Super Jet Whats up with a "flat top"motor"?

[Crab]

Just wondering what is the benefit when they use kawi pistons and cut custom domes to make one of these? Does it allow the porting to be altered in a good way since the piston sides are taller now? I would like to know more specifics.

 

[fast superjet chase]

x2

 

[easyrhino]

x3
Are flatop piston stronger than dome construction?
Is it for heat distribution?

 

[chriselmore_1]

I know the produce more torque...

 

[Matt_E]

I know the produce more torque...

How?


Flat Top pros:

-Shorter heat path to cylinder wall allows faster heat transfer
-Piston crown is in tension under load
-Ports timing is more accurate
-Flow from ports begins sooner due to not being masked by curvature of piston dome
-Combustion chamber can be a true hemisphere
-Usually lighter than a domed piston

Flat Top Cons:

-Aluminum does not have good strength under tension when hot
-Greater possibility of ring over-heating due to more rapid heat transfer
-Nothing to prevent gas crossing piston from transfers to exhaust port. (this is not always a disadvantage with a tuned exhaust)
-Squish band must be cut properly for a flat top piston. Getting it right can be dificult.


Domed piston pros:

-Piston crown is in compression under load
-Dome pushes incoming mixture to top of cylinder and reduces "short circuiting"
-Scavenging is better than with a flat top, so engine runs less erratic under light loads.

Domed Piston Cons:

-Heavier than a flat top.
-Combustion pressures try to push the center of the dome down, causing some distortion of the top ring groove.
-Slightly "fuzzy" port timing due to the curve of the piston crown.
-Greater surface area increases flame quench at the periphery of the combustion chamber.
-Combustion chamber shape is not as efficient.

 

[SuperJETT]

I think Tim Judge said once that they gave a 3% increase in power over normal pistons back when they did guest chats on pwctoday.

 

[chriselmore_1]

Matt that's just what several engine builders have told me.

 

[fast superjet chase]

what pistons would you order for a yamaha then.

 

[yankeeboy]

what pistons would you order for a yamaha then.

depends on the size and type of piston your looking for. Not every ( if any) manufacturer carries flats in all ( or any ) sizes.

 

[Pablo]

Wiseco makes Riva flats and kawi has flat tops that are used too.

 

[GIL]

Flat tops are better becuase they are more expensive and require machine work to the pistons to make them work. lol....................I run Wiseco 813M08550 flat tops in my Lamey.

 

[Nuklear6]

Everything matt said is very true, the one thing he said about the combustion chamber shape being less efficient with the dome tops is the major reason for add power when going to flat tops. This meaning that when the force of combustion is exerted on the top of the piston after the spark plug fires, the dome tops tend to distribute the force down and out toward the cylinder walls. Were flat tops tend to distribute the force directly down thus making it more efficient to the over all idea of internal combustion.

 

[D-Roc]

Flat tops are better becuase they are more expensive and require machine work to the pistons to make them work. lol....................I run Wiseco 813M08550 flat tops in my Lamey.

X2. I need that 3%hp increase. And putting flattop pistons in a yamaha just sounds cool to say. I run them in my DASA topend. That also sounds cooler than lamey topend.

 

[Waternut]

I'll chime and mention that there are kawi style flat tops and true flat tops. The RIVA pistons are true 0° flat tops and the kawi or dominator pistons have a 2-4° dome (can't remember which) but look flat. Apparently it makes a huge difference. I have the dominator pistons in my engine and when I rebuilt my engine last, my engine builder told me my engine wouldn't run right with the RIVA pistons. Since he wasn't getting paid for either the piston or the work, I have to think that he is telling the truth and looking out for my best interests.

 

[GIL]

I'll chime and mention that there are kawi style flat tops and true flat tops. The RIVA pistons are true 0° flat tops and the kawi or dominator pistons have a 2-4° dome (can't remember which) but look flat. Apparently it makes a huge difference. I have the dominator pistons in my engine and when I rebuilt my engine last, my engine builder told me my engine wouldn't run right with the RIVA pistons. Since he wasn't getting paid for either the piston or the work, I have to think that he is telling the truth and looking out for my best interests.

0* vs 2* = huge difference??? Who fed you that line of horse poop ??? Nevermind, I already know who fed you that line of horse poop.

Save your self some face and take it from someone who has been there and done that-flat tops are great for spending more money on pistons, having to cut the skirts, being tied to a given engine builder and thats about it. Granted I love my motor and it really is awesome IMO, but given the chance to build another one, it will be with Yami style Wiseco pistons with DOME tops.

 

[Waternut]

0* vs 2* = huge difference??? Who fed you that line of horse poop ??? Nevermind, I already know who fed you that line of horse poop.

Save your self some face and take it from someone who has been there and done that-flat tops are great for spending more money on pistons, having to cut the skirts, being tied to a given engine builder and thats about it. Granted I love my motor and it really is awesome IMO, but given the chance to build another one, it will be with Yami style Wiseco pistons with DOME tops.

Considering domes for a 2° piston and a 0° piston are different, I'd consider that grounds for a huge difference. But you're right, it's probably best we DON'T listen to our engine builders advice....especially when that advice is going to save you money and the builder isn't going to make a single penny off you regardless of what you buy.

 

[Pablo]

Originally Posted by GIL
"0* vs 2* = huge difference??? Who fed you that line of horse poop ??? Nevermind, I already know who fed you that line of horse poop.Save your self some face and take it from someone who has been there and done that-flat tops are great for spending more money on pistons, having to cut the skirts, being tied to a given engine builder and thats about it. Granted I love my motor and it really is awesome IMO, but given the chance to build another one, it will be with Yami style Wiseco pistons with DOME tops.

Considering domes for a 2° piston and a 0° piston are different, I'd consider that grounds for a huge difference. But you're right, it's probably best we DON'T listen to our engine builders advice....especially when that advice is going to save you money and the builder isn't going to make a single penny off you regardless of what you buy. "

This thread is starting to take off...
Gentlemen, start your "flat-top" engines!

 

[GIL]

Considering domes for a 2° piston and a 0° piston are different, I'd consider that grounds for a huge difference. But you're right, it's probably best we DON'T listen to our engine builders advice....especially when that advice is going to save you money and the builder isn't going to make a single penny off you regardless of what you buy.

So you like the kool aid huh???

 

[GIL]

Originally Posted by GIL
"0* vs 2* = huge difference??? Who fed you that line of horse poop ??? Nevermind, I already know who fed you that line of horse poop.Save your self some face and take it from someone who has been there and done that-flat tops are great for spending more money on pistons, having to cut the skirts, being tied to a given engine builder and thats about it. Granted I love my motor and it really is awesome IMO, but given the chance to build another one, it will be with Yami style Wiseco pistons with DOME tops.

Considering domes for a 2° piston and a 0° piston are different, I'd consider that grounds for a huge difference. But you're right, it's probably best we DON'T listen to our engine builders advice....especially when that advice is going to save you money and the builder isn't going to make a single penny off you regardless of what you buy. "

This thread is starting to take off...
Gentlemen, start your "flat-top" engines!

LOL, I have my 838cc / 2* flattop DASA fired up and rippin!!! (I guess now we are required by wingnut to specify 0* or 2* flattop). lol

 

[waxhead]

Flat tops do make more power and are technically better. However is it worth spending the extra money?? not unless your going to the world finials in my op