VXR8 Gearbox / Drivetrain Strength
Discussion
As the name suggests, was interested in how much power the std auto or manual gearboxes (ignoring clutch!) and associated drivetrain are likely to be able to take before seeing issues of longevity and depending on mechanical sympathy, what bits are likely to break first (ie half shafts or whatever).
Edited by paramoreg on Sunday 7th February 15:06
Gearboxes are strong. Output shaft is weakest point, but still pretty chunky.
Likley half shafts bust first assuming you get enough traction.
Not sure limit on box, but harryoz has ~800bhp or so no problem. Jez similar. Mine had 550ft/lb thrown at it numerous times still working ok.
Guy in the US run 10 second quarters on the std box. Things like synchro's and selector forks etc usually go first, but thats probably more from abuse than power issues.
Likley half shafts bust first assuming you get enough traction.
Not sure limit on box, but harryoz has ~800bhp or so no problem. Jez similar. Mine had 550ft/lb thrown at it numerous times still working ok.
Guy in the US run 10 second quarters on the std box. Things like synchro's and selector forks etc usually go first, but thats probably more from abuse than power issues.
don't know about the vxr8 but my Monaro put up with 800whp before breaking the diff and clutch. Torque, not power is the killer. On a turbo or centri blower it would be fine at that level but PD blowers like mine snap stuff because the torque curve is flat from 2500 rpm. Also, it will spin the wheels before breaking anything expensive. The problems come when it's strapped down on a dyno or if you lack mechanical sympathy.
paramoreg said:
As the name suggests, was interested in how much power the std auto or manual gearboxes (ignoring clutch!) and associated drivetrain are likely to be able to take before seeing issues of longevity and depending on mechanical sympathy, what bits are likely to break first (ie half shafts or whatever).
Edited by paramoreg on Sunday 7th February 15:06
I think it depends if we are talking turbo or supercharged. A turbo set up is kinder on the drivetrain which at exteme levels is a factor worth thinking about. Both harrys and Jez's gearboxes are stock.
That said, its all pretty tough unless you are a total clown or serious drag racer. I think id change the driveshafts though as a precaution.
The above applies to manuals. I think autos is a bit less certain!
you should bear in mind what causes the torque loading.....
It's really a "game of two halves" - on one hand, you have the engine producing the torque, but on the other hand, you have torque being reacted at the ground through the tyre.
A worst case would be a very powerful engine driving a very tall gear, resisting against slicks on a warm track.
Any less loading gives the transmission less grip. For instance, if you substitute road tyres for the slicks, then the torque that the drivetrain will see will be anywhere between 25 and 50% less, even with the same power.
Or for a car that will spin the wheels (through tyre size, gearing or whatever), the torque loading will be a lot less.
compare the two following cases :-
A 600HP Monaro doing a "run-what-you-brung" take-off down a drag-strip
A 200HP Omega trying to re-start it's towed caravan up Porlick Hill in 1st gear.
the second case results in more transmission load - and that's with a Getrag 240, not a T56
On top of this, there's also peak loadings caused by being a klutz, like taking off and landing with full clog on.
It's really a "game of two halves" - on one hand, you have the engine producing the torque, but on the other hand, you have torque being reacted at the ground through the tyre.
A worst case would be a very powerful engine driving a very tall gear, resisting against slicks on a warm track.
Any less loading gives the transmission less grip. For instance, if you substitute road tyres for the slicks, then the torque that the drivetrain will see will be anywhere between 25 and 50% less, even with the same power.
Or for a car that will spin the wheels (through tyre size, gearing or whatever), the torque loading will be a lot less.
compare the two following cases :-
A 600HP Monaro doing a "run-what-you-brung" take-off down a drag-strip
A 200HP Omega trying to re-start it's towed caravan up Porlick Hill in 1st gear.
the second case results in more transmission load - and that's with a Getrag 240, not a T56
On top of this, there's also peak loadings caused by being a klutz, like taking off and landing with full clog on.
Edited by 2woody on Monday 8th February 09:16
Not sure I'd agree with your comparison there.
A full bore launch on a 600/600 car with 2.97 first and 3.54 rear end would be applying some 6300lbft of torque to the rear axles.
No matter what weight the Omega/caravan combo is...I doubt it would ever break anything during that takeoff.
Its a safe bet there is a very high chance of something breaking at teh drag strip.
Even if the Omega was making say 200lbft at the engine, with a mega short 4:1 first gear, and 4:1 diff ( which it will have neither ) Thats still only half the applied torque of the drag case.
A full bore launch on a 600/600 car with 2.97 first and 3.54 rear end would be applying some 6300lbft of torque to the rear axles.
No matter what weight the Omega/caravan combo is...I doubt it would ever break anything during that takeoff.
Its a safe bet there is a very high chance of something breaking at teh drag strip.
Even if the Omega was making say 200lbft at the engine, with a mega short 4:1 first gear, and 4:1 diff ( which it will have neither ) Thats still only half the applied torque of the drag case.
that's just the point - the Monaro if on a "run-what-you-brung" would have street or near street tyres on it, which would not support the adhesion loading for those sort of numbers.
assuming a 1600kg car, and that during launch, 400kgs gets transferred to the rear, the rear tyres will spin at anything above 1280 lb/ft (each) - and that's assuming a coefficient of friction of 1 (very unlikely)
the diff output torque at onset of wheelspin will be 2560 lb/ft
driveshaft torque will be 1280 lb/ft
which means a propshaft torque of 725 lb/ft
assuming a 1600kg car, and that during launch, 400kgs gets transferred to the rear, the rear tyres will spin at anything above 1280 lb/ft (each) - and that's assuming a coefficient of friction of 1 (very unlikely)
the diff output torque at onset of wheelspin will be 2560 lb/ft
driveshaft torque will be 1280 lb/ft
which means a propshaft torque of 725 lb/ft
Edited by 2woody on Monday 8th February 11:37
Edited by 2woody on Monday 8th February 11:39
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