Corvette C5/C6 transaxle in a high horsepower GTV6 - Page 2 - Alfa Romeo Bulletin Board & Forums

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post #16 of 100 (permalink) Old 10-19-2012, 03:02 PM
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Originally Posted by boosted6 View Post
The trans can be built to take a lot of HP, but its expensive. Theres a guy here who has a 500+hp Alfa 75 track car with the rear transaxle.
Hey Garth, my transaxle is sitting on some make shift stands and while sorting out another projects clutch requirements, I happened to take the clutch disc from a very mundane car and slide it onto the input shaft of the Alfa's TA. I was not impressed with what I found

Just for pure comparison, the clutch disc was from a 1.8litre Corolla engine. An engine with 115hp and 115lb/ft of torque in a car that weighs a lot less than my 75 V6 does. The Corolla's input shaft is bigger than the nearly 200hp V6 Alfa's input shaft.

With big power, I wouldn't even bother trying yo get an Alfa transaxle to live, I'd just go either for a Corvette TA or a (not really nice to say it) 'cobbled together' TA set up of compact gearbox and IRS style diff held together in a frame of some sorts.

Slowly Progressing Vortech Supercharged 1990 Alfa Romeo 75 Potenziata. Out of Action Twin-Charged 1988 AW11 MR2. Current Daily Driver, The Glorified Taxi 2006 BF FPV F6 Typhoon.

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post #17 of 100 (permalink) Old 10-19-2012, 06:07 PM
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How much does it weigh I wonder, but the availability of ratios has sold me on the idea.

Pete
I can't comment on weight, but being based on the T56 gearbox, that would be a good start.
If you were serious about gearing, get in contact with PPG in Adelaide.
No price listed but 1st to 4th HEAVY DUTY Helical Cut Dog Set for GM / Holden - Pfitzner Performance Gearbox would be a good start with the lowest diff ratio you could find for the TA.

Another approach could be attaching a Corvette diff assembly to a regular T5 gearbox, but I don't know if that would work.

1 thing to keep in mind is that the Corvette TA is rather conventional in its gearbox layout. The lay shaft is under the input/output shaft, so the g'box is pretty tall rather than being laid on its side like the Alfa TAs g'box is. I doubt this would fit under the floor of a TA Alfa and would probably require a decent sized box section to be fabricated and installed. Not really a problem with a track car.
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post #18 of 100 (permalink) Old 10-20-2012, 01:42 PM Thread Starter
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Duk, that had been my initial thought. The C5 differential is ~60lbs according to some forum I read. Adapting it to another transmission would totally depend on the tranny but it could be incredibly easy or incredibly difficult.

The issue is that I think that diff is a clutch pack differential, which is NOT my preferred type. I would prefer a Salisbury, but I found this article about the C6 diff that talks about an aftermarket LSD. That's the exploded view, 4th picture down. It only costs $2300! So to have a diff as good as a Milano LSD you would need to spend that kind of money.

If you're making enough power to want to go to a bigger T/A you definitely want an LSD for anything but drag racing. That brings us back to square one on cost, advantage is still a stronger transmission and more gear ratios. Maybe even a six speed with the Vette diff.

Edit:
Giken also makes an ATB torque biasing diff, if that's your cup of tea. Also about half the price.
http://www.horsepowerfreaks.com/part...Slip_ATB/16679

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post #19 of 100 (permalink) Old 01-30-2013, 10:56 PM
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Im surprised nobody has mentioned a Colotti gearset at all. They're only 8000 euro, which may seem like a lot, but not really when you take into account how much a corvette conversion will set you back. And plus, if youre building a 500 hp Alfa engine, another 8000 euro is bugger all in comparison to the cost of building the rest of the car. Well, if youre doing it properly of course...

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post #20 of 100 (permalink) Old 01-30-2013, 11:18 PM
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At the end of the day, the casing, ring gear/pinion and input shaft are all pretty small. These things were designed to be powered by smallish 4 cylinder engines and that is really shown by how small the input shaft is.

