[Jack Ferris]

Has anyone ever had a dish area machined into their flat top pistons? Is this even a possibility? I have several sets of Ross flat pistons and I need a set of dish to lower compression.

[Tom Vaught]

Naturally aspirated engine? Have known several to machine old TRW pistons with a dish.

Tom V.

[Jack Ferris]

Yes Tom. Mild street motor.

[Kevspontiacs@aol.com]

Just had this done a few weeks ago on some sealed power flat tops. NA low power 400-425 hp deal. One shop told me my best bet was to send them back to the manufacturer. Next shop i called said 'absolutely, i just need to find my jig for the lathe'.

I needed a 10cc dish so he used the weight of 1cc to come up with the amount to remove

[Tom Vaught]

Good method as a cross reference. 535 tall deck.

Do you know the thickness of the Ross piston crown? Jack?

If the thickness was similar to the TRW, should not be a issue to machine on a lathe.

Tom V.

[taff2]

I machined a .100" deep dish in a set of 400 TRW's many years back without any problems.

[Lee]

I had this done a few times as well. You just have to pay attention to the minimum thickness, and how close to the edge you can go. The piston manufacturer can probably give guidance on those values, based upon your application.

[PontiacMatt72]

Jack, I'd get in contact with the Butler crew. They sell a lot of Ross Pistons, and would likely be able to answer this question.

[Jack Ferris]

''Do you know the thickness of the Ross piston crown? Jack? ''

I will measure. I doubt the depth would have to be deeper than the valve relief. But, it would cover more area.
I will call Butler's outfit and see what they say.

[PontiacMatt72]

I suspect a 10cc dish would be doable...

Here's a shot of my 4.350" Ross Forged Flat Tops purchased through Butlers shop. No measurements available, as my shortblock is already assembled.

[Tom Vaught]

Just my first impression of your pistoms PM72 is that they have very visible valve relief bosses on the underside of the piston and the crown may not be that thick actually.
As is is for a street deal you may not need quite as much safety factor for the flat portion of the piston. Butlers pistons are custom made for them so David should have the actual engineering dimensions and what is safe.

Tom V.

[Jack Ferris]

These are the Ross pistons I got from you. Worst part of it all is having to remove the dam spiro-locks to take the rods off. 10cc on top of what ever the reliefs are should get me in the 10.4:1 range with my 48 heads. That's where I am now with the 400.

[Lee]

Additional FYI

I was a bit concerned about how thin the pistons in my old '67 Firebird were going to be, after dishing them. For a little added insurance, I applied a thermal barrier coating to the top after the dishing was completed.

[steve25]

The dish is also the best way to go for combustion efficiency, to the point in fact that some closed mouth builders are finding that it allows for a shallower chamber which in turn allows for the valves being more unshrouded and better flow even when your shotting for high compression.
This of course requires a blank head casting.

[Tom Vaught]

Originally Posted by steve25

The dish is also the best way to go for combustion efficiency, to the point in fact that some closed mouth builders are finding that it allows for a shallower chamber which in turn allows for the valves being more unshrouded and better flow even when your shotting for high compression.
This of course requires a blank head casting.

Agree, 72 cc head with a dish, for the same compression ratio, gives a less valve shrouding, vs the 87 cc head, helps with some Tumble and Swirl, and lightens the piston somewhat compared to the same exact piston without a machined dish.

Tom V.

[bignate]

Originally Posted by steve25

The dish is also the best way to go for combustion efficiency, to the point in fact that some closed mouth builders are finding that it allows for a shallower chamber which in turn allows for the valves being more unshrouded and better flow even when your shotting for high compression.
This of course requires a blank head casting.

What about a 56cc chamber with a 25cc soup bowl dish? Lol. That's what I had to do in my little RAIV 406 for 10.25:1.

Nate

[steve25]

Besides your needed compression I bet due to your 56 CC chamber you needed the dish for piston to valve clearance also!

As I recall milling a 72 CC RA4 head even .038" t about fully removes the lip on the shallow side of the chamber , no?

[bignate]

Originally Posted by steve25

Besides your needed compression I bet due to your 56 CC chamber you needed the dish for piston to valve clearance also!

As I recall milling a 72 CC RA4 head even .038" t about fully removes the lip on the shallow side of the chamber , no?

Yes the lip is gone and the intake valve head actually stands proud of the deck surface slightly.

Nate