GregBBRD

People who frequent my shop know that I probably have 5-6 long term projects going on at all times, with probably another 10-12 cars that rotate in and out, for the routine things, which my son, Kyle, now manages (with me micro managing, over his shoulder.)
Long term projects generally take a long time, especially if we're inventing brand new pieces for them, doing a restoration, etc.
This is no exception. We started this car about a year ago.

Client brought me a less that 55,000 mile, virtually perfect, 1994 5 speed GTS for modification, with pretty well defined desires:
Extremely fast on his home track (Thermal), yet still be driven back and forth to the track, by simply changing from race tires to street tires (and maybe "turning down" the shocks.)
Car also needed to be very stock looking, with full interior, complete HVAC system, and be reasonably quiet and comfortable (for the street.) Minor brake squeak OK...nothing severe.
Since the car is not registered (nor stored in California during the off season at Thermal), California emission requirements were a non issue.
The car would "live" on 100% race fuel....all the time. My choice of octane.

Nothing to it, right?
Well, actually, to build a "state of the art" modern track/street 928 is.......very, very involved. Lots of things have changed in 26 years!

The very first thing we did was to buy Andy's almost perfect (605hp, over 450ft.lb. from 3800 to 7200 rpm, and over 500 ft lb. from 5600 to 7,000rpms) "monster GTS".
Andy had put about 100,000 miles on this car (35,000 since my 600hp stroker was installed) and felt it was time for him to "move on" to some newer technology. (He was a bit bored with his GTS.)

We removed the engine and disassembled it. Amazing condition! Absolutely no reason that it needed to come apart or would have needed to come apart, in the foreseeable future. Literally like the day I assembled it.
Perfect starting point, right?
Except....that torque would be very "hard" on 5 speed transmission pieces. (Andy's car was an automatic, which I built a super trick Porsche 928 transmission for. Torque is not an issue for my trick Porsche automatics. The new car is a 5 speed manual. Torque is an issue.)
So, I came up with a plan....reduce the torque and increase the horsepower. New goal...about 50 ft.lbs less on the "bottom end" and add another 50-75 horsepower on the top end.
Presto...different stroke, different length rod, different bore, different piston design, and different compression ratio.

And a completely new set of headers and exhaust.
And dry sumped, for track use....without the dry sump tank visible or inside the car.

And a phethora of other changes....including loosing 300-400 lbs, modern ABS, etc.

As some of you might be aware of, I (along with Jim Corenman) "invented" and built a brand new clutch, last year.
Before this clutch, having high torque/high horsepower and a "super smooth" street clutch were mutually exclusive.
Completely a non starter. "Chatter" is what you got.
For the manual transmission cars, I had "resorted" to only building 5.8 liter engines....until I could find a clutch that was "stock 928" smooth.
Our new clutch....butter smooth, with the ability to "hold down" more torque that anyone with a 928 has even dreamed of.
Clutch problem solved. Bring on the power!

We make torque tube shafts, out of 300M that function well with high amounts of torque....and more abuse than any torque tube shaft should be able to absorb (Endurance/torture tested by Rob Edwards....my "resident" test mule.)
And by using Constantine's (Black Sea Development) incredibly heavy duty torque tube bearings (with the torque tube damper, of course....sorry Constantine!), we should have a very smooth, robust torque tube.

For the transmission, we knew that the very old design PSD system would not be appropriate.....way, way to slow for a modern style 928.
So I drew up and "invented" a new limited slip (with the ability to turn the stock GTS transmission oil pump.) The "prototype" is inside this gearbox. Eight total friction disc surfaces and completely adjustable from a 20% limited slip to an 80% limited slip. (lots of options on how much torque it takes for the limited slip to release.)
I installed our custom carbon fiber synchros (made specifically for use in the 928 transmission) and did a few more tricks to help the transmission "live". (Details will follow...to a certain extent.)


Well, it's 8pm here, at the shop. About time to take my bride home.
I'll add more details and start adding pictures, as time permits.
It's a very "cool" project! Hope some of you enjoy this!

jcorenman

Jeez Greg, you know the drill: This Thread ...

Mrmerlin

IS Worthless....

Rob Edwards

Sans

GregBBRD

Patience?

928 GT R

Nope...

Pictures!

The Forgotten On

Out of curiosity is the LSD purely passive like a normal one or is it active like the PSD you replaced?

GT6ixer

That's bada$$ Greg. Looking forward to seeing the pictures!

GregBBRD

Almost passive. The percentage of "lock" changes between acceleration and de-acceleration, like a modern Porsche race differential.....and is mechanically adjustable.

To build an active limited slip would require a complete redesign of the electronics, plus a method of more quickly transferring the electronic signals to mechanical movement, which in the 928 PSD system occurs through hydraulics.
This is way beyond my abilities.
The "problem" with the current PSD system is that by the time the friction plates are activated to reduce slip, the car is already through the corner (unless the corner happens to be a long sweeper.)

GregBBRD

That is an "active" problem.
Because of the problems I have had with a certain guy in England (and the problem I am currently having with another vendor), who have been copying things I make, I'm afraid that the pictures will be very generic.
I'm very tired of others stealing my development work.
(Developing something new is generally long exhausting work....copying that work doesn't require the design, development, or testing time.

The only thing that I can do currently, is to keep "my cards very close to my chest", from here on out.

Yeah, I know that sucks, for the good, honest people out there....who want to see what I'm doing.

Please remember that it's your voices (and your wallets) that can discourage the copycats.

Rob Edwards

I like how "modern ABS" is just two little words buried in there. So much going on in this build that it almost gets lost.

IcemanG17

DROOOLL

MUST SEE PICTURES

Constantine

Thanks Greg! Was wondering where some of the Super Bearings you ordered would wind up. Sounds like a bad-*** project and glad we were made a part of it. Good luck with the rest of the build. And to echo others, pics would be great so the rest of us can live vicariously through the process.

Cheers.

GregBBRD

Like I've always said, your Super Bearings are fantastic pieces!
Yeah, we disagree about the damper, but I think differing ideas are fine..

Tom. M

Is your new LSD based on the PSD setup or are you modifying the standard LSD? Just asking as I have a 90GT trans with PSD in my track car (and of course no way to actuate it other than the old bolt method). Can the modified GTS pump be retrofitted to an older non-GTS transmission?