Thanks for sharing that video Gabor. Yes the Drenth is one viable direction, and early on, after his thread was posted, I actually reached out and contacted the manufacturer in Europe. It was a while ago, and now my brain is filled with C5 stuff... but if I recall correctly, the Drenth box was a $14K+ USD proposition a couple years back. I'm in to the Z06 transaxle, torque tube, and rear suspension assembly for about $2k... and that was eBay 'deal'watching and CL haggling. Fab costs will be much more for integrating the Vette pieces for sure, so where I come out in the end will be interesting to see. For me, its always easier to put some $$$ up front, and then 'bleed slowly' vs. putting a huge lump sum at the start.
Other viable options to consider were, as JJ had mentioned, the Getrag transmission (used in the M3) up front with conventional diff in the back... but I wanted to keep the transaxle arrangement, try to hold true to the overall design layout as much as possible.
I did ponder and look a bit to see if a Porsche 944 or 928 transaxle would be viable. Certainly they would be lighter and more compact I thought. I decided to skip the 944 (though the later Turbo and 968 variants did have higher power thresholds) and researched the 928 since it was designed to handle the hp and torque of the Porsche 5L V8 at just over 300hp in its final form. Funny thing is that as I researched, I ran across this: https://928motorsports.com/parts/tra...pgrade_kit.php
A website for Porsche T/A to Corvette C5 T/A conversion! Hah!! Seems Porsche owners were suffering certain ails, lack of parts, and the costs of those parts. Why not solve it all with the strength of the Vette T/A and a host of available parts, tech knowledge and upgrades available on this side of the pond?!
With that I decided to venture forth in to Chevy land. I figured that if this really wasn't going to fly, I could almost as easily sell the parts off as it was for me to buy them in the first place.
I was able to strike a deal for a Z06 tranny and torque tube combo from a Salvage yard in Denver. The Z06 is significant because it has the better gear ratios.
1st 2nd 3rd 4th 5th 6th
Z06 : 2.97:1 2.07:1 1.43:1 1.00:1 0.84:1 0.56:1
Reg : 2.66:1 1.78:1 1.30:1 1.00:1 0.74:1 0.50:1
The manual boxes come with a 3.42 rear end as standard. There are other (aftermarket ring & pinion) options available - 3.72, 3.90? and a 4.10 at least. After using a gear ratio-diff calculator, given the smaller engine & torque of the Alfa V6... I could definitely benefit from a 3.90 or 4.10 rear end... but first things first.
I knew the Vette transaxle was going to be bigger, but initially I held out hope that there might be some way to install and integrate it with the Dedion still in place. With a physical T/A in my possession for eyeball and measurements/comparisons against my GTV6 I could readily see that there didn't appear to be a viable way to save/use the Dedion with the Corvette T/A. I would need to use the Vette's IRS assembly. While part of me was sad I had to give up the Alfa's distinctive and unique suspension solution, another part of me was actually kind of excited about what a modern IRS system could bring to the handling characteristics and limits of the car. And before you disparage the rear suspension of a C5, please do some research. They are quite capable. Granted there's a leaf spring in the OEM basic set up - which seems like a neanderthal throwback - but there are a host of reasons why GM engineers selected that compromise. It can be easily removed and replaced with available aftermarket coilovers, which is what I plan to do.
Before I decided to get too deep in to all of this though (as I stated - T/A and torque tube could be easily sold) there was one riddle that needed to be solved, before even thinking about rear suspension, or how the underbody might need to be cut to accommodate these 'furrin' parts. How the hell was I going to mate the 26-spline GM driveshaft to the a$$-end of an Alfa engine? The Alfa flywheel is much too small diameter wise (~11") for the standard Vette Clutch assembly to be used (12"+). I wanted to use the OEM Alfa starter which meant keeping the OEM flywheel basic dimensions & starter ring gear. (Yes, the clutch moves up front, attached directly to the engine's flywheel in the Corvette driveline configuration.)
One thought off the bat was going to a Tilton racing clutch... they make a sturdy, high capacity 7.25" racing clutch... only problem is I wanted something that could be easily used on the street. Something that was progressive, could be used in stop and go traffic, and wouldn't make the car a bear to drive. I reached out to Turbonutter (who did that fantastic Lancia Stratos Replica using an Alfa Busso engine). He used the Tilton and his advise was, that if I could avoid it, use another solution. The Tilton couldn't be feathered ... its either fully engaged or not. Not a good solution for daily driving.
My clutch search was on....