More great info on combustion chamber & piston design http://forum.grumpysperformance.com/viewtopic.php?f=55&t=2718&p=12119&hilit=calculate+octane#p12119 http://forum.grumpysperformance.com/viewtopic.php?f=70&t=4683&p=12672&hilit=calculate+octane#p12672

Found a photo. Pretty sure it is not an ACN photo but it shows what is described in the articles above. The owner of this design basically started out with a clay impression of his head and replicated it on the piston. He kept refining the shape until he eliminated valve clash.

Been trying to find some cheap 85.5mm pistons with a crown with enough material to be machined into a squishy design. Diesels seem to be the way to go but most seem to have a hole in the crown. Also need to figure out the crown design that would work with twin plugs.

Wow been 6 years since I posted this up. I'm still slowly chipping away at making my own supersquish style pistons. I did reach out to John at ACN a few years back, to see if he would be prepared to do a run of standard sized pistons, but the lack of demand made it prohibitive (unless I wanted to purchase multiple sets). So, somewhere on the horizon I will eventually make something akin to a supersquish for the Okrasa engine I'm building.

Here's where I'm at...




I've scanned the combustion chambers of the heads, this has given me a 'plug' of the chamber shape. This shape needs to be refined so that there is a void at the plug locations. This will force the charge towards the plug and confine it ready for the ignition event.




Once the shape has been finalised I can then go ahead and machine the pistons.

Which leads me to my next challenge - upgrading my desktop CNC. Whilst it would just about machine the pistons, it's not really enough guts to produce the kind of results I need. So I really need to pull my finder out and get my CNC mill finished off.