Advice on Dyno results

#1

OK, so I’m completely ignorant with this stuff. I had a dyno run done at Summit in April and I just would like to know what it means. I do understand the Hp torque, but how can I tinker with things to try and make it better. I hear a lot of people commenting on air fuel ratios and don’t understand a lot of it so if you can keep it simple for me i would appreciate it.

#2

looks like your pic didn’t post.

#3

Can’t seem to edit the picture. Any help is appreciated.

#4

Host it at flickr, photobucket, or imagestation and then put it in a post. Unfortunately there isn’t anything you can really do to improve your air fuel ratio since we can’t chip our ECUs. You can try and swap out ECUs or make sure your mass air flow sensor is working properly. On the dyno you should be looking for somewhere around 13:1 AFR at wide open throttle with the wideband O2 sensor in the OEM location in the downpipe.

#5

Jason:

The rulebook on these things doesn’t allow you to do much, and I’m just too lazy to head to the dyno with 10 computers to figure out which one is the best.

Air/fuel ratio is just that - the ratio of air to fuel. 13/1 is 13 parts air one part fuel. The leaner the ratio the hotter the burn, and the better the chance you melt pistons and/or blow a head gasket. Traditionally, lean is fast, also, so you want to run on the edge of lean, if you can.

All of that said, I have hear a lot of stories about bad or partly clogged fuel injectors. That would create a lean condition. I might pull my injectors and have them flow tested and cleaned, particularly in light of the mess that my fuel system was, which I have now fixed.

What was your HP/torque numbers?

#6

I don’t have the sheet with me at work, but they were in the 145 range. I think the guy at the dyno said I was running really rich up until the higher rpms (5000?). I’ll get the picture posted this evening somehow.

Does a rich situation mean that the O2 sensor is bad?

Jason

#7

I will have to let the experts here diagnose the richness. On a Mustang, the car ignores the oxygen sensor at WOT over 3000 rpm, so the answer on those cars is no, but I have no idea what the programming on these cars are. 145hp isn’t a bad number I don’t think, so I would not worry about it.

-Scott

#8

O2 sensor doesn’t play at WOT (wide open throttle). My dyno tests last summer showed my .020 over motor had 149hp. I was able to get 1hp by swapping lots of AFM’s and ECU’s, but that still left it pretty weak for a fresh oversize motor. It was also running lean.

I would later find out that I had an injector running at 80%. You can get your injectors cleaned and flow tested at CruzinPerformance.

Comparing dyno results. The most common dyno here seems to be the Dynojet. They say that different dynojet dyno’s can be compared to 1-2%.

There is also the issue of correction factor. When you tell the software to show you the curves, you select a correction factor. “Standard” and “SAE” correction are common ones and the difference is 1-2hp. So if you are comparing dyno graphs you should doublecheck that both graphs are using the same correction factor which should be printed on the graph somewhere.

#9

I took my car to the dyno a few weeks ago to see what removing the adjustable FPR did to the A/F ratio. I raised (leaned) the mixture about .5 to .75 points. I don’t remember the exact numbers. The power and torque was about the same. One thing that we learned is that the amount of fuel sent to the engine at WOT is dependent on the amount of fuel needed before WOT. My dyno guy is a LS1/LT1 guru and really understands fuel injection although nothing about BMW’s. He is the one who asked me about his. He would have me hold the RPM’s steady in 4th gear at say 2700 RPM and then give me the thumbs up to go to WOT and he started his recording. We did this many times. He then asked be to hold the engine at 4000 RPM and then gave me the thumbs up to go to WOT. When we did this the A/R ratio was better across the recorded range. This was new and interesting to me. He explained that even though WOT is open loop, the ECU uses the most recent data to decide how much fuel to give. So, basically the O2 sensor does come into play at WOT because it is used to adjust fuel before WOT and set a base for what to give at WOT.

We were still unable to get the better A/F ratio as we had with the adjustable FPR.

Michael
#36

#10

Correct. My understanding is that above about 4500rpm only engine temp and rpm are used when at WOT. But the learned adaptation values are used to modify the built in wot maps. Supposedly, the AFM maxes out at around 4500rpm when the engine is at WOT. One of these days I’m going to log the AFM signal and see if that is correct.

#11

In the absence of a wide band O2 sensor, how can the engine learn?

#12

Sorry it took me so long to get back, but here is the photo. Thanks for all of the input so far.

http://www.flickr.com/photos/15837407@N08/4650780372/

Just seeing if this works.

Jason

#13

Hi Jason,

Based on my dyno experience with a blown Miata, I’d say your injectors are leaning out beginning @ 5300 rpm. I had one dyno guy refer to it as the “injector march of death”.

Don’t hang your hat on my $.02 worth, I’m interested to see what the others say. I’ll be going through the same exercise in the upcoming month or so.

#14

I just read in another “Dyno Report” thread, that made my head spin, that the lean situation might be an o2 sensor? But then it seems it could be plugs, wire, cap, rotor, AFM, DME… I don’t have money to throw at all of these things, but I don’t want to kill my mediocre motor either. Any suggestions?

Jason

#15

Your lean condition in the upper rpm range is due to lack of fuel. I’d start by sending the injectors off for cleaning/calibration. You may find that one or two are not delivering as required. Hopefully the cleaning will resolve the delivery problem. If not, you may have a tired injector or two.