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Join Date: Jun 2009
Posts: 1,241
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piston to head clearance
What is a proven performance but safe piston to head clearance dimension For a track motor. 7200-7500 RPM. have used .040'' as the standard, but am lately rethinking about a lot of what I thought was ''standard''. I have a motor on the stand that is measuring .039''-.046''. Can I run that safely, Thanks, Bob
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09-24-2020, 12:32 PM
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Join Date: Jun 2009
Posts: 1,241
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I should have added this. In pulling my motors down, I am not seeing bare spots on either the heads or pistons. I recall seeing years ago, I ran an EP roadster in SCCA, shiny spots on the pistons and heads which indicated to me they were next to touching. Casting about for causes for the bottom end issues I am having. Bob
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09-24-2020, 12:42 PM
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What bottom end issues are you having?
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Tony |
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09-24-2020, 01:13 PM
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Join Date: Jun 2009
Posts: 1,241
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Rod bearings. Am changing from -12 to -16 oil lines and moving the oil tank from in front of the rear wheel to behind it. Have no idea whether this change is needed, but have got to try something different.
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09-24-2020, 02:48 PM
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Registered
Join Date: Jul 2005
Location: Cleveland, OH
Posts: 1,367
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Are you logging oil pressure on a data logger?
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09-25-2020, 07:12 AM
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It's a 914 ...
Join Date: Jan 2008
Location: Ossining, NY
Posts: 4,706
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I've understood that .040" is a good number to shoot for. It's what I plan to use on the motor I'll be putting together.
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09-26-2020, 03:45 PM
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Join Date: Jun 2009
Posts: 1,241
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Have no data acquisition system. I do have a Gopro which can monitor the instruments and I plan on seeing what I can glean from that. I Don't think the stock oil pressure system responds quickly enough to give me good data. So am considering a quality oil pressure gauge. Any suggestions?
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09-27-2020, 10:57 AM
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Puny Bird
Join Date: Nov 2002
Location: Port Hope (near Toronto) On, Canada
Posts: 4,566
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No less than .040 but you can trim the piston top edge if you need higher CR. Of course proper clearance checks, CR, etc.
I've done this on a few builds using this trick with no problems.
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'74 Porsche 914, 3.0/6 '72 Porsche 914, 1.7, wife's summer DD '67 Bug, 2600cc T4,'67 Bus, 2.0 T1 Not putting miles on your car is like not having sex with your girlfriend, so she'll be more desirable to her next boyfriend. |
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09-27-2020, 11:20 AM
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