<img src="http://im1per.shutterfly.com/procserv?si=00002937301920021227022530119.JPG&ps=0 &rx=640&ry=490">
timing X vs ABT


<img src="http://im1per.shutterfly.com/procserv?si=00002937301920021227022527649.JPG&ps=0 &rx=640&ry=490">
torque &amp; power X vs ABT


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speed X vs ABT


I got some timing data on an X-chip car with aftermarket exhaust to compare with an ABT chipped car with stock exhaust. The tests were done in different locations at different times, but both were done on flat roads. Ambient temperature was about 30 degrees colder for the X-chip runs. The X-chip car had Mobil 93 octane gasoline. The ABT car had 93 or 94 octane gas (it was either Exxon, Mobil or Sunoco).

A rough rule of thumb is that changing ignition timing 1 degree will change the octane requirement 1 unit. The ABT chip shows no timing retard, leading one to believe it's designed to run 91 octane gasoline without knock. The X-chip however shows up to 6 degrees of knock induced timing retard. Timing retard was fairly uniform among the cylinders so 1 bad injector can be ruled out.

Shown are graphs of ignition timing, torque, power and speed. Data was collected in 4th gear with the accelerator fully depressed. 2 runs were made with the X-chip, 1 for timing data and 1 for torque data. 2 runs were made with ABT chip, both runs collecting data for timing and torque.

At idle ignition timing is retarded to minimize emissions. As speed increases timing is advanced. With further increase in load timing is retarded to limit peak combustion pressure. Ideally you would want peak pressure at about 10 degrees after top dead center to maximize efficiency. Combustion is a function both of time and turbulence. In the graph you can see how the ABT timing was quickly retarded as the turbo built boost and then advanced the timing as available combustion time decreased.

The first graph shows that the X-chip requests a more advanced ignition timing than ABT but actually gets less advance. The difference between requested and actual is split by the ABT timing. X-chip torque drops significantly at 4200 rpm, while ABT torque tapers off slowly. The drop in torque is real, as can be seen in the time to speed plot (graph #3). In this graph 3000 rpm was set as the 0 point because the X-chip ignition timing run did not have WOT until 3000 rpm (I wish people would log starting from idle speed). At 4500 rpms both the X-chip and ABT motors have about the same ignition timing but the ABT motor is putting out more torque, and as a result, accelerating faster. This suggests that ignition timing is not the source of the power loss for the X-chip car. A possible boost leak was mentioned, but this doesn't explain the timing retard. If less charge is reaching the cylinders then it should sustain more timing advance not less. If the cylinders received less scavenging then the fresh charge would be smaller but the temperature of the charge would be greater. In this case it would be possible to have a weaker charge that tolerates less timing advance. However the aftermarket exhaust should produce better scavenging not worse. An obstructed exhaust seems most likely; misplaced gasket, collapsed cat or whatever.

 

I don't have my timing data on these runs. However, I've calculated the net torque (ft*lbs) and hp. Here's a 4th and 3rd gear run, 95*F ambient temp. I don't have that drop, nor is it as surgy. BTW, this is the FMIC xchip.
<img src="http://pictureposter.audiworld.com/24538/image002.1.jpg">

Your data:
<img src="http://im1per.shutterfly.com/procserv?si=00002937301920021227022527649.JPG&ps=0 &rx=640&ry=490">

 

Rather interesting how the X-chip brings the knock sensor into the picture.

John you mentioned that, "The ABT chip shows no timing retard, leading one to believe it's designed to run 91 octane gasoline without knock. The X-chip however shows up to 6 degrees of knock induced timing retard. Timing retard was fairly uniform among the cylinders so 1 bad injector can be ruled out."

So what can we assume about the X-Chip? Is it not designed for 91 octane?

Just looking for a bit of clarity.


BTW interesting set of comments about the boost leak and the exhaust.

 

Need data from more cars, this one might have a problem.

 

I will have this data tomorrow. Either myself or some one else will email you the info.

How was your Holiday? How is the Mrs. doing? Please extend my hello to her.

Vishal