Compression and Leakdown test #'s, Puzzled!

Did a compression and leak down test over the weekend and got what to me looks like conflicting results. Here are the numbers:

Compression Leak Down

#1 160 19%

#2 151 26%

#3 157 22%

#4 158 22%

#5 153 24%

#6 160 21%

The compression numbers look good to me for 112K miles with all cylinders within a few psi of the new spec. However the leakdown percentages look a bit high. I was expecting them to be in the range of ~10%. My understanding is: generally good compression should also result in good leakdown, whereby low compression will generally result in high leakdown and the test will tell you where the leakage is coming from (rings, exhaust/intake valves, head gasket). I checked the compression gauge against another gauge and it is accurate, so compression is OK. The leak down tester is new. (I was surprised to see that the leakdown gauge face had 0-40% leak shaded as green/good, 40-70% leak yellow/moderate and 70-100% red/high).

The only reason I can think of for the high leakage percentage is that I did the leakdown after the compression test and the engine was quite cool by then possibly meaning the rings and/or valves were not quite sealing like at full operating temperature. Would leakage of a "just warm" engine be substantially higher than full operating temperature? Comments on the numbers in general? BTW: I have owned the car since new, never raced and nothing but full synthetic Mobil 1 since the first oil change at 1000 miles. EGR block off plates since about 80K miles. Car runs good but the leakdown numbers puzzle me!!!

They are OK for mileage and a cool engine. It is possible to build a race engine with under 3% leakdown, but they don't stay that way for long. My Toyota race engine was 4%, after 50 laps of Donington it's now 7% I would bet a stripdown ould show a good condition engine in your car, You shouldn't concern yourself.

Yeah, 19-26% is not too bad for a high-mileage engine.

If you had always used the stock paper airfilter it would probably be lower for all of them.

How *much* lower would depend on how long you've been running the K&N.

Don't be fooled by the 'high' compression figures, these usually mask carbon deposits that decrease the combustion chamber volume. Leakdown tests see beyond that.

JohnA, excellent point, and very true. My old Skyline ate its internals in 3000 miles of (probably gritty) trackdays, due to HKS air "filters". I was too idle to find and buy an OE air box and filter, despite Gibson Motorsport in Oz, probably THE leading Skyline experts worldwde, advising my first mod was to UN mod the filtration system...

Sorry for the slight shameful Hijack but how do you do a leak down check, i've only ever done compression tests with the screw in gauge.

Sorry for the slight shameful Hijack but how do you do a leak down check, i've only ever done compression tests with the screw in gauge.

http://www.moddedmustangs.com/forums/cylinder-leak-down-testing-vt3705.html

Nice, thats a good link Chris.

Thanks

Mike

Bit of a thread hijack, but how much would you charge to do a leak down / compression test, Chris? I'd like to check that everything's okay before I go BPU.

40 quid.

I had a K&N panel filter (still in original airbox) on the Calibra for a couple of years and I saw the leakdown figures go down by 10% in the first 2 years!

Once I rebuilt the engine, I only used paper filters in the airbox.

I continued to keep records of the leakdown figures and it only lost 3% in the next 3 years, despite running silly amounts of boost and suicidal experimental setups.

Food for thought.

Just a thought and slightly off topic, how would a K&N std panel compare with a cone type? i though the fact that they are a "wet" filter was an improvement over paper, also how about the Apexi paper cone type filter by comparison?

...how would a K&N std panel compare with a cone type?

using the airbox has the advantage of good protection from the engine bay heat

Filtration is equally compromised.

... i though the fact that they are a "wet" filter was an improvement over paper,

they are nowhere near good enough to catch particles of the same micron range as a decently-maintained paper filter.

Once cleaned and reoiled they are *far* worse.

also how about the Apexi paper cone type filter by comparison?

It has just over 1/5 of the active filtration area and all the issues of breathing warmed-up air

Hmm might be time to consider a Std air box replacement, trouble is not knowing just how long the K&N has been on there, and how much it has affected general wear! looking logically and not disputing the facts already gathered, as the induction only deals with turbos, inlet, cylinder head etc, i can't help but wonder just how much of bore, valve wear etc comes from dust particles entering the engine, as the combustion process also creates a fair amount of particle matter as well?