What is a compression test during PPI?

It tells you the health of each cylinder.

Each cylinder should have a similar amount (not more than 5% difference) - eg. each cylinder should do 160psi for example.

Any huge variation means trouble either rings, valves, pistons, and that means rebuild time.

T.

 

http://www.vclassics.com/archive/leakdown.htm

 

what is sort of standard on older (60's-70's) ferrari engines?

i understand the numbers themselves aren't entirely useful as the volumetric efficiency has far too many factors involved.

it's just the last 2 times i've measured mine (old fiat engine ) it had 210 psi across the board. anyone else's results i've seen have yielded numbers like 140-160, i've never seen anywhere near 200 before i got my car.

the engine's just been rebuilt for decent performance, so it'll be interesting to see what happens to the numbers... though there may be a lot of overlap on the cams. wiggle wiggle wiggle.

 

I've found such large differences between the readings on different gauges that I think the best is just to look at the variation between cylinders rather than the actual number on the gauge

 

BINGO!!....

 

figgered that, and happy that my readings have all been within 1-2 psi of each other, was just interested to know if there was an "average".

 

It is to quantify each cylinders ability to contain the expanding gasses that create the force that provides an engines power. It is as said in another post measuring the motors health much the same as measuring a persons blood pressure. As was also very accurately put in another post the equipment varies a great deal as does methodology so a certain amount of judgement is required to make an accurate interpretation of the data collected. It is one of many reasons that it is important to have not only a qualified individual but also one that has a great familiarity with the particular type of car in question.