im considering the t56 for my 20b with as many problems as the people have had with the factory fd transmission. I cant decide which to go with. I know the model from the viper has the ideal output shaft and the gto has the multiple syncros which should help with higher rpm shifts but, what about the gear ratios which one is appropriate? I dont want to kill my fuel economy ,however i dont need a top speed of 250mph either. I want to be be geared to a maximum speed of 202mph ish not that i will hit it but i want to know that i can. its hard to pick one when they all seem to be for high displacement motors that make peak power lower and dont rev nearly as high. which is kind of back *** wards of our rotary motors.

 

gm t56 dimensions

 

so the GTO transmission is nearly the same length as the factory transmission which should be perfect since i didnt push my 20b back. but what about the gearing between them

 

http://en.wikipedia.org/wiki/Borg-Wa...6_transmission

 

given what we currently know specific T56 model selection is not that simple...

choice depends on your objectives and an item yet to be determined.

as i see it there are two factors to consider:

Gearing and High RPM shiftability


Gearing

do you want wide ratios or close ratios?

there is a big diff between the GTO box and the F body box.

Gearing for me is the number one consideration because i run a 2 rotor and RPM is much more important (peak torque is 6500 and there certainly is less than a 3 rotor).

consider:

..................FD box.................GTO.....................F body

1.................3.483....................2.97... .................2.66
2..................2.015...................2.07... .................1.78
3..................1.391...................1.43... ..................1.30
4..................1..........................1... .......................1
5....................719......................84.. ......................74
6................................................5 7.......................50

shifting at 7800 next gear RPM entry point:

2................4512............5436............. ........5219
3................5384............5388............. ........5696
4................5607............5455............. ........6000
5................5608............6552.....................5772
6....................................5293......... ............5270

for me the F body is the best answer as my porting starts to power up my turbo midrange so as to deliver 400 rwhp at 5500. i want to stay above 5500. 2nd and third are marginal in the GTO box but very good in the F body. also i am wanting to runn 200+ at the Texas Mile and i need the .74 5th at close to 8000 to do 200. the GTO 5th is too short.

if we skip the Texas Mile however the shorter 5th and 6th are welcome. i actually plan to run a Ford 03/04 5th and 6th for my road racing as they are .79 and .63. i will just add them to the better geared (1-4) F body box.

3 rotors are a whole nuther world w all the torque you might want the wider spaced GTO ratios. of course it may depend on what you want to do w your 3 rotor....

then there is shiftability:

the GTO gets the nod here w better syncros. i was planning on buying the NEW
T56, called the Magnum. while retaining all the same exterior casing, the interior is completely re-engineered. priced at less than $3K it is good value. (BTW, used T56s sell between $1K and 2K).

i chose a 40,000 mile F trans just to see if it is up to the job. if it shifts at 8000 i will stick with it. if it doesn't we will have learned something and can just upgrade the internals a bit to fix the shifting.

as far as torque... the higher the torque rating the less likely high rpm shifts are going to be happy. T56 torque readings, as i recall, are for the number, say 450, for 10 hours. they, IMO, both from research and direct experience are way understated. there are lots of drag racers lifting the front wheels in 3400 pound cars w sticky tires running the F body trans.

assuming no delays or problems i should have the final final pieces ready to bolt in by the end of this week.

howard

 

great info ^

rotorooter, heres a simple gear calculator if u wana play with different tire or rear end

http://xse.com/leres/bin/gearratio?t...rofile=&wheel=

 

Thanks guys! Howard you, yet again have a great point. I too want to run my car at the texas mile but it is also a weekend warrior so its hard to say. I agree the GTO tranmission seems to be the best though since gearing is irrelevant if you cant shift at higher rpms anyway. if the gearing is not ideal i suppose i can always have them changed out.

I want the car to pull hard and to top out at just barrrrreeeelllyyy above 200mph. now if i can pick out a set of rear end gears

 

let me know how everything goes howard. I tried tony94s4 's calcualtor but with a redline set at 8300 with factory 4.10 gears and my 335/30/18 tires the calcultor shows my top speed somewhere around 247mph.... that cant be right. i may just be misusing it. either way i wonder what my mph to rpm would be with 4.10 gears and the different transmissions anyone better at doing calculations that me?

