Dak

Hey all. How bad is the turbo II transmission when used in a n/a application. Reason I ask is it is inevitable I will have to replace mine as it does flaky things every now and again. Also I have read in this particular section it's not that great though I think the context was in race cars being shifted in the 9k rpm area. My application is in a street car. Doubt it will ever see the track( road course) but if it did it would only ever be the occasional track day. Though I have on occasion went to the drag strip and probably will again. Also I thought someone said once the gear ratio's weren't that good for a n/a. Could someone expand on this as well? Main reason for considering the turbo trans is I haven't taken off the table that I may go turbo one day.

freddyrx3

iTrader: (14)

I have almost everything you need for the conversion, if you're interested.

23Racer

Other than the gear spacing being worse than the less than optimal NA trans gear spacings, the extra weight, the fact that you need to change the flywheel/clutch, starter, driveshaft and potentially rear end, its fine and more than strong enough.

I would just take the easy route and replace the NA box with a GTU box and a 4.77 rear gear.

Eric

Dak

Can you explain the gear spacing? I don't fully understand what people mean. I thought the higher numbers on the tII was better till I started hearing the spacing was worse than the n/a. What is the GTU box? Or did you mean GTUs? Did the S4 GTU have different gears. Going by Mazdatrix from 87 to 92 all n/a's had the same ratios except the GTUs which had a .756 5th. I left out the 86 n/a 'cause they said it had a .711 5th. Since I have a GTUs my best bet may be to see if I can rebuild the one I have myself. I really don't want to give up my 5th gear ratio anyway, so if I even went to a turbo trans I would prefer the 87-88 one since they say it's 5th is .762.

I have thought about swapping in the Miata gear set and probably could for less than swapping to a turbo trans if I did it myself. As long as the machining on the input shaft didn't cost too much.

diabolical1

iTrader: (3)

i will give it a shot, but keep in mind i'm being general. i'm not consulting an actual reference, so my number may be different from actual reality, but i'm more trying to convey the concept. fair?

it might help to think of it this way. let's say the T2 makes peak torque at say 3500 RPM and it stays relatively flat to say 6000, and it makes peak power at 6500 RPM. you can say it has a 3000 RPM powerband (6500-3500). it will be geared from the factory to stay in the powerband when you're accelerating and change from one gear to the next. it would make no sense to have it drop to 1000 RPM when going from 2nd gear to 3rd. agreed?

now let's say the N/A cars make peak torque at 5000 RPM and it starts falling off at 6000. then let's say it makes peak power at 7000 RPM. you can say it has powerband of 2000 (7000-5000). from the factory it would also be geared to keep it in the powerband when you're accelerating.

you're going to have 2 different gearsets for those engines because their powerbands are different. the T2, being more torquey and having a broader powerband can tolerate a greater difference between one gear and the next, so it can drop to lower RPM and still pull hard without missing a beat. likewise the N/A will be less tolerant of that spacing in the gearset, it will need gears spaced closer together. so if you put a T2 box in an N/A (with no significant changes in powerband), then it is virtually guaranteed to fall out of it's powerband between gears and will be unable to pull very hard.

what i typed is how i understand it, so i hope it's also correct.

aside from that, i remember a thread from a while back that also brought up the point that T2 tranny also takes more power to use. i'm assuming the physical differences that make it able to sit behind 4-, 5-, 6-hundred HP engines and survive, also make it heavier and harder to turn.

t-von

iTrader: (8)

Diabolical1 pretty much hit the nail on the head. Here's a gear ratio calculator to help further see where your rpms will drop based on your particular cars setup.

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

djSL

iTrader: (5)

Other than the cost of installing quality parts the first time. I have never looked back from my T2 trans installation. I did notice the difference in the low end "feel". The t2 trans coupled with my l/w flywheel was the one of the best upgrades I have done to my NA

Dak

Was the low end feel for better or worse?

I guess I'm going to have to break out Gran Turismo and put the different gear ratios in and drive to get an idea of where the rpms fall to. I'm still not wrapping my head around why the turbo trans ratios are worse. Mainly because every time I increase the numbers of each gear in the game the acceleration gets better. Yet it sounds like you guys are saying the opposite because the n/a and Miata boxes have lower numbers for each gear so I am confused.

SpikeDerailed

iTrader: (7)

I had a Tii transmission on my vert(na) and I can saw if youre going to do it dont use a stock weight flywheel, theyre a noticeable bit heavier and make it rev up slower. Diabolical mentioned the gearing difference between the two, and ill say even in a Tii application i hate the gear spread from 1st to 2nd. That said I would still do it, just with a lighter flywheel.

