I noticed that when you change your rear ratio in TunerCat (LT1edit also???), that the Shift Points do not change. I thought that these would be based on RPM rather than MPH...? (This is for a '95 Vette LT1/4L60e installed in a '76 C3 Vette)

Is there a "method" to altering these points based on gear changes? Does anyone know what ratio is used in the original GM programming (I had another member e-mail a "virgin" Y-body file, but now when I open it, it automatically opens w/ 3.36 ratio my car has...I guess it keeps the last ratio used in memory and applies it to any other files opened)

I know I can adjust all the changes to my liking, but GM must have had reasons for picking the MPH points they did. Just want to know how to adjust, since my 3.36 ratio is not an option for C4 vette.

Thanks!
:steering:


[Modified by DR'76, 11:55 AM 4/19/2003]

 

DR'76

TC remembers your last gear change regardless of what file it was. I am not sure why it does this. However if you look you can see that the values in the "currrent values" will be different than those in the "new values" window.

Shift points are based on speed and TC does not change them automatically. LT1 Edit however does make automatic table entries for gear ratio changes. If you are making a gear ratio change from say 3.07 to 4.10 gears your trans may have shift problems.

Your PCM constants is determined by the gear ratio that was installed for your car at the time it was built. You can find what gear ratio you have by lookin in your box behind the passenger seat and finding the option code that determines the gear ratio. Here are the option codes and gear ratios if you look you will see one of the following:

G44 - 3.07 ratio
G87 - 8.50 inch
G92 - Rear axle performance ratio
GH0 - 3.54 ratio
GM1 - 2.59 ratio
GM3 - 3.45 ratio
GT7 - 3.33 ratio
GU2 - 2.73 ratio
GW4 - 3.31 ratio
HE3 - 3.07 ratio

What gear ratio change are you going to and what was the stock ratio. If you have a virgin file I can make the change in Edit for you and email it back, or give me your VIN number and I can get a virgin GM calibration for you.


[Modified by tjwong, 6:45 PM 4/19/2003]

 

TJ,

Unfortunately, I don't have any of the option code info, since I only have the engine and tranny from the donor car, but I do have it's VIN: 1G1YY22P5S5113507

I always thought the tranny shifted way too early (probably a fuel-saving trick, like the 1-to-4 shift the manuals have), but since my '76's ratio of 3.36 is not an option, and TC doesn't adjust accordingly, I didn't know what values to put in. I also didn't know what ratio the donor car had.

Since there are SOOOOO many shift tables (hot, cold, normal, manual, cruise, upshift, downshift, etc....) I guess the easiest would be to retrieve the virgin GM calibration and update in LT1edit using 3.36 w/ tire size 255/60/15

I have a program called TuneConv, which should convert the .lt1 to .bin (although I have not tried it yet)

Thanks SO much for your assistance :yesnod:

You can mail the .lt1 file to donovanhalen@cs.com

Dr.