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just did mine 598 after 8 motor passes and 5 passes on 200-300 NX nitrous fogger. .028 & .032 ring gaps.
4 & 5% on all cylinders cold.
 

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I do leakdown test as normal maintenance to establish a history.If a cylinder drops 25% quickly I find out way.If you have over 15% on all cylinders you have alot of blowby and are giving up some power.
 

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Leak down is good if you keep a track of it between races for example and if you see a large increase you got problems. Leak down is only an indication as most rings top rings need combustion pressures to seal more effectively. The pressures that you check during a leak down are nowhere near the operating pressures so you could be getting false results . I have experienced a case where an engine had 8% leak down dissasembled the engine fitted a sleave then had 20% leak down but car went quicker straight off the trailer!!!
 

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.

As mentioned, it's a good tool for catching changes. Lower the better & consistency from hole to hole is what's important.
I've seen 20, 30, 40% & it still ran the number.


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Leak down is good if you keep a track of it between races for example and if you see a large increase you got problems. Leak down is only an indication as most rings top rings need combustion pressures to seal more effectively. The pressures that you check during a leak down are nowhere near the operating pressures so you could be getting false results . I have experienced a case where an engine had 8% leak down dissasembled the engine fitted a sleave then had 20% leak down but car went quicker straight off the trailer!!!
Pro does it make a difference if the car is cold vs just had a run ?

thanks

Nick--
 

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Always do your leak down tests in exactly the same way and circumstances. If not your wasting time and your results mean zilch.

Always keep records on anything you do with your car dated with comments of results. Engine, tires, suspension anything. Keep records of anything you change or adjust. You will be surprised at how much help records can be later.

You are not racing the engine cold. You are racing it warm or hot. Build some heat into it and quickly remove the plugs and begin testing.

If you are using those cheepie leak down testors that use two different guages (Most people do), you need to be sure the line pressure coming into the regulator is the same each time too.

In a Normal Aspirated Engine, as far as I am concerned 12% leakage in a cylinder is too much, But in a nitrous engine makes no difference. In a nitrous engine it gets negative near 30% to 40% and worse. Oddly enough though I had one guy with a bigger engine that was still running strong with over 50% leakage in a high nitrous sprayed engine. Compression looked bad. Leakage test looked bad, engine cranked over smoothly and evenly and still ran strong. I never did understand that.

Ed
 
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