Flat top pistons and flat cylinder heads - why?

[bmwsport]

Anyone know how flat top pistons and flat cylinder heads improve performance? or if indeed they do?

Also does anyone run a single ring piston on the road? i understand you get less friction with a single ring but i presume they dont last very long and probably smoke more?

Cheers.

[Pete.]

Flat piston and flat head? Where does the valve open-up into?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[NSR Mick]

You will only find single ring pistons on a 2 stroke where smoke isnt an issue.
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If you dont like the way that I ride.......Stop trying to keep up!!!

[Kickstart]

Hi

A domed piston gives a lousy combustion chamber shape. A flat head with a combustion chamber in the piston is cheap to make (used on the old Morini V Twins and the Alfasud, for example).

Only one that I know that switched around is Cagiva with the various Mito engines. Some had flat topped pistons, others slightly domed. Think both work pretty well , but mixing the parts up is at best going to lose a lot of power (flat piston with head for domed piston).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[bmwsport]

Thanks guys, ok keith, yea i wasn't planning on mixing the two, will go for flat on both i think, vhm do a a nice flat cylinder head.

Any views on the single ring piston?

No valves on a two stroke Geri!

[Kickstart]

Hi

Single ring piston just exchanges a bit of life for a tiny bit of power. Not sure it is worthwhile on the road, although single ring pistons tend to be cheaper which partly compensates.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[bmwsport]

Cool thanks keith, i think its worthwhile in that case, the forged wiseco single ring is half the cost of the two ring one as as i dont mind doing a top end rebuild every 4-5k i think it would be worth it, my only concern would be that i'd rather it wasnt seriously smokey, but i cant see that they can be that different to a two ring providing the piston is the right size.

[Kickstart]

Hi

On a 2 stroke I don't think it will make the slightest difference to how smokey it is.

Believe that forged pistons are meant to have a different clearance to cast pistons so make sure you take account of that.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing