piston ID
- Thread starter 6tfo
- Start date
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I've heard there are different crowns or tops of a piston that impact performance. As you can probably tell I know little to nothing about it but trying to learn. So I'm wondering if these are stock pistons or performance pistons, if they are performance are they any good or are there better ones out there? I've found a couple of piston 101 sites but they didn't seem to get into the crown design. Any insight would be appreciated. Thanks.
Locomotion
Well-Known Member
I'm no "expert", but I never cared much for that type of piston top design. The only reason I can think of for the valve notches on both sides is if the pistons are manufactured with a slight OEM pin offset, which helps stabilize and prolong the life of the pistons and rings. An old trick was to put OEM pistons in 180* turned around if it didn't cause any piston-to-valve issues. That caused more "piston slap" and noise, but reduced overall friction somehow for more HP. The design in the photo seems to give you a choice, especially when using high lift cams. Kind of a multi-fit design. But the extra notches make less compression and may cause the piston to weigh more.
For wedge head applications, flat top pistons (with only the notches needed for valve clearance) tend to be the most efficient. Domed pistons may raise compression, but interfere with the flame travel. That's why closed chamber heads and flat top pistons give the best of both worlds - higher compression without a dome and more efficient chambers.
Those pistons may be a replacement for OEM, but I don't recall if they are forged or cast or the compression. But if they are around the top of the deck at TDC, you may have about 10-1 compression. Much below deck probably ends up around 8 or 9-1, or less! A lot depends on actual deck #'s, head gasket thickness and chamber volume.
OEM bore is 4.04"
103 mm = 4.05511"
But it depends if you measured above the ring wear area at the very top or within the ring wear area.
For wedge head applications, flat top pistons (with only the notches needed for valve clearance) tend to be the most efficient. Domed pistons may raise compression, but interfere with the flame travel. That's why closed chamber heads and flat top pistons give the best of both worlds - higher compression without a dome and more efficient chambers.
Those pistons may be a replacement for OEM, but I don't recall if they are forged or cast or the compression. But if they are around the top of the deck at TDC, you may have about 10-1 compression. Much below deck probably ends up around 8 or 9-1, or less! A lot depends on actual deck #'s, head gasket thickness and chamber volume.
OEM bore is 4.04"
103 mm = 4.05511"
But it depends if you measured above the ring wear area at the very top or within the ring wear area.
Locomotion
Well-Known Member
Glad to help.
The 180* thing is ONLY for OEM and possibly some cheaper replacement versions. Not sure how to tell but I'm sure there is a way to measure for it.
The 180* thing is ONLY for OEM and possibly some cheaper replacement versions. Not sure how to tell but I'm sure there is a way to measure for it.
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