Bridgeported

I plan on doing a 20B conversion starting in the fall. I've been researching what gearbox to use in the conversion, since the TII transmission will not handle the planned power.

I know for sure that I want to use a production gearbox. Main reasons for this is that the car will be a street car, so the gearbox has to be smooth shifting, ability to downshift normally, etc. Using a production gearbox cuts the price WAY down, allows cheap repairs, and tones of gear ratio options which are cheap and are readily available.

So to sum it up, I need a production 5 or 6 speed manual transmission that can handle some serious power (700-800 rwhp), even if it means strengthening it a bit.

The best options I've seen so far would be a T56 or a Supra 6-spd transmission. Prices for used units of each are similar, with the Supra one being more expensive. I know for sure the Supra one can handle the power, and with using a 20B, the gearing should already be fairly well set up. The T56 on the other hand doesn't have the best gearing for a high reving engine.

Is there any reason the Supra gearbox may not be my best choice?

I made some posts on the 300zx/GTR forums to get info about the RB25DET and 300zxTT gearboxes to find out if they have good ratios and their power limitations. Any opinions on these?

That 2JZ box is looking the best so far though...
Thanks.

Node

iTrader: (1)

Isn't it very large and heavy?
With the talk of people having adaptors for T56's I would go with a T56 personally.
Don Marvel (is that his first name?) has some T56 adaptors. They were posted on the 20b Forum.

Node

iTrader: (1)

And another thing. Jimlab said that lots of F-Body people shift at 8,000RPM and some a little higher with T56's with no problems. It can definately take the torque.
I've seen that the hydraulics need to be freeflowing and it should be very good.
I'm assuming you're going to use the stock e-shaft? I believe 8,500RPM is its estimated redline unless you have a balanced one.
PM me if you would like any other information I have about T56's.

Bridgeported

Thanks for the reply, I sent you a PM for more T56 info.
I do plan on using an 8500 rpm redline on the 20B.

rotorbrain

theres also a difference in the build of the e-shaft on later model 20bs. they are tapered and therefore stronger. . . evidently.

paul

Node

iTrader: (1)

You have a PM.

Suds7

3 rotors and up utilize a 2 piece e-shaft which has a tapered (can remember name of connection) that is stronger, but 8500rpm is solid (unless this is a bridge or peri motor ) I have 5.0 friends that shift there cars in the higher rev ranges.

red 7

My friend has a supra and he said that their tranny isnt rebuildable ??? Im not positive on this but he has one and thats what he said

its a getrag right

crispeed

The Getrag tranny in the supra is rebuildable. You just have to know where to get the parts!
There are some of the Toyota dealers that have connections for the parts but it's not readily available from every dealer.
The only draw back to using the Supra Getrag would be the very low 1st gear ratio. I believe it's in the 3.6:1 region. That works fine on a Supra that weighs 3600lbs with a final drive ratio of 3.20 something but on a light weight Rx-7 with 4.11 gears and a 20B motor it might just be a little unuseable. Even the guys with high powered Supras complain about 1st gear being too low.

crispeed
87 Rx-7 TII
9.204@150.47mph
2600lbs
un-tubbed

HWO

I looked at the ratio's in the box for a 13B and i thought they would do me well, a 20B however, hmm not quite to good.

Wargasm

Hell, I think that the stock FD 1st is too low. Once you have some serious mods, it's very hard to keep the wheelspin to a reasonable amount... it would suck even worse with that 20B! Have you considered going with another rear ratio like 3.X?

Brian

Bridgeported

Well I plan on using a Ford 8.8" rear end - which endless sizes of gear ratios are available, so that can help me out.

600HP CLUB

what's a T56?
viper tans?

