360 fe compression question
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360 fe compression question
Compression ranges from a low of 140 to 170psi. I thought that those numbers are supposed to be within 10psi of each other. I guess I'm asking are those numbers acceptable or is something off.
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Well no, in some ways modern gasoline is better at least in terms of carbon and sludge buildup than the days of yore. Spark plugs should burn very clean, with hardly any "color" even in older engines. If they are running rich i.e. carboned up, the carburetor isn't dialed in. If extreme carbon is built up in the combustion chamber that might contribute to a skewed compression reading. How do the plugs look?
A high compression ratio means high octane fuel is necessary. A stock healthy factory-ish engine would only run around 150 psi on the compression and should run OK on pump gas.
A high compression ratio means high octane fuel is necessary. A stock healthy factory-ish engine would only run around 150 psi on the compression and should run OK on pump gas.
Lead Driver
Joined: Oct 2018
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Unless you changed the pistons it would take a pint of carbon per cylinder to make a 360 high compression.
Did you hold the throttle wide open while you did the test ? that should only make the compression higher but if you didn't it might explain the erratic readings.
I question your findings, but while the numbers are uneven they're all high so there's nothing you need to do .
Did you hold the throttle wide open while you did the test ? that should only make the compression higher but if you didn't it might explain the erratic readings.
I question your findings, but while the numbers are uneven they're all high so there's nothing you need to do .
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Post Fiend
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Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
For general engine diagnostics and getttng a good sharp tune, I like the vacuum gauge. It is more useful I think, a compression test is at best kind of a pain in the you know what, and a vacuum gauge is just a whole lot quicker and will more or less indicate cylinder compression as well.
Notice every Tune-Up manual ever published since about 1915 has "vacuum test" as #2, right after the compression test. The idea generally is to check cylinder compression first, and see if the engine is lunched and worth mucking around with, if it fails badly that usually, not always, means further Tune-Up, buying parts, is pointless because it will never run very good. Most engines will run very well if tuned up correctly so long as there are no major internal engine derangements. The one caveat to keep in mind is engines that have been sitting a long long time. Gum and varnish will tend to stick rings and show almost no compression. A solvent can really help with this.
Notice every Tune-Up manual ever published since about 1915 has "vacuum test" as #2, right after the compression test. The idea generally is to check cylinder compression first, and see if the engine is lunched and worth mucking around with, if it fails badly that usually, not always, means further Tune-Up, buying parts, is pointless because it will never run very good. Most engines will run very well if tuned up correctly so long as there are no major internal engine derangements. The one caveat to keep in mind is engines that have been sitting a long long time. Gum and varnish will tend to stick rings and show almost no compression. A solvent can really help with this.
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