comp test
12-08-06, 02:00 PM
#1
Hopeful Future
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comp test
So today I decided to compression test my N/A motor. I figured if I'm going to be adding the stress of boost (im turboing it) I might as well see the condition its in first. It was cold as hell this morning so I only did the rear rotor, but I'm happy to say it got an overall rating above 100 on the gauge, and with the valve open, 3 even bounces to 60 psi. Not bad for an engine with 141,000 miles on it! front rotor comes tomorrow.
12-08-06, 04:36 PM
#2
Now my 7 has been down for a whiiile but i know that the "overall" rating is useless b/c you need to get 3 readings from the 3 compressions'. Also 60 psi is incredibly low and needs a rebuild.
Maybe the cold weather or the way you did the comp. test affected it.... a good psi is between 95-115, pretty sure
Maybe the cold weather or the way you did the comp. test affected it.... a good psi is between 95-115, pretty sure
12-08-06, 10:21 PM
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Taken from RotaryResurrection's webpage on compression testing:
"observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range."
Oddly enough, mine all jumped to around 60. Anyone have any info on why this may be?
My friend was doing the cranking, maybe he wasn't holding the throttle open all the way, what effect would this have if he wasn't?
"
let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment."
"observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range."
Oddly enough, mine all jumped to around 60. Anyone have any info on why this may be?
My friend was doing the cranking, maybe he wasn't holding the throttle open all the way, what effect would this have if he wasn't?
"
let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment."
12-09-06, 10:13 PM
#5
is that really what kevin has for a write up for a compression test? never really checked his site for links to doing a compression test but that is a wonky way of doing the test.
normally you remove the valve in the hose to the gauge and don't touch the compression release valve, crank the engine with a booster hooked to it while both leading plugs are removed and crank the engine at WOT until you see the peak bounces, they should be in the 100+ range and even, i generally get 90psi or so on turboed engines.
doing a peak compression test like that really doesn't give any ideas about the internal condition of the engine since the bounces are what really matter.. holding the valve open while doing the test yielding lower numbers will alter the difference in each peak bounce, a bounce between 30 and 35psi can turn into the difference of 15psi once you get to the 100psi range, and that is a bad difference on rotor faces.
normally you remove the valve in the hose to the gauge and don't touch the compression release valve, crank the engine with a booster hooked to it while both leading plugs are removed and crank the engine at WOT until you see the peak bounces, they should be in the 100+ range and even, i generally get 90psi or so on turboed engines.
doing a peak compression test like that really doesn't give any ideas about the internal condition of the engine since the bounces are what really matter.. holding the valve open while doing the test yielding lower numbers will alter the difference in each peak bounce, a bounce between 30 and 35psi can turn into the difference of 15psi once you get to the 100psi range, and that is a bad difference on rotor faces.
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