Curing piston slap?
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TECH Veteran
Joined: Aug 2002
Posts: 4,055
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From: Hartsdale, NY
Curing piston slap? So the folks at NASCAR are exploring other ways to quench their ever-increasing desire for additional revenue.
They are now sponsoring Jasper Engine rebuilds. The ad says their rebuilds include longer skirted coated pistons that stop GM engines from slapping upon initial start-up. They claim this mod is one of many updates to the orginal factory design.
They are now sponsoring Jasper Engine rebuilds. The ad says their rebuilds include longer skirted coated pistons that stop GM engines from slapping upon initial start-up. They claim this mod is one of many updates to the orginal factory design.
longer skirts mean less rocking of the pistons when they are cold (when cold the piston is too small for the bore).....
coated pistons don't grow as much so the bores can be made closer to the piston size....
coated pistons don't grow as much so the bores can be made closer to the piston size....
Originally Posted by robertbartsch
Yeh, this make perfect since; too bad GM did not think of this in 1997.
I used the coatings (thermal top, teflon side) on my pistons (still have short skirt) and they helped a lot.....
I did some extensive testing of tech-line thermal barrier coating on pistons and came up with no positive results whatsoever besides the coating sticks to the piston given the surface is prepared properly, and they do not burn off the piston at up to 1600*F. It didn't slow heat transfer into the piston one bit.
I only tested the tech-line brand, and none of the other types like swain or jethot.
During my testing, by far the best reduction in heat transfer was achieved by polishing the piston top to a mirror finish. That slowed down the heat quite a bit.
For anyone versed in thermodynamics, you know that the heat isn't really blocked, but the transfer is slowed.... which simply buys you time at WOT.
As for the piston running cooler all the time... well that don't happen with coatings. The only way to cool the piston full time is to provide additional cooling as in oil directed under the crown, or simply running the engine cooler.
this should tell you something about how they tell you that you can run tighter clearances with coated pistons.
I only tested the tech-line brand, and none of the other types like swain or jethot.
During my testing, by far the best reduction in heat transfer was achieved by polishing the piston top to a mirror finish. That slowed down the heat quite a bit.
For anyone versed in thermodynamics, you know that the heat isn't really blocked, but the transfer is slowed.... which simply buys you time at WOT.
As for the piston running cooler all the time... well that don't happen with coatings. The only way to cool the piston full time is to provide additional cooling as in oil directed under the crown, or simply running the engine cooler.
this should tell you something about how they tell you that you can run tighter clearances with coated pistons.
