NA drivetrain behind turbo engine: info and update
 

FOr about a year or more, I've been running a modified turbo engine in my convertible (recently sold). Due to the fact that I already had a nice smooth transmission in good shape (original 140k) and a 4.33LSD GTUs rearend installed, I didnt want to swap out to a turbo drivetrain. I simply ran an upgraded clutch (first a CF dual friction, later an act 6 puck/XT) and kept my NA drivetrain. The upgraded clutch is required to do this, as a stock clutch will not hold the power of the turbo engine, even during "normal" spirited driving (as opposed to dragracing/burnouts).

Anyway, the reason Im posting this here is because of the many questions and debates about doing this. Many people said that the NA trans couldnt hold the power at all, and would grenade almost immediately. Myself and others proved this wrong by running them for many months and even years behind a turbo engine, by driving reasonably and not doing clutch dumps. Others said that it wasn't an accurate test of the transmission to say that it held up without hard launches, and that the true test was whether or not it held up under extreme conditions.

Anyway, as I said, I drove on mine for over a year with a stiff clutch (more stress on tranny) but no really hard launches from a standing start. I would often turn them over going into 2nd or 3rd with a hard shift. The trans never gave a hint of getting weak or going out...not so much as a scratchy synchro or whine.

Then about 2 weeks ago on the way back from the nopi show in atlanta the trans gave out on the interstate, cruising at 75mph with little load on it. All gears except 4th (straight through) were either locked out or completely gone. I had to bring her home 200 miles or so in 4th at highway speeds...no real problems there with a rotary engine, 5000rpm sustained isnt exactly a problem. As soon as I got her home I ripped the NA drivetrain out in favor of a t2 setup I had on hand, as the car as already sold and the new owner opted for the upgrade when I told him of the failure. I couldnt wait to tear the trans apart and see what had failed after such good service in the past.

After a bit of work to get it all apart, it was just as I figured...stripped off all the teeth to the front gear on the input shaft that transfers all power to the countershaft...which houses 1, 2, 3, 5, and R gears. The input shaft is also the straight through shaft, which houses 4th gear (1:1) which is why that was the only one left to drive on. I've seen a few trannies go out on an NA engine, even stock, from just age or abuse. I've seen a lot more go out from an unforgiving clutch like a 6 puck with a violent engagement. I think a lot of this damage was a result of the 6 puck I was running...all the energy that would normally be absorbed by the sprung hub of a stock disc gets transferred right through the trans.

What you're looking at here is the inside of the trans obviously. ON the right upper corner is the input shaft, which represents power from the engine as transferred through the clutch. The gear you see chewed up is the gear solely responsible for transferring ALL power to the countershaft for 1, 2, 3, 5, and R gears (lefthand shaft/gears). The right shaft houses 4th,, and continues on to the output shaft, to the rear wheels. Basically most of the time all the power of the engine is routed through the smallest, weakest gear in the transmission. My guess is that over time the engagement of the 6 puck coupled with the added power of the engine wore and chipped away at the teeth of this gear, and eventually only a few were left...which gave out on the trip home.

http://www.rotaryresurrection.com/kl...s/DSCF0001.JPG

http://www.rotaryresurrection.com/kl...s/DSCF0002.JPG

http://www.rotaryresurrection.com/kl...s/DSCF0003.JPG

So now you can see why NA trans is regarded as being so weak..in fact it is. Even so, it can be run behind a mildly modded turbo setup for many months if driven reasonably, and mine would probably still be holding up were it not for the unsprung puck clutch I installed a few months back.

Given the results myself and others have had with the NA trannies and puck clutches, I wouldnt recommend them for extended use on an NA tranny. Not unless you have a few spare trannies laying around ready to swap in, that is.

And for anyone whose trans gives out without warning, keep in mind you almost always have 4th gear to make it home with.

Good to know.

Well I guess I'll swap my driveline out for the complete TII job when my clutch gives up.

yep.. really good to know!
any way of changing that damn gear to the turbo 1 or re-inforcing that 1 gear??

For those of you wondering about the drag aspect of the N/A tranny, I've made about 15+ drag passes, and considerable ammounts of street launches without grenading the tranny, so far I've got about 3 months on it. I am using a sprung disc however. This is with about 250-260rwhp. Great info, at least now I'll know how to get home from the track when I kill the tranny. :)

Great info

Very interesting. I wonder how well a high capacity street/strip clutch and good pressure plate would last with a turbo motor or highly modded/boosted n/a block with an n/a tranny would last.

