Piston rings or head

[-Dan-]

Hi all, posted up a week ago regarding power difference between 2 identical cars

performed a compression test and the figures are not great to say the least all over the place

1st test I got from cylinder 4 - 1

120 - 100 - 130 - 189

2nd test

140 - 145 - 153 - 190

3rd test

110 - 145 - 143 - 187

4th test

187 - 177 - 168 - 198

5th test

170 - 150 - 148 - 193

so as you can see all over the place!

im going to perform a wet test tonight as I forgot to do that

How likely is it to be the piston rings are the common? or is it more likely to be a valve

Regards Dan

 

[-Dan-]

Obviously test 4 being the closest to the 200 it should be

 

[NorthloopCup]

You need to do a wet test really mate. Does it use any oil? It could be one of many things, or a combination tbh.
Could be rings, could be valves need lapping in again, could be a head gasket on its way out, could be cracked ring lands on the piston (burns oil as well though usually), could be a slightly bent valve, could be cam timing as well believe it or not.

 

[-Dan-]

Doesn't use any more oil than I imagine normal 1l roughly every 4k miles and a few track days Inbetween?

I don't know what's normal, I've had the car 2 years and it's always felt the same way power wise so perhaps it's never been 100% in my ownership

 

[NorthloopCup]

Doesn't use any more oil than I imagine normal 1l roughly every 4k miles and a few track days Inbetween?

I don't know what's normal, I've had the car 2 years and it's always felt the same way power wise so perhaps it's never been 100% in my ownership

I've never had to top the oil up on mine mate, even after road, trackday and Nurburgring abuse. Yeah it uses a tad, but nowhere near 1L.
It could well be pistons/rings showing signs of wear then mate.

 

[-Dan-]

Tests were all done from cold, fuel pump disconnected, plugs left in and removed 1 at a time (I'll try them all out tonight), WOT and till the needle stopped moving 6-7 cranks maybe

 

[-Dan-]

I've never had to top the oil up on mine mate, even after road, trackday and Nurburgring abuse. Yeah it uses a tad, but nowhere near 1L.
It could well be pistons/rings showing signs of wear then mate.

Okay maybe that's bit of an exaggeration there just been informed it's more like half 1 bottle after 6k and full track days

It's never ever ever smoked at all, I put a go pro on the bumper last night and went for a proper rag and there no snake from the exhaust

 

[NorthloopCup]

Okay maybe that's bit of an exaggeration there just been informed it's more like half 1 bottle after 6k and full track days

It's never ever ever smoked at all, I put a go pro on the bumper last night and went for a proper rag and there no snake from the exhaust

Ah yeah that sounds more normal then mate.

 

[-Dan-]

Well I don't have a fecking clue

Just done the tests now

Dry

4 - 192
3 - 189
2 - 189
1 - 200


Wet

4 - 240
3 - 210
2 - 190
1 - 210

What would you say to that

 

[bloke]

did you do the last ones with all the plugs out?

 

[-Dan-]

Exactly the same Plugs out, WOT, Cold engine, Fuel pump disconnected just with a tad drop of oil in the cylinder for the 2nd test

 

[Dan@SJM]

Disconnect the injectors too.

 

[-Dan-]

Didnt do that no, just imaged the pump being disconnected would be fine?

 

[Dan@SJM]

The injectors will still fire with the residual pressure in the line until the pressure has dropped.

 

[-Dan-]

How will they effect compression at all?

Dan

 

[NorthloopCup]

How will they effect compression at all?

Dan

They will add the leftover fuel from the line into the cylinder when you turn the engine over mate. It could potentially try to fire slightly and give false readings

 

[bloke]

borewash