flame propagation v high comp

[clubagreenie]

big cams

hmm, sorry thats 'how' youd get it to run

'how' youd actually get the 12.5:1 ratio without a piston swap? errrr.....

remove head gasket

[Billzilla]

FWIW here's a rare-ish photo of a 2000 spec Cosworth V-10 F1 engine, of the top of the block with the heads off. You can see the shape and very shallow dome of the pistons. They'er still dished despite the high compression ratio of the engine anyway.
(This is a lot what my new 4A ones look like)

[Polska]

good info thanks guys

[clubagreenie]

Bill are they actually domed (do the crowns project past the deck) or are they relieved and the valves project into the combustion area and the ridge between In/Ex sides is raised?

[Billzilla]

Bill are they actually domed (do the crowns project past the deck) or are they relieved and the valves project into the combustion area and the ridge between In/Ex sides is raised?

Kinda depends on your point of view I guess. They're dished as they have nothing sticking up above the deck of the piston, but inside that dish there is a distinct shallow dome.
They usually tailor the cam profile so the valves just miss the piston on the way up & down. They keep the odd kidney shape on sides of the piston to get a large squish area, to help generate turbulence - it also pretty much squirts all the gasses in those squish areas right at the tip of the spark plug, and that helps with combustion as well.
(trivia - at certain times, some F1 engines can run as much as 60deg advance ....)

[clubagreenie]

I'd always taken domed to be above deck, dished below, but also not just relieved for the valves, actually dished (circular).

I once cheated with a 5k and shaved the rocker blocks down then took to the pistons with a die grinder to increase lift and get valve clearance. Kept the base circle std, and lobe height std but added lift and weld/ground for duration.