The Ratio Calculators below allow you to approximate any given engine setting.
Developed by Triumph Oracle, you can see what changes affect your engine performance.
Download OpenOffice, and follow the instructions.
Speed is relative, different calculators will show different results as the theoretical outcome of speed to ratios is governed by the parameters used to set those outcomes. The Oracle calculator is designed to be with minimal losses, in other words, a perfect world running without the weight of the machine, rider, wind resistance, tire friction or internal engine, gearbox losses, all of which vary considerably. To build any of these factors into an all encompassing calculation to give a standard would be dishonest. It is the relative ratio of progression or restriction of speed vs gearing that is important.
Compression is relative, different calculators will show different results as the theoretical outcome of compression as results are governed by the the parameters used to set those outcomes. The Oracle calculator is designed to be without any losses, in other words, a perfect world running without gas leakage on valves, piston rings etc, all of which can vary considerably. To build any of these factors into an all encompassing calculation or attempt to take account of would be incorrect. It is the relative ratio of compression or loss off that is important.
If measuring plug hole compression, the figures are given for a 'WET' test. Read the instructions given in Oracle 'Cylinders', Pg 27-29.
Remove air filters & spark plugs. Start with a cold engine & 'Dry' test. Test each cylinder with throttle wide open. 5 full kicks. Record results. Insert 5cc engine oil, retest. Repeast with hot engine.
How to do a compression test.
Technically, you should do this when the engine is hot. Without burning fingers, do it when the engine is cold. This will tell you what you need to know.
Remove Air Filters, Before removing the spark plugs, it’s a good idea to loosen and blow around them with compressed air to remove dirt that might fall into the engine. Screw the compression gauge into the spark plug hole, hold the throttle wide open, and operate the kick starter up to fifteen times. Note the gauge reading and release the pressure. Run the test on the other cylinder. Both cylinders should be within 10% of each other. If you have low compression i.e. below 100psi or 7 bar, a ‘wet’ test is helpful to narrow down the cause.
Squirt two teaspoon's worth of oil into the cylinder over the piston crown and on to the top ring. Complete the test again. The oil will hold compression for a while. If your retest with oil gives significantly higher compression, the rings are worn. If there’s little change in compression, it's the valves or cylinder head joint that’s leaking. If you think it's the valves, it's worth checking the valve tappet clearances. If the gaps are tight, they could cause a compression leak. If the gap are tight, reset them to the proper clearances and test again.