Since I swapped to a T56, I have to slip the clutch alot or the car shakes because of the stock 3.23's, so I wanna change them. This is my daily driver, so what I want to know is the difference I am looking at in performance and gas milage. I plan on going to 3.42 or 3.73 (no 4.10). I know I will see some performance gain, but not sure how much. And how big of a difference will I see on the highway in terms of gas milage? I get about 23 mpg now. And do I have to edit the PCM for the new gears?

 

for sure you will. i've heard that the hypertech III does just fine to tune out your gears. where in L.A. did you swap your trans? im in the L.A. area myself. I just got some 3.73, but havent installed them yet.

 

You shouldn't be having to slip the clutch with 3.23's.... that's only a 5.9% difference from the M6 stock 3.42's. Moving up to a 3.42 isn't going to make much of a difference over the 3.23's..... I doubt you will notice it. The 3.73's would be a better choice.

There will be minimal change in gas mileage, and I base that on swapping the 3.42's for 3.73's when my car still had the T56. It actually makes it a lot easier to run in 6th gear at 50MPH, something that's not really productive with the 3.42's. Unless you are running for extended periods of time at 80/90+ MPH, I doubt you will notice any change in gas mileage.

Yes, you either need a Hypertech, or a mail-order tune for the PCM. Since pcmforless already did your tune, it shouldn't cost much to have them tweek the gear ratio.

 

I also have 3.23's in an M6 car and don't have any trouble at all pulling out from a dead stop. I didn't see a cam upgrade in your sig so the stock cam should have lots of torque for getting you moving. I don't think the problem is in the gearing. Could it be a clutch or alignment issue? I'd look into that before going to the expense of a gear swap. Incidentally, 3.42's would make a negligible difference. If you still want gears, go with the 3.73's.

 

The shaking should have nothing to do with the rear gear ratio, IMO. More likely a clutch issue (which you would still have after swapping the gears).

 

Did you get the flywheel resurfaced when you did your swap? Did you put in a new clutch kit?

 

2.73's in my car for the time being and it pulls fine from a stop no lugging at all

6 gear with 2.73's is rediculous highway

 

The flywheel is a stock one I got from a junkyard, and I had it resurfaced before I put it in. I put in a brand new Ram HDX clutch. Did all LT1 flywheels come balanced the same? Just wondering, since I don't know what year the one I have came from. The shaking is mostly when the car has been sitting for a few hours, and then I have to bring the RPM's up to about 3K and slowly slip the clutch to get it going smooth. I just wasn't sure if that was normal (this is the first car I have driven with a stick). Thanks for the replies.

 

i did daily drive my car, gain .2 and 2 mph from 3.42's to 3.73s. My 60fts picked up and i would run out half of fourth gear opposed to shifting into it 20ft before the trap. it also makes it easier to hang with ls1s on the street.

 

Definitley not normal.... I could just let the clutch out slowly at idle, without touching the accel pedal, and nothing would shake.... the car would just start moving. Worked that way with the stock clutch and with a Street Twin.

I can't imagine why there would be any difference at all in the external balance weights for a stock LT1 engine.

 

Ok, I got around to playing around with the clutch and tried what you said Injuneer. The car will start moving without giving it gas, just a few feet before it starts to die. What it feels like is like the clutch is grabbing hard then releasing, it does it a few times then finally catches. Kind of like when starting from a stop in 2nd gear, or when the traction control kicks in. I do have traction control, if it makes a difference.