Below some compression testing tips, maybe useful to someone not familiar with doing a compression test.From Andrews website:With a warm engine, remove both spark plugs, ground spark plug wire leads and insert the gauge adapter in one spark plug location. Now, holding the throttle wide open, crank the engine until the needle stops and read the pressure indicated on the gauge. Then repeat the procedure on the other cylinder.
• Warm the engine to operating temperature to insure the metal parts are expanded to their normal running tolerances. A cold engine will give low readings.
• Use a screw in type gauge - Twin Cams use a 12mm adapter.
• Make sure the battery is in good condition, and fully charged. The starter (cranking system) will need to be in good condition to achieve a high, consistent, cranking speed for the duration of the test. A battery with a low charge will give low compression readings because of reduced cranking speeds.
• Disable automatic compression releases (ACRs) in CVO bikes with ACRs
• It might help to remove the fuse to the headlights to minimize battery drawdown
• Remove fuel fuse or disconnect the electrical connections to the fuel injector on each cylinder. This will prevent fuel injecting while cranking the engine, a situation that will flood the cylinders with fuel.
• Twist throttle wide open.
Generally, higher cranking compression pressures mean more torque at lower RPM ranges but the trade off is that above a certain point (around 185 PSI) the risk of detonation enters the picture. What happens at higher RPM is less predictable and can’t be easily determined from a static pressure reading. What is important is that the cam timing (intake close), duration and compression ratio all be properly matched so that each compliments the others. It might help to remove the fuse to the headlights to minimize battery drawdown
When installing cams with high lifts and long durations, a few general observations are worth keeping in mind. Remember that additional cam duration can produce more usable power but too much duration may actually hurt overall performance. The problem of poor engine response begins when too much duration results in lower cylinder compression pressure (at low RPM) which in turn can reduce low RPM torque and power. Too much duration in a camshaft is not necessarily a good thing.
S&S web site:S&S Cycle recommends you check your engine's cranking pressure with a good screw in compression gauge. They recommend 180-190 psi for street use and up to 200 psi for those who "insist on pushing the limits".
MIKUNILow compression pressure:
http://www.mikuni.com/fs-tuning_guide.htmlThe higher the pressure within the combustion chamber when the air/fuel mixture is ignited, everything else being equal, the more power your engine produces and more efficiently it runs. However, if the pressure is too high, detonation (pinging) may occur which can destroy an engine.
Each combustion chamber design has an upper pressure limit above which serious, damaging detonation is likely. With modern American 92 Octane lead-free gasoline, a reasonable upper pressure limit is 180 psi for the Evo Big Twin and 190 psi for the Twin Cam. A well-tuned motor should not suffer detonation with these pressures.
The standard method for determining the compression or cranking pressure of an engine is to warm up the engine, remove the spark plugs, install a standard compression gauge into one of the spark plug holes and, with the throttle fully open, crank the engine over with the starter motor until the pressure gauge needle stops rising. This usually takes 4 - 8 compression strokes. Both cylinders should be tested.
Stock Evo and Twin Cam motors develop cranking pressures in the 150-160 psi range. If a late-closing cam is installed, with no other changes, the cranking pressure will go down. The reason high compression ratio pistons and racing cams are so often associated is because the higher compression ratio pistons (and/or milled heads) are needed to regain even the normal moderate cranking pressures, let alone raise them for more power and efficiency.
Low cranking pressures (because of late closing cams and stock pistons) can significantly reduce performance in the mid-rpm range.
From the Harley Tech Talk forum.From: Mike Roland, Kuryakyn Wild Thing Products
Sent: 11/23/2005 3:17 PM
http://groups.msn.com/harleytechtalk...=797275&CDir=1On the performance panel I was on last year at the Cincinatti V-Twin Show with Danny Fitzmaurice (Zippers), Ron Dickey (Axtell), Scott Sjovall (S&S), and Tom Pirone (TP), it was pretty much agreed that 190 PSI cranking pressure is the highest cranking compression you should run on most street Harleys. Others such as John Andrews (Andrews Products) and Reggie Ronzello (R&R Cycle), along with many others, have said the same thing. I hope this doesn't start a big war. If someone wants to run higher pressures, fine. This is just my opinion mirrored by a lot of other industry people.
Info from another web site I ran across some time ago:
Compression testing is usually performed on a warm engine because that is the state that the engine operates in most of the time. Both the engine block and the pistons and rings will expand when heated and the most accurate indications of engine condition are obtained with the engine at operating temperature. This does not mean, however, that you cannot perform a test on a cold engine and get useful data, it simply means that the data collected may be slightly less accurate than when the engine is at operating temperature.
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Topic: ccp 07 CVO (Read 5454 times)