bigger piston = more hp?

[jack vo]

ok long story short i was talking to the engine builder i was told that a bigger piston on a banshee will not give me more hp but a stroked banshee will,

his explanation was that a bigger piston will slow the engine down due to rotational mass 

so is this true

[ClaudeMachining]

ok long story short i was talking to the engine builder i was told that a bigger piston on a banshee will not give me more hp but a stroked banshee will,
his explanation was that a bigger piston will slow the engine down due to rotational mass 
so is this true

Interesting.

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[SKEETER]

You're in the wrong place.  Go to banshee hq Facebook page please. 

[97Screamer]

I agree with the builder that bigger pistons in a stock cylinder is not a way to noticeably increase power. Always run the smallest pistons your bore allows. While he is correct that larger pistons have more rotating mass I disagree that is why they don't make more power. Maybe something was lost in translation, if not call a site sponsor and use them.

[registered user]

the piston doesnt rotate. either u misunderstood what that builder said or  he doesnt know shit and needs to get out of the game for saying such a stupid thing

bigbore piston may give a small amount more power, probly because the piston now has more surface area for the combustion to act upon. but they likely weight more which puts addes strain on the rod and bearing and friction losses surely are higher

[ClaudeMachining]

Guys please, more cc is more better. That builder is dumb.

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[ZillaFreak]

13 hours ago, jack vo said:

ok long story short i was talking to the engine builder i was told that a bigger piston on a banshee will not give me more hp but a stroked banshee will,

his explanation was that a bigger piston will slow the engine down due to rotational mass 

so is this true

This builder is a joke.

Longer stroke usually decreases revs. There is a max speed pistons can moves, longer strokes means pistons has to move faster for same rpm.

Rotational mass isn't a bad thing and doesn't slow an engine down, just slow the acceleration down.

Reciprocating mass is bad. Piston weight is reciprocating mass.

[ClaudeMachining]

The interesting discussion to have is the ratio between bore and stroke. Short stroke, square stroke or long strokes vs application.

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[ZillaFreak]

10 hours ago, registered user said:

the piston doesnt rotate. either u misunderstood what that builder said or  he doesnt know shit and needs to get out of the game for saying such a stupid thing

bigbore piston may give a small amount more power, probly because the piston now has more surface area for the combustion to act upon. but they likely weight more which puts addes strain on the rod and bearing and friction losses surely are higher

Longer stroke adds more stress on everything at same RPM.

Friction isn't higher for bigger bore than longer stroke. 

 

If anyone has ever looked at some of the high power vehicles for racing, all have bigger bore than stroke. 

 

25 minutes ago, ClaudeMachining said:

The interesting discussion to have is the ratio between bore and stroke. Short stroke, square stroke or long strokes vs application.

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If really comes down to, space and application. One might do shorter stroke to save on height of engine, or longer stroke to save on width of engine.

For application, you will see F1 engines that rev very high and make power are oversquare. For trucks, you normally see undersquare.

[registered user]

4strokes r diferent. larger bore means larger valves. 2stroke has valves (ports) in the wall. sqaure is the best compromise for 2stroke. most banshee r over sqaure simply because its cheaper and less machine work to go up in piston size that to use huge stroke cranks

[ZillaFreak]

2 hours ago, registered user said:

4strokes r diferent. larger bore means larger valves. 2stroke has valves (ports) in the wall. sqaure is the best compromise for 2stroke. most banshee r over sqaure simply because its cheaper and less machine work to go up in piston size that to use huge stroke cranks

A larger bore can mean wider ports in the cylinder wall. 

How is square the best compromise? TRX250R, LT250R, CR250R and most bikes are all undersquare. Quadzilla is square. Banshee and CR500 are oversquare.  So which engine is the best, the quadzilla engine because it is square?

As for the banshee being oversquare because it is cheaper and less machine work to go up in pistons than stroke.... how does this equate for yamaha when designing? 

[ClaudeMachining]

472 better than 521??

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[ZillaFreak]

29 minutes ago, ClaudeMachining said:

472 better than 521??

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No one said that. Question is, is a 392cc banshee better in 68mm bore with stock stroke or stock bore with 7mil stroker? Or is a 472cc better with a 68x58, 66.5x68, or 65.5x70.

[sheerider11]

I remember back in the day this came up. I think I remember some one saying the square engines just wouldn't be as efficient as the others.
This was when people cared and had better conversations tho.

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[specialblend07]

It’d be awesome if someone with a clue chimed in




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