120 good compression? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Asahi123 · 01-09-2012, 05:17 PM

I have 71 Chevy 350/350. I did a compression test I got 120 on all the clynder. So is that good or bad? Mileage is 147,000.
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storm9c1 · 01-09-2012, 05:39 PM

Quote:

Originally Posted by Asahi123

I have 71 Chevy 350/350. I did a compression test I got 120 on all the clynder. So is that good or bad? Mileage is 147,000.
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It depends. Shooting from the hip, I'd say it's low but reasonable for those miles. However, did you have the throttle plates propped open when you did this? If not, it may read low or uneven depending on your technique. And what is the goal here? To diagnose a problem (ie: cylinder not firing, excessive blow-by, leakdown) or what? Usually it is more important to note that the compression doesn't vary more than 10% amongst cylinders, and in that case the details don't matter as much. But if you are trying to figure out something more complicated, then the details of how you did the test do matter.

a2tripp · 01-09-2012, 10:11 PM

I just did one on a mopar motor last week, came up 130 psi through all cyl, ended up being the guage. like said above, more than 10% is what your looking for.

edhtrd71 · 01-09-2012, 10:15 PM

I wouldnt be worried about it with an old motor sounds like its in descent shape, and definetely a good thing that there all even.

Asahi123 · 01-09-2012, 11:15 PM

Nothing wrong with engine other than oil leaks. Which I plan replacing the gaskets this spring.
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edhtrd71 · 01-09-2012, 11:23 PM

By the way asahi how did you get the name? Is it the beer? They make fantastic stuff.

Asahi123 · 01-10-2012, 02:20 AM

It was the name of our beloved Akita. Asahi means morning sun in Japanese. Akita's are excellent protectors and great family dogs. Our Asahi is greatly missed.
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storm9c1 · 01-10-2012, 10:40 AM

Akitas are indeed great dogs. My Lab is 12 and I dread the day..........well you know.

Anyways, you never answered if you did the compression test with the throttle blocked open or not? (ignition disabled)

Asahi123 · 01-10-2012, 01:29 PM

Sorry throttle was closed
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**truckdude239** · 01-10-2012, 04:24 PM

do it with the throttle open and it should be higher

davepl · 01-10-2012, 08:25 PM

Quote:

Originally Posted by truckdude239

do it with the throttle open and it should be higher

Indeed, just went through this on another thread, and my 130s came up to 170s. There was a bunch of wailing and gnashing of teeth about whether or not you can still use it to compare cylinder-to-cylinder, but for overall wear you need the throttle blocked open.

Someone (HEI?) had a good idea about disabling the ignition, which is a good idea anyway, but more so that you don't forget, put it all back together, and then fire it with the throttle blocked open to WOT.

I'm sure we've all been down the "There's no way I'd forget X" highway.

edhtrd71 · 01-10-2012, 11:02 PM

Sorry about your loss. Im sure we all wish they could live much longer. I have two 13 year old goldens. Akitas are awesome dogs.

01-09-2012, 05:17 PM	#1
Asahi123 Registered User Join Date: Jul 2011 Location: Texas Posts: 42	120 good compression? I have 71 Chevy 350/350. I did a compression test I got 120 on all the clynder. So is that good or bad? Mileage is 147,000. Posted via Mobile Device

01-09-2012, 10:11 PM	#3
a2tripp Registered User Join Date: Aug 2011 Location: Southeast Alaska Posts: 122	Re: 120 good compression? I just did one on a mopar motor last week, came up 130 psi through all cyl, ended up being the guage. like said above, more than 10% is what your looking for. __________________ 89 GMC V3500 Alaska members check in

01-09-2012, 10:15 PM	#4
edhtrd71 Registered User Join Date: Jan 2011 Location: Edinburg, Texas. Posts: 194	Re: 120 good compression? I wouldnt be worried about it with an old motor sounds like its in descent shape, and definetely a good thing that there all even.

01-09-2012, 11:15 PM	#5
Asahi123 Registered User Join Date: Jul 2011 Location: Texas Posts: 42	Re: 120 good compression? Nothing wrong with engine other than oil leaks. Which I plan replacing the gaskets this spring. Posted via Mobile Device

01-09-2012, 11:23 PM	#6
edhtrd71 Registered User Join Date: Jan 2011 Location: Edinburg, Texas. Posts: 194	Re: 120 good compression? By the way asahi how did you get the name? Is it the beer? They make fantastic stuff.

01-10-2012, 02:20 AM	#7
Asahi123 Registered User Join Date: Jul 2011 Location: Texas Posts: 42	Re: 120 good compression? It was the name of our beloved Akita. Asahi means morning sun in Japanese. Akita's are excellent protectors and great family dogs. Our Asahi is greatly missed. Posted via Mobile Device

01-10-2012, 10:40 AM	#8
storm9c1 * That's interesting * Join Date: Oct 2008 Location: Pittsburgh, PA Posts: 2,772	Re: 120 good compression? Akitas are indeed great dogs. My Lab is 12 and I dread the day..........well you know. Anyways, you never answered if you did the compression test with the throttle blocked open or not? (ignition disabled) __________________ Tom Chevy by day... 1969 Chevy C30 Rollback Tow Truck -- 383 stroker, 4L80E 2011 Chevy Caprice PPV 9C3 6.0L 1995 Chevy Caprice 9C1 1994 Chevy Caprice 9C1 #3 1995 Chevy Caprice Wagon #2 1995 Chevy Impala SS Mopar by night... 1969 Dodge Charger 1972 Chrysler Newport 2dr Hardtop (27K miles) Plus others...

01-10-2012, 01:29 PM	#9
Asahi123 Registered User Join Date: Jul 2011 Location: Texas Posts: 42	Re: 120 good compression? Sorry throttle was closed Posted via Mobile Device

01-10-2012, 04:24 PM	#10
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,217	Re: 120 good compression? do it with the throttle open and it should be higher __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

01-10-2012, 11:02 PM	#12
edhtrd71 Registered User Join Date: Jan 2011 Location: Edinburg, Texas. Posts: 194	Re: 120 good compression? Sorry about your loss. Im sure we all wish they could live much longer. I have two 13 year old goldens. Akitas are awesome dogs.



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