Piston crown shape?

[Metals406]

I saw a piston online somewhere, while I was doing an image search, and it had a crown shape like the picture below. It wasn't a 2-stroke piston but...

What would be the benefit to this concave type piston?

 

[blsnelling]

What would be the benefit to this concave type piston?

None. That was likely in a low compression 4-stroke engine.

I like mine quite the opposite!. This one's in my 084.

 

[Metals406]

I agree, and understand the concept of the pop-up piston... Just wondering about this concave shaped one? They made'em... Must have had a reason?

 

[stihl only]

Well, if you have a very small combustion chamber, then you need a "dished" piston to keep the compression in line with pump fuel.

 

[blsnelling]

I think the Husky 261 is dished out and is often replaced with a 262 P&C. The only thing it can do is reduce compression. Not something we want. I would think it would hurt scavenging and flow as well.

 

[brages]

Swirl? Valve clearance? I think my diesel VW has dished pistons to help clear the valves (high compression ratio).

 

[neil_004]

If it was a pic of a car pistion it was probably for a turbo application. It allows you to lower the compression so you can crank the boost.

 

[timberwolf]

+1 allows room for valves in 4 strokes while still keeping the outside edge squish / quench height. Dished pistons don't go with typical 2 stroke valveless engines.

+1 for turbo too, allows the same block and head to be used with turbo set up by dropping the CR back half a point or so.

 

[Metals406]

Well there ya go... Thanks for the replies fellas!

 

[Javelin]

2150 jonsered is dished like that!

 

[ShoerFast]

Dished combustion areas promote consistent higher pressure fuel burns, more designed for higher firing pressures, (different from compression pressures) for more power.

Think of a very slow-motion progression of how the flame expands out from the spark?

Think of how a dished piston will concentrate that flame prorogation more evenly centered in the combustion area?

Now put that together with ideas like a Hemi shaped cylinder head and getting the maximum in, and the maximum out each cycle and how much more power you can get over conventional 'D' shaped heads with flat stagnant areas (called quench areas) of standardized heads and combustion areas designed to promote lower emissions.

 

[Cadenhill]

The Husky 261 piston is dished like the top photo to lower compression. Brad is correct. Flat or crowned the other way increases compression. I don't know if any other Husky uses a dished piston. The dealers would know this, both Stihl and Husky.

 

[Tzed250]

A dished piston is typical of a Heron-type head. 0deg. included valve angle with the combustion chamber in the piston.

 

[BuddhaKat]

Most stock diesel's have a dished piston. Lowering compression is usually the primary reason for doing it.

 

[Tzed250]

Most stock diesel's have a dished piston. Lowering compression is usually the primary reason for doing it.

Diesels have nutty high compression...

 

[yo2001]

Keeping the top ring away from the flame front keeps the ringland from breaking under severe pressure condition like diesel and forced induction.

 

[dt6266]

ive seen mostly diesel with this design and a few gasoline engines too. there are a few reasons for it in which they have been mentioned.

 

[Jacob J.]

In saws you'll see dished pistons in models bound for third-world markets where the gas is known to be real crappy or low-octane.

 

[woodchuck361]

I saw a piston online somewhere, while I was doing an image search, and it had a crown shape like the picture below. It wasn't a 2-stroke piston but...

What would be the benefit to this concave type piston?

Low compression for a turbo or supercharged motor most likely

 

[leeha]

Most stock diesel's have a dished piston. Lowering compression is usually the primary reason for doing it.

Almost all diesels have a dished piston because of the
flat head design without any combustion chamber. It's
there way to control compression ratio. Iv'e seen diesels
with ratios rangeing from 14-1 to 23-1

Lee