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D- or round dish pistons for Iron CJ's (460)

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Post  Calypso September 26th 2020, 7:29 am

Planning to get custom pistons for 460 Iron CJ build. Have a choice between different dish shapes for adjusting the compression ratio. Which type of dish to get, having the choice?

Calypso

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Post  rmcomprandy September 26th 2020, 9:53 am

Calypso wrote:Planning to get custom pistons for 460 Iron CJ build. Have a choice between different dish shapes for adjusting the compression ratio. Which type of dish to get, having the choice?

"Reverse Dome"

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Post  Calypso September 26th 2020, 10:22 am

Thank you.

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Post  gt350hr September 29th 2020, 1:11 pm

It depends on how much volume you need. 20 or more might have to be round. The diameter of the round dish is the critical factor versus a "mirror image" dish.

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Post  gt350hr September 29th 2020, 1:13 pm

duplicate post

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Post  Calypso September 29th 2020, 3:02 pm

gt350hr wrote:   It depends on how much volume you need. 20 or more might have to be round. The diameter of the round dish is the critical factor versus a "mirror image" dish.

Good point. What I need for 10-10.5:1 is 10-15cc dish.

Out of curiosity, is it preferable to keep the round dish diameter in the small side to retain squish/quench, or will it work better with a narrow squish band?

Calypso

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Post  gt350hr September 29th 2020, 4:44 pm

The "minimum" I use is .375 wide. I found that out courtesy of my former Nascar customers. We did allot of testing when we were doing the spherical dish program back then. Less that .375 liked to detonate easier. The squish is certainly more critical on cast iron heads than aluminum and much less critical when "boosted".

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Post  Calypso September 30th 2020, 8:35 am

gt350hr wrote:   The "minimum" I use is .375 wide. I found that out courtesy of my former Nascar customers. We did allot of testing when we were doing the spherical dish program back then. Less that .375 liked to detonate easier.  The squish is certainly more critical on cast iron heads than aluminum and much less critical when "boosted".

Thank you. Are you (still) in the piston business?

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Post  gt350hr September 30th 2020, 1:34 pm

Yes but I don't go on forums to promote the fact. I am here to learn and help when I can. PM me if you like about my day job.

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Post  Mark O'Neal October 6th 2020, 3:51 am

Calypso wrote:
gt350hr wrote:   It depends on how much volume you need. 20 or more might have to be round. The diameter of the round dish is the critical factor versus a "mirror image" dish.

Good point. What I need for 10-10.5:1 is 10-15cc dish.

Out of curiosity, is it preferable to keep the round dish diameter in the small side to retain squish/quench, or will it work better with a narrow squish band?

At that volume, even weight isn't an issue. Reverse Dome.

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Post  gt350hr October 6th 2020, 12:11 pm

+1 dish volume is low enough that an inverted dome would be better with the quench pads.

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Post  Calypso October 7th 2020, 12:47 am

Curious about even weight. When does that become an issue and why?

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Post  Mark O'Neal October 8th 2020, 9:03 pm

Calypso wrote:Curious about even weight. When does that become an issue and why?

As more depth is required, the piston deck has to be increased to accommodate.

Two things happen. First, at some point the weight increases more than you might like, second, the space available for the rod is decreased.

Either way, those of use that "design" pistons can do anything we want....as long as Newton agrees.

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