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Old 03-02-2011, 09:35 AM   #68
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 7,602
I thought only the stroke changed max piston speed at 90 degrees. I have never seen anyone throwing rod length ratio into calculating max piston speed?

Some consider a longer rods increased acceleration an advantage since the increased acceleration is AFTER a slower start from a dead start. It's the initial jerk from dead still that actually effects the setup more adversely than increased acceleration after the piston is already rolling. It's kind of like how long ramps on a cam can prevent valve float.

Some also consider the increased acceleration an advantage in maximizing the flame front's energy since at higher RPM's by the time the Longer rod's piston starts really moving most of the flame fronts ability to push on the piston has passed anyway.

That same increased acceleration is seen by some as an advantage on the intake stroke as well.

Whether or not it actually works out like that depends on the entire situation. Sometimes engines really respond to different rod length ratios and sometimes they don't. Personally, I think in some cases that they don't respond well to longer rods are instances where the longer rods were not long enough but that is another story. Airheads respond very well to longer rod length ratios. I have seen it. Comparatively speaking, the Carrillo rods and Venolia pistons that the mod takes are very inexpensive bang for buck wise. Since Dr. Curve pioneered the setup in our airheads, the mod has proven to be very reliable.

supershaft screwed with this post 03-02-2011 at 09:43 AM
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