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Question - Pistons

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I have also from running lean, not square either. Must ave been the wrong plugs.
 
I don't know about the 75 having flat tops (haven't taken my '75 engine from Mark apart yet), but I know for absolute certainty that 76's had them. With 9:1 you can run 87 octane stock, I did when I first got the car. I wouldn't do any major performance mods and try to keep running 87, though. The timing's pretty retarded with the stock settings, so you'd probably do the engine good to advance it a bit. Mine's advanced to something like 16 degrees at idle ... I digress ... at any rate, flat tops will give you better performance, and I doubt you need to change octane with stock ignition settings. The change from 10.5 (what I've currently got) to 13 would make a neglible difference, but from 7.5-9 is a significant improvement (law of diminishing returns). Just install everything on the car and don't worry about the pistons. /ubbthreads/images/graemlins/smile.gif The dish (in my opinion) isn't desireable, mostly for the lower compression ratio. They say it promotes better combustion, but I'd wager it's mostly negligible. As to turbulence, there's already an enormous amount from the piston thrashing about and the valves slamming open and shut at a ferocious rate!
 
actually the dish doesn't make any more turbulance. It just keeps the flame front heading to the center of the piston. Kinda keeps it in a ball...more so than a flat unit. this improves fuel burn. More power less unburned fuel going out the tailpipe. Keeps the heat away from the ring lands(bad place for heat to be. did you ever notice that detonation damage is normally found at the edge of the piston not the center. If flat tops were better they would be in all the cars. Just like if a hemi(and the new so called hemi is not one it is a pent-roof combustion chamber[kinda hard to market a pent] were really good all the cars would have those. Like I said if ya want compression, mill the head.
Yes I do have an engine with flat tops. I would rather have dished units. They were just too expensive to have made at the time. Yes all heck is breaking loose in the chamber and I really don't believe in swirl-port ideas, I don't think that there is enough time to make the molecules line up like that. I could be wrong.
The flat top does work well for forcing all the mix into the combustion chamber and creating tubulance. The little flat area in the head that forms the top of the heart shape squishes all the gases into the spark plug area. It is in fact called the squish area. Dang this hurts my head just thinking about it. I have to stop now.
 
Other than the basic "squirt, squish, BANG, shove" chain of events, the domed pistons DO help maintain a circulation of flow to aid the process. Volumetric efficiency increased, a *mite* less chaos in the CChamber. "CC-ing" the chambers and smoothing out the sharp places helps a lot, too.

Down-side is as mentioned above: lowers compression some.

Up-side is that yer butt likely won't notice a bit! /ubbthreads/images/graemlins/grin.gif
 
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