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View Full Version : RPM DIFF logging on 7531


68bird
05-14-2007, 09:00 AM
After logging a few runs, I started looking at the RPM DIFF function. What exactly is this curve / data showing me? Is it plotting the time it takes for every 90* of crank rotation? If that IS the case, and the graph is really inconsistent and jumping all over the place, what does that mean? Misfires? Or better yet, what SHOULD a typical log look like for this function? Should all the peaks be the same height approximately?

Someone please enlighten me.

Thanks!
Craig

msdtech4
05-15-2007, 07:51 AM
68bird,

The RPM diff is looking at the trigger between each firing of the crank trigger or distributor. The numbers are going to range from 0-255 and will look like it is swinging wildly up and down this is normal. Depending on the application it might go to 255 at the release of the trans brake or clutch and stay there until you lift off of the throttle. This normally indicates movement in the trigger source. There is not a "norm" for this as it depends on the application, with a crank trigger on a normally aspirated application it is usually in the mid to high 100's and something with a power adder would be in the 200 range. What this tells you if you see something like a limiter comes in early etc., if the RPM diff is maxed out you know this is what happened.

Thanks,

MSD tech4

68bird
05-17-2007, 07:11 AM
Thanks for the reply.....does this RPMDIFF line look 'normal' to you? This is on a forced induction motor.

Thanks,
Craig

msdtech4
05-17-2007, 09:33 AM
68bird,

Yes that does look normal. It would not be something I would be concerned with.

Thanks,

MSD tech4

Kevin O'Dell
05-17-2007, 12:44 PM
Is that what the automatic compensating rev limiter will correct? I have mine turned off if for no better reason it's because of lack of knowledge about it. What are the Pros and Cons of turning it on? No hurry reply needed just asking.
Thank you
Kevin O"Dell

68bird
05-17-2007, 03:59 PM
Thank you MSD Tech4

Craig

msdtech4
05-18-2007, 08:10 AM
68bird,

No problem if you have any other questions let us know.

Kevin O'Dell,

No that does not have anything to do with the auto compensating rev limiter. This changes how the limiter works. If you monitor all 8 EGT's and if you notice certain cylinders getting colder then the others when you turn the auto compensating limiter on it the unit changes how the limiter acts and will even out this issue. You will hear a difference in how the limiter "sounds" bit it will be just as accurate.

Thanks,

MSD tech4