I'm in the process of installing 4.10 gears in my truck (from the factory 3.42s). I know I need to change the gear ratio in the TCM tune, but wanted to know what other things like shift speeds etc., I might need to change in the tune. I have the E38 ECM and am using EFI live. Thanks for any input on this.

 

Just as you have surmised, when you change the gear ratio in the speed calibration tables, you can do an auto calibrate, which will show you the correction factor, but even so you will most likely still need to go into the shift and lock-up tables and make some adjustments. I find that most of the time, when the computer auto calculates for the gear change or when someone makes a fairly drastic change in tires sizes, it actually goes too far and you will need to raise the tables back up somewhat. As an example, just using bogus numbers, if you had an original shift point on the 1-2 shift of 41mph and after the program re-calibrates the tables for the gear change using a correction factor of .834 it goes to 34.2mph, you may find you really need to bump it back up to 37mph to feel right.

 

Thanks Bear. That is what we found out last night, except that we had to go the other way?? On the first TCM retune we dropped the shift speeds down way lower (we've always had to do this on my truck, for some reason?) than what the calculated top speed in each gear is. For example, the calculated shift speed @ 6700RPM for 1-2 w/ a 4.027 first gear, 31.9" tire, 4.10 gears with 1% convertor slip is like 37.x MPH, but we dropped it down to 32MPH. We had set the shift rpm at 6700rpm and the truck still shifted 1-2 at 6921RPM! The truck is now an animal w/ the 4.10s though! With me (258lbs) and a 200lb friend, the one full run we did, the log shows 10.00 seconds 0-100MPH!!! And 4.1 secs 0-60MPH!!! I think the speedo is off though, and I noticed this morning that we changed everything in the TCM tune for speedo calibration except for {H0102} VSS Pulses per Revolution, which is still at 36, so I am pretty sure that the VSS is not accurate. So we still have some tweaking to do. It's going to be interesting to see what happens at the track this evening...
Thanks again.

 

I'm still trying to learn EFI Live myself I tried making the changes on mine after a gear change but didn't apply the shift table corrections. I asked Justin to do an update to my tune and make it right for me. I was comparing the two tunes, before and after, {H0102} is the same with both gear sets. Like I said I'm still learning here but I believe it should stay the same. I have the truck down right now because I need to put the front diff back in this morning but I am wondering if the speedo in the cluster will be correct now.

 

You're right. the {H0102} VSS Pulses per Revolution stays the same at 36, which is the number of teeth on the reluctor.
I found out through searching through the EFI Live forums that the problem was that the settings in the ECM had to be changed as well. We've done that and the Speedo is now accurate. Apparently the speedo (the dash) reads from the ECU.

 

Track time improvements?

So you are running the 4.10s with a 6L80 6 Speed?

 

Yes, 4.10's with the 6L80E. Track times have improved about 2 tenths (N/A) over previous track times with the same tune and on an unprepped track, even though it spins a bit now off the spray and a whole lot on N2O.

See this link:

https://www.performancetrucks.net/fo...=471534&page=2

 

Nice to hear man, a lot of people on here told me that the combo wouldn't work well or that I would hate it, but I met some guys from the deep south of Texas running 6L80Es with 4.30s and 4.56s even. Then I starting talking to the Camaro crowd and all the serious guys over there are running 4.10s and some are running 4.30s and thats even with 28.5" tires.

I am having my Detroit TruTrac and Yukon 4.11s installed November 23rd.

 

I have re-geared every truck I have had with 4:10's and loved them every time. I just picked up a new 6.2 truck it's got 3:73 and I think that in sixth gear the 4:10's would give it that little bit of extra torque to keep it from shifting to fifth on minor hills. I just haven't been able to make myself want to tear apart a new truck just yet.