[Mike S]

I am going to build a pump gas engine. I have a set of ross flat top pistons sitting in the garage. I was wondering if it is feasible to dish these 15cc? Will there be enough material to dish them?
Or should I look at buying new?

[steve25]

What size will the bore be at?

[chiefbigb]

You need to measure the crown thickness. Might me better to cut the whole top across for maximum loss

[tom s]

Mike,check with Ross?Tom

[Skip Fix]

Often also on their spec sheet they send with the pistons it has thickness, But I agree with Tom. Usually they have a job number stamped on the bottom pin boss area they can look up the specs too.

[steve25]

With a 4.150” bore you would need to mill off the whole top of the piston by .066” according to my math to end up at 15 CCs gain in volume.

If your block has no intake valve notches then putting such in would buy you back 3 CCs and you could then reduce that .066” by .012” to end up at needing only .054” taken off the piston top.

I would think that such is livable and you will not melt out the top ring land if your not looking to make more then 600 Hp.

Burn wise and power wise I would much sooner mill the needed amount off the whole top of the piston then mill in a dish.
You would also be unshrouding the intake valve more above the .400” lift point.

[John Langer]

I wouldnt really like cutting the top of the piston off. What thickness head gasket do you have now? I would start with a thicker head gasket and look at opening up the combustion chamber on the head as well. You could always put a shorter rod in it or offset grind the crank to put the piston further in the hole. Many ways to skin that cat if you want to reuse the old pistons.

[b-man]

Selling your pistons and buying new ones built to the specs you need would likely end up being the cheapest and easiest route.

[Skip Fix]

I think when H-O cut a dish in TRWs the were .100 deep and 2.800 diameter.

[b-man]

Originally Posted by Skip Fix

I think when H-O cut a dish in TRWs the were .100 deep and 2.800 diameter.

The TRW flat top pistons had a top thickness of .375” and could be dished about .180” deep if you wanted.

Lightweight Ross flat tops I’m sure are a lot thinner where you’re going to cut a dish, of course as one would expect their dished forgings are designed for the dish.

[Stan Weiss]

Originally Posted by Skip Fix

I think when H-O cut a dish in TRWs the were .100 deep and 2.800 diameter.

What the dish volume would be depends on if there is a radius where the side meets the bottom.

2.8" diameter by .100" deep with .no radius 10.09 cc's

2.8" diameter by .100" deep with .100" radius 9.78 cc's

3.5" diameter by .100" deep with .100" radius 15.38 cc's

Stan

[tom s]

Here is a 22 cc dish in a 4.185 bore.Tom

[tc]

On a set of 428 pistons, I milled .156 deep in a D shape, to keep the quench area. Was about 15-18 cc's, don't remember exactly.

[b-man]

Ross 4.135" bore 26cc dished 421 piston, note that the valve reliefs for the early 20 degree 421 heads are almost gone.

They ended up measuring 27ccs.

[chiefbigb]

Send them back to Ross and let them do what's needed. They probably know something about Pistons.

[Dragncar]

Yes they do, when I was getting info on my pistons ring lands to see exactly what was involved to back cut some gas ported Total Seal rings they had the spec for every inch of that piston. I bought them in 2003 from Butler, they were not in their computer database, but in a room upstairs they still had the info in a file cabinet.
I got a education on pistons-rings from Ross and Total Seal with this experience.
Let the experts decide.

[Skip Fix]

but in a room upstairs they still had the info in a file cabinet.

Yep, a set I picked up used they had to do the same.

[tekuhn]

If the piston casting is XL408, this is what a 14cc dish looks like on one. The dish is .0875" deep.