Compression check, what normal?

Skoobie

Damn...Tyler65's hot!

May 25, 2003

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Vancouver, WA

Jun 24, 2005

#1

• Jun 24, 2005

• #1

Finally broke down and had the local shop do a compression check on my 188K shortblock just to guage how much time I had left on the motor. All cylindars checked in at 160-165 psi. I asked him what that ment and he said it wasent really important what the #'s were, but more so that they all read the same. It showed that all my valves were ok. He also said that there is no set "good" psi as it can vary widely depending on your cam choice. I currently have an E cam in with 1.6 RR. How does my compression compare to a new motor? Am I still in the black, or should I start saving for a rebuild?

 

1EVIL88VERT

New Member

Jul 12, 2004

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Dyess AFB, TX

Jun 24, 2005

#2

• Jun 24, 2005

• #2

those are good numbers, as long as they are all within 10%. My 3000 mile shortblock only has 155psi.

 

D

Daggar

New Member

Jul 19, 2004

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Jun 24, 2005

#3

• Jun 24, 2005

• #3

The shop manual shows a 25% difference to be acceptable. If you're within 10 then you're golden!

 

D

double drop top

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Apr 25, 2005

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Chandler Arizona

Jun 24, 2005

#4

• Jun 24, 2005

• #4

The second test you need to do is a leak down test. This will give you a better read on the condition of your rings and valves then a compression test.

 

Skoobie

Damn...Tyler65's hot!

May 25, 2003

655

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Vancouver, WA

Jun 24, 2005

#5

• Jun 24, 2005

• #5

double drop top said:

The second test you need to do is a leak down test. This will give you a better read on the condition of your rings and valves then a compression test.

Click to expand...

The leakdown was an hours labor by itself...that can wait

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

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Jun 24, 2005

#6

• Jun 24, 2005

• #6

Or just buy yourself a compression gauge (20-40 bucks at parts stores) and do it yourself.

I would have done a wet compression test afterwards, but I would not have paid someone to do the test, esp after the numbers you put up (very very good, IMHO).

Good luck.

 

90mustangGT

I felt sorry for girls because

Founding Member

Jan 15, 2002

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Dallas, GA

Jun 24, 2005

#7

• Jun 24, 2005

• #7

The compression test, like said before, the numbers really don't matter unless they are really low becuase you need at least 70psi for combustion. It's evenness that your are looking for.

The leakdown was an hours labor by itself...that can wait

Click to expand...

Actually, this is the really important test to check engine performance condition.

My old motor, read between 155-165 across all cylinders. Great right?
Wrong, when I did a leakdown test I was getting 26% leakdown on #3 but all the rest werein the hight 30's low 40's, and #6 was at 50%.

10% or less = Excellent
Under 20% = Good
Under 30% = Acceptable
31% or more you have problems.

 

Skoobie

Damn...Tyler65's hot!

May 25, 2003

655

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Vancouver, WA

Jun 25, 2005

#8

• Jun 25, 2005

• #8

HISSIN50 said:

I would have done a wet compression test afterwards, but I would not have paid someone to do the test

Click to expand...

What kind of equipment do you need for the test? Cost Vs. having a shop do the test?

 

Vipersix

Founding Member

Feb 25, 2001

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Clarksville, TN

Jun 25, 2005

#9

• Jun 25, 2005

• #9

You might be able to rent one from Advance or Auto Zone, otherwise you can buy one from Summit for $70.