Stepped Dished Pistons?

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Stepped Dished Pistons?

Post  XF-66 on November 25th 2012, 1:09 am

I understand that rational for piston quench with dome or flat top pistons.

What is the reason for a 39CC dished piston to have a raised step incorporated into the Dish piston design?
Combustion chamber turbulence?

I have a set of Icon IC852's for a SCJA heads with this design.

I fully understand the piston quench concept, but how does the step/dish design effect my quench numbers? Do I measure from the step, or the ring area around the dish portion of the piston? Does the step create enough turbulence along with the SCJA's efficient combustion chamber design to negate normal quench concerns?

The step seems small compared to total piston surface area? 25%-30% of surface area.

This is all new to me.

Thanks Art

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Re: Stepped Dished Pistons?

Post  LivermoreDave on November 25th 2012, 11:13 am

This may offer a bit of insight, rather lengthy but interesting.
Dave.

http://racingarticles.com/article_racing-10.html

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Re: Stepped Dished Pistons?

Post  4604X4 on November 25th 2012, 12:27 pm

Good article. Thanks for the link.
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Re: Stepped Dished Pistons?

Post  dfree383 on November 26th 2012, 1:12 am

4604X4 wrote:Good article. Thanks for the link.

Watch the clearances they are suggesting, they are typicaly only for about 4" bores, with a BBF bore you'll want to add about .007 to .010 to those clearance numbers for piston rock and clearance due to the bigger bore.
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Re: Stepped Dished Pistons?

Post  XF-66 on November 26th 2012, 3:44 am

Ok, after doing a lot of reading this weekend the reason for the step is to force the flame front across the dish to promote a better/faster burn in the combustion chamber/piston dish eliminating the chance of detonation.

So with a flat top piston I need min of .041 worth of quench. Dfree says to add .007-.010 more for piston rock with a flat top piston. .048 cool

I'm thinking with the Icon's step piston's large 39 cc dish area ability to act as a quench factor and the SCJ combustion chamber's design that I can close up the gap between the step portion of the piston to the head (less the .041 say around .035) to gain a slight bump in compression.

I have a 4.3 X 4.440 533 pump gas build and would like to not leave any HP/compression for my given build on the table on the table.

Can I close up the step portion of the head to piston clearance utilizing the design of the step dish piston to still work for me on a NA engine?

I'm new to the BBF. Last V-8 I built was 30+ years ago, it was a Ford though. Very Happy


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Re: Stepped Dished Pistons?

Post  dfree383 on November 26th 2012, 10:40 am

0.043 ish..... Add .007-.010 to the .035 suggested in the artical posted.
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