4T65 Gear Change

[jjaromin]

First, heres my transmission mods on a 1998 Grand Prix GTP...
3.69 gears, 3250 TC, 30 tooth VSS reluctor wheel.

I've tried numerous times in HPT to get the car to accept this gear change. I have failed each time and have to use another tuner program to get it to work properly. In the HPT, I've changed the drive sprocket ratio to 0.892 (which is from 33÷37). Changing this value in the HPT results in permanent hard shifts, but oddly no DTCs.

If I change 1 parameter in another tuner (calc_pulses_per_rev) from the stock value of 22.30 to 28.03, proper shifting pressure returns to normal. I believe this is working around the way it should be applied on HPT. The value VSS Pulses per Rev-Trans seems the way to adjust this parameter, but I have not figured out the correct way.

Can somebody verify that either the Calc_pulses_per_rev should be added as a parameter or if the VSS Pulses Per Rev-Trans is the way to perform an adjustment to the the reluctor wheel. I've looked at the HPT help file, but it seems to imply that the VSS Pulses Per Rev-Trans should be the number of teeth on the VSS wheel. The stock cal value is 9.1172, which is nowhere near what the stock VSS wheels tooth count of (i think) 38.

Has anyone else successfully performed a gear change (and VSS reluctor wheel change) and have the HPT accept those changes?

edit: Just realized I put this in the wrong forum...apologies.

[ct06gto]

This has been a issue for a while. People that have done gear changes have multiplied the gear size by 1.121 and but that in the calculated gear location.

Example-- 2.93 is the stock gear X 1.121 = 3.29 thats the stock setting.

if you have 3.29 gears you will want a 3.69 calculated gear.

if you have 3.69 you will want a 4.13 calculated gear.

[jjaromin]

This has been a issue for a while. People that have done gear changes have multiplied the gear size by 1.121 and but that in the calculated gear location.

Example-- 2.93 is the stock gear X 1.121 = 3.29 thats the stock setting.

if you have 3.29 gears you will want a 3.69 calculated gear.

if you have 3.69 you will want a 4.13 calculated gear.

I'll give that a try... Thanks...

[louvered97gtp]

Looking for update, this this ever get resolved?

[Bandit gs]

I've done it two ways, first way is by calculating the values which works ok. .89 isn't correct, if you read how its calculated its 33/37 = .89 then divide that into 3.29 (diff ratio), which equals 3.69. Also the 9.1172 value will throw a code if your using a stock wheel, that value is around 7.xx something. Check your in 3rd gear calculated ratio, it should read 1.00, if it doesn't that number is off. Divide the actual value you get into 1.00 to get your % your off by then fix it. You'll also need to manually scale the shift tables by a percentage, button under the speedo tab. 2.93/3.69=.794 which gets the close, not right but close. Lastly you can calculate the other numbers.

The other way like they mentioned, which is to just insert a new ratio of 4.13, i use 4.11 it gets the vss number closer, 4.13 is off by a slight amount where the 4.11 seems to work better. This is by far the easier way