Question: Transmission torque limits

[d00df00d]

Just want to make sure I understand something. Let's say I have two engines with the following output numbers:

1. 800 hp, 300 lb-ft
2. 350 hp, 450 lb-ft

If my transmission is rated for 400 lb-ft, does that mean Engine 1 will be fine but Engine 2 might break it? Or is there more information needed to make the call?

 

[XS650]

Originally Posted By: d00df00d
Just want to make sure I understand something. Let's say I have two engines with the following output numbers:

1. 800 hp, 300 lb-ft
2. 350 hp, 450 lb-ft

If my transmission is rated for 400 lb-ft, does that mean Engine 1 will be fine but Engine 2 might break it? Or is there more information needed to make the call?


Engine 1 will be spinning over 14,000 rpm to make 800 hp. You tranmission prolly wouldn't like that.

Combo 2 stands a better chance of surviving if it isn't abused.

 

[Camu Mahubah]

Originally Posted By: d00df00d
Just want to make sure I understand something. Let's say I have two engines with the following output numbers:

1. 800 hp, 300 lb-ft
2. 350 hp, 450 lb-ft

If my transmission is rated for 400 lb-ft, does that mean Engine 1 will be fine but Engine 2 might break it? Or is there more information needed to make the call?


Are you just making up numbers?

 

[d00df00d]

Originally Posted By: XS650
Engine 1 will be spinning over 14,000 rpm to make 800 hp. You tranmission prolly wouldn't like that.

And there it is. I knew I was missing something. Not sure how I failed to imagine RPM would be a factor. Thanks for the reality check.

 

[d00df00d]

Originally Posted By: Camu Mahubah
Are you just making up numbers?

Yes.

 

[punisher]

Torque is the real trans killer.

In response to the first post, yes, the trans will be more reliable with lower input torque.

How is RPM a factor? F1 transaxles had input speeds of 20K+ RPM, gears less than 1cm wide, and handled 800+ HP. As with anything, there are extremes, and happy mediums.

 

[d00df00d]

Originally Posted By: punisher
How is RPM a factor? F1 transaxles had input speeds of 20K+ RPM, gears less than 1cm wide, and handled 800+ HP. As with anything, there are extremes, and happy mediums.

They probably have really nice bearings, extremely rigid construction, very good fluids and cooling (to minimize hot spots), and features to minimize resonances.

Isn't an F1 transaxle a stressed member in the car? I would imagine that would imply very solid construction and help to deaden some vibration.

 

[SteveSRT8]

actually it's NOT torque that kills driveline parts.

It's TRACTION!

 

[BeanCounter]

To get more technical, I'd probably argue that where the torque arrives in the rpm curve has an effect as well, in conjunction with the traction comment made above.

Massive torque available immediately with awesome traction = broken parts.

Massive torque available immediately on little to no traction = less broken parts.

Peak torque available well after traction is crucial in particular application/environment = less damage as well.

But that might just confuse things more, so oh well.

 

[rslifkin]

Yup. Lots of torque, lots of traction and a heavy load on the output (heavy vehicle, big tires, etc.) is what breaks things. The more of those conditions are met, the easier it is to break stuff.

 

[IndyIan]

Also you have to consider a clutch doesn't care what rpm its at with its torque rating.
I think in practice if you are not going to beat the tar out of your "Can-Am" car at the dragstrip you can probably exceed a transmissions factory rated torque by quite a bit.
The manuals on Neons are only rated for a stock engines torque, but guys do tend to break several(sometimes dozens) axles from launching with slicks before the trans goes.
I think lots and lots of home built road track toys have way more torque than their trans is rated for but they aren't doing hard launches at the strip.