compression testers

Up until a year or two ago, I was happily ignorant believing that a compression tester was a compression tester.
Then it was pointed out to me that at least some compression testers are offered in both a <5" bore and >5" bore version.
The Continental 470 has a 5" bore, which one should be used?
If I get the chance, I' gonna try to do a compression check with each & see if they read differently.

I’m certainly no expert but here’s my experience. My hangar buddy has the small bore tester and I have the large bore version. I bought the large bore because my engine has >5” bore. We’ve used both testers on both airplanes and my big bore tester yields higher compression numbers than his on both engines. Typically 6 to 8 pounds different. That’s all I know.

I would read this thread. https://www.supercub.org/forum/showthread.php?53144-IO-520-Compressions/page2

Previous versions of AC43.13-1 called for a different orifice size for engines below 1000 cu in, and engines a over 1000 cu in. The current version change from cubic inches to bore diameter.


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dgapilot said:

Previous versions of AC43.13-1 called for a different orifice size for engines below 1000 cu in, and engines a over 1000 cu in. The current version change from cubic inches to bore diameter.


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Click to expand...

Yea, that is quoted in the thread I linked along with back to back compression test on same engine with different gauge sets of differing orifice size.

Steve Pierce said:

I would read this thread. https://www.supercub.org/forum/showthread.php?53144-IO-520-Compressions/page2

Click to expand...

Looks like you already tested the two different sized testers back-to-back, thanks Steve.