Can I get some opinions on these wet/dry compression figures? :)

Hello everyone,

I will soon be starting a build on the top end (head) of my B18C2 as I am fairly sure my valve guides are getting worn. However just to be sure my bottom end would be ok as is, I wanted to do a wet/dry compression test comparison. Here are the figures:

DRY TEST (8-10 cranks to reach full comp)
1: 200PSI
2: 195PSI
3: 197PSI
4: 200PSI

WET TEST (5-7 cranks to reach full comp)
1: 215PSI
2: 210PSI
3: 212PSI
4: 215PSI

so there is a difference of approx 15PSI in each cylinder between wet and dry tests. and a largest dry variation of 5PSI.

the numbers themselves appear to be good as other peoples B18C2's appear to be getting between 170PSI-190PSI and are confident that it is healthy.

But I'm not sure how big a difference is acceptable between wet/dry tests.

any opinions on this test would be greatly appreciated!

looks like a healthy engine, why do you think the valve guides are worn?

thanks for your input man :) because it seems to use a bit of oil sometimes (doesn't really smoke for what I can see and what people behind me have said) but i've had the valve seals replaced and the comp results seem ok. not really that bad but I want to build the head with performance parts anyway.

but yeah interested in getting everyones input on these numbers and their variations before I jump in to the build.

Looks excellent to me. Good high numbers and no drops/variances.

How much oil are you using?
What kind of oil are you using?
Do absolutely thrash the fuk out of your car every time you drive it?
Are you sure there are no leaks anywhere?

I know you're not some noob fellow, just thought i'd sk the obvious.

Quote:

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Originally Posted by dougie_504

Looks excellent to me. Good high numbers and no drops/variances.

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thanks buddy :)

Quote:

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Originally Posted by u mad?

How much oil are you using?
What kind of oil are you using?
Do absolutely thrash the fuk out of your car every time you drive it?
Are you sure there are no leaks anywhere?

I know you're not some noob fellow, just thought i'd sk the obvious.

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I used to use fully synthetic 10W-40 but it would burn above 6000, so I have been using fully synthetic 15W-50 for ages since then.

its very strange with it's behaviour, because sometimes I can gun it just about all the way through a couple of gears, and my oil is still full the next day, but sometimes after a number of drives (with the occasional vtec) it will drop a couple of 100ml, say like a quarter to a third lost between the dots on the dipstick (which is approx a litre between dots.

I don't thrash my car, it's actually pretty rare that I floor the gas but as stated above the times I have it hasn't really seemed to affect the amount of oil in the engine much if any.

although this said it isn't my daily driver so when I do drive it I try to still have fun (usually mountain runs) but I always let it warm up before I drive and I will drive normally before about 15-20 mins before I start to kick it up a notch.

I know its not much, but I would like to be able to use a thinner oil, and want to rebuild the head with supertech parts to go with my buddyclub cams and the rest of my mods.

and all leaks I have fixed long ago, which helped but it just has strange behaviour.

I notice you say you always warm it up before driving. If you mean by that you idle the engine with just a few rev-ups till it reaches temp, then you are doing the worst thing possible for it. Best to get in and get going, driving normally and that will get the oil around the engine to where it's needed and will get it up to operating temp much faster. The other thing is that condensation and combustion contaminants that occur at startup need to be burnt off as quickly as possible too otherwise they will get into your oil. This may account for you using some oil after the occasional blast.

While, as others have said your dry test figures are good, 15 PSI seems a bit much between the wet numbers, under 10 would be better, so some ring leakage might exist. Did you do both tests with the thottle held wide open?

I would PM Adrian at TODA, get his opinion.

Quote:

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Originally Posted by hondapop

I notice you say you always warm it up before driving. If you mean by that you idle the engine with just a few rev-ups till it reaches temp, then you are doing the worst thing possible for it. Best to get in and get going, driving normally and that will get the oil around the engine to where it's needed and will get it up to operating temp much faster. The other thing is that condensation and combustion contaminants that occur at startup need to be burnt off as quickly as possible too otherwise they will get into your oil. This may account for you using some oil after the occasional blast.

