4mm pistons create interference motor?

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friedman
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4mm pistons create interference motor?

Post by friedman » Sun Jan 13, 2019 8:47 am

I don't think this has ever been discussed here. One of my 1500 non-interference X motors has HC pistons and is now clearly an interference motor. Does putting the typical HC street pistons on a 2L motor (4mm domes) make that motor an interference motor? Just curious.
Carl in Virginia
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fp55scca
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Re: 4mm pistons create interference motor?

Post by fp55scca » Sun Jan 13, 2019 12:58 pm

friedman wrote:
Sun Jan 13, 2019 8:47 am
...........Does putting the typical HC street pistons on a 2L motor (4mm domes) make that motor an interference motor? Just curious.
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--Carl, I think you are asking a generic question, and I think our vendors could answer if their "specific pistons" would be interference in an otherwise "stock" motor. But, when adding HC pistons, most don't keep their motors stock.

--So, the general answer depends on the definition of "the typical HC street piston". Without a specific piston in mind, I don't think the 4mm dome, by itself, would create any interference. The answer depends on valve cutout size in a particular piston, valve size, and cam lift, and of course head gasket selection.

--As dome size alone increases, eventually we have interference issues on #1 and #4. Add to that making a piston proud out of the block can further contribute to the potential for interference.
Jim Scurria
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1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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friedman
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Re: 4mm pistons create interference motor?

Post by friedman » Sun Jan 13, 2019 1:15 pm

Thanks Jim, obviously no simple answer.
Carl in Virginia
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bartigue
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Re: 4mm pistons create interference motor?

Post by bartigue » Sun Jan 13, 2019 9:45 pm

They usually have cutouts in them, so technically no, if they have cutouts. But if you break loose at speed the likelihood of elasticity causing something to slap something else is pretty high.
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Brad Artigue
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