1998 Compression Test Results

You're fine.

As a general rule a compression of 135 PSI or better is excellent, and a compression of 85 PSI or lower is extremely bad.

The most desirable situation is that all cylinders give the same or close to the same reading, and that reading is above 135 PSI. Uneven readings are not uncommon on worn engines, and as long as the difference between the highest and lowest readings are no more than 21 PSI and the lowest reading is 100 PSI or better, then the engine is acceptable. Greater differences between cylinders indicate worn or broken rings, leaky or sticky valves or a combination of all.

 

Those rules of thumb are outdated to the extreme.

 

Did you label each cylinder sparkplug? So someone can read them.
How many cranking compression pulses? 3,4, 5 or more?
What type of tester?
throttles open?
battery charger on battery to get maximum voltage?
What weight engine oil do you use? Miles on that oil?
What sparkplug are you using? miles on those plugs?

What I'm getting at is theres are alot of variables to consider, but no matter how you do it, the numbers should be alot closer to each other than they are.

not bashing ya, just trying to gather info. Been doing this for over 30 years.

 

Also, looking at your numbers again, I see one bank is lower overall than the other. If they pull the heads off, check;

Piston to deck clearance
Head gasket thickness
CC combustion chambers

I almost bet the deck height on the block is different 1-4 and 5-8. Doesn't take much, we're talking only thousandths of an inch

 

The absolute accuracy of any compression test gauge is a bit iffy anyway, but at what elevation above sea level was the test performed and was it raining or nice weather? The reading on the gauge (for the same engine tested in the same way) is directly proportional to the (true) prevailing atmospheric pressure -- in weather reports, they "correct" the local atmospheric pressure for the local elevation.

 

Even is very important. That we all agree upon. The absolute numbers can vary for a variety of reasons but at the 100 lbs mentioned, that is under half of the correct sea level compression of a 355 and cannot be considered OK under any circumstance.

Another thing to consider that negates all the old rules of thumb is modern engine manufacturing. Methods and products used create a situation, and the 355 is an excellent example of this, where original compression, or very close to it is maintained for most of the useful life and once it starts to go it goes quickly.

The bottom line is, coming on here and asking if xxx compression is good is a waste of time. The guy who did the test, if he is any good will understand how those variables apply to his situation and tell you "this is good". If he can't someone wasted their money.

 

Or it could be what it is in 99.8% of the cases and it is a symptom of inconsistently timed cams.

 

would you say about 20 years out dated?? hahaha

 

Brian
Do you think its better to do the compression test warm or cold?Which is better.

 

I'd be happy with those numbers.

The two cars that I've had tested were at 175 on the high end, and some cylinders around 125-130. I wasn't happy with those results so I passed on them.

175+ in my opinion is a happy motor.

 

SOP is to do it hot.

The Mahle ring material used in the 355 among other cars is so perfectly matched in in it's thermal expansion coefficient to the cylinder that there is no change in the ring gaps from hot to cold. I have tested a great many of those motors for both leak down and compression both hot and cold and have found no measureable difference on motors in good condition.

 

Updates???

 

Look forward to it. Thank you

 

Wow, must be a neat shop. 355 next to a pink '59 Ford. Looking forward to the progress!