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| Compression and Cylider leakage | ||
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| THEWORKSMINI |
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  Registered Member #486 Joined: Sun Dec 09 2007, 09:37AMLocation: Alton Hampshire Posts: 93 | In the following thread I will explain the difference between a compression test and cylinder leakage test. I will also explain why these tests are necessary to determine the condition of your engine. Compression is achieved when changing a large volume into a small volume, the piston in the cylinder bore moving upwards is responsible to this process. Along with air, there will also be a measured amount of fuel too. When a spark occoures the air and fuel mixture expands rapidly forcing the piston back down the bore. (This is where the power comes from) Compression testing uses a pressure gauge screwed in where the spark plugs fit, the engine is then turned over 6-8 times using the starter motor. The gauge displays the pressure generated by the piston moving up and down. In simple terms, Compression testing gives a quick idea as to the efficiency of each cylinder. Should a Compression test give cause for concern or you simply want a more accurate diagnosis a Cylinder leakage test can be carried out. Air is pumped into the cylinder using a compressor, the gauge reads the percentage of air that escapes. Not only does the amount of air escaping from the cylinder register on the gauge, it can also be heard, enabling the source of the leak to be pinpointed prior to stripping down the engine. All cylinders leak a little. Racing engines lose only 1 to 2%. Production engines in good condition leak 5% or less and no more than 10% regardless of the mileage. More than 10% leak means there's something wrong. This factor can provide and explanation as to why two identical cars produce different power outputs, before and after modifications. In simple terms, Cylinder leakage testing measures how much of the rapidly expanding air/fuel mixture is retained in the cylinder and actually used to push the piston down and how much is wasted. More leak = Less power Less leak = More power Causes of Cylinder leakage are as follows: Blown Head Gasket Worn Cylinder Bores Worn Piston Rings Worn Valve Guides Inlet or Exhaust valves not sealing correctly Before carrying out performance upgrades it is beneficial to carry out these tests to determine an engines health. Often it is necessary to rectify underlying problems first before going ahead with other costly modifications if they are not going work at their most efficient. LS Tuning is equipped with both Compression and Cylinder leakage test equipment should you be interested. These tests account for approximately forty minutes work at a cost of £30. Article brought to you courtesy of LTS Tuning (Lee) [ Edited Mon Mar 24 2008, 08:32PM ] www.detailperfection.com | ||
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| Dave |
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Mini Turbo'd   Registered Member #140 Joined: Mon Mar 13 2006, 12:00AMLocation: Southampton Posts: 2481 | Defiantly a very important test as Lee has said  Final compression ratio is what matters and must be the same on all cylinders. I say final compression ratio as with a forced induction engine like the Cooper S you raise compression ratio when you compress the air into the cylinder before the compression stroke. This is why the Cooper S comes with lower compression pistons compared to the One or Cooper as the final ratio would be too high otherwise and this gives a much higher chance of detonation and so a wreaked engine. If you think yours isnt quite as powerful as it should be then get it compression tested as it might just be one cylinder that is down or even just a re torquing of the head bolts. £30 is little to pay to know your engine is running right before you go and put any pullies on. [ Edited Mon Mar 24 2008, 08:49PM ] MINI Project 370hp and counting... : MINIProject.co.uk | ||
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