My buddys got a gauge that goes in place of the spark plug. He says you let it turn a few times and you got your result for that cylinder, put the plug back in and repeat on other seven. Is this how or is there more to it than that?

 

nope thats about it. leave all the other plugs in, just incase there is some confusion there.
spin it over 3-4 full times, or until it stops going up.
it makes it easier to have 2 people

 

k, what type of comp should i be at? The only mods i got are in sig, 5.0, HO, SD, yada yada

 

my '93 is getting tired, i was only about 125 each cylinder.

i haven't heard a definiate number myself, but could be as high as 165 , i think 150 would excellent , also you want a small percentage of diff from each, no more than a 10% variance

 

i think you're supposed to block open the throttle plate when you do it. and disconnect your coil wire so it wont start.

 

+ a few...........
Good idea to have engine warm too.
Look for no more than a 10% +/- for all 8 cylinders like somebody already said.
If the car hac any sort of an aftermarket cam, it may well show low numbers.
When I raced 440 Mopars, the strongest 440 I ever had only showed about 120# and that was with 5% leak down rate (differant subject).........

 

You will want the throttle body propped open, and I was always told you take all the spark plugs out to do it right. If you have two cylinders next to each other with low readings, you have a leak between the two, something that may not show up if you leave all the plugs in.

You should disable the fuel pump/pressure and also the ignition system. Doesn't hurt to cover yourself here.

For each cylinder, you will want to crank the engine and watch for 3-5 pulses of the gauge. After the last pulse should be the approx. highest you get. You will want to do each cylinder twice. Add the two numbers and divide by two, and get your average.

Do this for all 8, and what I suggest is draw a picture of your engine and write down the numbers you get next to the corresponding cylinder. Then you can see kind of WHERE any issues are, if you have any and you get a kind of visual of the condition of your engine.

And on most stock motors with stockcams and average compression ratio, say 8:1-9:1... I've always been told around 150 psi is good. The big thing you want to look for is consistency. You want all the cylinders to be very close to eachother, with no more than 5-10 psi of difference between the highest one and the lowest one.

I've done this a few times but have not had a chance to test our 5.0. My 4.6 had great compression but burned oil hideously... cylinder head issues.

 

if u thought that u were gettin blow by and u wanted to rule out blow by if ur down on compression put like half teaspoon of oil in the cylinder that will seal the rings enough to find out if it blow by or not

 

Yes I forgot about this test... adding oil to the cylinder should not effect your readings much, if at all. If it makes a huge difference, you have sealing issues