# What is a good compression test reading?

## What is a good compression test reading?

According to professional mechanics, a healthy engine should have compression of over 100 psi per cylinder, and the deviation between the maximum and minimum readings should not exceed 10%. It might surprise you, but you don’t need special skills to do it.

## What is the normal compression for a gasoline engine?

Since the gasoline engine has a spark plug, only moderate compression is enough, requiring about 140-160 pounds per square inch (PSI). Depending on their size and application, some engines may require a higher compression such as 220 PSI.

Is 140 psi compression good?

As a general rule a compression of 135 PSI or better is excellent. Similarly, 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. Furthermore, that reading should be above 135 PSI.

What is the compression ratio of a General Motors engine?

“Bore” refers to the diameter of the cylinders within the engine that house and seal a moving ring and piston assembly; “stroke” refers to the distance that those pistons move within the cylinders. The engine has a compression ratio of 8.9 to 1.

### How many cylinders are in a GM 3.1 V6 engine?

by Anne Davis. General Motors began producing 60-degree V6 engines in 1980 with its 2.8-liter engine. Over the years, the company began manufacturing slightly larger engines with larger bores and higher output potential. The GM 3.1-liter engine has six cylinders in a V formation that are opposed at 60 degrees — each cylinder has two valves.

### Is it normal for engine compression to vary between cylinders?

CASE 2: Low compression in one or more cylinders. To a certain point, it’s normal for the compression to vary a little between cylinders (as the engine accumulates thousands of miles). But if these values vary too much, then you’re gonna’ have a bona-fide misfire on your hands.

What’s the best way to test engine compression?

Hand-thread the engine compression gauge into the spark plug hole that you’ve chosen to test first. Do not use any type of tool to get it tight, hand tight is enough! Once everything is set, have your helper crank the car or mini-van.