Quote:

Pretty much out of the Datsun world, I dont think anyone has a gear box that would have such a crazy first gear either.

I guess if you change from torque at the crank to torque at the tailshaft/diff you will have it nailed, then you have to take into account the ratio of your lowest gear too. In a rough way most people would just multiply the engine torque by 4 to get torque at the diff.

Quote:
datsik gets me.

I guess my understanding is slightly swayed then from this discussion. I suppose horsepower alone may be misleading, depending on what sort of an engine we're talking about - diesel truck engine, 4cyl motorcycle engine, etc. However I do believe that torque ALONE is just as misleading as horsepower; in literature you'll find the terminology is intermixed when describing the need for a beefier diff because you have "more power".

I think the Tech Wiki might need to be updated to at least include a reference to gear ratio alongside the engine peak torque, if its agreeable that engine torque alone does not dictate the torque found in the driveshaft.

I like that we've also discussed "tramping" (although I've never heard it described with that term) - I race shifter karts and here we have a similar problem... however since there is nothing but wheels, a hollow axle, chain, and transmission, this instant torque caused by an engine spool when the drivetrain bounces can cause CRANKSHAFT shearing!

Thanks for the discussion!

or 2 strokes

Not in F1

Are you saying that engines reving to 14k is out of this world?

in my project car - July'74 120Y (B210) I had planned replacing it's original H145 centre with a H150 I had, but as I plan to eventually run a nice L series - I replaced it with the Borg warner 68 out of my first 120Y...

I tend to drive my cars a little on the hard side so it was extra insurance too...

as for traction it very rarely sees bitumen - and in the previous car I have seen it smoking it up on a very dry piece of dirt... to the point where the tyre could not be seen in the wheelarch...

all with 69 horsepower...

So he's saying both those motors output the same torque at the output shaft? Well then they would need a diff that could handle that same torque out the end of the gearbox.

That demonstrates that torque is still what breaks diffs, hp is still irrelevant.

They only reason we all talk about torque (lol) is the cars driven in Datsun land will all be about 4:1 out the output shaft in 1st which will send the most torque to the diff.

An engine that spun at 140,000rpm and produced 10ftlb torque that was stepped down the same way would have the same effect - but using out of this world comparison has only managed to distract crispdollaz from the actual issue.

I think what crispdollaz is saying is : given the two engines specified, were put into cars with identical ratioed diffs, and if both have a gearboxes with ratios which meant that at max rpm both cars had the same velocity, the forces the diffs would see would be identicall, because the high revving motor would need to be have a large reduction in speed. this large reduction increases the torque at the tailshaft.

the only time more torque is true...is if both engines have gearboxes with equal gear ratios.

Tire grip is not the limiting factor. Even with skinny 12" tires you can get the rear suspension hopping and break the differential. And hopping (tramping) can happen accidentally so the automaker takes this into account when sizing the diff. Tire grip does have an effect on it, but not usually considered with road cars. With extremes like drag racing slicks it becomes an important factor.

You are all correct, differentials are rated for torque, not horsepower.

The "estimated" ratings given assume a gearbox first gear typical for passenger cars fitted. So for the H145 with a 1.3 liter or less engine, a first gear around 3.7:1. For the H165 cars a first gear around 3.5:1. These gears won't vary too much if it a high-RPM engine, for example if the engine RPM is double, the 1st gear won't be double in practical usage. And Yes, these factors all matter because they are all inter-related, but for practical purposes, a simple torque figure tells the story best.

Your right bob, but I think for arguments sake grip is asumed unlimited.