Trans Revolutions per Mile - Wizard - Something Not Right

[slarsen47]

Here are the speedo calibration numbers for a stock 4L60e 2002 Camaro SS.

The stock tire is approx 25.7 inches with a circumference of 80.6 inches and turns about 787 revs per mile. With the stock 3.23 axle the calculated transmission revs per mile is 2,542 revs per mile. This compares favorably with the 2,615 that shows up under the calibration tab.

Here is the modified calibration using wizard for 26.4 diameter MT drag radial with a circumference of 83.0 inches and turns about 764 revs per mile. With the 3.70 axle the calculated revs per mile is 2,826 revs per mile. The does not compare favorably with the 3,781 that the wizard calculates.

Even doing a simple compare ratio of 3.70/3.23 applied to the factory 2,615 results in a value of 2,995 which is a long ways off the wizards value of 3,781.

I took the car out on the highway and the speedo, scanner and GPS were all very close at 60 mph.

In the note it states that the output shaft rpm is used to calculate shift rpm and tcc. Could this be why I have no WOT 1-2 and 2-3 shifts even though the mph and rpm targets are exceeded by quite a bit.


What am I failing to understand here?


2002 Camaro SS auto 3.70 26.4 drag radial.jpg2002 Camaro SS auto stock tire.jpg

[TheMechanic]

So are you saying that at WOT it is bouncing off the RPM limiter?

[jsf55]

Read the bottom of each screen shot, there not the same, not that i know the difference !

[slarsen47]

So are you saying that at WOT it is bouncing off the RPM limiter?

Yes, and I believe I have found the problem. Now I understand!!

I replaced the wizard's 3,781 with 2,826 under Speedo, Calibration, Gear Ratio & Tire Size.

And scaled the transmission shift mph tables by the ratio of 3.23/3.70 to lower all the shift mph points.

With the Trans Revolutions per Mile edit...........it is driving and shifting without a lot of rpm's.

Had earlier attributed the "looseness" to having a 3600 converter, but it was the bad Trans Revolutions number.

My lockup rpm now matches my commanded lockup rpm.

Speedo, scanner and GPS all match pretty close at 60 mph.

I have no doubt now that it will shift pretty close to commanded rpm's.

[TheMechanic]

This was an issue that I had on a Corvette a few years ago.
https://forum.hptuners.com/showthrea...ht=rev+limiter

[gottogo]

I've just noticed a difference between revs per mile from my current tune to a previous tune on a manual trans.
Could this be causing a problem?

[slarsen47]

This was an issue that I had on a Corvette a few years ago.
https://forum.hptuners.com/showthrea...ht=rev+limiter

I looked at your post and agree with changing the shift mph as you have done. I did the same.

BUT............the transmission rev's per mile is the key.

What is missing from your post is the transmission rev's per mile number. Do you still have that number?

I've just noticed a difference between revs per mile from my current tune to a previous tune on a manual trans.
Could this be causing a problem?

Do the simple calculation and compare it to the number in your tune. As per my original post.

Compare the calculated number to the ones in your previous and current tune.

Not sure if this is an issue with a manual transmission, but it sure can cause problems with the automatic.

[TheMechanic]

Screenshot 2023-06-22 100154.jpg
Does this help?
MODIFIED 2001 COUPE TRANSMISSION.hpt

[slarsen47]

Thanks and Yes, you have 2,446 transmission output shaft revs per mile.

Assuming Corvette with 275x40R18 stock tire and 757 revs per mile and 3.42 gears works out to 2,588.

So your PCM value is not that far off from the calculated number. About 142 to be exact.

Mine was 955 difference!! No amount of tweaking rpm shift points was going to get it to shift!

[TheMechanic]

Did this one a couple years ago before I kept better records. Can't remember if this was the original configuration or it was the one I actually modified for his diff gear change. That is what was causing the bounce off the rev limiter at WOT.

[bk2life]

Here are the speedo

google bluecat transmission tuner, use that.
super easy, and itll help with your prgramming