[Alfar7]

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.

 

[giuliettaevo]

Nissan GTR also has a nice transaxle nowadays. offcourse the flapper-shifting would need eliminating as well as the transferbox for the AWD.

 

[pushrod]

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.

 

[xander18]

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: http://www.alfabb.com/bb/forums/alfetta-gtv6-1972-1986/197678-gtv6-3-2l-24v-600whp.html#post1154289) 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.

 

[Gabor K.]

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: http://www.alfabb.com/bb/forums/alfetta-gtv6-1972-1986/197678-gtv6-3-2l-24v-600whp.html#post1154289) 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.

 

[Greg Gordon]

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

 

[Gabor K.]

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.

 

[Duk]

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.

 

[junglejustice]

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"... :smile2:

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!

 

[junglejustice]

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.

 

[junglejustice]

I was amazed by two initial findings:

1) How light that entire Corvette rear setup was - and
2) How close the initial measurements are for the length of the setup!

I was really worried about shortening the drive-shaft inside of the torque-tube - in addition to shortening the tube itself - in addition to all of the other variables! It looked SO long! Well, just from the initial eyeball that we have on it, we may not even have to touch the length!

The Corvette rear stance is WIDE though and we'll have to section the rear sub-frame to narrow it considerably! That - and then shorter side-shafts and a shorter anti-roll bar obviously. But that's it in terms of modifying the rear unit itself. Then there's the conversion to the bell-housing at the front and the front clutch arrangement, which is another story.

 

[junglejustice]

The Corvette transaxle stops right behind the bulkhead - let's say right behind a rear passenger's heels. The torque-tube makes a perfect distance run from there right to the rear of the stock Alfa V6 engine! I mean, I couldn't have planned it better myself - it's like it was made to go there. The Corvette just looks SO long to me though! (The nose is long and it houses the extra two cylinders - must all be forward of the torque-tube!) The Vette engine must sit pretty far back in the chassis, I suppose...

Stated differently, the distance in the Vette from the rear of it's V8 engine to the center of the rear axles / side-shafts, is virtually identical to that same distance in the GTV6!

The biggest changes are going to be -
a) The amount of sub-floor that we'll have to cut away to make room for the Vette transaxle. (It's much taller than the Alfa transaxle. The Alfa box is actually quite flat on top! The Vette box is tall and round.) And -
b) The clutch arrangement. The Vette's clutch sits up front. (Ron opted for a Mantic clutch from Australia and had I a custom flywheel made that excepts it, but still has the correct forward and aft spacing and the starter ring-gear in the correct location!)

I'm still blown away by the paltry weight differences...

 

[PSk]

198 versus 149 AND the 149 of the Alfa transaxle includes brakes! Plus the rear suspension is 186 versus 111kg. That is another 75 kgs

I don't consider 125 kg's to be a small increase. I remember putting an extra person in my Sud and it felt like the handbrake had been left on

I guess this shows how strong the Corvette transaxle/components must be
Pete

 

[pushrod]

198 versus 149 AND the 149 of the Alfa transaxle includes brakes! Plus the rear suspension is 186 versus 111kg. That is another 75 kgs

I don't consider 125 kg's to be a small increase. I remember putting an extra person in my Sud and it felt like the handbrake had been left on

I guess this shows how strong the Corvette transaxle/components must be
Pete

I thought he wrote the total difference was 107 pounds (~48kg).

This gearbox was originally paired to an LS2 V-8 which makes 400 lb.-ft. but guys are running stock T-56s in 10-second cars. The differential case was strengthened in '06 (the one in the photos is an '05 but I suspect it should survive all right).

Dialing in the custom suspension will be interesting. Cool project.

 

[PSk]

I thought he wrote the total difference was 107 pounds (~48kg).

He did, so I guess my maths is wrong or I do not understand the scale pictures ...

Anyway hope he is right
Pete

 

[Gabor K.]

I just thought, disregarding the extra weight, that big lumps seem to be going into that little Alfa, probably not necessary to hold the undisclosed power from the engine.

Seen other solutions without those bulky parts, but I guess everything is possible if there is a will!

G.

 

[Duk]

This kind of transmission strength is definitely only needed for bonkers levels of power!
Am thinking 500+hp with uber amounts of torque to back it up. So big capacity twin turbo V6???

