that do tune with that insert probe but I personally don't like them.

When I use the CANScan unit, I read between 14.5 and 14.9 while driving in city/highway. I am not sure it is accurate, seems too high compared to the plot here. I would expect better milage but it is from 17 to 19 mpg. Car is fairly new though - did 5000 miles today.

It hits open loop somewhere after 5000 rpm. Any location before that it's closed loop and the ECU will try to hit stoich (14.7 to 14.9.) I did notice that the lowest AFR seems to be 12.05 while tuning my CZ/eManage. I see 12.05 at about 7500 and above.

All these readings came from CanScan.

I'm making the assumption your comment "... compared to the plot here." is in reference to the dyno + accompanying A/F graph I posted. And the comparison being made is to data you've pulled out off your car's ECU/databus with one of the scan tools out there.

I don't know (my guess is with the newer engine management programs & wide band O2 sensors, it should not but.....) keep in mind

(a) the A/F results graphed by the dyno equipment was done with a tail pipe probe sniffer. While this seems to be satisfactory to our local, Colorado, state emission testing stations, I know it is NOT acceptable to the Swiss/German tuners I've seen working on shop Audi's and Porsches~ they insist on a wide band bung located within a short distance of the exhaust ports, and a thorough, complete exhaust inspection to be sure there are no air leaks, especially on the turbo engines, before begining to tune an engine.

(b) 2nd (again, the ECU/wide band should compensate and correct for it), the run was made at +5,000 feet ~ we're down 15% to 18% on available oxygen up here. Since I got the car used, I have been logging mileage, and for the most part been averaging 20 to 22 mpg in combined city/highway. Driver "performance" school/track events however, where the engine is frequently in the 6k to 8.5k band range, is more like 10 to 12 mpg. A dyno pull would be of the 10 to 12 mpg kind of range.

HTH

It really depends, granted that their not the most accurate, but if you dynoing 187 and according to that at around 13.7 your right where you want to be to make max power under WOT.

But if he got his AFR reading at the tailpipe, wouldn't some of the fuel be soaked up by the cat thereby giving him a lean AFR reading?

I've talked to Hymee about it, i asked him how much of a difference they found between his CAN buss unit and one of the units suck into the tailpipe.

He said that as long as those things are stuck far enough down the tail pipe the difference isn't huge, but it varies too much dyno to dyno.

And at 187SAE he's running what my car is running on my best day, and your not going to get much more then that.