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Author Topic: After compression test can I get opinions what compression you think my 440 is.  (Read 3047 times)
1Bad70Charger
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« on: August 30, 2010, 12:51:35 PM »


Here is my DILEMA, I just had a compression test done today and the cylinder pressure seems very low for what supposedly was an engine making about 10 to 1, but now I am not so sure.  shruggy

Here is what the numbers I got for cylinder pressure dry and wet and let me know what the most compression this engine could be based on these numbers. Is it possible my engine could be at least 9 to 1 or 9:5 to 1 with these numbers and what is your educated guess that it would be?  I was told the engine was built close to stock specs. for a 1969 440 engine and I don't know what iron heads it has either.

2 questions, what is the most compression this engine can be making and did the engine pass its compression test?

Cylinder 1     dry-110psi      wet-120
Cylinder 2     dry-115psi      wet-124
Cylinder 3     dry-110psi      wet-125
Cylinder 4     dry-115psi      wet-125
Cylinder 5     dry-115psi      wet-126
Cylinder 6     dry-114psi      wet-126
Cylinder 7    dry-115psi      wet-125
Cylinder 8     dry-117psi      wet-130


Engine was cold when test was done.

Engine has a 750 Proform Carb and Holley Street Dominator Manifold Intake.  Plugs I was told by the compression tester looked pretty good and I believe they are stock mopar plugs. 


Thank you very much in advance for your thoughts.  cheers
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48 year old Self Employed Trial Lawyer (I fight the ambulance chasers); 1969 Plymouth Roadrunner A12 Tribute Car, Built 505ci; Silver 2008 Hemi Dodge Challenger SRT8, Black 2006 Corvette Z06 427ci LS7-Keep God First, Family Second and Horsepower Third.  Interests:  God, Fast American Cars (old and new), Classic Muscle Cars, German Sheperds, Guns, Animals and the Great Outdoors (sick of Chicago).
Brass
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« Reply #1 on: August 30, 2010, 01:52:21 PM »

Oh, I can really relate to this.  I was told "rebuilt to 68 specs" but later found out that the original 1972 low-comp pistons were used, after the car made less RWHP than expected.  With 906 heads, my cranking pressure is ~120lbs for each cylinder, which I think ends up being around 8.2:1 compression.  I may need to be fact-checked here, but I believe that is the stock compression for 1972 and later 440's.  Older, higher compression engines should be somewhere around 150-160 lbs of cranking pressure.  What year is your engine?
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1Bad70Charger
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« Reply #2 on: August 30, 2010, 02:20:01 PM »

Oh, I can really relate to this.  I was told "rebuilt to 68 specs" but later found out that the original 1972 low-comp pistons were used, after the car made less RWHP than expected.  With 906 heads, my cranking pressure is ~120lbs for each cylinder, which I think ends up being around 8.2:1 compression.  I may need to be fact-checked here, but I believe that is the stock compression for 1972 and later 440's.  Older, higher compression engines should be somewhere around 150-160 lbs of cranking pressure.  What year is your engine?

Man that really sucks and makes me sick and that's what happens when you buy  a used car with no documentation!  eek

Was told built to specs of 1969 engine but that appear to be a bunch of bullsh it right about now!   eek
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48 year old Self Employed Trial Lawyer (I fight the ambulance chasers); 1969 Plymouth Roadrunner A12 Tribute Car, Built 505ci; Silver 2008 Hemi Dodge Challenger SRT8, Black 2006 Corvette Z06 427ci LS7-Keep God First, Family Second and Horsepower Third.  Interests:  God, Fast American Cars (old and new), Classic Muscle Cars, German Sheperds, Guns, Animals and the Great Outdoors (sick of Chicago).
jlatessa
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« Reply #3 on: August 30, 2010, 02:50:58 PM »

Did you check your compression with throttle wide open?
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1Bad70Charger
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« Reply #4 on: August 30, 2010, 03:28:09 PM »

Did you check your compression with throttle wide open?

