Gas Ported 3" Pistons

Jimbo

Premium User


Gas ported pistons for Model 15 Briggs blocks.
Get the details. Click on the link below.
MODEL15WITH3INCHBORE.HTML

Custom billet rod for this application.


Model 15 block with Sleeve installed
 
Last edited:

Jimbo

Premium User
It has been brought to my attention that some people don't understand the reason for gas porting pistons.
The holes you see it the top of the piston do not leak compression!!!
The holes are precisely drilled so that cylinder pressure is applied to the top piston ring on the compression stroke so that the ring seals better and actually contributes to making more compression. The pressure forces the top ring to the bottom of the ring land and also out against the cylinder wall.
After ignition the much higher combustion pressure forces the top ring down against the ring groove and out against the cylinder wall even more so to help prevent blow by and also make more power.

These pistons also have and accumulator groove machined into the piston between the top compression ring and the second (scraper) ring. Its purpose is to provide additional relief space for pressure escaping past the top ring to build up before it attempts to pass the second ring. It supports top ring sealing by relieving pressure and it helps reduce ring flutter due to pressure changes. Accumulator grooves have proved most effective and they are a common feature on many, if not most, high performance and racing pistons.
 
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