Compression test for a standard VN 5.0L V8

[raw]

Hey guys, I've got a standard 1989 VN 5.0L V8 and have just done a compression test
The results were consistent, but seem to be VERY low
Seven cylinders were 95 PSI and the other cylinder was 105 PSI (spark plug was darker than the others so I assume this cylinder had a bit of carbon build up which gave the slightly higher compression)
What does it mean if all cylinders are this low on compression?

[muttley383]

Did you have the throttle fully open and was the battery fully charged before the testing?

[Ian Johnston]

Is having the throttle wide open needed these days? Had my daughters VT Clubby 5.7 stroker done recently, and the mechanic didnt even get in the car, so no full throttle.
Comps on that were all around the 200 psi mark.

[VR38]

You can open the throttle from under the bonnet...

[VR028]

i remember reading 150psi was normal for a oldish 304. how many kms on your engine?

[raw]

The battery was fully charged, can't recall if throttle was held open - will have to ask (hopefully this is the reason for low numbers)
Haven't changed the plugs for ages so when I take them out again I'll redo comp test
Never done a comp test on it before so I've had nothing to compare it to
It may be a VN but it's only done 110,000 legit kms
It's running like crap and has the symptoms of either a head gasket or intake manifold gasket (there's nothing else it could be - I've changed/tested everything else!)

[Ian Johnston]

VR38, I was watching when he did it, and just lent in the window, and turned the engine over.
I actually turned it over for the last 4 cylinders.

[VR38]

I use a chock such as a screwdriver to wedge the throttle open when working alone.

[phear11]

so what should the average compression be for a healthy 100k vs 304 motor as im about to do mine in the next couple of days just so ive got something to work from if i ever have any issues.

[VR028]

so what should the average compression be for a healthy 100k vs 304 motor as im about to do mine in the next couple of days just so ive got something to work from if i ever have any issues.

160-170 would be acceptable. higher is better but what you want is consistancy over all 8 cylinders

[raw]

Throttle was not held open during testing. Also found out the test should be done right after the engine has reached normal operating temp - mine was barely warm
Will redo test on the weekend and post new reults

[kojab]

Just curious, are you in Sydney? Would be interesting to do a DST (diagnostic scan tool) log on your car.

[Reaper]

My old one with well over 350k on the motor was around 140 - 150 pound. Went like stink though.

Reaper

[GTP 85]

my tuner just did a comp test on a VQ that was "meant to be a 360 stroker" lol. turns out most cyls were under 70 and two were just over 100 haha. That would explain why it idled so bad. Owner was dark as coz he just bought the car but anyway...

told me that on average comp on a reasonably healthy 304 should be around 140's