Monday, May 4, 2009

lightweight.

These are the flywheels for the turbo bike, they started out at 11pounds 12ounces per half, first thing I did was knife edge them to see how much weight I could pull off of them. It took a nice bit off, but they still weren't quite where I wanted them so I just knocked the knife edge off and reduced the diameter of them. I was shootin' for seven pounds per half once they're finished but I left them a little heavy so I have plenty to work with when I balance them right now I'm at seven pounds 12 ounces per half. That's eight pounds off of the combined set. Should be damn snappy.





shaving them down that far really fucked my scraper clearance, but it's nothing that a little welding and machine work can't correct.


I'm also running S&S rods, but they're for an evo sportster, which changes things quite a bit. First off, the biggest difference is that they're just under a half an inch shorter than ironhead rods are. If I remember right the ironhead rods are .480" longer. The shorter rods increase the rod angle during the middle of the stroke, which basically gives them better leverage on the crankpin for more torque. Another thing that the shorter rods do which will really benefit the turbo is that they increase the piston speed during mid stroke, more piston speed means gases moving through the motor faster, which means a faster spool. The shorter rods do bring some problems into the picture though. First off, if the flywheels weren't shaved the pistons would crash right into them, secondly your pistons are now way down in the bore compared to where they should be and if you don't correct that you're gonna end up with a mighty 4:1 compression ratio. To correct the compression problem and prevent the rings from being raked across the drain holes near the bottom of the cylinder I'm going to have to machine .050" off of the cylinder decks on the case and .150" off of the cylinder bases, then I'm gonna have to knock off around .300" off of the head gasket end of the cylinder I'm not sure exactly of that number, the determining factor on that will be setting up the squish area in between the piston and head. After I do all that it'll be time to break out the burette and figure out the compression ratio and determine how much of the dome I have to mill off of the pistons to get an 8:1 ratio out of it. Another little issue is the one of the pistons wanting to crash into each other at the bottom of the stroke, but that is easily fixed with a little bit of clearancing on the back skirt of the front piston.






I just got my Keith Blacks in about a week ago. I love these pistons, I run them in everything I can get 'em for. They're Hyperutectically (high heat, high pressure) cast in steel molds out of a high silicon content alloy that holds up to tremendous amounts of heat, they have some of the lowest thermal expansion rates of anything out there which lets you fit them very tight in the bores and not have to worry about scuffing the skirts, and the alloy that they're cast out of is hard as hell which coupled with the tight clearances means you've got a piston that you can run extremely hard and still get 50k+ miles out of easily. And to top it all off they're quite a bit lighter than a stock or forged piston.








I also got my new trap door for the tranny, ditch the frail aluminum one in favor of a cast iron piece and you're well on the way to a stronger transmission.





That's all I've got for now, I just dropped the cylinders off to be bored, once I've got those back I can do the final fitting on everything. Ride fast and smart. -Dave

2 comments:

Milo said...

this post was amazing - maybe time for your next monthly update?

JasonMcElroy said...

Great post!