AFARR

I see lots of posts about TT, SC, etc. on the Sharks.

At what stage do you have to worry if your: 5 spd, 3 spd Auto or 4 spd Auto can take it (i.e. "I better upgrade the clutch...etc.")?

Thanks!!

m21sniper

I've read 600hp max for the MB 4 speed autos, but no idea how accurate that figure is.

IcemanG17

Sniper seems about on target for the auto transmission. It seems that the auto is regarded as slightly stronger vs the 5 speed in handling high torque.....but there are several track cars with very high power engines that get along well with the stock 5 speed. You can get the automatic rebuilt using hardened AMG internals....that should support a 1000hp engine....keep in mind mercedes still uses a 5 & 7 speed version of this transmission....the 4 speed we have in AMG cars typically had 400+hp & torque in a car that weighed at least 1000lbs more!
Brian

tammons

I doubt the automatic will handle ay more than an S4 5 speed without some serious work. There were a group of porsche builders down here that built a 950 hp TT S4 and it broke every part in the drivetrain including couplers, input shafts and the maiin drive shaft. Maybe if you have some bigger input/driveshafts machined out of chome moly and other heavy duty parts installed like clutches etc.
It would be interesting to know, but personally i think it might work better to put 930 turbo gears in a 5 speed box (super expensive if even possible). At any rate those builders gave up.

Its a shame really, because a 924 turbo gearbox is just that. Packed with 930 parts and can handle around 800 hp.

I have built 3 turbo setups and never had problems, but I kept the power down. I think the general concensus is that 500-600 hp is the breaking point for 5 speeds. 928intl mentioned that they knew of a SC 928 racecar making 600 hp did blow transaxles. Also from what i have heard the later gearboxes are stonger than the early gearboxes. I also asked about auto's but they responded nobody really knows. I guess nobody has pushed autos to and past the breaking limit like they have 5 speeds.

m21sniper

My trans guy says the MB A/T can be built to handle insane levels of power. He's done several of these boxes(all in MBs though), and he said that if you shave the clutch plates and pack in more clutches that they're almost indestructible.

It's a pretty reasonably priced modification too, if your'e already getting the trans done. Figure on an extra 300 bucks over the cost of a std rebuild, and maybe another 100 for a reworked performance valve body.

I suspect that ultimately the weak point in the 928 driveline are the CVs. Of course you can get custom shafts made for about any car out of chrome moly steel, but they AINT cheap, lol.

TAREK

WOW !! how exactly did they get there? 23 lbs of boost and 8:1 CR on forged pistons and metal gaskets?

Fastest928

Has nothing to do with hp, it is allabout torque ...torque breaks trans..

About 450+ rwfttq will shred a manual trans....I am on trans#3

tammons

They never would give me all the small details. From all the hints I could pick up it was a twin turbo with customs, probably t3/t4's or K26/27/8's or something like that, massive intercooler, but gees where did they put that thing. Along the way they blew the motor, melted the pistons bent the rods, fried quite a few clutches and broke everything else in the drivetrain. He did mention after the melt down they bored it out to a bigger displacement and put in Carrillo rods. Yeah they were probably running an o-ringed block and at 20-24 psi. There are a few Porsche/ and other car turbo builders down here that make crazy horsepower in street cars on race gas. 1200 hp corvettes, 750 hp 911's, 2000 hp big block chevelles, 350 hp jap bikes etc etc.

Normy

As I was about to add about the fact that horsepower isn't a consideration: torque is.

Marc-

What about all the "boostards": it occurs to me that these people are driving around with upwards of 600 ft/lb's of torque. Either I don't know about them blowing transmissions, or somethings missing here. Care to explain how their cars stay alive?

N!

m21sniper

K-27s are too small for that kind of power level, or rather, they'd have to run at crazy boost levels to deliver that kind of flow. Even K-28s would be marginal i'd think.

Probably explains why they blew the motor up.

You'd want something like two Turbonetics TA-44s for a 1000hp 5.0L engine to keep the boost level down around 1 bar i'd think. With a really good front mount intercooler, superior plumbing and seriously flowing heads/intake you might hit 1000hp at 10psi with twin TA-44s.

AO

YES! Please do tell! I'm about to pick up a 5-speed "boostard". Would hate to start budgeting trans replacements as part of my annual maitenance costs.

tammons

From what I understand they ran the initial setup with stock rods. Not sure about the pistons, but it does not take much of an error to melt down at 1000 hp on a dyno.

They did mention they were custom turbos, but he would not tell me what they were. At the time I just figured twin t4's but later I wondered, because there is just zero room for anything bigger than a t3 on the drivers side. looking back now I expect they were some sort of hybred K's.

Most of the guys I have run into down here that build that sort of high HP setup run on race gas and 20-24 psi.

He did mention at the end of it all, they sorted everything out, and had all the engine and drivetrain problems solved except for the transaxle. They could never get one to hold together so they gave up.

Also when I told him of my plans to TT a 928, he said you should be driving a 930.

Vilhuer

I've been wondering how different 911 G50 gearbox is compared to 928 G28.10 and later boxes. It's said in factory documents they share some common parts. Syncro related I think. If syncros have similar design if not even same measurements maybe gears are interchangeable between these two box types. AFAIK G50 can take insane amount of hp when right parts are in. Maybe same parts can be used in G28? Design problem of pinion shaft being inside input shaft is harder to remove. No matter how good gears are they will break if shafts can move.

tammons

If you could stuff those internals into a 928 box I think the weak link would be the input shafts. driveshaft and couplers. The guys i mentioned above broke a couple of driveshafts, and had one custom machined (ouch).

From the way this guy talked about breaking everything in the drivetrain, you would basically have to address every part from the clutch through the transmission. I am not sure if the stock ring and pinion could even handle that kind of power.

All of it would be super expensive and possibly cost more than a nice car. i did have an aquaintance down here running a 750 hp 911 with a ceramic clutch and he had 40K on it, and he drives like a demon, so something like that would work for the clutch.

Funny that a 924 turbo trans could handle gobs of power, but not a 928.

Fastest928

1000 bhp at 1 ba boost requires a 500 hp NA engine from a 5.0 l ..... Lets think about that fofr a minute ...ok, who is going to pay for that effort.

...it is just a matter of time....and if there are those in denial, either Don H or I can demonstrate

I was at Bob Norwoods awhile back when he was dyno'ing the 3l, 1100 rwhp engines for the dragster cars ... YES, I SAW the runs and the sheets .... NO BS here.

Hmm...does that mean a 2000 rwhp 6l?

Spooled it up with NOS, and lit it off.

Marc