Latest dyno and 1/4 mile results = Bad AF ratios!

[jgkurz]

Hi all, I finally got my car off jack stands recently and was able to get a few dyno runs and a trip to the local drag strip. So far the car is running as well as could be expected. On a Dynojet 248 I put down 356 HP and 424 Torque. In the evening I went to the track and ran a best of 12.8 @ 115mph with a 2950lb 280z on 205/60-15 tires. It may be unrealistic, but my goal is 400RWHP and an 11.9 at the strip. My AF ratios are beyond horrible so I think I can make some power there. This run was done at about 16psi so of course more boost will bring up the HP. The only way I'll ever get close to the 11's is to shed some weight and get some drag radials.

 

As a side note, I run a standalone EFI and my AFR adjustments are made on a 16x16 point map. I've been trying make adjustments to the MAP with the help of my FJO wideband but can't seem to make any real progress. I'm starting to see the advantages of an OEM setup. My AF ratios are extremely erratic. Does anyone have suggestions for getting a stable AFR?

 

Thanks,

 

 

 

[Drax240z]

What stand alone system are you using?

 

I am not sure what you mean you can't make progress on your AFR adjustments, looks like you are pretty darn rich until the topend on the dyno chart, and still rich there too. Why can't you just lean it out more?

 

I guess I need some more info. 8)

[jgkurz]

Drax, I use an Electromotive Tec3. I guess what I'm frustrated about is the amount of time it's taking me to make small steps forward in my tuning. In my mind I have two options for testing. 1) Pay a minimum of 75.00 for three dyno pulls or 2) do some 6000RPM datalogging on the freeway which could resulting a costly speeding ticket(s). Either way it looks to me like a major PITA. I have 256 points on my MAP which I can obviously narrow down to a select few for making changes on. Once I've found the errant spot I then need to determine how much fuel to add or remove. The system has an auto-calibrate function which does not seem to be accurate. It's putting values in the MAP I now are totally wrong. Sorry for the rant, I guess I'm just venting. I wish there was a simpler way to get my MAP perfected. Oh well..... off to the on-ramp I go.

[Drax240z]

Don't you have the ability to datalog with the wideband/tec3 combination? I would think that would cut down on the tuning time considerably.

[jgkurz]

I do have the ability to datalog, but finding the errant spot on the MAP then how much fuel to add or remove is the difficult part.

 

Last night I compared my FJO datalog in Excel to the Dynojet AFR and the chart matches. However, the FJO has much more granularity. I'm also noticing that the FJO O2 sensor in the downpipe is picking up the AFR about 400 rpm's sooner than the Dynojet sensor in my tailpipe. I was making adjustments in the wrong area of the MAP! I would also guess that the FJO datalog is still about 100 rpm latent from the actual event in the engine.

 

Looks like my only option is to keep making small increments forward until I get it right.

[speeder]

John,

 

Great numbers, and pig -rich too! You can probably meet your horsepower goal with tuning.

 

TEC and FJO is my setup.

 

Looks like your basic fuel curve (IOT and TOG) needs to be leaner throughout the whole range..

 

Send me some shots of your calibration and some FJO .wbo files and I''l take a look.

[jgkurz]

Thanks for your comments Rick. I'm starting to realize that everyone who has a standalone EFI has to go through the AFR pains until the MAP is where it should be.

 

I'll send you some files when I get some quality datalogs completed.

 

 

Regards,

[TimZ]

Thanks for your comments Rick. I'm starting to realize that everyone who has a standalone EFI has to go through the AFR pains until the MAP is where it should be.

 

I'll send you some files when I get some quality datalogs completed.

 

 

Regards' date='[/quote']

 

John...

True - it can be painful, but just imagine what it would be like without datalogging...

 

I can't remember - were you datalogging the FJO separately, or is it actually the TEC's EGO input? If it isn't the TEC's EGO input, it should be.

 

First off, I personally don't trust Electromotive's autotune feature, as it relies on the EGO feedback loop to try to figure out how to correct the map - this doesn't work very well.

 

I think we talked about this a bit before, but turn the EGO feedback off until you have the VE table where you want it.

 

To figure out how to change your VE table, take a datalog and open it in Excel. Sort the file by RPM. You can then make a series of scatter charts of MAP vs AFR, one for each of your RPM breakpoint ranges. This should give you a very clear picture of exactly where you need to adjust your VE table, and how much.

 

You were correct in noting that there is latency (time delay) involved in the AFR measurement. However, it is actually an RPM-dependent time delay, not just an error in rpm. It's a combination of sensing delay and the amount of time it takes the exhaust to travel from the port to the sensor (i.e. longer delay at low rpm). The slower you change your rpm while testing, the less effect this has. Do not try to tune on quick 1st gear throttle bursts. One effective technique is to drag the brakes in second or third gear, allowing plenty of cool-down time between runs. Also, for tuning purposes, roll in and out of the throttle slowly to avoid getting wonky readings due to the acceleration enrichments - these need to be done seperately from the VE table.

 

Feel free to give me a call if you have questions...

[Clifton]

I would find a shop with a dyno that charges by the hour. I had to do that as I can't drive one of mine on the street. For my other Z I bought an LM1 wide band, easier than running to the dyno to check a/f.