Flat top or Dish

[dr gary turner]

What are the pros and cons of a Flat Top piston vs. a Dish Top piston??

 

[Danny King]

It allows a shallower chamber in the head button without sacrificing volume. While allowing the element to be more centered.

 

[John Beardslee]

It’s also used to cool the top of the piston with the fuel charge to prevent burning a hole in the piston

 

[dr gary turner]

Which one produces the most power??

 

[Danny King]

Which one produces the most power??

Honestly, the one you work the hardest tuning. IMO

 

[Wally Duarte]

I have engines with flat topped pistons and ones with domed pistons and they both make great power. There’s more than one way to skin a cat , just depends on the builder and his Knack for extracting any given power

 

[ALLAN YUEN]

Which one produces the most power??

I found out my self that seem compare two different : best flat top piston most power and high nitro . The dish top piston tricky power ( depend on low or high nitro also change measure shims ) and best turbo plug button if you use std plug button but if see glow coil pull out sometime happen

 

[Timbo Whalen]

It’s also used to cool the top of the piston with the fuel charge to prevent burning a hole in the piston

Yep, more surface area.

 

[John Beardslee]

Yep, more surface area.

If I remember the first Quincy Loopers (Alky outboards) had flat top pistons and went to a slight dome to prevent burning a hole in the piston.

 

[Timbo Whalen]

If I remember the first Quincy Loopers (Alky outboards) had flat top pistons and went to a slight dome to prevent burning a hole in the piston.

Yessir, ol' O.F. Christner, of Quincy Welding fame, never tired of toying with the

Merc racing outboards- hence, the development of the Looper. There was quite a battle

between Merc based deflector engines and the Konigs. Konig departed from cross flow

to loop charged and left O.F. in the dust- then came the birth of the Quincy Looper.

He put one of his 6 cyl. Looper Beast powerheads on a Merc standard mid and gc, clamped

it to a 15' Dunphy and terrorized the OPC guys on the Mississippi River-

'A very prominent Quincy resident had a huge V8 powered California built V-drive that he
was very proud of. He happened to be on the river that day and pulled along side of the
Quincy crew and challenged them to a race on the river. As the story goes, the Beast, when
O. F. nailed the throttle, not only left the huge V8 V-drive behind, it almost threw son John
out of the back of the boat because John wasn't hanging on tight enough. The Beast beat
the V8 so badly that day that it's owner, when O. F. finally let off of the throttle and the other
guy caught up, tried to ram the Quincy Welding crew's boat. O.F. avoided the other boat's
contact by taking off again in a burst of speed.'



Dick Austin over in Ludington has a Looper Beast on his F Alky Hydro....

 

[Steve White]

What are the pros and cons of a Flat Top piston vs. a Dish Top piston??

Flat, domed, dished, wedge, baffled and probably a few others.

For me a domed is not the same as a dish top. Dish top would be concave while domed would be convex.

Interesting question and thread.

 

[Jeff Lutz]

What are the pros and cons of a Flat Top piston vs. a Dish Top piston??

In theory , fuel burns better in a spherical combustion chamber. The dished piston should burn the fuel better.

 

[Terry Keeley]

It’s also used to cool the top of the piston with the fuel charge to prevent burning a hole in the piston

Ha! Remember this one John?

For my money I'll take the flat top, why thin the crown right where it's hottest?

 

[Danny King]

Ha! Remember this one John?

For my money I'll take the flat top, why thin the crown right where it's hottest?

Looks like an attempt at variable valve timing. Lol

 

[Ricky Neal]

This is one of the areas I am looking at now and I have sought some advice. I had a conversation with Peter Halman (designer and builder of Halman special F2A control line speed engines) This was part of a much larger conversation and not specifically about piston design but engine design in general so was just a passing point on piston design rather than a detailed analysis of why.

"A domed or chamfered piston is stronger than a flat top piston and is important when run for long periods as in circuit car racing, this is as important as maximum power. Flat top pistons give more power as the combustion force is transmitted more directly straight to the crankshaft."