 

ignore 6th gear for calulating top speed. its too overdriven, 5th is faster.

 

I just picked up a newly rebuilt Fbody t56 with the upgraded internals good for 700 ftlbs for under $2k from a forum member...let me know if you would like his info

i went with the fbody but also have pfs 4.33 gears so we shall see how this goes lol

 

phoenix 6.0 so maybe replace the 6th gear with a different ratio? .65 maybe i think with 4.10 gears the car should just top out a little over 200mph at 8000 ish

 

another question what to do about the ppf. i believe the t56 just bolts to the chassis so i eill have to fabricate some mounts for it but what about the diff? same thing?

 

I have been looking at the clutch options howard coleman has shown and I really wish there was something a little easier. I want to keep my exedy carbon twin disc clutch and flywheel but they dont make a hub for the t56 inputshaft in the twin disc so instead of going through the trouble of buying a t56 clutch, pressure plate flywheel and and hub and getting everything to match up i was considering just having a new input shaft made t56 internals dont change just the splines. In theory if the clutch and fly wheel fit up then the only thing needed is a push type pressure plate or am I mistaken?

 

Not a bad idea.. The only problem with your 20b, that twin carbon exedy will not last long that clutch is over rated for the power it can take.

You need a 3 plate carbon carbon clutch if you want to stay carbon, at least a 2 plate ceramic plate clutch with a high clamp presure plate.....
Your best bet is to sell that clutch and get something that will hold the power....

Will save you money in the long run...

 

If it doesnt hold then the tripple would be the next setup, I just dont want to have to buy another clutch if i can use this one. This is all given I can get a push type version of my current pull type pressure plate. If I can get the push type then i wont need that flywheels either way though I will need that adapter plate.

 

newb question, i apologize..... bu the gm t56 bolts on or has a modified bell housing that fits the rotary?..... the 6 speed trans would fit a 13 B ?

 

Shifter location can be swapped between the f-body and GTO setup. the f-body shifter feels much better than the GTO setup, sorta rubbery feeling. you just need a couple of pieces inside the shifter cup to change between. i would suggest a camaro MGW shifter or a pro-5.0 w/ steeda triax handle

for transmission mount and diff mount, check into samberg(v8 sponsor). im guessing the trans location will be about the same as the v8 swap so i think the mount might work. the v8 guys are loving the diff mount setup.

 

to slow, I will have to get both the flywheel and the adapter plate as exedy doesnt seem to make a push type pressure plate that will fit the carbon twin disk clutch. so its back up for sale. Im asking $2000 shipped I have pics or it and a carbon fiber driveshaft in a for sale thread.

 

I use the Hinson trans mount and Sanberg engine and diff mount and couldn't be happier. Granted this is a v8 but still applies for the trans and diff.

For the speed you must ignore 6th and maybe even 5th as the T56 is considered a 4 speed with double overdrive. 5th wouldn't be as bad with a 8k red line but 6th is just too low without the low end torque of a v8. If you are looking at 202mph gear the rear for 5th gear. 202mph in 5th with a 4.10 rear and 25.8" tires should get you about 7990RPM given the LS1 trans.

As said earlier the GTO and LS1 Trans are pretty much swappable as far as physical requirements go. Also, You could look into a LS1 Twin Plate clutch. A 800ftlb model with VERY nice street drivability runs about $1250.00. A flywheel may have to be custom made.

 

I wouldnt mind using an ls1 twin plate clutch but I have not found one that will bolt to and rx7 flywheel or an ls1 flywheel that the automatic starter will engage. so It looks like a custom flywheel is the only option either that or a button flywheel like howard did but i question how well it will stabilize at higher rpms comapred to a billet flywheel.

As far as the transmission im putting my f body t56 up for sale and wait to finish my project as i have a bunch of expenses at the moment, so i have to put my extra cash into put into my company so the project looks like its going on hold.