While, as others have said your dry test figures are good, 15 PSI seems a bit much between the wet numbers, under 10 would be better, so some ring leakage might exist. Did you do both tests with the thottle held wide open?

I would PM Adrian at TODA, get his opinion.

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yeah i did both tests at WOT. and I haven't really heard that warming the car up has negative effects before..? strange :/

I would like to avoid doing the bottom end too but if it needs doing then it will be easier to rip the whole engine out and do it all at once...

does anyone else think these wet/dry variances are too much?

something I didn't take into account is that the three squirts of oil (15W-50) I put into each cylinder would have essentially the same effect as shaving the head, as the oil ontop of the piston would fill in some of the space between the piston crown and the head, not just seal against the rings. this would explain the majority of the 15PSI difference. so it sounds pretty good to me now that I think about it that way. :)

5ml of oil (teaspoon) is sufficient to seal the rings when doing a hot compression test, anything more would just get shot out the exhaust valve (or out the plug holes which should be open when testing as well, in order to allow the engine to spin as freely as possible).

I'm not trying to be smartarse when I say that the practice of warming up an engine before driving went out in the 1960's, particularly with the introduction of multigrade oils around about that time, It's a well established and recognised fact that getting a motor moving at normal speeds from cold prevents corrosive wear from the acids that form in the combustion chambers/cylinders during cold running.

I went to school with Fred Flinstone and you never saw him warm his feet up before he tore off, eh.

Quote:

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Originally Posted by hondapop

5ml of oil (teaspoon) is sufficient to seal the rings when doing a hot compression test, anything more would just get shot out the exhaust valve (or out the plug holes which should be open when testing as well, in order to allow the engine to spin as freely as possible).

I'm not trying to be smartarse when I say that the practice of warming up an engine before driving went out in the 1960's, particularly with the introduction of multigrade oils around about that time, It's a well established and recognised fact that getting a motor moving at normal speeds from cold prevents corrosive wear from the acids that form in the combustion chambers/cylinders during cold running.

I went to school with Fred Flinstone and you never saw him warm his feet up before he tore off, eh.

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haha, i like the fred flintstone analogy :P ok cool thanks for your detailed input man :)

Basically you just drive your car at 2500 rpm max if possible until warm, rather than let it sit there idling high for a while?

Just remember, if you're letting your car warm up by ideling for 20 minutes, that means only the engine will be warmed up. Gearbox/diff need time to warm up as well.


Another thing to consider re your oil consumption is you PCV.

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Originally Posted by u mad?

Just remember, if you're letting your car warm up by ideling for 20 minutes, that means only the engine will be warmed up. Gearbox/diff need time to warm up as well.


Another thing to consider re your oil consumption is you PCV.

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thanks man! yeah I understand this, and the pcv valve is new :)

Quote:

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Originally Posted by u mad?

Just remember, if you're letting your car warm up by ideling for 20 minutes, that means only the engine will be warmed up. Gearbox/diff need time to warm up as well.


Another thing to consider re your oil consumption is you PCV.

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20 mins of idling could use the same fuel as 10 mins of normal traffic driving. Do that 10 times a week and that's like 40-50kms off the range of a tank.

Quote:

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Originally Posted by bennjamin

20 mins of idling could use the same fuel as 10 mins of normal traffic driving. Do that 10 times a week and that's like 40-50kms off the range of a tank.

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I think this warming up business needs to be in a different thread.. lol

U are right , by gosh !

Back on topic.

Have you considered a leak down test to find exactly where there is , if at all there is a compression leak ?

I did think about that but I dont have the equipment to perform one. :(

although after talking to adrian I think it should be fine, I think it's just the valve guides that have wear on them. so once I do the rebuild it should improve.