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 flat or domed pistons?

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Number of posts : 362
Localisation : gravesend kent
Registration date : 2011-10-23

PostSubject: flat or domed pistons?   Wed Apr 29, 2015 10:44 pm

whats the better option for piston ported motors? simple question.............. no doubt a simple answer ? !

im thinking domed as with no reeds to keep things in the cylinder and crankcases the dome would help tumble the mixture upwards rather than out.

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Trevor Amos

Number of posts : 876
Registration date : 2010-08-13

PostSubject: Re: flat or domed pistons?   Wed Apr 29, 2015 11:41 pm

The method of induction will have no bearing on what goes on from transfer port closure onwards. At least for the average Bantam engine, so the flat/domed question does not arise.

Domed chambers and flat-top pistons don`t work too well. The best overall geometry is a low profile combustion chamber with a piston that has a,large radius, low crown. 3mm high crowns work well on 64 bores, scavenge flow can adhere to the crown and help to direct flow where you want it to be, it also helps cool the crown. Active squish with minimal clearance and a 50% band also work well. You need the maximum turbulence during combustion that can be provided, with the kinetic velocity of the squished mixture stirring things up and continually exposing unburned mixture to the expanding flame front. Mind you, the combustion chamber is the ONLY place in the engine you need turbulence!

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