-mike

Bridgeported

Yeah, it's found in a few cars actually. Vipers, trans ams, camaros, firebirds, corvettes... not sure what else. The transmission varies though from car to car, things like gear ratios and how much power it can handle.

gofast-

yay transmissions =) here's my department...

supra ge-trag is good but i wouldnt use it because of these reasons:
1. like you said, its difficult to get parts gotta know where & how
2. its no longer a production gearbox also, relativly hard to find wrecked supras

however,

T56 out of a WS6 firebird/firehawk would be awesome & you could just get mark williams gearing to wahtever rear ratio floats your boat (mark williams internals are bulletproof btw)

the reason I reccomend the T56 is due to these reasons:
1. it was a widely used transmission as you previously stated
2. a myriad of stock gearing is available so you can just use the one that suits your needs best and many domestic hotrodders provide alternative or custom gear ratios for cheap
3. there are TONS of camaros/firebirds out there that are sitting at a wreckers with T56's that can be had for cheap
4. its a domestically produced product - dodge/chevy/pontaic interchangability is a HUGE plus here, the fact that there is so many just makes it cheaper =)

be wary of the camaro T56 ... its pretty weak

300ZX TT transmission has a 4.11 rear if i remember correctly (main reason why when you swap the VLSD from a 300ZX into a S1X chassis car you use the 300ZX NA or J30 VLSD..also the halfshafts & axles have an odd spline number dont remember how many on the 300ZX TT)

sorry if its a bit disorganized if you would like me to clarify it send me a pm or contact me over AOL @ danielssnxp

- Daniel

Bridgeported

Ok, looks like the 300zxtt and RB25DET R33 transmissions are extremely similar, if not identical. It seems their power handling limit is about 650-750 rwhp... so they are out of the equation

In my area there are no supras at all (well a few early 80's ones) so finding a tranny would definitely require purchasing one from the internet and having it shipped... $$$

The T56 looks better and better every day. I know I can pick up a used one for under $800, which is pretty damn good if you ask me. I know the gearing can be totally custom suited. I know they can handle the power I want to make. That leaves me with 1 question about the T56...

Which cars did it come in, and what were the main differences? You stated that the Camaros had the "weak" one.

gofast-

right then here we go.
off hand here's what they're offered in:

Camaro SS/Z28
WS6 Transam
Firebird
Firehawk
Viper
Transam

try and get the newest YEAR transmission you can...I say the camaro one was the weakest because a lot of them had high rates of faliure...they mated a relativly high end transmission (T56) to a pretty weak 305ci V8 just mass driveline problems...the best would be wither WS6 Transam, Firehawk (special edition firebird if you find one of these BUY IT) or Viper...why? well...the WS6 came with 450 someodd ftlbs tq from the factory IIRC, this means its got a stronger pressure plate to keep tame engagement for the old timers who drive em ... viper...just because you can say I got a viper trans but seriously...i think its got the strongest driveshaft out of all of em & its got a stronger case but...this is unrealisitic if its from a viper it prob equates to mad dollers & how many wrecked vipers are there?

so...to make a long story short try to get one from a:
96+ Firebird
96+ WS6 Transam
96+ Transam

just call your local wreckers they should have a TON if not, a goodwrench replacement transmission doesnt cost much at all -- what are you planning to do for driveshaft and rear end? only thing i was wondering about...otherwise T56 is king

btw when you swap a V8 into a 240Z...the manual transmission of choice is T56.

The Fairlady Z32 and R33 GTS-t used similar transmissions however there's differences in bellhousing etc.,

*edit*

to answer your second half of the question main differences off the top of my head was just gearing & driveshaft but thats gotta be custom anyway so it doesnt matter

most the cars it came in were powered by the LT1 engine and across the board hp was pretty much the same.

also...you know you gotta get a McLeod clutch now right? hehe =)

Bridgeported

Thanks! That info helps me out alot, and gives me a starter for information to research and take note of

I should have no problem finding a used T56 from a WS6 or TA of the years you mentioned... I imagine it will be easy enough that when the day comes to buy one, I will be able to find one "locally" within a few days.

For a rear end, I plan on using the Ford 8.8" rear end assembly. Reasons for this are...
- it will handle the power I want to make (800-875 20B rwhp)
- can be EASILY found locally for less than $100
- large selection of gear ratios commanly available for it

I will be having a driveshaft custom made by a machine shop.