Throttle was not open.
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48 year old Self Employed Trial Lawyer (I fight the ambulance chasers); 1969 Plymouth Roadrunner A12 Tribute Car, Built 505ci; Silver 2008 Hemi Dodge Challenger SRT8, Black 2006 Corvette Z06 427ci LS7-Keep God First, Family Second and Horsepower Third.  Interests:  God, Fast American Cars (old and new), Classic Muscle Cars, German Sheperds, Guns, Animals and the Great Outdoors (sick of Chicago).
green69rt
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« Reply #5 on: August 30, 2010, 03:29:52 PM »

According to the shop manual, a 1969 440 with 10.1 to 1 compression should read 130-165 psi with no more than 25 psi difference between any two cylindars.  Just for grins I looked at a 318 with 9 to 1 compression and the specs were 120 - 155psi.  Something sounds funny here.
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Q-ship
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« Reply #6 on: August 30, 2010, 05:49:25 PM »

1Bad70Charger. Without cam specs, it would be impossible to guess what your compression could be, but compression is irrelevant, as cylinder pressure is the only important factor.

If you have a stock to mild performance cam, your cylinder pressure is low unless you have a stock, late 70's engine.

For pump gas (91 octane), I shoot for 160 lbs cylinder pressure for a street type cam, maybe 145# for a race type cam on pump 91.
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jlatessa
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« Reply #7 on: August 30, 2010, 10:11:06 PM »

THROTTLE NEEDS TO BE OPEN,  ENGINE NEEDS AIR TO COMPRESS. NO AIR, NO COMPRESSION.
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1Bad70Charger
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« Reply #8 on: August 30, 2010, 10:31:32 PM »

THROTTLE NEEDS TO BE OPEN,  ENGINE NEEDS AIR TO COMPRESS. NO AIR, NO COMPRESSION.


 scratchchin

This is out of my area of expertise I relied on my local mechanic to be able to take a basic compression test.

Who else can confirm this info as accurate and how much of a difference might this make?  shruggy
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48 year old Self Employed Trial Lawyer (I fight the ambulance chasers); 1969 Plymouth Roadrunner A12 Tribute Car, Built 505ci; Silver 2008 Hemi Dodge Challenger SRT8, Black 2006 Corvette Z06 427ci LS7-Keep God First, Family Second and Horsepower Third.  Interests:  God, Fast American Cars (old and new), Classic Muscle Cars, German Sheperds, Guns, Animals and the Great Outdoors (sick of Chicago).
frederick
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« Reply #9 on: August 31, 2010, 02:19:20 AM »

 yesnod Throttle has to be held wide open.
Ideally with a warm engine and the other plugs removed to increase cranking rpm.

Throttle closed or open made 20psi difference on my engine.

Cheers,

Frederick

ps I agree with Q-ship, without your cam specs it's impossible to make a guess at what your static compression is.
And even with them it's still a guess. (leakdown, cam installed retarded/advanced, valve seal)
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1Bad70Charger
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« Reply #10 on: August 31, 2010, 12:38:46 PM »

THROTTLE NEEDS TO BE OPEN,  ENGINE NEEDS AIR TO COMPRESS. NO AIR, NO COMPRESSION.


OK, just spoke to the mechanic who did the compression test to nail down a few more facts, engine was cold and throttle was not activated at all, and the spark plugs were all OUT of the car when he did the test.

Can you gentleman give me your educated opinions regarding how much (realistically) do you think my cylinder pressure (psi) would have increased if the engine was warm, and more importantly, if the throttle was wide open when the compression test was performed.

Thank you very much  in advance.  cheers
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48 year old Self Employed Trial Lawyer (I fight the ambulance chasers); 1969 Plymouth Roadrunner A12 Tribute Car, Built 505ci; Silver 2008 Hemi Dodge Challenger SRT8, Black 2006 Corvette Z06 427ci LS7-Keep God First, Family Second and Horsepower Third.  Interests:  God, Fast American Cars (old and new), Classic Muscle Cars, German Sheperds, Guns, Animals and the Great Outdoors (sick of Chicago).
charger_fan_4ever
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« Reply #11 on: August 31, 2010, 01:28:47 PM »

Not to be a smartass or anything but what is the concern ? Are you looking to go back on the seller or is this a race car or ?

Without all the plugs out,throttle open, cam specs its hard to say.

Also you want to only get about 5 hits on each cyl cause if it takes 10 cranks to get to the number there is a problem. I don't think there is a ring seal issue as your wet #'s are no big jump.

