Why don't the aftermarket pistons use the ski jump?

amy

I've never really got a decent answer on this so figured I'd finally ask. Why do some aftermarket pistons go dished vs the stockers? Flame suit on,

the skyjump as you call it helps with emissions, and is used by JE
JE 8.0:1 Compression Pistons 03-05 SRT4 / 95-05 Neon 2.4L Swap - Pistons amp; Connecting Rods
other vendors claim the dish style helps prevent top compression ring failure

Ski jump, lol. How are they for performance compared to the dished?

While they were engineered for emissions, primarily, there is performance merit in their shape and design.  A quick look at piston design for some of the original 426 Hemi engines will reveal a somewhat similar design - and I guarantee emissions was not the goal on a Race Hemi.  
I have been around (as turbovanman knows) to try dish, flat top, 'ski jump' and other designs of pistons, all with varying results.  The JE pistons are what are in my current build.  
As an aside, I was in Venice, Italy last week, and went to the Ferrari store, and you could buy a piston and rod from an F1 car (used, for a mere 1200 euros!), and wouldn't you know it, it had a ski ramp design to it.

Thanks Neil, I was told emissions years ago but figured there had to me another reason. We had a big discussion about pistons on Turbo-mopar and these type got shot down, the reason was they block the transfer of the air/fuel mixture across the chamber. I still believe a dome/ski jump shape is better for better power.

just an idea, but maybe they used it to help keep the piston quot;centeredquot; on the power stroke? Same idea as a piston pin offset to help keep the piston from scraping down on the cylinder wall when moving down on the power stroke
quick search on google and found this
Dodge Neon SRT-4 - Project Cars - Sport Compact Car Magazine
actually lots of good info on our motors and explains the ski ramp design

the domes are normally used for higher comp engines from what i remember but i assume it is used in the srt engine for more efficient combustion