Plechtan 12wt. crank question

[jsawduste]

Mr. Plecthan,
read with interest your request for a 12 wt. crank. Assuming this is going into the Bonneville MJ.....

Curious why you want a 12 wt ? It would seem you would want a 4 wt so the engine would spool up faster.

Just wondering........

Thanks !!

[1bolt]

My 2 cents: In a LSR attempt you've got a couple miles to achieve and sustain top speed. Being able to Rev high up into the 7000 RPM range without breaking things is more critical than being able to accelerate quickly. Acceleration is relatively unimportant, as is lower RPM performance.... In fact if his Comanche is set up (geared) optimally he might very well have a hard time getting it to launch under its own power due to poor low RPM performance (low RPM bog due to huge intake ports and radical cam). Admitedly he does need to get up to speed in a reasonable amount of time, it's just not the critical factor as if he were drag racing a 1/4 mile or something. The 12cw crank is also said by HESCO to be less prone to harmonic torsion than a stock 4.0 crank with 8cw's. Some people have inferred from this that more counter weights must be better, which impies that the 4cw crank must be worst of all... Unfortunately there's nothing to this, there's no evidence to suggest that one is stronger than the other.

Without actually testing the torsional stiffness (resistance to twisting along its long axis) it's hard to say. The 4cw's dramatically lower weight suggests that it should have a higher RPM onset of the harmonic but that doesn't tell us anything about how much it will flex under the harmonic. Couterwieghts do not add much/any material to the parts of the crank that would flex, they just add mass that would make the harmonic set up sooner in the RPM range...

Considering the stock 4.0 is somewhere around 5300 RPM's and Pete wants to be running flat out in top gear somewhere around 6500 RPM's, it may not matter at all to him, but safe to say having the harmonic RPM higher (lighter crank) closer to the peak hp RPM of his engine is not the ideal, safer to move it down lower where his engine will spend less time. The 12cw should do that. Maybe even down into the mid 4000 RPM range where his engine should spend very little time.

[jsawduste]

Thank you.
Well explained, thought out reply.
I do indeed see your point(s).
Very well done, Sir !!

[Plechtan]

Like he said !

Rock crawlers also like the 12cw because the crank acts like a flywheel, and it gives them some additional stored energy to get over things.

[gradon]

Your 2cents always adds up to more(must be a hidden multiplier). . .