I had a couple cylinders that didn't seal on a 351w with aluminim heads,cam, single plane pro form ect. Ran like a raped ape never would have known there was an issue if it wasn't for the dipstick getting blown up and an oil smoke show on the headers. You could run it to 7k 1st,2nd but by the top of 3rd poof. The wet test gained about 30lbs pressure on the 2 cyls. Rehoned it an re ringed it problem solved. Didn't notice any performance gain in the seat of the pants meter. This was a 10.25-1 engine and rang in fresh at 190lbs. The initial 2 weak ones were down at 135 dry.

In your case there really isn't a big issue if its down a point or so if its just a cruiser.

Definately not worth the $$ to swap out pistons,bore,balance. I'd be willing to bet you wouldn't notice a difference. If its under 100lbs cranking or 1 cyl is way low i'd be worried. Not in this case. Drive it and enjoy it  cheers  

Warm the engine up and take the plugs all out cap off the fuel line wide open throttle  and crank it 5-6 hits each cyl and then see what it gives you. I'm sure your number will jump 10-15lbs anyway.

another thing if the mechanic does not know how to do a proper compression test I don't think I'd want him to wrench anything on my car other than changing tires and a shock.
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1Bad70Charger
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« Reply #12 on: August 31, 2010, 01:52:25 PM »

Not to be a smartass or anything but what is the concern ? Are you looking to go back on the seller or is this a race car or ?

Without all the plugs out,throttle open, cam specs its hard to say.

Also you want to only get about 5 hits on each cyl cause if it takes 10 cranks to get to the number there is a problem. I don't think there is a ring seal issue as your wet #'s are no big jump.

I had a couple cylinders that didn't seal on a 351w with aluminum heads,cam, single plane pro form ect. Ran like a raped ape never would have known there was an issue if it wasn't for the dipstick getting blown up and an oil smoke show on the headers. You could run it to 7k 1st,2nd but by the top of 3rd poof. The wet test gained about 30lbs pressure on the 2 cyls. Rehoned it an re ringed it problem solved. Didn't notice any performance gain in the seat of the pants meter. This was a 10.25-1 engine and rang in fresh at 190lbs. The initial 2 weak ones were down at 135 dry.

In your case there really isn't a big issue if its down a point or so if its just a cruiser.

Definately not worth the $$ to swap out pistons,bore,balance. I'd be willing to bet you wouldn't notice a difference. If its under 100lbs cranking or 1 cyl is way low i'd be worried. Not in this case. Drive it and enjoy it  cheers  

Warm the engine up and take the plugs all out cap off the fuel line wide open throttle  and crank it 5-6 hits each cyl and then see what it gives you. I'm sure your number will jump 10-15lbs anyway.

another thing if the mechanic does not know how to do a proper compression test I don't think I'd want him to wrench anything on my car other than changing tires and a shock.

This is PERFECT type of info and advice (don't waste money on the shortblock) I am looking for and I thank you.  The reason this is a big deal to me is b/c the car is using oil (but I think I have the problem narrowed down to valve guides), and my plans this winter are to put on some Eddy 84 cc alum. heads, along with a fast rate Engle Cam, along with a brand new dynamic street/strip converter sitting in my basement and transo shift kit, and I want to make sure I am not building this 440 on weak foundation (shortblock that is shot), etc., hence why I did the compression test and am trying to make sense out of the numbers.  I am looking to build the fastest street car that I can without breaking the bank cheers    If I put on the Eddy heads and stick in the engle cam and the bottom end lets loose, at least HOPEFULLY i could reuse the Engle Cam (if not wiped) out and the Eddy Heads and then build a new snotty 440 from scratch; or if I was really smart and patient, save up for that 650HP/650TA 500+ ci stroker wedge motor and not put a dime into my current engine.  Wink

I also agree with you 100% about this mechanic but he is one block from my home and not my regular hi-performance mechanic, and I thought he could handle a simple compression test (but he cannot), and yes, in the future he will just continue to do oil changes for me on my daily drivers!   2thumbs
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48 year old Self Employed Trial Lawyer (I fight the ambulance chasers); 1969 Plymouth Roadrunner A12 Tribute Car, Built 505ci; Silver 2008 Hemi Dodge Challenger SRT8, Black 2006 Corvette Z06 427ci LS7-Keep God First, Family Second and Horsepower Third.  Interests:  God, Fast American Cars (old and new), Classic Muscle Cars, German Sheperds, Guns, Animals and the Great Outdoors (sick of Chicago).
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