Hi Guys,

I did a compression test yesterday on my 72 with a stock 350 4bbl with at least 125,000 miles.

Here are the results:

#1 - 105
#3 - 105
#7 - 104
#5 - 105


#2 - 110
#4 - 105
#6 - 105
#8 - ????? couldn't get the gauge on b/c of the a/c box.

What do you think? Time for a rebuild?

The car runs great, nice and smooth, sounds good. Stinky exhaust though. I have had a couple of fouled plugs and some smoke puffs after idling at stop lights, so I just changed the valved seals and added a pertronix and coil. I don't yet know if this has cured the problem.

 

What caused the plug fouling, oil or gas?

If the engine runs great and is not burning oil, why go to the expense of a rebuild? - unless you just want to make drastic improvements for fun, of course.

Seriously, the cylinders are all close together, so there is no major issue indicated. They might be a little on the weak end, but if the engine runs great, leave it alone. I would get the reading from #8, though. Find a tester with a flexible hose, if you can't fit yours on.

 

I think it was oil.

 

Sounds like you may have fixed the problem then. I wouldn't tear it apart unless you have a decent budget and you're looking for more power.

 

I was hoping to get a few more years out of it and then put a 455 in it.

 

You know a normal compression test reading is all cylinders above 100 lbs and the lowest reading cylinder should not be less than 70% of the highest reading cylinder. So for 110 being the highest, 70% of that is 77...I believe you have absolutely NO problems with the engine that's in there.

 

Hi MaxDog:
I saw your compression number and got curious about my engine. I think the 71 and 72 engines are almost the same. My setup is, 1971, Supreme 350 4bbl, Single exhaust, with AC, 8.5 CR, Net HP 180, all stock engine, 22,000 miles. I have only had this car for less than a year and have not modified the engine.
Here are my numbers (all Dry, with 5 cranks, Head temp 160F).
#1 - 151
#3 - 154
#7 - 149
#5 - 153

#2 - 155
#4 - 155
#6 - 150
#8 - 166


The big difference I see is the Millage; I have a 100k less miles. Now I have a baseline set of values for future monitoring. I used a tester with multiple threaded adapters and a flexible hose. I would attached the plug adapter first, then screw on the hose and last Plug in the Gauge. Plug #8 was a challenge behind the AC box. To install the adapter into #8, I made the plug adapter longer by attaching a 3 inch pen-cap to the adapter with black tape. The pen-cap gave me more leverage and allowed me to find the threads in the blind. Once hand threaded, I just pulled the cap and black tape off and then installed the pressure hose.
Good Luck


The attached pictures shows the #8 plug, with a pen-cap taped to the plug adapter for a compression gauge. The pen cap made it easier to align the adapter threads to the plug hole.

 

Thanks Miles, great idea regarding the pen cap. Very creative. By the way, the engine color/paint looks nice.

 

You do need to find out what #8 is for sure. The numbers so far are all together but borderline low across the board.

Are you holding the throttle wide open and letting the engine make at least 5-6 compression strokes when doing the test? If you are I would do a leakdown test next and see what that gets you.

 

Either the test wasn't accurate or your '72 350 is a little tired. By comparison, i had a one-owner '70 'S' with 350 2v 9:1 compression. Right before i sold it in '93, it had 180,000 miles and compression readings from 165-175. I don't miss that car but i sure miss that 350 .