Short Piston Skirt Design
Short Piston Skirt Design
(OP)
Over the last several decades piston design has evolved to shorter skirts. I would like to know the limit on how short piston skirts can be and what trade-offs are involved. Tribology, stability, piston material strength requirement, cylinder wall loading, other?
Thank you.
Thank you.





RE: Short Piston Skirt Design
The piston skirt is a spring and it has to be designed as such. I have asked about this formula when talking tech at the vendors, but they don't convince me it's a moot point. Someday I will run into this work when I do my reviews in my library. But, these guy's are suppose to know their work more than we.
RE: Short Piston Skirt Design
Will you please elaborate on "The piston skirt is a spring and it has to be designed as such."
Thanks.
RE: Short Piston Skirt Design
I had thought that the original Packard study of piston problems were brought on by the use of the "war power" detent on the throttle quadrant. When used from high altitude to low and from lower boost to higher boost levels caused significant localized overheat and thus engine failure. I may not be remembering this article correctly as I believe I read it back in 1955 or there-a-bout.
It may be that Cosworth uses some sort of exotic alloy, they sure COST a lot more than any other!!!
Just some more rambling thoughts this morning, sorry.
Rod
RE: Short Piston Skirt Design
What I have noted in limited involvement concerning the piston acting as a spring, was notable in thin wall engines. In that case, the skirt tails had again, a determined point of legnth for especially cold start. OEM style. This goes away back. As a piston transfers from cold to operating values, a piston transfers heat into mass, then out to min. mass, dissapating. The metal bridge limits that growth, the slots halt the expansion,around the pin bore on into the band. If it failed to accomplish this, sezure would occurr. @, a spring in tension. ---- On into the racing venue, early attempts in providing flexable forgings to satisfy those requirments were failiars. The cloverleaf did not fill the need, as it dissapated more heat into the band delivering diameter in the process. Relieving those high mass corners created additional issues in the piston, being forced into 'beyond tensile values' and they fractured. @ spring. It's an evolving process. In this day with thick wall blocks, artifically or meatalurgically, it has allowed the piston to evolve as we see it. Metals are probbably where they are because of the cold war being over. Yet, I still see with the pistons getting increasingly ridged, that spring effect dissappearing, all caused by metalurgy. Stregnth vs. stregnth. It must fit the application. Thin,thick,flexable,ridged. My oppinion.
John Haskell
Aire Research Engr.