does going to dished pistons change the AF ratio?

 

On an injected engine, the A/F ratio is set by the PCM. It has no way of knowing the type of pistons you have in the engine. It's conceivable that the degree of the dish could alter the combustion chamber "swirl" and stratify the A/F charge, but it isn't going to change the overall composition of the combustion chamber contents.

Or did I miss the point of your question?

 

Well, actually I suppose it might change the AF ratio a tiny bit, but not enough to matter.

Rich

 

im not sure if i can explain what im thinking but ill try....

with the dished piston displacing less airspace, would the amount of fuel being injected need to increase to compensate for the extra air? thus making the true AF ratio leaner? or is it not a drastic enough change to matter?

 

How can a dished piston displace less airspace?
A 'domed' piston crown can/will displace less airspace.

...would the amount of fuel being injected need to increase to compensate for the extra air? thus making the true AF ratio leaner?

Yes, and it will. One needs to understand/acknowledge that fuel is metered based on the amount of air entering the cylinder. More air equates to more fuel dispersed. This applies to a cylinder 2" in dia., as well as a cyllinder 5" in dia.

 

[QUOTE=arnie]How can a dished piston displace less airspace?
A 'domed' piston crown can/will displace less airspace.

the domed piston takes up more space in the cylinder.......displacing more of the air. the dished piston will take up less space in the cylinder....displacing less air. right?

 

[QUOTE=ss#1230]I'm confident you know what you mean, but the way you worded it, I must interpret it accordingly. Quoting you, yes, the domed piston takes up MORE space in the cylinder......displacing more of the air. THEREFORE, a domed piston displaces MORE air space, causing the space in the cylinder to be of a lesser volume. Quoting you, yes, dished piston....displaces less air. THEREFORE, dished piston will cause the space in the cylinder to be of a larger volume.

 

Dome piston lessens overall combustion volume, dish increases it. We're talking compression here.

The volume of air being drawn into the cylinder is a function of intake valve duration, lift and piston speed (the static stuff). It won't care what the piston looks like.

-Mindgame