Gear Change In A 4t60-e

[95Grand-Am]

I have a 95 Grand Am with a 3100 and a 4T60-E that I oval track race. My problem is at the end of the straight away I'm only turning 4900 rpm in 2nd gear. I want to change the final ratio to 3.73. Someone told me the easiest way to do this is to get a trans out of a DOHC car' which should have the underdrive chain drive in it. Then put my gears in it which should give me 3.73. My question is since the speedo will be off will the trans still perform ok, I want it to stay in 2nd gear and not shift into third. Does any one know at what rpm will it shift into 3rd or does it go off from speed. I have received some mixed info on this and I would like to have a better idea before I go through the work. Any Ideas, advise, or info will be apprecated.

[torq455]

http://60degreev6.com/forumdisplay.php?f=75 Read up man. All you need to know.

[blackbombshell95]

You would also have to find a way to program that new gear into your PCM.

[3100 MPFI]

There shouldn't be any programming needed.

I did it in my Cutlass Supreme, and didn't have any issues with the speedo being off.

[Azrael]

All you need is the transmission from a 95 grand prix GTP and swap in your existing differential and you'll have the 3.73 FDR. Might want to grab a few different differentials to toy with as 3.73 is a steep change from 2.97.

[torq455]

a gear swap won't affect the speedo. just the shift points will be higher as the PCM shifts at a specific MPH for TPS.

[sharkey]

what sort of racing do you do??? what sort of modifications are allowed???

i would say if the rules allow, get a th125 3 speed auto and swap the wiring harness/pcm to a 93 cavalier auto. this will save a pile of weight and rotating mass and allow you to be able to custom burn chips. this would be of coarse if your not allowed to run a standard. in the case you could, find a 4:10 fdr mucie 4 speed from a fiero.

[95Grand-Am]

Thanks alot for the info. But i keep getting mixed information about whether reprogaming the PCM would be needed. It doesn't matter to me if the speedo is wrong or not. Does anyone know if the PCM shifts at a certain MPH or rpm? I think with the gear change I will be turning 5600 to 5700 rpm at the end of the straight away in 2nd gear. My fear is that it will shift into 3rd at 5500 rpm which will not work good, I need it to stay in 2nd. I looked for performance chips and was told that no one make them for the 95 Grand- Am. I believe I have 3.33 gears now. Thanks again for all the info please keep it coming until I figure out how I can make this work.

[1988GTU]

what sort of racing do you do??? what sort of modifications are allowed???

i would say if the rules allow, get a th125 3 speed auto and swap the wiring harness/pcm to a 93 cavalier auto. this will save a pile of weight and rotating mass and allow you to be able to custom burn chips.

Ding ding ding

[sharkey]

95 is obd1.5. basicly its an obd 2 chip (soldered to the board), obd 2 plug, but obd 1 programming. nobody is able to tune it. changing the gear ratio will not affect the roadspeed the tranny shifts at, the speedo pickup is on the outside of the diff and basicly reads the speed the wheels are turning at. what the pcm does look at is engine rpm, your map sensor and tps for full throttle shift points.

there are a couple things you could do to avoid having the car shift out of 2nd. the easyest is to put it in manual 2nd and itll stay in 2nd gear till it hits the limiter, then it would make a 3rd gear shift (all in the programming). it also would start in 1st gear and shift at its normal time. getting more complex, you could run the transmission with a pair of toggle switches instead of the pcm. basicly you wire toggle switches to the solonoids and depending on whats on/off will determine what gear you have. this would however have the pcm in limp mode becasue it doesnt have the tranny hooked to it, so this would take us back to the tuning thing, either swap to obd2 (hard and comples) or swap to an older (93) ecm and wiring harness and burn chips.

[95Grand-Am]

Thank you Sharkey for the information. The rev limiter is a 6000 rpm do you think if I pull it into 2nd it will stay in 2nd until 6000 rpm or will it shift at 5500 rpm into 3rd? Because if it would stay in 2nd until 6000 rpm it would work perfect because I don't think I would ever get to 6000 rpm in 2nd gear. According to my calcuations I should only turn 5600 to 5700 rpm with th 3.73. Please let me know at what rpm will the pcm command 3rd gear even if I have it pulled into 2nd manualy. Thanks alot for all your help.

[sharkey]

it all depends on what its programmed for. pcm programming for the transmission can varry from platform to platform, even with just a different gear ratio.

in most electronic transmissions, if you put it in manual 1st it will run up to the rev limiter, bounce off the rev limiter a couple times then the pcm will force a shift as an anti abuse feture. it should od the same thing with manual 2nd, the only thing you can do is try it.

[torq455]

ohhh duh! sorry, i forgot the VSS was on the diff. FYI, Sharkey is the tranny guy. he knows his stuff! a powerful asset to our forum.

[torq455]

wonder how much that 4:1 diff is...it have an LSD too?