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Author Topic:   ? for Steve or anyone
posted January 31, 2004 07:45 PM
i have an engine with flat top 4 valve relief pistons in it with a straight edge and at top dead center i can get10 thous feeler gaugejust under the straight edge all this motor needs is re ringed or i have another motor with forged flat top 2 valve relief and it would be decked to 3 thous now my question is will i gain that much building the new motor or just rering the 1st one

posted February 01, 2004 08:30 AM
every little bit helps. i've ran them as much as .010" OUT of the hole. be sure to check piston-to-valve clearance.

another thing that a lot of engine builder overlook is this...

if you've clipped the pistons to get zero deck height and you have big valves, be sure to check piston-to-valve clearance where the valve fits into the notch in the pistons. sometimes the egde of the valve will be too close to the side of the recess in the piston. i believe the only way to check this "side clearance" is with clay or maybe a borescope. i've run into this problem before and had to re-cut the notch in the piston to a bigger diameter for extra side clearance. if you don't have enough side clearance and the guides get sloppy, you could run into problems.

posted February 01, 2004 03:54 PM
thanks for answering, i guess what i am really after is it worth redoing what i have with just the price of the ring job, or going 2000 to rebuild the, or if i might find some horsepower some other way...keep the answers coming, thanks

posted February 01, 2004 05:54 PM
Assuming the same bore size The different pistons will make more difference than the deck heights. .007 difference in deck height on a 4.030 bore is only like 1cc maybe just a hair more. But thats it. If all you need is rings then thats prob the way i'd go. Although technically it would be a little less HP it woudl be minimal and prob not worth $2000 to pick up 5-10HP. You could always go to a thinner head gasket if you wanted to bump the compression up while you were putting it back together, just make sure you have enough valve to piston, and piston to head clearance.

posted February 01, 2004 10:44 PM
I would go with the 2 valve relief piston combo. Your average 4 valve relief piston adds about 6-8 cc's with the extra valve reliefs. The piston being .010" in the hole is not helping much either. The whole key to flat top motors is to squeeze every bit of compression ratio into it that you can. I'm not trying to make you spend extra money or anything, but the gain would be noticeable.

If your allowed to, I would run the piston .006" out of the hole, use your 2 valve relief pistons, a Ferrea head gasket (.035" thick x 4.060" fire ring), and get your heads cut down if they are not already.


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