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| | | | Joined: Jun 2006 Posts: 34 Apprentice | | Apprentice Joined: Jun 2006 Posts: 34 | Did a compression test today and the numbers seem a little low to me. But I'm not to familiar with the Chevy straight six engines.
From front to back they were 115, 115, 110, 112, 115, 117.
What do you all think?
1955 Chevy Dumptruck
2003 Chevy 2500HD: Crewcab, Longbed, 2wd, 6-speed manual
2005 Pontiac GTO: 500hp and a transbraked TH400
| | | | | Joined: Jul 2004 Posts: 5,708 'Bolter | | 'Bolter Joined: Jul 2004 Posts: 5,708 | jon6.0,
The book shows 130 lbs for most of the 250 engines. I know you already know this, but low figures are to be somewhat expected with age. More important than factory pressures is consistency between cylinders. Your figures are all pretty close which means there doesn't appear to be a problem with any single cylinder.
Depending on how you did your test, the values can vary. If you pulled all the plugs and blocked the throttle plate open, while cranking three or four times, you might get slightly higher readings...is this how you did it?
Stuart | | | | | Joined: Jun 2006 Posts: 34 Apprentice | | Apprentice Joined: Jun 2006 Posts: 34 | I pulled the plugs and just cranked it with the throttle closed.
1955 Chevy Dumptruck
2003 Chevy 2500HD: Crewcab, Longbed, 2wd, 6-speed manual
2005 Pontiac GTO: 500hp and a transbraked TH400
| | | | | Joined: Feb 2004 Posts: 29,792 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,792 | It's possible to get widely different compression pressures just by switching gauges. The percentage difference between cylinders is the important thing to watch, with 10% being a maximum allowable difference in most cases.
Also, doing a "wet" compression check by squirting a little oil into the cylinder before cranking will often raise the pressures noticeably. If that's the case, leakage past the piston rings is probably the source of a low reading.
Use a well-charged battery, remove all the plugs, disable the ignition, and block the throttle open. Let each cylinder "hit" about four times, and record each reading, then compare the pressures.
Jerry
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| | | | | Joined: Jun 2006 Posts: 34 Apprentice | | Apprentice Joined: Jun 2006 Posts: 34 | Hmmm. Maybe I'll do it again then. You gotta love how easy it is to work on the straight six engines. I'm probably going to keep it or go 292 just for that fact alone. Heck, maybe I'll even put a turbo on it.
1955 Chevy Dumptruck
2003 Chevy 2500HD: Crewcab, Longbed, 2wd, 6-speed manual
2005 Pontiac GTO: 500hp and a transbraked TH400
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