Van

If you have access to a large lathe, chances are you have access to a milling machine and a rotary indexer... This will go much faster on a lathe - your tool cutting surface is much larger on an endmill, and you're spinning a much smaller amount of mass.

Chris White

How about a Harbor freight angle grinder and a six pack of Red Bull?

bebbetufs

Thanks. I already milled windage ports in my block (only ruined one block while learning to operate the mill) so I guess that could be a way to do it. That way I could assymetrically shape the CWs to make them more aerodynamic, but I don't know if that is even possible unless the crank has been designed to deal with the uneven weight distribution of each CW.

bebbetufs

After reading a lot about crank shaft design I'm beginning to think this is not such a good idea. I'm thinking a lighter flywheel is an easier option with infinite less risk of something going wrong. I guess I'll go back to trying to design a windage tray and baffle system for the sump instead, but there is no room to work with

Chris White

For street engines I usually recommend a light flywheel or crank lightening - but not both! A light flywheel will give the engine a much better throttle response when matching revs. I like the feel and sound a lot better than stock. The affect on actual performance is so small you can't measure it, it more for the ability to rev match on downshifts quicker.

bebbetufs

Thank you for sharing your thoughts. I find this subject very interesting.

It is tempting to reduce the crank dia rather than lightening the flywheel considering aereation of the oil is thought to be a contributing factor to the #2 bearing failures. If enough weight can be removed from the crank, without runining driveability, to allow a significant reduction it's diameter it could possibly help reduce aereation, since the amount of oil coming in contact with the crank, especially when it sloshes forward under braking may be reduced. This assumes the oil actually stays in the pan if there is room for it to do so. If the oil is simply whipped around in the crank case by the hurricane force windage the instant it sloshes forward it will not work. If so it will take much more than simply reducing the diameter to reduce frothing. Perhaps a smaller dia crank combined with sump baffles and crank scrapers could help. After looking closely at the pan my guess is that the clearances between the rod pins and bolts and the pan are so small that recuding the CW size is unlikely to make a difference as the oil will be whipped up by the rod pins and bolts anyway. If this is the case a ligtened flywheel is the way to go as it may be changed more easily.

I've been told reducing the rotating mass could make the engine run much rougher, but then I've been told the inline 4 crank is self balancing. How much of a concern are vibrations for those running lightened cranks?

Thoughts?

V2Rocket

How much more buzzy/annoying would the 2.5 engine run in a street car with a "medium-lightened" crank balanced to its fancy pistons/rods, while using stock-weight flywheel?

..like this?