Piston dish shape?

[Geo.]

I went to pick up my parts from the machine shop and was disappointed to discover that they had not machined the pistons yet. The shop does not have a cnc mill and wants to know if they can chuck them up in the lathe and turn a circular dish as it would be much faster than milling the stock shape manually. My first reaction was no way but I am sure I have seen stock chevy small block pistons dished like that.

Does the shape matter that much? I am worried about reducing the quench area. If it's acceptable would a smaller in dia. but deeper dish be preferred to a wider but shallower shape?

Thoughts?

[Flash]

In either case, the thickness of the piston bowl will be you stooping point.


Flash

[dwg86]

It would be better to keep the original shape. It will produce a better quench. The flat spot on the piston matches up with the flat spot on the head.

[SilverXJ]

I asked a similar question here: viewtopic.php?f=5&t=273 I.e. full circular dish vs stock D dish

Only Flash responded though.

[oletshot]

The way quench works is with air movement. With the pistons flat surface coming within .050" or so of the heads flat surface, the air is forced out of that area creating the cooling effect. IIRC, the pistons in the picture posted by silverxj were going to be used with forced induction and they may have had no choice but to remove the quench area of the piston to get compression ratio down enough, but I could be wrong.

[Geo.]

Yeah, I thought so. So by milling the flat area on the piston I am reducing the amount of area available to "squish" the charge into the combustion chamber.

I am going to have to find a machine shop with a cnc mill. Sigh....... living on the edge of civilization sucks at times.

[SilverXJ]

Do a search on here as I believe someone on here does them.

[oletshot]

I've dished stock pistons for myself and 2229 silvolites for yuppiexj on this forum. I'm always looking for side work. I leave on vacation tomorrow so if you try to contact me I wont be back until next weekend.
Here are some pictures of my stock pistons that I dished to 23cc's from another thread.
viewtopic.php?f=15&t=108&p=844#p844

[yuppiexj]

I've dished stock pistons for myself and 2229 silvolites for yuppiexj on this forum.

here's a beauty shot.


http://i320.photobucket.com/albums/nn35 ... piston.jpg

[oldseddie]

My Nascar engine building buddy says that the optimum shape of a dish is a mirror of the combustion chamber. This optimizes the available quench area. It probably won't work on a Jeep stroker piston as this would not allow as large of dish area as we need to reduce the compression to 9:1 which he says is max for cast iron heads on pump gas.