firefrost gold

High performance pistons . Thoughts on Performance pistons I know flat tops are the piston of choice but : What about the Idea or thought that a small dish makes the combustion more centered and for a better push like a small combustion chamber within the chamber ? If designed into the build what would the pro's con's of a say dish , flat , or dome ?

wr1970

Good question mine on my motors are valve relieved.I may be wrong but i think the dome would be better.I am not a expert on pistons so i hope someone chimes in gives some examples.

young olds

I always thought a bit of a dish might help some what vs a flat top or dome, I think of it as cupping the explosion. I always here that domes aren't really that good for power

rootney

First consideration is what heads are you running and what compression ratio you desire ? Then the choice of piston dish, flat or dome, and their displacement in CCs either positive (dome) or negative (dish) or flat (zero), plays into how you are going to achieve the desired compression ratio. The piston displacement, combustion chamber size of the heads and whether you choose to deck the block and/or mill the heads to get to the final compression ratio. Head gasket thickness can be used to fine tune, however, the chosen scheme of parts and machining should provide a quench area of around .050" nominal at TDC.

The selection of Piston should also consider total piston and pin weight.
A fair amount of horse power is lost each time you accelerate a piston from TDC and BDC (essentially accelerating from zero to 1,000 Inches per second in a few msecs) . This also translates into lots force on the rod bearings. Something an olds motor can do without. A light weight modern piston set is well worth the extra couple hundred denaro.

So, there many other things in piston selection that need to be part of a good combustion system design. Flame propagation across the combustion chamber as a function of piston shape in an Olds motor? A high HP hemi or high revving nascar engine perhaps. Just try to get the basics right.

George

cutlassefi

Mostly correct. But with the std Olds combustion chamber piston design isn't as critical or as beneficial as it could be.
Nascar is using dish pistons to keep the heat and pressure further into the piston. Domes are most often the least efficient but sometimes necessary to achieve the desired comp ratio.
A better/thinner ring pack can give as much as or more benefit as a lighter piston. Better ring sealing thru less flutter and more flexibility is beneficial across the board.

firefrost gold

So what makes a Ring better than a Ring form another mother ? when playing with two stroke snowmobile engines pistions form year to year in the same sled would change form chrome or L style . single vs double . I know the reason and the theory behind the perfect circle ring but what are your thoughts on ring land space and placement along with squish band

cutlassefi

Huh?

Not sure what you're asking there but the thinner and lighter the ring the better it responds to wall deflection and also operates with less flutter.
Virtually all new engines being produced use top rings in the 1.1 to 1.2mm thickness range. It helps ring life when the application is fuel injected but even carbed engines can go 50,000 or better with these new ring packs.

firefrost gold

My point to this post was to get people to post up piston info why they went with what they went with . Sometimes some one has a article in there back pocket they whip out and it is a good read that may have been hard to find. With this new Race Engine forum im just trying to live and learn .

wr1970

That's what these changes were for to generate more interest and discussions that were lacking. Mark is giving out some real good info.

wr1970

Mark what piston is available thru your new source that would be good for a 434 D block diesel build? Let say 13/1 compression and at what weight? Would you use the sbc rod journal and what wrist pin size for these pistons or would you have something else in mind.

wr1970

Hey mark why did you bail on this thread? It was just a question i thought you might be able to answer!

cutlassefi

I didn't bail, just busy! I have builds to do
Yes I'd do a sbc Rod journal and a LS h beam rod. Unlike a reg sbc they're a centered Rod.
For a piston you'd need a dome to get 13.0:1, or cut a whole bunch off the heads. I'd do the latter if possible.
Ffg good post. Been trying to get feedback on piston here and on rop for a couple of weeks. Hopefully this will help stir the pot.

firefrost gold

I might not always know how to ask it ( as Mark Knows ) but I can stir the pot LOL
SO what do you mean by centered Rod ? Why would centered be a good thing ?

cutlassefi

A regular sbc is offset, the beam favors the side opposite the chamfer iirc.
An LS Rod is centered, just like an Oldsmobile so the pin end will also be centered. Otherwise when using aftermarket sbc rods sometimes you have to cut some off of one side in order to clear the pin boss in the piston.
Bbc are the same way, offset.