After trying to get the off-the-shelf 93 octane TBE map to work on my car, I finally called it quits. For some reason my car did not react to well to these maps and the knock sum was consistently around 7-10 which I did not like.

Then I decided to try and modify the custom 91 octane map that I had to work with 93 octane gas. I knew from Alfred @ tuning tech that my car was finicky when it came to timing adjustments so I figured that the custom tuning map that he created for me would be better than the off-the-shelf map.

When I ran the 93 octane gas on the 91 octane map there was 3-2-1 KS in the peak torque/boost and on one run had zero KS throughout. So the car ran great on the taht map, albeit a little rich for 93 octane map with the AFR at 10.9:1 from 4-7K rpm.

I did not lean the AFR in the peak torque area. I leaned it by about 0.3 from 4000 to 7000 rpm. When I did that the Knock Sum started to increase above the consensus acceptable level of 3. I was also getting spikes in the knock buffer. So I was forced to back off the timing. The odd thing is that the KS increased in the peak torque/boost area even though I did not lean the map by anything significant in that area

My question is: How much power did the car gain from this tuning? It seems to me that it did not gain much since I was forced to back off the timing in order to lean the car out. I have attached the chart and welcome your comments.

 

You're better off running a bit richer, especially if it allows you to run a little bit more timing. I have had my car on the dyno, tuned to 11.3 AFR ... then richened it up to run at 11.0 AFR and logged ZERO power loss (timing unchanged).

Having logged my car in different types of driving scenarios, I have noticed that while I can get my AFR to stay right around 11.0:1 during 90% of my WOT runs, every once in a while (maybe 1 in 20) I will see a run that goes as high as 11.5:1. Bearing that in mind, I'd say that once you've found the limit of how lean you can run your car, I'd add some fuel back in to richen up the AFR by at least 0.3 points.

l8r)

 

Out of curiosity....

When you say you pulled timing you mean you increased the negative value in the Xede map thus retarding the timing a little bit right?

Can someone explain to me exactly how the ECU varies the timing physically?

 

Yes, that is what I did. I increased the negative value in the timing table. I noticed that a a 0.9% pull in the top end was approx 1*. In the low end when I pulled 0.9% in the xede table the average pull in timing was 2*. I do not know why there is this difference in timing pulled when you change the values in the table in the high end vs. the low end!!!

 

from my observations, running the car richer with more timing produces better results than a leaner mixture with less timing.

 

What AFR would you recommend for 93 octane gas? Is 11.3:1 the most that we can run on a mild timing set-up like mine?

 

Pretty broad statement, wouldn't you say? There are situations where one can argue either approach over the other. Just depends on the situation (rpm, temp, octane, etc,.)

shiv

 

In this particular instance, meaning stock turbo car with a turboback exhaust on 91 octane. I guess everyone has their own style and individual way of doing things, so I'll clarify further by saying what works for me is running 11.0 from peak boost to redline on an EVO8. On more knock prone engines I have seen substantial gains by running it even richer 10.7~10.8 to allow for the same timing I use on normal engine.