+1...My 327/350 is right there too....because I made it so....
There could be a myriad of things that cause this low compression....

A leakdown is in order first.

Jebby

 

Has the performance deteriorated over time or has it run the same since it was rebuilt some 5K ago?

 

Did I miss something or did someone already mention that the new "livelier" cam (more overlap I would guess) will lower static CR?

 

Thanks again for the suggestions. I just e-mailed the shop regarding the head gasket(s). We'll see what develops next.
Tom

 

Something that you can do is a leak down test (see: http://www.youtube.com/watch?v=ofSiT...eature=related) on each cylinder.

When you are doing this, listen as described at http://www.allpar.com/fix/leakdown-test.html). You will be able to tell if your valves are tweaked (and which one), rings are bad, etc. Note that this is not a compression test.

Also, you can check to see if there is exhaust fumes in the antifreeze (see: http://www.ehow.com/video_12213890_c...ntifreeze.html). If there is, change the head gaskets. I suspect, though, that if you do a leak down test and you have your radiator cap off, you'll know in quick time if you are leaking into the cooling jacket by looking for bubbles (and coolant escaping).

From the compression test, all cylinders are low. 145psi is the bare minimum I would look for, with +-5% difference from the lowest to the highest. It's kind of funky how they are all low, but the odd bank has consistent numbers and the even bank has significantly lower and more variation.

Personally, I would be talking with the folks who rebuilt the engine. Yes, it was in '08, but with ~5k miles on it your just breaking it in. It could be they installed the piston rings incorrectly (depending on the ring, this could cause cylinder bore damage, leaking, etc.), did not torque down the heads properly, or a myriad of other things causing the issue.

Just my 2 cents worth, you mileage may vary.



-- Joe

 

If the heads were swapped in the rebuild to 76cc chambers this might be the compression range, should still be consistent between cylinders.

I went back and re read your Compression Test numbers, and compared to your leak down numbers. This engine is screwy. A cyl with 15% leak down is only 125 PSI while another with 53% leakdown is at 110 pounds. Could this livelier cam have huge overlap building no low RPM compression? This engine does not add up to me.
Maybe it has huge ring end gaps?

 

I read your leakdown numbers....
Did you ever break in the rings on this?

Have you ever run it "hard"

You need to run an engine like you stole it after cam break in for the rings to seal.....

Jebby

 

The engine was rebuilt by my brother-in-law and nephew. Both pretty reliable when it comes to engine building, but no ones perfect on any given day. The heads are the original. I do drive it hard on occasion, as children love to play!
Question: What is a sonic test and how is it done? Can it be done on a block with the rotating assembly intact. Who performs them?
Thank you for your comments.
Tom

 

Tom,

You didn't say but do you know if they checked during the leak down test to see where the leakage was? It's easy to do and would tell you a world of information before you pull the head. #6 and 8 sure could be explained by a blown gasket between the two. Were it mine, I'd pull the head before going too much further.

Steve

 

Steve,
Because there was so much blow-by they figured the rings were shot.
they thought the carb may have washed the cylinder walls.
The carb is a Holley street avenger 650cfm.
Tom

 

A sonic testisjust that...it sends out high frequency vibrations and reads
how "long" it takes forthem to come back.
It is a dead nuts way to determine the thickness of a cylinder wall....
Most of the time they are thin at the bottom....
A 327 does not pull the piston down the bore as far as a 350 or 383.
Therefore you might miss the bottom of the waterjacket.
So, yes it can be done with the rotator intact....but maybe not 100%

A good shop who has the BHJ checker (which is the industry standard)
Will measure at 3,6,9 and 12 o'clock around the bore....at three points vertically.
Rule of thumb is at least .100 thickness.

Your leakdown makes sense though if you calculate the percentage.

Best to worst is 45% difference....or about 45 psi.

You are less than 45 psi in difference but not off the map.

Jebby

 

This is necessary to select a good block with beefy cylinder walls. Too many people trying to sell junk, which is what most of these 45-50 year old blocks are, now. Many of them have been in marine use and water jackets are badly corroded. Many were taken out of service long ago, for good reason due to severe core shift.

Select a block with at least 0.100" wall thickness on the non thrust faces and 0.150" on the minor and major thrust faces. This is OK for a mild build and probably the best you're going to find among all the junk "numbers matching" blocks for sale out there.