Wierd compresion numbers(gone up by 15psi since last test 4 months ago)

[locote]

As the title says..
Last time i test my compresion i got 225psi on all 4.
Today i got 240 on all 4..
Would changing the exhaust from 3inch to 2.5 inch do it...
Or maybe goin to a 2inch in out cat??
Im confused as to how this could have happened..
And before any one ask if i tested it the same way both times i did..
WOT and turned it over a few times, 1 at time...

Can any one shed any light as to if this is normal...

[Drew]

Mechanical or Electrical gauge?

If it's electrical then there's your answer right there

[locote]

mech guage...
Same guage used aswell

[Drew]

Tried it again?

Possibly you didn't tighten it the first time and some pressure escaped

Or your gauge is fux0red... If it's even been dropped or anything then that could have screwed the gauge itself

Tried it again?

[locote]

i tighten the F out of it last time i tested and the time before my mate tighten it..
Both times before i got 225psi on all 4...
Only today i got 240...
If its not tighten properly itll show less not more..
I tested it heaps of times today 240 on all 4..
If there was a prob only the 1st one would have showed different but all 4 showing 240 today..
I cant work it out ive never heard of anything like this happening!!
If anything i would have thought it would have been lower..
As i give it to it just about everyday!!!

[bennjamin]

was your engine cold last time , and hot this time ?

did you put abit of oil around the rubber O ring on the bottom of the gauge thread 1st / last time ?

[yourfather]

yeh me was thinkin its a warm motor with oils

[dsp26]

either the above 2 responses or you've been running so rich that you have carbon buildup on piston top hehe

[locote]

ahhhh...
defenetly not rich...
but i cant remember how long the car had been off for last times i tested..
I think it was colder this time round..
but not dead cold. just spdent like 2 hours with out running last time it was operating temp warm...
But 240psi on all 4 is good..
But wat does that equate to in compresion ratio???

[bennjamin]

But wat does that equate to in compresion ratio???


The compression ratio is


http://upload.wikimedia.org/math/3/a/f/3afd933b679b7b20f1561c841867f901.png, whereb = cylinder (http://en.wikipedia.org/wiki/Cylinder_%28engine%29) bore (diameter)s = piston (http://en.wikipedia.org/wiki/Piston) stroke (http://en.wikipedia.org/wiki/Stroke_%28engines%29) lengthVc = volume of the combustion chamber (http://en.wikipedia.org/wiki/Combustion_chamber) (including head gasket (http://en.wikipedia.org/wiki/Head_gasket)). This is the minimum volume of the space into which the fuel and air is compressed, prior to ignition (http://en.wikipedia.org/wiki/Ignition_system). Because of the complex shape of this space, it usually is measured directly rather than calculated.

[creativepunka]

Id say carbon under the valves causing a slight loss of psi, then the carbon got loose and you have more compression. just my 2cents

[fatboyz39]

i wouldnt be concern about those number. Just as long eaach cylinder give or take 10psi i.e 200, 210, 200, 205 then its all good.