A Corvette transaxle is designed for 650Nm+ supercharged 6.2 litre engines.
Even with a Collotti gear set (there are others out there), you just can't make the Alfa TA that strong. Yes it will be stronger, but it's not 650Nm+ strong.
And that torque capacity will give it a massive resilience to shock loads.

Slowly Progressing Vortech Supercharged 1990 Alfa Romeo 75 Potenziata. Out of Action Twin-Charged 1988 AW11 MR2. Current Daily Driver, The Glorified Taxi 2006 BF FPV F6 Typhoon.
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post #21 of 100 (permalink) Old 01-31-2013, 05:49 AM
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Alfa Transaxles

I wouldn`t think of changing the Alfa TA to a Corvette unit.

The Alfa unit is plenty strong unless you are doing very dumb things to the unit (drag racing, or burn out starts).

Shaft size isn`t indicative of strength. It is alloy composition. None of the Supercharged or Turbo cars break the input shaft. They destroy the LSD clutch disk inner splines. For that reason 4 disk setups are the solution. 2 disk just don`t have the material to transfer that much torque.

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post #22 of 100 (permalink) Old 01-31-2013, 02:34 PM
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Nissan GTR also has a nice transaxle nowadays. offcourse the flapper-shifting would need eliminating as well as the transferbox for the AWD.
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post #23 of 100 (permalink) Old 02-02-2013, 04:49 PM
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Originally Posted by smotheredsteak View Post
another interesting thought would be the porsche 928 transaxle, although im not sure if the 5 speed boxes had the clutch next to the engine or in the back.. the 3 speed Auto boxes had the torque converter in the back with the transaxle.
Manual C5s and C6s have the clutch up front, just like manual 928s. So the prospective transferee would need to come up with a new plan for the clutch and rear brakes, both of which are missing from the Corvette transmission/differential assembly.

But hey, in for a penny... it sounds like a worthy project to me.
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post #24 of 100 (permalink) Old 02-02-2013, 05:25 PM Thread Starter
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I dunno guys, even though I started this little brainstorming session I'm starting to balk at the Corvette thing. It just seems too heavy and too much work. I'm leaning a little more towards MoRu's method, mating a performance trans to a modified or custom diff casing. (his thread: GTV6 3,2L 24V 600whp.) If I'm going to be practically ground up engineering anyway I might as well go all the way and build something very light and bulletproof. I was looking to the C5/C6 for a potential cheap, drop in kind of a solution.
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post #25 of 100 (permalink) Old 02-03-2013, 05:23 AM
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Originally Posted by xander18 View Post
I dunno guys, even though I started this little brainstorming session I'm starting to balk at the Corvette thing. It just seems too heavy and too much work. I'm leaning a little more towards MoRu's method, mating a performance trans to a modified or custom diff casing. (his thread: GTV6 3,2L 24V 600whp.) If I'm going to be practically ground up engineering anyway I might as well go all the way and build something very light and bulletproof. I was looking to the C5/C6 for a potential cheap, drop in kind of a solution.
Yes, agree, the MoRu choice with the Drenth box seems to be a much wiser and lighter choice than the bulky Corvette box. :



MPG | Drenth Motorsport Gearboxes

Reason for this arrangement, in contrast with with for instance the South African solution to move the box up front in high power solutions, is that in our racing series the gearbox must be in original place(transaxle). So the position has to be the same even if anything else than the original box is used!

G.K.

Last edited by Gabor K.; 02-03-2013 at 05:28 AM.
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post #26 of 100 (permalink) Old 02-03-2013, 10:02 AM
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This Drenth gearbox certainly looks like the answer. It physically fits, it can handle the power, and it's already been put into a GTV6. Judging from the one picture, the fabrication required to mount it, isn't trivial, but a least it's standard machine shop type work.

Anyone know how much those cost?

Greg
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post #27 of 100 (permalink) Old 02-03-2013, 01:31 PM
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Hi Greg,

I am sorry to say but its probably out of range for normal tuners. I think you could buy a very nice GTV6 (here!) for that price! Well, such is pricing in the racing business!

G.K.
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post #28 of 100 (permalink) Old 02-03-2013, 05:00 PM
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It's always 'catch 22' when it comes to modifying cars, especially ones where there isn't much aftermarket support, so you end up going it alone.
The end results is always a high financial cost.