Dak

If I switch I will definitely go with a lightweight flywheel. Maybe even an aluminum one. I have a lightweight steel one now and have no trouble driving with it.

lim_fc3c

iTrader: (4)

I run a tii trans with 4.77. Bridgeport 13b with itb's and exedy hyper single clutch/flywheel. Hauls so much *** staying in the power curve with 4.77 compared to 4.10 with a tii trans.

TonyD89

iTrader: (10)

Kia gears?

Dak

Mazdatrix sells them. They say they make them from the 79-85 ring and pinion. They need our pinion to make it. I do recall someone saying something about Kia gears though.

j9fd3s

iTrader: (3)

the 90's Kia sportage used the Mazda ring and pinion in the front, and some of them came in a 4.77 ratio.

Dak

Well I finally drug Gran Turismo out. Seems the difference between the two is marginal at best. Couldn't tell much difference though in hind sight I should have detuned the car back down to near stock TII levels rather than the upper 300's I was at. The Miata gear set was an improvement. Just for kick I put in the ratios of the RX8 6 speed. It seemed to be the biggest improvement though 4th was kinda funky. The 6 speed Miata gears were the best of the stock Mazda gears( though identical to the 04-08 Rx8 except 4th).

In conclusion I think I'd like an Rx8 transmission. Too bad it's not a drop in because the shifter ends up in the wrong spot and it supposedly isn't much if any stronger than the n/a FC box. Though I know of at least two FC's on here using them and I know one of them relocated their shifter so it is doable with some fabrication.

TonyD89

iTrader: (10)

Am I wrong or does the TII trans have faster gears than the NA RX7 trans except for 5th?


https://www.mazdatrix.com/g1.htm

Dak

That's what I thought and 5th as well when compared to the standard n/a box. I may be mixed up though as I keep reading the TII gear spacing is worse though I don't know why. My Gran Turismo test says it's almost a wash. Both fall to about the same rpm on each upshift. The GTUs has the best 5th of the n/a( listed as 89-92 with LSD on their chart) and better than the 89-91 TII and FD boxes. If I were to get a TII box I would prefer the 87-88 one with it's .762 5th as I like the .756 5th I have. It and the 4.3 rear does have the revs spinning on the highway say 4k at 80 but it will actually pull in 5th.

TonyD89

iTrader: (10)

I brought this up before but was kinda slammed because I was considered to be comparing piston engines to a rotary. My old Honda Prelude was exactly that way in top gear, 3k at 60mph, 35k at 70mph, and 4k at 80mph, and so on. I think it's more of a function of small engines and where the power is.

So the .756 5th with a 4.3 is the same? Interesting...

peejay

Solomiata : Drivetrain : Interchange

FC to FC, the difference in ratios is so infinitesimally small that they can be said to be identical. You're not going to notice a difference between, say, 2.015 and 2.002.

Past that... what is "faster"? Taller gears are "faster" but accelerate more slowly. The point of more power is more acceleration, so lower gears feel better because you get more acceleration.

And that is why I'm putting 5.43 rearend gearing in my car...

Dak

So the only real disadvantage of the TII box is it is heavier. It may take more power to spin but does it really since the stock turbo flywheels are heavier? If one uses a stock flywheel might the perception be it feels slower when with the same weight flywheel the difference may be negligible?

At this point I think I really want the Rx8 trans. but may put the Miata gears in my trans. It will depend on what my finances are like when mine finally breaks. I found some other threads and Have an idea of how I would like to go about relocating the shifter on the Rx8 box. Relocating the shifter seems less intimidating than changing the gears as I plan to do either one myself. There is also the functioning speedometer hurdle to overcome but it sounds doable as well.

Dak

I may have been a little off. While driving today it looks like 80 is more like 3700 or 3800rpms, but when checked against GPS my speedometer is a little off. Reads a maybe 3 mph faster than I am going.

I agree it is about where the power is for a given engine. On a V8 you may only spinning 2000rpms at 80 due to the gearing being set up for where the power is for that particular engine.

Kenku

A point that's being missed is that ratio wise, the NA RX-7 boxes are pretty crappy too. Miata / RWD 626 gears or RX-8 box are about as good as is doable cheaply.

diabolical1

iTrader: (3)

agreed. if i had never driven/owned an Rx-8, i'm not sure if i would have ever been any wiser.

Dak

Well I guess it's settled. Rx8 box it is. Cost wise there isn't much difference between it an the Turbo box. They can be got for 350 or less locally according to car-part.com. I have to get a flywheel/clutch and a drive shaft to mate to my rear for either. So the only real additional cost is the fab work to mount it and relocate the shifter and a speedometer solution. I found some HUD displays on Ebay that use GPS. Lighter than the Turbo box, stronger than the n/a( though still weaker than the turbo) and better ratios than either. Win/win for me.

TonyD89

iTrader: (10)

Greater ratio is what I call faster. 5.43 is a faster gear than a 4.3 because it gets to the redline faster and is usually faster at moving the car.