I still have figured out what I will be doing for rear-end suspension yet. I'm not too experienced with suspension components on such a highpowerd street car. Any advice?
I should PM turbostreetfighter, I know he knows about this type of stuff.

What do you have to say about Mcleod clutches? All I know is they are great clutches that can handle some serious power and they cost a LOT! Are there other good options?

gofast-

okay..well McLeod clutches are....godly? nope that doesnt sum it up enough...they are THE clutch to be had...my dad has a 700 hp street nova 14.2:1 compression 50/50 116octane 94 octane + nitrous and he's got a McLeod clutch & flywheel assembly w/ a 2900lb Kennedy pressure plate and well...it handles it w/o breaking a sweat.

a word from the wise regarding ford 8.8s...dont get one off a lincon as they're not an independent rear ends =\ kinda a bummer about that but just warning you

if you want a serious ford 9/8.8 chevy 12/10 bolt check out http://www.currieenterprises.com/htm...ndproducts.htm

Bridgeported

Hey thanks for the link, there is some good info there. I'd say there is a 99% chance the 8.8" i get will be from a mustang.
Do you know if there is much of a difference between the older (85-93) 5.0 mustang rear ends and the newer (94+) 4.6 mustang rear ends?

Bridgeported

I did some research on transmission and rear end gear ratios tonight.
gofast- (and everyone else) take a look at this picture file I made.

It shows the complete final ratios of each gear, by multiplying the gear ratio by the rear end ratio.
I did this for the RX-7 drivetrain, the Surpa drivetrain, the WS6 drivetrain.
Then I compared those with a WS6 transmission (T56) mated to a Ford 8.8" rear end, using 4.10 gearing.

I think the T56 combined with the Ford 8.8" rear using a 4.10 gearing would be a pretty good setup. Take a look at the numbers compared to most importantly the WS6 and the Supra drivetrains in stock form.
Looks fairly ideal to me... what do you guys think?

Hmm... maybe isntead, use a 4.56 ratio in the 8.8" rear end to help acceleration even more, and then lower the T56's first gear ratio a bit since it would be up at 12.13 which is a little too high I think.

Or am I just way off track with all of this? Like I said, I don't know THAT much about drivetrain setups as I would like to know.

Node

iTrader: (1)

A 4.3 rear end would do great
T56 4.3
2.66 x 4.30 = 11.43
1.78 X 4.30 = 7.65
1.30 X 4.30 = 5.59
1.00 X 4.30 = 4.30
0.74 X 4.30 = 3.18
0.50 X 4.30 = 2.15

Bridgeported

I REALLY like the look of those numbers Node... I'll strongly consider that option.

gofast-

4.3 gearing while numbers look good...isnt to hot...i'd much rather have something a bit more streetable (3.90) and suffer in acceleration just a bit in first gear

2.66 x 3.90 = 10.374
1.78 x 3.90 = 6.942
1.30 x 3.90 = 5.07
1.00 x 3.90 = 3.90
0.74 x 3.90 = 2.88
0.50 x 3.90 = 1.95

i mean since you're already going custom you might as well just use something a bit more streetable...that 4.10 gear isnt fun...my dads got a 4.56 on his 12 bolt...its kinda hard to control in LA traffic...the first gear ratio is just insane and it barely is streetable at the top of thrid even with a 3500 stall converter

the 5.0 rears were a bit stronger i think the ring & pinon was thicker but honestly unless you want 1200+ hp...any 8.8 is fine i'd much rather have a full 9 though, a curries 9 is...really capable of taking what you can dish out & they really work with you so you get the best for YOUR application

bridgeported : it seems as if you're just concentrating on the performance of your drivetrain -- imho you shouldnt do this...although performance is important a good balance between performance AND streetability is MUCH more important unless 80% of the time the car is running is at the track

good luck with wahtever path you intend to take -- I'll be here to give you advice/help when needed as im sure the rest of the board will

Bridgeported

Thanks a lot for the help! I still have lots of research to do I think. I'll PM you if I ever need some advice or info though.