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Classic Mustangs Tech Forum

Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 12-10-2009   #1 (permalink)
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Default compression on a stock 302 1968 mustang?

anyone know what the stock cylinder compression be on a 68 mustang 302 engine... im assuming most 302s are the same as far as compression goes? does 95lbs sound about right for a rebuilt stock?
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Unread 12-10-2009   #2 (permalink)
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Hi! how did you check it, warm the engine and let it cool off 15- 20 mins, remove all the plug and disable your coil and take reading with throttle full open. you should be between 130-170 psi and within 15 psi on all cylinders.
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Unread 12-10-2009   #3 (permalink)
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*scratches head* Your title is misleading. I didn't know if you meant compression ratio of the entire engine or each cylinder.
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Unread 12-10-2009   #4 (permalink)
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The compression ratio of a '68 302 could be anywhere form 8.7 to 10.0:1 depending upon what version you have. But if you are doing the compression test correctly as described above, a reading in Sacramento of 95 psi for any of them means something is wrong and the engine needs work. If someone claims it has been re-built - don't walk, run.

As you go up in elevation the compression psi would be lower. But for 95 to be an OK number you would need to be sitting at an elevation of around 10,000 feet above sea level.
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Unread 12-10-2009   #5 (permalink)
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Quote:
Originally Posted by Ivy66GT View Post
The compression ratio of a '68 302 could be anywhere form 8.7 to 10.0:1 depending upon what version you have. But if you are doing the compression test correctly as described above, a reading in Sacramento of 95 psi for any of them means something is wrong and the engine needs work. If someone claims it has been re-built - don't walk, run.

As you go up in elevation the compression psi would be lower. But for 95 to be an OK number you would need to be sitting at an elevation of around 10,000 feet above sea level.
supposedly its a 68 mustang with stock 302 motor with new seals and gaskets
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Unread 12-11-2009   #6 (permalink)
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That might be accurate but it takes rings, pistons and valves to correctly rebuild an engine. If you only replace the seals and gaskets the engine will run just as poorly, it just won't leak oil.
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