Compression Help

[Roo]

hey just did a compressioin test on my 4k and got 160psi on all cylinders

 

was just wondering what the compression is meant to be? my 4k is meant to have higher compression so seems abit low to me

 

cheers andrew

[Felix]

If it has a big cam with a lot of overlap that should be expected.

 

Read up a bit on dynamic/effective compression.

[Roo]

ok yea got a abit of a big cam in if

 

cheers will read up about it

[philbey]

Those numbers sound reasonable. The problem is usually seen when one cylinder is different to the rest.

 

The relationship between cylinder pressure and compression ratio is complex and cylinder pressure won't tell you the comp ratio.

[Evan G]

160 sounds rite (my cylinder 4 got 140psi :P, no smoke but )

[78ke30]

Those numbers sound reasonable. The problem is usually seen when one cylinder is different to the rest.

 

The relationship between cylinder pressure and compression ratio is complex and cylinder pressure won't tell you the comp ratio.

 

anything over 10% will cause a noticeable misfire.

[Felix]

anything over 10% will cause a noticeable misfire.

 

Not necessarily. It will cause the motor to be down on power and run rougher due to cylinder imbalance.

 

Evan I'd be doing a wet/dry compression test to determine if it is the rings or valves/headgasket. It is common for cylinder 4 to go first if the motor has been run without a thermostat for any length of time.

[78ke30]

Not necessarily. It will cause the motor to be down on power and run rougher due to cylinder imbalance.

 

^noticeable misfire