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BoxxerSix BoxxerSix is offline
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Join Date: Jun 2006
Location: Ballston Spa, NY
Posts: 528
Originally Posted by Flieger View Post
Shuffle pinning = putting a steel "sleeve" or "tube" into the case where the studs are that hold the case halves together. This sleeve is concentric around the stud and takes some of the shear load away from the stud, allowing it to focus on clamping and stand up to high performance stresses.

Oil modifications:

Oil-bypass modification = bypassing the excess scavenged oil into the pressure side of the pump rather than the sump, leaving less oil in the sump.

Cross-drilled cranks = (important for high rpms and power) The crankshaft oil passages are drilled out through the crank throws, on the bearing journals. This allows more oil to the connecting rods' big-end bearings.

Windage modifications:

"Mooning" = cutting a semi-circular or "half-moon" shape into the bottom of the cylinder spigot (the "skirt" inserted into the case). The relieved area allows gas to flow out of the cylinder easier when pushed by the piston on the downstroke.

"Boat-tailing" = Smoothing the crankcase main webs (or any other webs) which hold the main bearings. This allows gases to flow easier around the webs and cause less drag resistance for the piston when it moves all that air around while running.

"Knife-edging" = Sharpening the crankshaft shoulders between the throws, where the counter-weights are. This causes less drag as the crankshaft rotates through air/oil.
Couple things just from my experience, and other smart folks here too:

"Boat tailing" webs.....has not proven itself greatly, at least in my opinion. Some say it does wonders, others nay. I tend to side on the later....

"Mooning" case reinforcements.....I'm warry on this are well. They're in there for a reason. If I we concerned greatly about windage that much I'd run a vacuum pump on the case to an air/oil separator...Now I know it's probably not a huge issue currently, but it would be a lingering though in my head had I done this to one of my motors.

"Knife edging crank"......this is good, and typically I find that smooth rounded radii vs sharp edges on leading edge of throws helps even more for low windage.(same principle behind why rounded submarine nose is more efficient than a sharp pointed one in the water)

Adam Hennessy
Old 11-11-2008, 07:44 PM
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