Piston Top Shape and Wet Flow?

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Re: Piston Top Shape and Wet Flow?

Post by JohnsnsFord2@aol.com »

Juho_ wrote: Wed Dec 13, 2017 1:25 pm I'd think a large (tall) dome would eventually cause a restriction near TDC, when the inlet valve is open and mixture flowing to cylinder.
And the air-fuel mixture would be way slower to burn since the dome is getting on the way of flame after mixture near spark plug is ignited.

Not sure, how to explain it any better.. hope you'll understand - english is not my primary language.

In my opinion a flat top or slightly dished piston would be the best compromise. If combustion chamber volume can be kept low enough without ruining it's shape to achieve a high compression ratio, which you are probably looking for with a domed piston.
Low valve angle will help keeping the combustion chamber volume at bare minimum.
With low valve angle , when inlet and exhaust valves are both same time open, the mixture can escape to exhaust ports easier, since there'll be less space between the valves than with a greater valve angle.

Just some thoughts.

I might be wrong tho.
There are many B and K series Honda engines that are capable of producing more than 150hp per liter naturally aspirated, and have a huge dome on the pistons to achieve a static compression greater than 14:1 (often with E85 or methanol).
They do rev very high, and piston speed can be quite extreme like many engines do have that are capable of producing very high BMEP.


alot of times when the dome is big, and there is an issue of blocking flame travel the engine builder will notch the piston and create a fire slot or, if the plug angle on the head is slightly away from intake valve that helps..
Stephen Johnson #2162
Horace Johnson #2167
SS/D 427 Ford Fairlane NHRA-IHRA
Ex-Jim Van Cleve
1985 Mustang GT N/A 331
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Re: Piston Top Shape and Wet Flow?

Post by JohnsnsFord2@aol.com »

David Redszus wrote: Sat Dec 16, 2017 3:35 pm Piston dome shape contributes to several aspects of combustion from filling, to flame speed, to piston temperature, to scavenging.

While it is tempting to flow a domed piston at max air flow, (which occurs at/near max piston velocity not max valve lift), the piston is very far down the cylinder and not likely to have much effect on flow.

However, during overlap, the piston is very close to the valves and could affect flow dynamics. A further consideration is that a moving piston will cause a squish velocity motion which could have a considerable impact on flow before and after TDC.

Sometimes simple question have very difficult answers.
this is definetly good answer here!!
Stephen Johnson #2162
Horace Johnson #2167
SS/D 427 Ford Fairlane NHRA-IHRA
Ex-Jim Van Cleve
1985 Mustang GT N/A 331
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