Compression test? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

jthall · 09-30-2017, 07:15 PM

Anybody know what these 6.2’s should run for a compression test?

silversleeper · 09-30-2017, 08:36 PM

Not offhand, but usually you are looking for one or a couple cylinders being 15% or more lower than the highest. That will tell you what you are most likely to be looking for by doing a comp test.

Russell James · 10-02-2017, 03:02 PM

Throttle has to be wide open while cranking.

Min is 100. Lowest from the highest cyl is 70% but not below 100.

You want to watch 4 puffs, 4 compression strokes. If first few puffs are low and it is slow to build compression, add oil to cyl. If now it builds compression fast, rings/ring seal is weak.

That 30% is pretty generous. In reality a really good engine will be <10/15% ish.

The service manual gives that 100 min and 70% rule. But.... if one cyl had 150 and another 105.... technically it passes that rule... but that's a screwed up engine. More common readings on a good engine ...115, 118, 111, 112, 117, 107, 112... a pretty close grouping.

My more critical guide is about 10% ish. I have a BBC drag motor. It never varies more than 5 %. But that is a blueprinted motor with every part perfected. With mass production slop, there is going to be a bit more, more like 10% is very common to see. If I saw a cyl down 30% from the highest, it's got issues. And definitely if below 100.

You can tell a weak cylinder in watching all 4 + of those cranking puffs... if it struggles to get to 100... like 60, 70, 80, 85, 90, 95, 100.... it's weak. First good compression stroke should be nice and high like 105... then the next few just add a bit more. Like 4 puffs going from 100 to 115.... that's a good cylinder.

09-30-2017, 07:15 PM	#1
jthall Drives: 2010 camaro ss Join Date: Apr 2017 Location: Hanley, Sk Posts: 13	Compression test? Anybody know what these 6.2’s should run for a compression test?

09-30-2017, 08:36 PM	#2
silversleeper Big Crow Drives: '13 ZL1 Join Date: Mar 2017 Location: California Posts: 1,489	Not offhand, but usually you are looking for one or a couple cylinders being 15% or more lower than the highest. That will tell you what you are most likely to be looking for by doing a comp test.

10-02-2017, 03:02 PM	#3
Russell James Drives: '15 SS 1LE, '69 Z28 drag car Join Date: Dec 2009 Location: Mich Posts: 4,482	Throttle has to be wide open while cranking. Min is 100. Lowest from the highest cyl is 70% but not below 100. You want to watch 4 puffs, 4 compression strokes. If first few puffs are low and it is slow to build compression, add oil to cyl. If now it builds compression fast, rings/ring seal is weak. That 30% is pretty generous. In reality a really good engine will be <10/15% ish. The service manual gives that 100 min and 70% rule. But.... if one cyl had 150 and another 105.... technically it passes that rule... but that's a screwed up engine. More common readings on a good engine ...115, 118, 111, 112, 117, 107, 112... a pretty close grouping. My more critical guide is about 10% ish. I have a BBC drag motor. It never varies more than 5 %. But that is a blueprinted motor with every part perfected. With mass production slop, there is going to be a bit more, more like 10% is very common to see. If I saw a cyl down 30% from the highest, it's got issues. And definitely if below 100. You can tell a weak cylinder in watching all 4 + of those cranking puffs... if it struggles to get to 100... like 60, 70, 80, 85, 90, 95, 100.... it's weak. First good compression stroke should be nice and high like 105... then the next few just add a bit more. Like 4 puffs going from 100 to 115.... that's a good cylinder.