Not being in any stretch of the imagination a tranny specialist(I am a great mechanic tho hehehe), What makes the T2 tranny any better using this example(as stated I have left tranny tech up to others). Are the gears related to this failure truly better material or set up any different in the T2 tranny?
Just trying to get a better understanding of the inner workings of the 2.
Wouldnt an unsprung clutch put the same stresses on the T2 possibly resulting in the same type of failure? And what type of fluid did you use in the tranny(dont "think" it would make any diff in this situation but curious again)

And finally thanks RR for the info and pics great food for thought

Terry

Redline fluid was run in the trans since I had the car, even before the turbo swap.

I have never disassembled a t2 tranny, but the design is significantly different and stronger. How much, I do not know. I have never heard of a t2 tranny totally dying on the street, where I have heard of tons of NA trannies doing it.

Ya guess that what it really comes down to, one was designed for more power then the other.
Still, my thinking is an unsprung clutch will definately be the main factor in an early retirement of the tranny, all that forse almost instantly,without that extra slippage factor, being transferred to the gears...

In order for gear teeth to chip, you would need some kind of mechanical impact...This would translate to "slop" in the transmission, caused by worn gears.

Any idea how much mileage was already on that transmission?

I just bought a 6 puck for my setup, so we'll see if I have similar results (once it's finally done). My transmission is freshly rebuilt (ran low on oil), so it should be reasonably tight. I've never actually killed one due to power-related failure, but did break an input shaft due to lack of oil...not fun.

As stated above, mileage was around 135-140k. But, if you figure that just about all the NA trannies in existence have over 100k miles these days, it's a moot point to consider what a new transmission would or would not do. Just about everyone who will attempt to run an NA tranny on a turbo setup will do so because of cost or availability, and will do so on an original used one. I would think that before you'd put the money into rebuilding an NA tranny, you'd put the money into a stronger drivetrain.

Sorry, I must have missed the mileage statement above...That's quite a bit of mileage, so I would expect significant wear on almost everything....

I had my NA transmission rebuilt because it was a nice, tight transmission. That is, before it ran low on oil (leaking front seal due to shaft play due to missing pilot bearing).

I wouldnt say that it had a lot of wear...I wouldnt say that it had much of any wear. Look at the other gears in those pictures...perfect. It made minimal noise in neutral and no noise in any gear, and all the synchros even worked perfectly. I had my pick of probably 20 NA trannies and chose that one to run in my personal car, for a reason...it was tight. This one didnt break because of normal wear, it broke because of power transfer.

So is it possible to replace that one gear that failed with it's T2 counterpart or are the trannies engineared completly different??

Frank

OK but what about launching? Will it blow up? what about the rear? I broke an axle in my NA with a 7k launch, so i'd think that if i launched with a t2s power it would kill it, and how was the CF clutch i've heard not so good things on here about em but everyone i've taked to in person whos had one for any car liked it i orded a stage 3

Awesome thread, this one should be archived for all of the questions it answers. I have the same question as RXciting btw ^

I broke a motor mount and a tranny mount, plus a driveshaft on 7k clutch drop launches at the drag strip over time. Tranny is still good, takin the abuse like a champ with my act street/strip clutch and HD pp, no grinding or anything.

I won't even go into the "I told you so" chant... :D

I've seen the NA transmission let go at the 160hp at the wheel (DynoJet) levels.
Of course, we're not talking "granny shifting" either. :)

Realistically, I would only use the NA tranny on anything under 200hp at the wheels or less.
This is purely a RECOMMENDATION.
Some people need to get that in their heads.
Sure, it's possible to make more power and have the transmission still work.

For the majority of people, risking a transmission failure is just not convenient.

At the 130k to 140k mileage level, that's a reasonable average for NA transmission.
If anything, I think that's a bit low. :)
Unless you're going to assume a fresh transmission rebuild before going turbo, that's a very expensive assumption...

(P.S. - pics don't work. :( )


-Ted

Pics are fine for me...

LOL i am curiouse to see how much my tranny guy would charge me to rebuild my N/A tranny with strong stuff.. i just don't wanna lose the N/A's taller Gear ratio's! :D

Frank

I dunno, im new at this, but let me get this right. Your saying that you can either have a working tranny, or a burnt out clutch with the N/A setup?

You either use the better clutch, but puts more force on the tranny, or the stock clutch, wich puts not as much force on the tranny, but burns out quickly.

If you don't have a choice, I'd rather have a burned out clutch than a tranny.

Curious, can an n/a flywheel be used with a TII tranny? Any way? Say down the road after some power adders my tranny blows. I have an RB aluminum flywheel, would I be able to keep it with the TII tranny or would I be fucked?

You could get a custom disc with the tII spline made to fit the N/A PP/flywheel.

The question has yet to be answered, "How is the TII transmission different?" I'm curious too!

-=Russ=-