SS piston dish

[Mike Graham]

Here is my sad story and question. I ordered a duplicate set of pistons for my SS motor from Brand x. They missed the dish cc by one full cc. After months of discussions they agreed to fix them. Instead of milling the dish deeper they plunge cut a semi-circle that intersects with the dish. This changes the shape of the dish dramatically.
Does anyone have any direct knowledge of how closely NHRA tech stays to the rule that the dish must remain the original shape? Especially at Indy.
Thanks

[SSDiv6]

Originally Posted by Mike Graham

Here is my sad story and question. I ordered a duplicate set of pistons for my SS motor from Brand x. They missed the dish cc by one full cc. After months of discussions they agreed to fix them. Instead of milling the dish deeper they plunge cut a semi-circle that intersects with the dish. This changes the shape of the dish dramatically.
Does anyone have any direct knowledge of how closely NHRA tech stays to the rule that the dish must remain the original shape? Especially at Indy.
Thanks

Could you post a picture and more detailed information about the application?

[Mike Graham]

The application is a low compression 460 Ford with a 15 cc dish. The dish is like a sideways D. The dish was too shallow by about .005. The "fix" was to plunge cut what I can only describe as a secondary valve relief near the intake relief. The cut is perpendicular to the piston top and half into the quench area. As you know this is a canted valve motor so this cut looks mighty strange. Now the flat side of the D has a bubble in it. Mechanically I don't see any problem, but visually it is obviously different.
The dish is correct depth and correct cc.
Don't have access to camera at this time.

[SSDiv6]

Originally Posted by Mike Graham

The application is a low compression 460 Ford with a 15 cc dish. The dish is like a sideways D. The dish was too shallow by about .005. The "fix" was to plunge cut what I can only describe as a secondary valve relief near the intake relief. The cut is perpendicular to the piston top and half into the quench area. As you know this is a canted valve motor so this cut looks mighty strange. Now the flat side of the D has a bubble in it. Mechanically I don't see any problem, but visually it is obviously different.
The dish is correct depth and correct cc.
Don't have access to camera at this time.

Is the plunge cut part of the valve relief? If it is, It could be considered as part of the valve relief.

[tj310]

I have a similar question about this although the motor I'm working on is Chev. The rulebook refers to design pattern , surely the valve notches could be figured into the dish CC s ? ---Trevor

[Sean Cour]

A dish could be 40 holes drilled in the piston. Unlike stock, the piston just need to be measured legally for some kind of dish.

[Bob]

Originally Posted by Sean Cour

A dish could be 40 holes drilled in the piston. Unlike stock, the piston just need to be measured legally for some kind of dish.

Unless something has changed in the 2015 rulebook, 40 holes weren't and wouldn't be legal. The rule has always been (straight from the rulebook):
"Replacement pistons permitted, provided they do not increase
stock compression ratio and retain overall design pattern as
specified by automobile manufacturer. Dish pistons must retain
half of original depth, and original diameter and configuration."

That is to say, yes you need to keep the original dish design. And you need to keep at least half the original depth. The remaining CC lost by a shallower dish can be acquired by valve reliefs.