I would not order pistons until the machine shop measures your block. That's just common sense. You don't know what you have until they tell you. The pistons will opnly take a couple day to get to them.
If your not using a large amount of oil and the engine runs well, you should be able to stay with a standard bore with forged pistons. But wait till they measure.
I'm sure the machine shop will tell you the same.
My main point is don't spend money where it's not needed.
My DD wagon has the heads ported in the valve pocket and the dividers thinned, with minor clean up at the ports. The car feels great in mid range power, which is what I wanted for my back roads driving. 2nd and 3rd gear have nice pull.
Be careful about port matching, there is a thread over on NASIOC that talks about where you get the most out of these engines. When I talked to my machine shop, they already knew that info.
here's my thread.
I haven't raced mine in the 1/4 mile since the rebuild, But my son who raced our Civic and I feel its a high 12 second car. It has some of the feel of my old Duster 340 that ran 13.00 back in the day with bogging out of the hole.
Oh yea, do you have the service manual and know about the "opposed forces" link at the top of the very first forum here ? http://people.csail.mit.edu/ilh/vacation/
224,000miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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