Compression Test - Alfa Romeo Bulletin Board & Forums
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post #1 of 8 (permalink) Old 04-21-2019, 07:30 PM Thread Starter
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Question Compression Test

Dear all

Today I did a compression test (with and without spark plugs) on my Alfa Romeo GTV 1974 with has 71.500 miles and is 100% original (Spica fuel injection):

TEST A:

Cold car, not running for 15 days
Without any spark plugs
Throttle wide open

Results:

Cylinder 1: 9,7 BAR - 140.6 PSI
Cylinder 2: 9,8 BAR - 142.2 PSI
Cylinder 3: 9,6 BAR - 139.2 PSI
Cylinder 4: 9,3 BAR - 134.9 PSI

TEST B:

Cold car, not running for 15 days
Spark plugs installed on the other cylinders
Throttle wide open

Results:

Cylinder 1: 9,7 BAR - 140.6 PSI
Cylinder 2: 10,0 BAR - 145.0 PSI
Cylinder 3: 9,5 BAR - 137.8 PSI
Cylinder 4: 9,1 BAR - 132 PSI

The car runs good and solid. On the other hand, Im waiting for a rebuilt fuel injection pump by Wes Ingram in order to fine tune everything (valves, dwell, timing etc)

What can I interpret from these numbers? is the engine ok? Only if the car is too low of compression I will consider to rebuilld it, because its unopened.

Thanks in advance


Gonzalo
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post #2 of 8 (permalink) Old 04-22-2019, 01:26 PM Thread Starter
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Dear all

Today I did the test again, "dry cleaning & wet"

TEST A DRY:


Without any spark plugs
Throttle wide open

Results:

Cylinder 1: 9,8 BAR - 142,1 PSI
Cylinder 2: 9,5 BAR - 137,8 PSI
Cylinder 3: 9,3 BAR - 134,9 PSI
Cylinder 4: 9,6 BAR - 139,2 PSI

TEST B WET:

Adding oil to the cylinders
Throttle wide open

Results:

Cylinder 1: 10,6 BAR - 153,7 PSI
Cylinder 2: 10,7 BAR - 155,2 PSI
Cylinder 3: 10,3 BAR - 149,4 PSI
Cylinder 4: 10,3 BAR - 149,4 PSI

Differences:

DRY. WET. % CHANGE
Cylinder 1: 142,1 PSI - 153,7 PSI. 8,1 %
Cylinder 2: 137,8 PSI - 155,2 PSI. 12,6 %
Cylinder 3: 134,9 PSI - 149,4 PSI. 10,7%
Cylinder 4: 139,2 PSI - 149,4 PSI. 7,3%

Could you help me with a diagnostic?

Regards

Gonzalo
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post #3 of 8 (permalink) Old 04-22-2019, 06:36 PM
I'd say those are decent numbers. I imagine you'll see 20-30 PSI increase with a hot motor. The % increase between dry and wet will likewise decrease once the motor is recommissioned.
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post #4 of 8 (permalink) Old 04-26-2019, 03:09 PM Thread Starter
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Thank you for your reply.

Does anybody know which are the standard manufacturer values for the engine compression? I read all the manufacturer's available manuals and I cant find these information.

Regards

Gonzalo
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post #5 of 8 (permalink) Old 04-27-2019, 12:03 AM
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Your results kinda make me question my results when I did a dry compression test on my project car. All cylinders were around 175-180psi on my 69 gtv 1750.
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post #6 of 8 (permalink) Old 04-27-2019, 03:42 AM
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Quote:
Originally Posted by maire View Post
Your results kinda make me question my results when I did a dry compression test on my project car. All cylinders were around 175-180psi on my 69 gtv 1750.
But did you do your dry test with the engine hot ?
It ideally should be done with a hot engine, this would show higher figures than a cold one.
See gprocket's post above.
My rebuilt 2000cc engine produced between 190 / 193 psi on all cylinders under a hot, dry test.
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post #7 of 8 (permalink) Old 04-27-2019, 07:22 AM Thread Starter
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Dear all

Thank you for your answers. I did in cold, today I will repeat it with hot engine.

But my question is , which are the manufacturer (Alfa Romeo) spec values for the compression of the car? GTV 2000 American version 1974.

What I saw is that everybody tells about their values, but at no place I can read the manufacturer spec

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Gonzalo from Uruguay/ South America
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post #8 of 8 (permalink) Old 04-27-2019, 09:12 AM
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Do the test hot, hot with oil and keep a battery charger hooked up so on your last readings the battery stays reasonably charged. Yes wide open throttle. Yes all plugs out. Compression can vary with Compression ratio, cranking test speed and cam timing and duration. Also condition of rings pistons valve seats etc.... Your readings look pretty good for a cold engine.

http://www.alfabb.com/bb/forums/alfa-romeo-club-canada-toronto-chapter/149533-alfa-parts-garage-sale.html
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