Weighted cranks

Z_man

Z_man

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Nov 29, 2008
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Does anyone weight their crank? If so how much weight and what are the benefits?
 
Some have, not sure on the exact amount. I want to say 65#?

Reasons to do it is so your not dropping as many rpm coming out of the whole. RPM's are also less sensitive (bouncy) going down the track. Its a ***** to recover rpm if you loose it though.

At least that is what im told.
 
I beleive it is also done to help the main bearings live at the upper rpms.?.?.?.?
 
im not sure how much they add either. but they do it so the engine will make more torque adding weight has almost the same effect as stroking the engine but does not add any cid. and it makes the crank easier to ballance.
 
25lb is what Southern Ill' Crank put on there when they do it.

Dale
 
I am curious - would it not be more benficial to keep the crank lite so easier on the bearings, and weight up the flywheel which would be more along the lines of "stored energy" ?
 
seeker1056 said:
I am curious - would it not be more benficial to keep the crank lite so easier on the bearings, and weight up the flywheel which would be more along the lines of "stored energy" ?
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Nope. If it was better to do it that way the tractor pullers would be doing it. Adding weight to the webs on the crankshaft creates balance and inertia. Inertia is a good thing in a game of inches.
 
Snedge said:
Nope. If it was better to do it that way the tractor pullers would be doing it. Adding weight to the webs on the crankshaft creates balance and inertia. Inertia is a good thing in a game of inches.
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Plus the weight just keeps the crank spinning, instead of the rod having to take all of the brunt.
 
Inertia from the crank or flywheel, I don't see what's the difference.

It's X pounds of rotating mass no matter where you put it, from the driveshaft's perspective, eh?
 
nwpadmax said:
Inertia from the crank or flywheel, I don't see what's the difference.

It's X pounds of rotating mass no matter where you put it, from the driveshaft's perspective, eh?
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At least theoretically there is difference.
 
I was told once that the flywheel is a better place for the weight as it is a larger diameter and hence increases the weights ability to keep the mass turning as compared to the relatively small diameter of the crank - leverage effect?

the example made to me was like those kids toys that you push to wind up the internal flywheel to make it run , or a gyroscope

This will be a very intersting thread I think
 
I think it's possible that from an engine balance and longevity standpoint, maybe the motor is happier with the mass in it.

But I don't see how the wheels know where all that twisting force is coming from. You could have two flywheels with the same exact rotational inertia....one from a dense material like iron that's small in diameter and long, versus an aluminum one that's bigger around and narrow.

It all just comes out to foot-lbs of energy storage, methinks. Work to accelerate = work to decelerate. You store up the energy on the line spooling it up, and you get it back at the end of the track when the sled goes *wham*.
 
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