Since I'm selling my car, this is all a hypothetical excersize for me. To keep me from getting to upset about selling the car, because I'm planning what I want to do when I buy another one.

Well, I guess it's pretty much decided that we can make gobs of power. Between the strokers, superchargers, and even nitrous oxide there's plenty of power to be had.

And it seems like the double disk clutch will take gobs of torque. Shorter life to be sure, but it'll still take the torque.

It seems the weak link is the gear box. Has anyone mannaged to strenghten the gear box some how? What exactly is the weak link in the gear box? Gears, bearings, shafts, the caseing? How does one strengthen it?

 

In your case, VU, the syncros are truly the weak link. In later model boxes the fifth gear imput shaft can break, but the biggest issue is the countershaft being held in place by two little bearings and being hollow with just a rod to reinforce it. Duing shock loading it flexes significantly and can allow the gear overlap to decrease and shear off gears.

Hope that helps.

 

So, lets say I find a winning lottory ticket tomarow. (Kinda hard to do, since I don't buy lottry tickets, but lets say I picked this one up off te side walk or something.) I now have some ungodly sum of money to spend on my 928.

Now, with that money, I've mannaged to put together a plan for a 800 hp engine, with like 750 ft/lb of torque, and some sort of a clutch that will hold under the strain.

What would need to be done to allow the gear box to stand the strain?

From the sound of it, replace the lay shaft with a solid one, replace the lay shafts bearings with a stronger set. Yes, no, maybe?

 

VU . . Buy yourself a GTS and call it a day!

 

Since you now have a big budget, and are talking about 800 + HP, I would install either a Hewland or an X-Trac gearbox. Both are race gearboxes, available as either a 5 or 6 speed, with straight-cut gears (no syncros), a variety of limited slip options, a variety of ring-&-pinions, changeable ratios, etc, etc,

 

Check out the Hewland availability for 600+ HP and I suspect you'll come up a bit short. Unless they've advanced a lot in the last couple years from the ~~400 lb/ft limit they had then. The fast guys in 928's have been running GTS boxes I think, and tearing the input shafts/5th gear bits when they fail, per my memory of posts here.

Anybody who has raced a car with straight-cut gears and no synchros wiil tell you that it would be pretty much unacceptable for street use. the noise and the attention needed for shifting are both high.

 

Dear drbob:

Some points to ponder:

-this was a post answering a hypothetical question - for an unlimited budget.....
.....but since you choose to take issue with this, permit me to clarify..........

-no, Hewland has not needed to advance (even though they have) - they have had gearboxes
that would take 800+ HP for more than 10 years.....example - the Hewland boxes in the older
Indycars and GTP cars with 900+ HP.......

-X-Trac, Emco, & Riccardo gearboxes the same....."check out" the availibility - (if you need contact names & numbers, please feel free to contact me.....)

-Hewland, X-Trac, Emco, & Riccardo make more than one model/ application
of gearbox

-a non-synchro box is not hard to drive, nor is it noisy - if you know how to
shift by the tach, and know how to double-clutch.......
........almost "anybody" could drive one......after all, the F-1600/F-2000/
F-Mazda cars used in racing schools use this type of gearbox........
......and these are "school" cars used by novice drivers..............

-to shift up in a non-synchro box, one merely has to center the throttle
to release the torque, then move the lever....
-to shift down, double-clutch to match the revs, then move the lever.....

-competent race drivers only use the clutch to stop and start........

-these cars are normally set up to work with sintered or carbon clutch, one
would only have to change the driven disc material.....


Now, I did not say that this is a "bolt-in" installation - but since we're talking hypothetically, and with an unlimited budget, any good fab shop could do the installation.........

 

One night, while perusing Rennlist, I read something that is sooo prophetic:

"Whats the difference in quarter mile times between a 600 hp Supra and an 800 hp Supra?"

[the answer is that there really isn't any difference. The law of diminishing returns means that the two cars would be nearly equal in performace, the extra 200 hp would vanish in a cloud of blue smoke]

The G28 gearbox is, I've read **somewhere** on Rennlist supposedly good for 600 ft/lbs torque, which is where people like Lagavulin are at right now. What this means is that people like him can expect the gearbox to survive...if they don't drive their cars abusively. And since an 800 hp 928 wouldn't be significantly faster than a 600 hp 928, it occurs to me that there is little to gain in beefing up this transmission.

UNLESS...you want to go racing, or are naturally a hard driver. Or if you really hate the notion of tearing it apart far sooner than typical, since increased power always wears things out quicker.

You're thinking right however; really, it is better to upgrade all the support systems on a car before upgrading the power!

N!

V- It sucks that you have to sell your car. Hope you can figure out a way to keep it!

 

Normy:
Talk to ANY driver racing a spec series - they would sell their mother for 10 HP !!!

Ask a NASCAR crew chief what is the difference of 50 HP - it is the difference between pole and 35 th...

Assuming that we're talking about a car that can use the added power (put it to the ground)
a 200 HP difference is ..HUGE !

 

This thread is diverging. Anyway, just put in a race prepped Corvette transmission out of a C5 and you will be good to go for 800 horsies and 800 foot lbs for awhile if you drive it sensibly. Hewland, X-trac and emco make trannies that will easily handle these specs and at much higher rpms. But yes they do get a little hard to shift for street driving and the 8 disc sintered metal clutches are tough as well!

Take care.

 

Just for discussion, why would you spend the time and money to replace one gearbox that has limitations, with another that has limitations?
.....the original post from ViribusUnits said unlimited budget.....


fst951:
..."these cars are normally set up to work with sintered or carbon clutch, one
would only have to change the driven disc material....."

there are several companies that do "street compound" discs for multi-plate clutches.......