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Old 01-05-2006, 04:36 AM
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Piston ring end gap

I'm assembling a sbc 350 with the stock 4" bore to use on the street. I'm using total seal's maxseal gapless rings on the original GMPP hypereutectic pistons. The motor was low mileage when torn down for another issue.
The paperwork that came with the rings recommends a file to fit end gap of .065" per inch of bore (.026" in this case), then says to check the piston manufacturers recommendation if the pistons are hypereutectic. That's not going to work since they're GM pistons so I put the original rings back in the block to check their gap. In each case I found the gap to be < .020". This caused me to wonder why total seal would recommend .026". During a web search I learned that Keith Black recommends using .065" per inch for their hyper pistons. Yesterday I called total seal to get their input. With my 4" bore using hyper pistons they recommend filing to a .032" gap.
I'm wondering why the wide variance between what was in it, KB, and Total Seal's recommendation. I'm inclined to think that Total Seal knows their product, so I should go with .032".
I'm not quite confused enough. I know the downside of not enough end gap, what happens if I have too much?
Anyone have any sage advise or direct experience?

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Old 01-05-2006, 06:28 AM
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Since you are not using KB pistons which does need the top ring gap set up wider than others due to the piston top reflecting more heat into the chamber which tends to heat up the top ring more. With the original GMPP pistons, I would go with the the .032 which is what TS recommended.

I had Total Seal TS1 rings on KB's in a 400 and the top ring gap was set by my engine builder at .026 per his build sheet. The motor didn't last 1500 miles due to 3 breaking pistons. I went then with Speed Pro rings set at .038 which is .001 bigger ring gap then what KB recommended since I do mudbog and turn the motor regularly at 6200-6700 rpm. I lost right at 1.5 inch vacuum at idle but have had no problems. With the bigger top ring gap, I have seen no oil usage and the oil at 2500 miles on this oil change looks just as clean as it was out of the bottle. It is also driven on the street.
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Old 01-06-2006, 02:33 PM
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Thanks for taking the time post Tornado. I feel a little better going with the .032" gap after reading your note.
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