And don't forget, 1st gear is 2.66 vs 3.06 of the 4l60e. You have to have more gear to make up for that difference alone.

 

hmmm..all of this does make good sence..is there a gear/mph ratio chart on here anywhere for the six speed? i found one for the 4l60 but not the T56

 

http://www.f-body.org/gears/

Select 1998 F body M6 at the top.

 

Trans gear ratios:
4L60E: 3.06, 1.63, 1.00, .696, 2.29 Reverse
T-56 F-body LS1: 2.66, 1.78, 1.30, 1.00, .74, .50, 2.90 reverse
T-56 GTO: 2.97, 2.07, 1.43, 1.00, .80, .62, 2.90 or 3.28 reverse (have seen conflicting data regarding ratios)

70 mph = 1914 rpm w/4L60E, 3.73 gears, 31.9" tire for all examples
49.9 mph @ 1st gear @ 6000 rpm

70 mph = 1375 rpm w/T56 F-body, 3.73 gears, 57.4 mph in 1st gear @ 6000
70 mph = 1681 rpm w/T56 F-body, 4.56 gears, 47.0 mph
70 mph = 1891 rpm w/T56 F-body, 5.13 gears, 41.7 mph

70 mph = 1705 rpm w/T56 GTO, 3.73 gears, 51.4 mph in 1st gear @ 6000
70 mph = 2085 rpm w/T56 GTO, 4.56 gears, 42.1 mph
70 mph = 2345 rpm w/T56 GTO, 5.13 gears, 37.4 mph

T-56 F-body ratios (2.66 1st) a 5.13 looks good for both street and strip.
If using a M12 T-56 (Like GTO) 4.56 looks good for the steet.
Since both trannies have 1.00:1.00 4th, the 5.13 gear looks better for 1/4 mile drag racing, since 6000 rpm in 4th gear = 111 mph, a reasonable trap speed. The GTO trans in 4th with 4.56 gears = 124.9 mph @ 6000 rpm.

The F-Body type gearing, w/2.66 1st has nice, progressivlely closer gear ratios 1-4, 1-2 shift 33% RPM drop, 2-3 27% drop, 3-4 23% drop, great for best acceleration.
The GTO gearing w/2.97 1st has larger rpm drops in the 2-3 and 3-4 shifts.
1-2 30% drop, 2-3 31% drop, 3-4 30% drop and only 20% drop 4-5 shift.

I've used both of these transmission in a LT4 equipped project car (25 in tires, 3.73 axle, 6400 rpm shift point). The GTO type geaing felt odd, with the 1-2 shift being almost too close in ratio, while the 2-3 shift felt ok and the 3-4 shift felt to big, and then shifting from 4-5 @ 120 mph was super close ratio, useless for drag racing but perfect for road racing.
The F-body type gearing 1-4 felt perfect for drag racing. The 4-5 shift was a big rpm drop, but provided a perfect top speed gear ratio.

An advantage of using the 4.56 gears with the GTO trans is you keep the driveshaft rpm down. Make sure you don't hit the critical rpm of the driveshaft when using a long single piece.

 

hey guys yall have really helped me alot! thank you all!

 

My normal driving I skip 2nd and 4th. 1-3-5-6 is my daily shift pattern. The others are too close together to be worth it. If I had a few more cubes or a slightly smaller cam, or just cathedral port heads with more velocity at low rpms I'd probably just do 1-4-6.

I have the Aluminum Metal Matrix custom shaft from these guys and it is dead smooth with my 5.13's. Around $425 with yoke and joints.

http://www.dynotechengineering.com/

 

Anyone have experience using the Cadillac CTS-V M12 T-56 in a NBS?

 

What differences would there be in converting an '07 and newer Silverado (GMT 900, New New Body Style: NNBS)?

Is the engine programming a lot different?

Has anyone done a manual transmission swap on a NNBS yet?

Thanks!

 

Ok, I have an 04 scsb that was a 4.3 / 5 speed. Now it is a 7.4 / 5 speed. I can reuse the throw out assembly and just use an ls1 trans correct? The truck with me in it weighs 4500. Should I step up to a 4.10 (4.11?) 4.56 gear?

 

ok boys i just picked up a t56 for the avi i guess ill be reading thru all 50 pages real soon