Results 1 to 20 of 22
Thread: T56...rear gear selection HELP.
-
10-07-2004 #1
T56...rear gear selection HELP.
Ok, the million dollar question. My T56 has a .75 5th and .5 6th gear. I need some help figuring out what rear end ration to run. I have 3 choices, 3.73, 3.90 and 4.10:1.
My goals for this car are more based on open road, road course or auto x, although it will see the strip a little as well. I am leaning toward the 4.10:1 because of the really tall 6th I can still cruise at just under 1900 rpm at 70 mph but my concern there is that 1st gear will become all but unusable. Will traction be a complete nightmare in the first couple of gears. Will 6th gear even be of any use in the high speed runs or is it too tall for the amount of horsepower I have (+/- 400hp with a 125 shot N2O)
I would like to eventually race the car in some open road events and would like the car to be capable of 160-170 mph once my skills catch up.
Has anyone with this tranny used any of the above mentioned gears and if so what would you suggest.
I am running an LS1 that will have a cam and headers installed and a redline around 6200 rpm.
Appreciate the help. Noel.
-
10-07-2004 #2Registered User- Join Date
- Aug 2004
- Posts
- 582
Some calcs that may help guide your decision:
Assuming Cd = 0.40, frontal area = 2.33m^2, , air density = 1.293 kg/m^3, I get a terminal velocity is 79 m/s (about 177 mph) for 300kW
For 57%/43% weight distribution, 0.5m CG height, 1360kg mass, 2.74m wheelbase
I get a speed for power limited acceleration of 32 m/s (about 71 mph)
10-07-2004 #3Holy S**t. Ok bro, you can't just drop bombs like that and walk away! hahaha. I got the top line, based on your assumptions I should be able to reach 177mph. Now, the second line...I'm not sure what a speed for power limited acceleration is all about. Can you explain it to me and tell me how this data will/should influence my rear gear decision. These assumptions don't take into account the rear gear ratio and how close it can come to putting me in my power band. Or does it. I'm lost, someone turn on a light.
Chill, Noel.
10-07-2004 #4Starting The Transformation- Join Date
- Aug 2004
- Location
- Alta Loma,SoCal
- Posts
- 396
I'd use the 4.10's. Even with 3.55's you will have traction problems with the power you have and low profile tires. I think the 4.10's will let you pull the high gears better.
Just an example from my experience :
I have a 77 Chevy 3/4 ton truck. Had a 4speed manual trans with 1-1 4th, and 4.10 gears. Pulled great on the freeway, although crap for milage. Swaped in a 5speed manual with .68 5th. Much better milage, but couldnt pull 5th on any hill or towing. Swaped in 4.56's, now its great for everything.
Goes to show, it doesnt take much to make a drastic difference.1965 Buick Skylark
10-07-2004 #5Originally Posted by Fuelie Fan
I’ve got a 396 BBC with a t56, 4:10 gearing and a 275/40/r17 tire. I cruise at 80 mph and 2k rpm. I have raced many cars on the highway and get it up to 155 mph in 5th. True the first gear is very short but with some drag radials (nitto 555 r to be exact) you will do fine. If you want to race at 160-170, make damn sure that your car is built for impact just in case.
All in all, I’m happy with mine. Low end torque is not my friend (I don't like my big block and will be switching to an ls1).
oh and by the way, terminal velocity is pointless when horse power is involved .It's shake and bake!!! and i helped!
Drewco Homes
10-07-2004 #6