piston skirts

[FLDavetrain]

   FULL ROUND VS SLIPPER DESIGN 
   
   Can anyone comment on the difference as it would relate to power HP/TQ output on a big inch build? How
   much would the full skirt affect numbers if at all, thanks.

[rigidthumper]

Here is a great article.
Full skirt is heavier, so the energy used to move the extra mass doesn't get to the tire, but you're picking fly poop out of pepper at that point...

[Don D]

We have to keep the discussion constrained in the context of a long stroke HD Vtwin. In doing this first thing that comes to mind this lightening to leverage more power may be impossible and / or illogical in the interest of a reliable build. There is essentially no room to have a gauge point. This combined with a relatively short compression height does accomplish the lower weight goal but also yields a very unstable piston in the bore. This affects ring stability and seal. Having a dome and weight up top makes the problem worse. Over the long haul this could affect heat transfer and then cylinder distortion occurs. Another aspect of this lightening to consider is engine balance. There is a certain amount of latitude with weight changes but we must remember the flywheels were balanced for a certain piston weight gross and at a certain percent of the reciprocating weight. Bust out too far and things get unhappy without a flywheel rebalance. Now you are married to this lightweight piston design. Third and last consideration is leveraging lower friction. Again for the same reasons the very thin low tension rings and slipper skirts are cutting edge. But in a TC also close to bleeding edge.
Bottom line, lighter has the potential to make more power but also adds a large element of risk. The better pistons I have used over the years were a tad heavier, 4032 forging so they could be fit tighter yet still have good strength, and were full skirt design with inboard pin bosses. I credit Randy Torgeson and Reggie Sr. for many years ago giving me some of their time and explaining piston design as it relates to the VTwin. My context and knowledge was closer to high performance car engines. Here is what I consider a good skirt design, assumes the cam and barrel work well for the application.

[FLDavetrain]

     Thanks for the replies. I've read the article and others. Knowing the pros and cons, trying to get an idea quantitatively how much a long stroke TC motor would differ power wise between these 2 style skirts in the same application. Is the slipper type good for 3/3, 5/5, 10/10?? Or is it to benign to measure?

[Nastytls]

Interesting question. Is there really any difference in power? I would imagine someone would need to do some back to back testing to see.

[Deye76]

informative explanation, Don. If one is racing, and tearing down every few runs, then go for the weight savings. The majority on this site, are not. Stability and seal is everything to the average rider, even if they don't know or realize it.

[Ohio HD]

Stability and seal is everything to the average rider, even if they don't know or realize it.

[koko3052]

Longevity over bragging rights, every time!