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las drogas son malas
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As we all know, there are a lot of very knowledgable, highly-skilled mechanics on this forum who can answer every H-D question known to man. But sometimes those of us who are mechanically uninclined need it laid out in an easy-to-follow, dumbed-down language. I found Chris Maida's explanation on increasing engine size to be very helpful and so thought I'd share for any non-American Iron subscribers. For the experts, please expound on anything you feel pertinent.



 

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The thing that limits the redline on a motor is the piston speed.

Long stroke motors have a higher piston speed for a given RPM than a short stroke motor.

There really isn't much difference between piston speed at redline on a HD motor than a UJM inline 4.

A HD 103" has a piston speed of 76 fps @ 6250 RPM. (What my redline is set at)
A Honda CB1100 has a piston speed of 62.5 fps @ 8500 RPM.
A Honda CBR1000RR has a piston speed of 78 fps @ 13000 RPM.


Hmm, a Harley has a piston speed closer to the Honda race bike than the Honda street bike.... How can that be with the oft maligned "antiquated technology"?? :what?

Pure simple physics. Nothing magical about designing a motor.
Forged engine components enable a higher piston speed than cast parts, and within the metallurgical constraints, the maximum piston speed is the limiting factor and is a known fixed value.

How the UJM bikes get such a high redline is by making short stroke, big bore motors, and a higher number of cylinders.

Want high horsepower? You want a short stroke motor.

Want high torque? You want a long stroke motor.
 

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las drogas son malas
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Discussion Starter #4
More really good info - thanks Kainam!
 

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las drogas son malas
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Discussion Starter #8
Dr. Stangs recommends the Fuel Moto 107" Big Bore Kit, for anyone who's interested in upsizing.



The Fuel Moto 107" Big Bore is a complete kit with the absolute highest quality components, all of which have been extensively tested in house both on the dyno as well as in real world conditions to deliver top level performance. This kit works on all 2007-2015 Twin cam 96" and 103" motors and delivers absolute top level performance and reliability. Our Fuel Moto 107" kit works with stock cylinder heads and valve train, or if you are looking for the next level of performance complement your build with our Fuel Moto Level B heads.
 

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Señor Member
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Make your engine big, bro.
 

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Dang, that's interesting stuff that even I can wrap my head around. Thanks for sharing.
 
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