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post #29 of 100 (permalink) Old 02-21-2017, 06:14 AM
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We've now started the conversion and the initial findings look VERY promising!

Some (not so quick) history: When I converted my 3.7 Milano to a forward-mounted 6-speed Getrag transmission with a conventional rear-mounted differential arrangement from a Sedan (Alfa Sei), it was less about the STRENGTH of the box, or the strength of the internals, and much more about the QUALITY of the shifts!

After going through many-many standard gearboxes and having everything break from the LSD, to the side covers, to the clutch housing cover, to the stupid Italian-snot GUIBOS, I decided that living with the weak synchros was to be the final insult! Up until that point we had lightened the gears by cross-drilling and back-cutting, we tried lightened front flywheels, lightened rear flywheels, small-diameter clutch kits, shimmed-up LSD units; we tried EVERYTHING that you can on these Alfa boxes! We got them to shift better, but not perfect.

You get in my car now with that 6-speed Getrag (unit crosses over to the E90 / E92 / E93 V8 M3 box and several other European models), and you just shift it. You don't even think about it. Shift up. Shift down. Slow. Fast. Smile. Don't even think about it. Heel and toe. Double-clutch it - or don't. Slam it home, or go smooth. It really doesn't care, it just does its job like it should!

Yes, it was the effen syncros and the weak 1-2 up-shifts and 3-2 / 2-1 down-shifts that finally did it for me. That and serviceability. I can live with many things, but pulling transaxle Alfa boxes in and out is a soul-sucking job. Call it what it is. Add that to the weak peripheral design of components OTHER than the actual gears themselves (the LSD, the weak syncros, the case, the dumb 2-piece driveshaft, the rubber donuts etc.) and that's what it took for me to just say "no more"...

I love my conversion. It was expensive and difficult, but I have never looked back. (Hell, all of the money spent on Alfa transaxles was just as expensive - not to mention the frustration!) To mention the turbo cars (with EXPENSIVE Colotti gear-stacks) as a comparison is ludicrous! Failing to mention works cars (without the context of legions of mechanics swapping boxes during and between races) is misleading. No one else in the US has ever run 400+ horsepower through one of these transaxles, so to reference a fix that will only work MARGINALLY on a modified standard bore 12 valve power-plant is not realistic.

The OP asked about a Corvette transaxle solution for a "high horsepower" GTV6, and that's what we should be talking about! We have started the conversion on a GTV6... Here are some pictures of the initial disassembly and eyeball work! We'll first address the big question of weight!
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Full-Race 3.7 Litre 24v Milano & 6-Speed Getrag; 3.7 Litre 24v Turbo Project!
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post #30 of 100 (permalink) Old 02-21-2017, 06:33 AM
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Enter my friend Mr. Ron who agrees and wants a better solution for himself, but who also wants to keep the transaxle layout of his GTV6. I was very concerned about the weight. We talked about it a-LOT and then he decided to just go for it. He acquired a complete C5 Z06 rear sub-frame, suspension, transaxle, brakes and torque-tube setup.

107 pounds! That's it folks! Only 48 kilos - with 24 of those kilos (53 pounds) of it, being nicely distributed for you along the tunnel of the car - BETWEEN the front and rear axles, along the center of the car, and at the lowest point of gravity that you can have!

The other measly 54 extra pounds going to the rear of the car (but still INSDE the axles! Keep in mind that the gearbox of the Corvette transaxle (as with the Alfa boxe it will replace), sits in front of the differential! (It's not like the Porsches where the gear-stacks over-hangs the rear of the car - BEHIND the differential...) This remaining bit of weight is again very low in the car, at the center of the car and INSIDE of the front and rear axles!

This bit of weight being the only penalty - against the backdrop of HUGE gains made in structural rigidity / engine to transmission connectivity), gear ratio options, final drive ratio options, strength, ease of removal and re-installation for service, etc.
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Full-Race 3.7 Litre 24v Milano & 6-Speed Getrag; 3.7 Litre 24v Turbo Project!
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Last edited by junglejustice; 02-21-2017 at 06:38 AM.
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