It will be interesting to see how much transmission tunnel work is required.
The firewall's opening would have to be modified and that would give the owner a great oportunity to move the engine back a bit for better/more central mass locating. The bell housing needs to be modified anyway. :wink2:

For the rear suspension, modifying the aluminium subframe would be a huge :nono:
Same said for those suspension arms. Making new steel/chromoly arms that are shorter would be the safest way to do things.
Or keep the effective and definative characteristic of the Alfa deDion suspension.

 

[cda951]

I just thought, disregarding the extra weight, that big lumps seem to be going into that little Alfa, probably not necessary to hold the undisclosed power from the engine.

Seen other solutions without those bulky parts, but I guess everything is possible if there is a will!

G.

This kind of transmission strength is definitely only needed for bonkers levels of power!
Am thinking 500+hp with uber amounts of torque to back it up. So big capacity twin turbo V6???

It will be interesting to see how much transmission tunnel work is required.
The firewall's opening would have to be modified and that would give the owner a great oportunity to move the engine back a bit for better/more central mass locating. The bell housing needs to be modified anyway. :wink2:

For the rear suspension, modifying the aluminium subframe would be a huge :nono:
Same said for those suspension arms. Making new steel/chromoly arms that are shorter would be the safest way to do things.
Or keep the effective and definative characteristic of the Alfa deDion suspension.

The 100+ lbs weight gain does seem to be huge, but the initial post says it all: the guy was breaking stuff right and left, and that becomes tiresome and expensive. Not to mention the availability of all kinds of off-the-shelf gearsets, etc, and the fact that said weight is low and centralized.

Yes, the one-time cost of custom fabrication will be expensive, but it will likely be worth it in the end for such an extreme project versus the prospect of constantly paying for the repair of broken components when running an Alfa with that level of power.

The other benefit that has not been highlighted too much is the gain in torsional rigidity---the Alfa unibody is pretty flimsy and needs all of the help it can get. A torque tube that ties the front and rear sections of the chassis together will go a long way towards mitigating this!

Obviously all of this is overkill and not feasible nor practical for 99.9% of us, and this project will have its challenges even for skilled fabricators, but I am looking forward to seeing its progress!

 

[Renaldo]

"The 100+ lbs weight gain does seem to be huge," Depends on the perspective...

For the car that the Vette bits will be added to, let's consider weight gains vs. horsepower gains:

Granted the final #'s aren't in as to where this car will end up weight wise when completed... but from these initial findings... 107 lbs added replacing existing parts... for a stock 2822lb car (US version)... equates to a 3.8% gain in weight. Now then... let's compare changes in horsepower due to an engine upgrade for this car. Stock 2.5L 12v Busso V6 = 160hp. A big bore, naturally aspirated 24v 3.5L Busso, depending on modifications, is rated @ 300-325hp... but for arguments sake let's be conservative and say 275hp (my modified 24v 3L in my 164LS is 250hp). That's still a 72% increase in horsepower over stock configuration...at a minimum. Is a ~4% gain in weight going to be a disadvantage here?

To equate to lbs per hp. Stock config 2822lb/160hp = 17.64lbs/hp. This project, 2929lbs/275hp = 10.65lbs/hp

That's at least a 65% improvement/reduction. I'd say a ~4% weight increase in this scenario does not matter.

Some additional bracing will be employed, but then some interior weight removal, torsion bars removal, and lighter brake calipers & brake rotors will also be used to counter weight. Also the rear IRS cradle will be narrowed, as well as half shafts shortened. So it will be interesting to see where the car finally ends up, weight wise. But in the end, given the BIG HP gains, whatever gains in weight that might be incurred, statistically are not enough to be of a significant detrimental effect. And the end goal here is that I get a bullet proof drive train aft of the flywheel. (Not to mention better shifting, 6 speeds, large selection of gears and final drive ratios, C6 diff upgrades options, large racing/aftermarket support for this Tremec based T/A, better availability and pricing of parts, etc, etc...)

 

[Gabor K.]

I have reason to believe that all that work is unnecessary and that upgraded propeller and drive shafts together with another transaxle gearbox would be enough to cope for an upgraded 3,2 twin turbo engine.

Actually focus on making the engine big power relyably would be a concern!

G.