I feel that the design of the piston is dictated by the application, actually, a lot of the engine design is. Porting design, material choices, etc, Let's not get into liner taper for different applications as well....

My point would be that it depends on the application, what is used for? - work back from there.

The basic rules appear to be that a domed piston is better suited for longer, high-loaded applications, and flat-top pistons are more suited to shorter runs where ultimate power is the main priority and where you are unlikely to go beyond the thermal capacity of the components.

The amount of power difference between the 2 will be small but may be important if you are trying to eke out the last %

Ricky

 

[Jeff Lutz]

This is one of the areas I am looking at now and I have sought some advice. I had a conversation with Peter Halman (designer and builder of Halman special F2A control line speed engines) This was part of a much larger conversation and not specifically about piston design but engine design in general so was just a passing point on piston design rather than a detailed analysis of why.

"A domed or chamfered piston is stronger than a flat top piston and is important when run for long periods as in circuit car racing, this is as important as maximum power. Flat top pistons give more power as the combustion force is transmitted more directly straight to the crankshaft."


I feel that the design of the piston is dictated by the application, actually, a lot of the engine design is. Porting design, material choices, etc, Let's not get into liner taper for different applications as well....

My point would be that it depends on the application, what is used for? - work back from there.

The basic rules appear to be that a domed piston is better suited for longer, high-loaded applications, and flat-top pistons are more suited to shorter runs where ultimate power is the main priority and where you are unlikely to go beyond the thermal capacity of the components.

The amount of power difference between the 2 will be small but may be important if you are trying to eke out the last %

Ricky

A DISHED PISTON IS NOT DOMED. SHOULD I REPEAT THIS AGAIN ? IT CAN BE DOMED AND DISHED BUT THAT IS NOT WHAT THE ORIGINAL POSTER ASKED ABOUT. TOP FUEL DRAGSTERS RUN 100% NITRO AND DISHED PISTONS USUALLY BECAUSE THEY HAVE MADE MORE POWER WITH THEM THAN FLAT TOP. ALL BECAUSE IT BURNS THE FUEL BETTER/FASTER.

 

[Ricky Neal]

A DISHED PISTON IS NOT DOMED. SHOULD I REPEAT THIS AGAIN ? IT CAN BE DOMED AND DISHED BUT THAT IS NOT WHAT THE ORIGINAL POSTER ASKED ABOUT. TOP FUEL DRAGSTERS RUN 100% NITRO AND DISHED PISTONS USUALLY BECAUSE THEY HAVE MADE MORE POWER WITH THEM THAN FLAT TOP. ALL BECAUSE IT BURNS THE FUEL BETTER/FASTER.

Calm down Jeff, no need to shout....

I was fully aware of the specifics of the question, hence the first paragraph where I said that the conversation was not piston-design specific. I passed on what was said (because it was specific to model engines) but the point I was making was that piston design would be led by the application because there is no binary answer.

 

[John Beardslee]

It’s also used to cool the top of the piston with the fuel charge to prevent burning a hole in the piston

I was thinking here of the NR21DD’s that Doc and I run that have a bevel and then a slight dish in the center of the raised part of the piston.
Most automotive dished pistons are flat top with a dish in the center, maybe easier to dish than put huge eyebrows in to clear the monster valves

 

[John Beardslee]

A DISHED PISTON IS NOT DOMED. SHOULD I REPEAT THIS AGAIN ? IT CAN BE DOMED AND DISHED BUT THAT IS NOT WHAT THE ORIGINAL POSTER ASKED ABOUT. TOP FUEL DRAGSTERS RUN 100% NITRO AND DISHED PISTONS USUALLY BECAUSE THEY HAVE MADE MORE POWER WITH THEM THAN FLAT TOP. ALL BECAUSE IT BURNS THE FUEL BETTER/FASTER.

They are also running super chargers which is also a significant factor in their piston design

 

[LohringMiller]

Another factor is scavenging. A two stroke engine's power is very sensitive to scavenging efficiency. There's no question that domed and flat topped pistons scavenge well. Does that dish leave an area of residual exhaust gas in the combustion chamber?

Lohring Miller