Question : Chain ratio swap, '96 4T60E

[LeftVentricle]

1996 Buick Century. According to the SPID tag, I have a 2.97 final drive. During the brief time before it popped a head gasket, I felt that that was just too lazy. I'd like to make it a 3.29/3.33.

- With a 2.97 final, what diff ratio and chains does it have? Are we talking about a 3.29/3.33 with a 37/33, or 35/35 2.97? Gosh, I hope it's not a 33/37 2.73/2.84...
- HP Tuners website does not list any '96 vehicles as being tunable by their software. How do I make the PCM happy with the ratio change? Is there another company that makes tuning software for '96 cars?
- Is this something that can be done with the transmission still in the car? If so, is it just a matter of pulling off the side cover and swapping the gears? Will the axle have to come out?

Thanks.

[TurboGTU]

3.33 with 37 drive and 33 driven. Drop the trans is easier to swap gears sets. While your there might want check the condition of the rest if the trans.. maybe someone might chime in on tuning

[3400-95-Modified]

You'll go with a 35/35 sprocket to get 1:1 drive ratio and since you have a 96 It's probably a 3.29 diff, not the 3.33, not a huge difference though.

Your best bet is pulling the trans to swap this because you have to pull the full side cover and then the pump channel plate and valve body... See below.

Side cover removed


Pump and Valve body removed


Channel plate removed


You can remove the Pump Valve Body and Channel plate as one whole assy though so you don't disturb the ball bearings and such on the spacer plate.


Standard 37/33


My 33/37, you'll do 35/35 though


Tuning, DHP does offer 96 Buick Century or similar IIRC... I did one in the past I think... You will need Tiny Tuners to make the change though since I do not think DHP had the drive sprocket ratio mapped out properly. I know just before they closed up shop they mapped it in the 96 Beretta file but it was 2 times what it should be, so I had to set it to 2 for a 1:1 ratio.

I'll see what I can find for the Bin file.

[LeftVentricle]

Great information. Thanks guys. Looks like a proper mess for someone who isn't intimately familiar with automatic transmission guts though. I guess for now I'll deal with my lazy old man wagon. If the trans is gonna have to come out, may as well put a new one back in, ya know?

[Purple pit]

I had a GP trans put in my Beretta. I can tell you that going from the stock 2.97 to 3.33 was nice. Still I feel that a little more would have been helpful. But I got lucky because it is a 95.

[LeftVentricle]

I had a GP trans put in my Beretta. I can tell you that going from the stock 2.97 to 3.33 was nice. Still I feel that a little more would have been helpful.

I feel that less is more, honestly. Back when I had my 2.8 Celebrity wagon, I had a transmission built with a 3.73 overall final. Being able to burnout on command, even with only 98 whp, was fun, but it didn't really translate into better performance. My quarter mile improved by about a tenth of a second, while I lost 3 mpg on the highway. I've always felt that 3.29/3.33 is the happy medium: better acceleration than 2.97/3.05, better highway economy than 3.69/3.73.

[Purple pit]

Ok, a 3100 is not a 2.8/3.1L. The 3100 is built more for top end power(that is TQ for sure and a bit of HP). The 2.8/3.1 is low end power, all power is made under 4,900rpm. If you want good MPH on the street or the highway you want low end power(that is where you spend most of your time). I don't remember where peak torque is made on the 2.8, but it is much lower in RPM. Do to the lower gear ratio/better gear spread the 2.8(that you had) and the 3T40 gave better MPG over all.
If you want to get the best out of a 3100 you must have more gear(FDR). There is something that you can't avoid and that is the crap gear spread of the 4T60e(1st to 2nd ratio).
To get the most "power" and MPG out of an engine that has a higher power band you must have three things. One is(as it always is) cruise at or near peak torque, two is a close ratio gearing(which GM does not understand anymore) and the correct FDR that works with both.
GM went with the popular, the 700r4(the 200 4r is much better in ratio and the forth gear is not too far off). They have kept that going and you can see it in the 6sp auto. They say the wide spead is good for MPG, but how is adding more load adding to MPG? That is because there is no Fed mandate for over all MPG(that will change).

[Purple pit]

Now you could say that GM has made up for the problem these days(with FDR), but they still hold on the bad raito and have given cars more size/weight. Weight is a point that I didn't talk about, but you don't have the same problem as the new cars. They and others have tired to use aerodynamics to overcome that problem(which is a stop gap for weight). The other problem there is that they are building cars for fat people and/or(or both) those that need tech(which adds weight).
There is one way out of the ratio problem, but it costs alot. There is a company that can rebuild/build a trans(700/4T60e style) that has a higher 1st gear. The cost is a deal killer though(around $2,200 dollars).

[TurboGTU]

Lousy 1 to 2 would have to go to my Fusion. What a gap! That Buick was meant to be a cruiser with that final drive.