Hi Tony,
Can I send you a PM ?

 

David,

Yes sir, that would be correct.

BTW, lighter Pistons and Rods are coming.

 

Hmmmm how much can a stock be reduced to safely?

 

Does anyone actually have any HP data for lightened cranks? On chevy motors I've seen as much as a 5-10HP gain from 6,000 rpm on up.....but our motors don't spin that high and make less power, so I'm wondering if there's anything to be gained by lightening the crank.....other than a quicker reving car in neutral.

 

I'd have to confirm it by calculation, but I think that knife edging the crank and lightening the flywheel have a negligible effect on power to the wheels. The only effect would be to reduce the moment of inertia of the crank and flywheel, but when the clutch is engaged, the moments of inertia of the transmission gears, the driveshaft, the ring and pinion, the cv joints, the driveshafts, and (especially) the wheels and tires would be so much greater than the reduction provided by the knife edging and the lightening as to make the difference negligible. At a steady rpm, the only way there could be a difference in horsepower would be through a reduction in crankshaft windage. The main reason for lightening the crankshaft and flywheel is to reduce shifting time, i.e. the time when no power is transmitted, which can have a measurable effect on both acceleration and lap times. That effect comes from having the horsepower available a higher proportion of the time, not from an increase in horsepower. Anyway, that's my view, and stand to be corrected by data or analysis. I have both a knife-edged crank and a lightened flywheel, and the difference on the track is noticeable, but not earth-shattering.

 

The wheels and tires have great inertia but remeber the gear ratio, in first gear they are geared down almost 12 times compared to the crankshaft. If you divide their moment of inertia with 12 then the number will definitely be much smaller than the moment of inertia of the flywheel. In fifth gear the gear ratio will be around 3 and then the effect of the wheel will probably be comparable with the effect of the flywheel.

If you do a stady state dyno test then any horsepower increase from a lightened crank will be because of reduced windage. Acceleration tests may show the reduced weigth as an horspower increase.

Tomas

 

Tony and Tomas,

In my "climbing the hill" example, it seems I didn't clarify the parameters. Yes, indeed, I meant that there is no power left to accelerate up the hill!
I tried to imply that by saying basically that 'you're at full power in high gear approaching a fairly steep hill'. I should have been more accurate with my scenario.

 

Tomas L, very good points about the gear ratios. Hadn't thought of that. The simplest test would be comparing before and after times from standstill to redline in first gear.

 

 

I know that this is an old thread but anyone who has ever done any form of cycling would call a BIG B.S. on a heaver flywheel not costing you energy (HP). Bikes do not have flywheels but they do have rotating masses (Wheels and Rims) and the lighter the rotating mass the faster you go with the same energy input. I do not want to argue that on a car it might be a small increase in HP but never the less. A lighter flywheel will give you more HP and better acceleration.

 

I noticed my car was a bit faster in the lower gears with an aluminum flywheel.
This thread popped up just in time, I was actually debating whether or not to lighten my crankshaft (being that its out of the car)

Who here has a lightened crank?

 

It can never give or take power but it can affect acceleration.
It's the same with a bike, you apply the same power and you feel a difference between different wheels. The lighter wheel does not mean that you as the driving force produces more power.
Just wanted to straighten that up

 

I agree but the vehicle (car or bike) will go faster with the same power. The same way that lighter with the same power=faster. Is not faster what we are after not just HP?

 

somedays i wish i could have a heavier flywheel to make it smoother off the line..

 

Naw, you're just looking for a smoother driver.