Compression test

Zuc

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I did a compression test on my ebony 03. Not really sure why i did just bored i guess but my numbers are very low compared to what ive seen some guys say there getting. Cylnders 1-5 were 140psi with 6-8 being 130psi. I bought this car back in 10/2019. I bought it with 3,207 miles on it. Ive put 150 miles on it. No i didnt do nor did i have a compression test done prior to buying. I figured with only 3,200 miles on it should be tip top. I had it dynoed and it made 380 hp and 445 tq at 5400 ft on mustang dyno. I live at 7500 ft above sea level, would elevation affect my compression test this much??? I pulled fuel pump fuse and held throttle wide open. Engine was cold and i did it 1 plug at a time. any suggestions on where to go from here would be great.
 

john11gt

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I think consistency among the cylinders is more important than just a high psi, although I’m not sure what a cobra should put out on a compression test.

try squinting some oil in the cylinders before the test and see if it helps.
 

01yellercobra

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You're more worried about consistency between numbers. Lots of things will skew the results as far as how high of a number you'll see. A buddy of mine had a gauge 4gsy for some reason never read above 100psi.
 

Zuc

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What do you have done to the car?
3" upper, 9" lower (6lb), accufab oval tb, bassani off road x pipe, and magnaflow exhaust. Car made max 12.7 lbs of boost. Like i said that was at 5250 performance in longmont CO which is 5400 above sea level but i live in mountains at 7500.
 

me32

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3" upper, 9" lower (6lb), accufab oval tb, bassani off road x pipe, and magnaflow exhaust. Car made max 12.7 lbs of boost. Like i said that was at 5250 performance in longmont CO which is 5400 above sea level but i live in mountains at 7500.
Does the car ever feel low on power?
 

Zuc

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Does the car ever feel low on power?
Ive only put 150 miles on it. And 135 of those had my kids in there so drove like a grandma. But that 15 mile trip i was able to take by myself. I would say no not at all! but i drive fairly responsible since car only has 3300 miles dont want to tear it up. I mean ive stabbed it in 1st -3rd a couple times feels damn powerful. This is my first terminator. My dream car
 

me32

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Ive only put 150 miles on it. And 135 of those had my kids in there so drove like a grandma. But that 15 mile trip i was able to take by myself. I would say no not at all! but i drive fairly responsible since car only has 3300 miles dont want to tear it up. I mean ive stabbed it in 1st -3rd a couple times feels damn powerful. This is my first terminator. My dream car

I wouldn't worry about the compression numbers then. A cobra with more boost and less compression will feel laggy.
 

ashleyroachclip

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Like hotcobra... said , always do the test on a warm engine, and pull all the plugs at one time .
Like was said, consistency is what you are looking for .
 

Zuc

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Like hotcobra... said , always do the test on a warm engine, and pull all the plugs at one time .
Like was said, consistency is what you are looking for .
ok, I will try again with engine warm with all plugs out (what a 5 minute idle then shutoff?) I was allways taught to never pull plugs on a HOT engine with aluminum heads... I work out of my home town mon-thu, I will have to do the test again on Saturday morning. I will post results after I get it done.
 

fivelitrecobra

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I think your just fine, consistency between cylinders is the main thing. I checked my compression on a cold motor and my numbers were very similar to yours, car never missed a beat.
 

Zuc

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I think your just fine, consistency between cylinders is the main thing. I checked my compression on a cold motor and my numbers were very similar to yours, car never missed a beat.
ok, ya car runs good, no smoke at start up nothing during hard acceleration or deceleration. like I said earlier nothing is going on that made me think it was low or to justify the test, just the COVID boredom really!
 

ashleyroachclip

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Frankly , the results only vary slightly between a warm engine , and cold .
Reason for warm engine test , is so everything is at its operating size , as piston and ring clearance expand during normal operation.
I think you are fine with those numbers , tho I think you left out results of #7 .
I have removed spark plugs from hot aluminum heads many times .
Never had an issue , but I use copper base anti-sieze .
 

Zuc

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Frankly , the results only vary slightly between a warm engine , and cold .
Reason for warm engine test , is so everything is at its operating size , as piston and ring clearance expand during normal operation.
I think you are fine with those numbers , tho I think you left out results of #7 .
I have removed spark plugs from hot aluminum heads many times .
Never had an issue , but I use copper base anti-sieze .
ok, ya I use copper based anti-sieze as well. cylinders 1-5 were 140PSI on the dot and cylinders 6-8 were 130 maybe 131 PSI. I was honestly more concerned how 1-5 were so consistent then all of a sudden 6, 7, and 8 dropped by 9-10 PSI. with the whole head tick issue these cars potentially having and have heard so many guys talking about #6 being problematic as well is what got me to post the question to begin with. The first thing I did when I purchased the car was the GEN II head cooling mod from lethal performance followed by the bassani off road x pipe.
 

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