VetteLS3

Hello, I just received my 3.42 diff and am also about to get a Yank SS3600 converter to install in my 02 vette. Half of the things I have read say that you don't need to change the gear ratio in HP Tuners on vettes after the gear change, and the other half say you do still have to. Just looking for some clarification before I do this swap. My car has 2.73 gears right now. Thanks.

enoniam

You don't absolutely have to do a computer tune change, but I wouldn't do those changes without planning on doing a few tune tweaks.

VetteLS3

Oh, I was definitely planning on making changes for the converter lockup and everything. The part I was confused on was changing the actual gear ratio in HP tuners. A lot of people said to leave it as 2.73 on HP tuners even though I am really switching to 3.42, because the Pick up for the speedo is on the output of the transaxle instead of the output of trans, so it doesn't need to be adjusted in HP tuners. Then some people said it does need to be adjusted, so I was trying to clarify what to do about that.

RonSSNova

Yes, you need to change it.
All the Trans functions rely on mph/rpm. Your rpm will now be higher for a given mph.

When you change this, there is a box you check to autoscale the transmission functions.

Good luck!

Ron

AFTRBRNR

At the very least your shift tables will need to be adjusted otherwise you are looking at bouncing off the rev limiter at WOT. I went from a 3.15 to 3.73 with SS4000 stall. I believe I multiplied my entire shift table by 1.1 or something close to that and my car retains a stock smoothness and predictability with shifting. With the higher stall I would bump shift pressure a tad.

enoniam

The only area where rpm comes into play with the transmission shift points is the WOT shift points, and even then they can be governed by either speed or rpm. I personally prefer rpm and in that case wouldn't be bouncing off of the rev limiter.

AFTRBRNR

When changing gear ratio, both speed and RPM will now be different. To shift at the same speed the RPM will be higher, to shift at the same RPM the speed will be lower. To maintain a familiar ride all MPH points under part throttle need to change. You're absolutely right though about WOT, but you should still adjust the MPH at WOT shift as well with that high stall. High stall TC's get to red-line really fast and will keep you in the powerband after shifting. My car is set so that there is redundancy to prevent bouncing off the rev limiter... this is what happened when I kept the RPM commanded shift for WOT the same but MPH was not compensated. The computer couldn't keep up with the car.

enoniam

It isn't the computer keeping up with the car - it's the transmission shift time. There is going to be a time lag from when the computer orders a shift until the transmission responds. In that time the rpms at WOT are going to keep going up until the shift forces the rpms down. For the 1-2 shift it's going to be at least 100 rpm, and the transmissions seem to be slower (in my experience) when warmer. I set my WOT shift rpm 150-200 rpm lower than the rev limiter to keep from hitting it.

Well said.

VetteLS3

There is a thread just a little down from mine in this section called "Torque converter + plus gears =P1870" where somebody says "1st On a C5 when you change gear ratios----you do NOT make a speedo correction in your tune ----Put those numbers back to stock". This is my main confusion and reason for posting this question. Half of the people say not to change the speedo and half do. Can anyone clarify?