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richard

drive shafts

6 posts in this topic

It is said that for every pound of driveshaft rotational weight you reduce, you gain an effective 10hp at the rear wheels!*

Is there any truth to this.

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There is something to it, as it takes energy/hp to increase rotational speed of components proportionate to weight in the same way it takes energy/hp to increase road speed proportionate to car weight.

Might be in that sort of ballpark in 1st gear, but as you go up the gears, acceleration drops, so does the effect of drive-line weight.

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also diif and axle sizes .

on couple of my cars we swap medium case diff to large case

 

and on another did a large case to medium diff swap and there was about 8-10kw at the wheels difference even with the same ratios

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Junk science detector in alert mode -!!!

The real science behind the driveshaft comment is that the reduced inertia of a drive shaft allows it to spin up faster - The lower inertia allows you to  transfer  more (of the available)  power over a shorter period of time  by reducing what is converted to inertia.

You can achieve the same 'faster spin up' if you have more power but you will also have more inertia

What you measure (steady state ) on the dyno is the same - this is one reason why dyno results don't always translate into real performance on the road - because rotational inertia counts.

Brents comments are also wide of the mark- changing diff size will change frictional losses  and rotational mass - the trend to smaller diffs and less oil that is much slipperier does release more power to the wheels ( rather than suck it up & slow it down)

 

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I throw this question out there because I'm thinking of buying a 1 piece driveshaft in chromoly , I did look at carbon fibre but cant justify the price for only 1.5 kgs savings over chromoly, nearly 2x the price.

They have a claim on their web site about the power gains.

I'll price up one in NZ before I order.

thanks for your input guys.

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It is also a lot easier said than done to remove weight from driveshafts without compromising strength.

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