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We have been looking at engine upgrades from the stock 2.5L 12V. It looks like there are lots of ways to increase your HP. However, it looks like the weak point of the GTV6 is the transaxle. I know there are these 3.7L 24V 425 Hp out there but I have yet to see one in real life. The ones that I follow are still in the project stage and there are no running examples. I might be wrong so please correct me if so.

This leads me to this question, what is the max HP that our transaxle can handle without breaking? Actual running GTV6 would be preferred examples but concepts are fine just as well. We were just thinking that it probally is a waste of time and $ to have a 425Hp engine if the transaxle will not be realible. Therefore, we are trying to back into the engine hp by first determining the max hp that the transaxle can take.

Thanks for the suggestions and comments.

As mentionedon earlier previous threads, its not only the HP but more important is the torque factor, the weakest link in the transaxle is the crownwheel and pinion as testimony by our racing experiences here and also with Dawie in Sth Africa. The3.7 racing here uses an imported US transaxle but the LSD is not working properly

gtv6sa wrote:As mentionedon earlier previous threads, its not only the HP but more important is the torque factor, the weakest link in the transaxle is the crownwheel and pinion as testimony by our racing experiences here and also with Dawie in Sth Africa. The3.7 racing here uses an imported US transaxle but the LSD is not working properly

OK, thanks for giving me the 411 on the weakest link of the transaxle. I think the stock 2.5L has 160 bhp (DIN) and 157 LB Ft torque. I am not sure what the torque a 3.7L 24V 425 Hp motor. Does anyone know? What is the max torque that the transaxle can take?

I don't know on either.
But a NA 3.7 should have maximum about 400 Nm and this is less than a 1.8 with high boost so I guess it should cope with it.

According to Barry, who I have 100% faith in on this subject, at 350rwhp the transaxle fails. He has had a lot of practical experience with this, so it's not just theory. Obviously there are some variables here, fatigue, torque, rpm, heck even the method of measuring the rwhp will have a big effect on this number.

I have personally seen pinion gears come apart on transaxles with stock 2.5 engines, so there may have been some factory flaws. In both cases, the failures I have seen were on 1983 pinion gears.

There is also an issue where the gears can drive themselves apart and then crash back together. There are a few mods to control this, but the point at which it happens is so close to the pinion gear's limitation, I am not too sure about the value of these mods.

To make matters worse, we are dealing with some very old and probably fatigued parts at this point. My dad's supercharged 2.0 Nord had a transaxle failure recently that was really bazaar, and we determined it was from metal fatigue. It actually stopped the car dead. Fortunately it was cheap to fix as no major parts were damaged.

Greg Gordon,
www.hiperformancestore.com

400 nm equals about 300 pound feet of torque right? So is that flywheel power or rear wheels? The reason I ask is that I'm considering using the alfa trans-axle in a kit car with a saab motor... Stock, at the flywheel, the motor I'm using makes 258 pound feet at 1800rpms, or about 350 newtons... An open exhaust and a little computer work could put me well above that number. Would the trans survive daily driving/occasional track abuse with this power potential?

Don't do it.

Saab engines are designed as gearbox killers. So unless you plan some nice hardware changes on the engine to move the whole torque curve to peak around 7000 instead of 1400 you will break boxes.

My undesrtanding is that the transaxle was good for 300 flywheel hp. How much torque that is equal to depends on the type of engine it is.

So krepus are you meaning hp or torque when quoting your figures?

I can modify the boost and timing maps to push the torque curve up to around 4.5 to 5k, not sure about 7... lol! That's right about the top of the rpm band on an otherwise stock b234r... Do all Alfa t/a's have the inboard brakes?

Torque; I was using the reference of the 400nm 1.8 running high boost as comparison to my comment/information.

300 horsepower from the b234r will get you near 330 to 350lb/ft of torque in the 2500 rpm range, without messing with the factory boost controllers software

It's for a Locost kit car, I just noticed I hadn't mentioned it before. I've seen some footage of the racing series in Sweden, very competitive!