Compression test standard 4 litre engine

[QBee]

I know nothing. I have had a compression test done by my local garage and the results are all between 148 and 160 psi dry (mainly 150) and 5 to 10 psi higher wet, though the number 8 cylinder was 150/168.

Is this what you would expect from a standard four litre engine, 73k miles on a 99 car? Do I have any serious problems?
Thanks in advance.

[phazed]

From memory my old 5.0 in good fettle averaged about 210-220.

As yours are pretty even I wouldn't worry too much.

Awaits further imput

[Sardonicus]

Looks OK but a cylinder leak down test will tell you more

[QBee]

Okay, I will organise a leak down test now I can see I have some pretty even results. Alex did suggest on seeing the detailed results that I might spend my hard-earned better by skipping the leak down test and putting the old dear straight onto the rolling road - what do you guys think? I will do both tests if there is merit in both. My nearest rolling road appears to be about an hour and a half away.

I am slightly suspicious of the number 8 cylinder, but only because the variation dry to wet, at 18 PSI, is larger than any of the others. Of the other 7, the largest variance dry to wet is 11 psi, with the average at 7 psi. I would expect a 13 year old engine (first reg 19 Nov 99) to be a bit worn.....does the wet compression test imply that all piston rings are a bit worn, and if so, enough to worry about, given that I am planning to try to drag more horses whinnying and neighing out of my engine?

[Sardonicus]

Compression difference may be down to camshaft woes, the wet test is always slightly higher as injecting fluid raises the CR anyway and your wet findings are not high enough to suspect worn rings

[QBee]

Sardonicus said:

Compression difference may be down to camshaft woes.....

Is that easy to inspect (for an agile GasMunkey I mean, not an old codger like me)?

[Sardonicus]

QBee said:

Sardonicus said:

Compression difference may be down to camshaft woes.....

Is that easy to inspect (for an agile GasMunkey I mean, not an old codger like me)?

Bit of spanner-ing involved to check for that, you can see the cam with the sump removed but it wont tell you that much or if your loosing lift etc, easier then to remove the intake manifold that way your also part way to replacing the cam gear anyways

[QBee]

Thanks Sardonicus. I realise the leak-down test has nothing to do with the camshaft, but will the rolling road be able to analyse camshaft woes, or do I simply need to get the GasMunkey and his spanners out?

[Sardonicus]

QBee said:

Thanks Sardonicus. I realise the leak-down test has nothing to do with the camshaft, but will the rolling road be able to analyse camshaft woes, or do I simply need to get the GasMunkey and his spanners out?

If the cams bad enough power will be well down

[QBee]

So skip leak down and go straight to rolling road.....or do both?

[Hedgehopper]

http://www.dietersmotorsports.com/Compression-leak...

This is quite an informative article if like me you don't know what a leak down test is.

[QBee]

Thanks, I will read it.

I could well be wrong, but in my innocence I thought it was effectively a high pressure air supply pushing air into a specific cylinder, measuring the pressure as it goes in, and a pressure gauge inserted into the adjacent cylinder to measure any change in pressure in that cylinder. This will detect a leak between cylinders via say the head gasket.

[QBee]

- now i see it detects all leakages, not just between cylinders

[Sardonicus]

QBee said:

- now i see it detects all leakages, not just between cylinders

Valves, rings ,HG,etc my best cylinder was 3% my worst 7% so was happy with that

[QBee]

Right, I will find someone to do it for me. Then rolling road.....thanks for all your advice, Sardonicus (and Phazed) and thanks for the article, Hedgehopper, even though it refers to some German brand of car with the engine at the wrong end.....

[macdeb]

phazed said:

From memory my old 5.0 in good fettle averaged about 210-220.

As yours are pretty even I wouldn't worry too much.

Awaits further imput

Looks high Peter, skimmed heads?

[QBee]

I thought I was going to have to go nearly to Skegness (Oh I don't like to be beside the seaside, when the weather is driving sleet and snow) or Northampton, or Norwich to find a rolling road, but then I thought about it and found one to the west of Cambridge run by a well known (around my parts) motor-sport guy called Peter Baldwin. I will ring him tomorrow and get both things done at his next week. Watch this space for a report.

[Sardonicus]

macdeb said:

phazed said:

From memory my old 5.0 in good fettle averaged about 210-220.

As yours are pretty even I wouldn't worry too much.

Awaits further imput

Looks high Peter, skimmed heads?

Just for reference one of my early Ford X Flow builds had 11.5 1 compression and that turned 230 psi compression pressures as Mac says that was high.