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--- techtalk:ref:svcproc20 [2019/10/16 22:18]
ixl2relax [Test Each Cylinder for Compression]
+++ techtalk:ref:svcproc20 [2020/03/02 05:38]
hippysmack
@@ Line 91: / Line 91: @@
 **Pics of the Damage**: ((Photos by sep69 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1567509&page=2))
 |{{techtalk:ref:svcproc:piston_damage_1_by_sep69.jpg?direct&300|}}|{{techtalk:ref:svcproc:piston_damage_2_by_sep69.jpg?direct&300|}}|{{techtalk:ref:svcproc:piston_damage_3_by_sep69.jpg?direct&300|}}| \\
+====== Compression Calculator ======
+So how much compression can you run with what cams, and still be able to run pump gas? \\
+This question comes up from time to time on the XLFforum. \\
+And unfortunately, the answers tend to either be inaccurate, incomplete, or just downright vague. \\
+The right answer is that you should figure out your corrected compression ratio. \\
+Which is the compression ratio of the motor considering the intake valve close timing. \\
+In a nutshell, as the piston starts the compression stroke, the intake valve is still hanging open. \\
+Until the intake valve closes, no compression will be built. \\
+What corrected compression ratio tells you is what CR you have after the intake valve closes. \\
+This is the number to look at when deciding if your bike is going to run okay on pump gas. \\
+So how do you figure it out? Well, it's not as simple as it sounds at first. \\
+The big end of the rod travels in an arc and the connecting rod is not infinitely long. \\
+So you end up with a non-linear relationship between piston position and crankshaft rotation. \\
+For example, in the first 10 degrees after bottom dead cylinder, the piston barely moves at all. \\
+By comparison, 10 degrees of crank rotation that happens after the piston is halfway up causes a relatively large amount of piston movement. \\
+It's basically a geometry problem.
+To solve the problem, you need to dust off your trigonometry textbook and make right triangles out of it. \\
+Or, you could take the easy way and [[http://hammerperf.com/ttcompression.shtml|click here to download a free copy of the HAMMER PERFORMANCE Compression Calculator]]. \\
+Store the file somewhere on your hard drive where it's easy to find, and then double click on it to execute. \\
+The program is very easy to use, and it will give progressively more info as you enter more data: \\
+  * For just displacement, enter the bore and stroke.
+  * To also get static compression ratio, enter the piston dome, chamber size, piston height, and gasket specs.
+  * To also get corrected compression ratio, enter the intake close point (.053 lift crankshaft degrees) and connecting rod length.
+This program calculates both static and corrected compression ratio. What's the difference? ((http://hammerperf.com/ttcompression.shtml)) \\
+The static compression ratio takes the full compression stroke into account. This is the standard way of doing it. \\
+The corrected compression ratio, however, only counts the portion of the compression stroke after the intake valve closes. \\
+Corrected compression ratios of around 9.2:1 are considered the max you can run on U.S. pump gas, with a reasonably turbulent chamber. \\
+Since no compression builds until after the intake valve closes, \\
+It's the corrected compression ratio that gives the best indication of how pump gas friendly your motor will be. \\
+Premium pump gas in the U.S. will generally tolerate corrected compression ratios of somewhere between 8.8:1 and 9.3:1. \\
+With a poor chamber that has little turbulence ( i.e hemi chambers and no squish band), stay on the low end of that range, maybe even lower. \\
+With a good, turbulent chamber (think squish bands), you can run more toward the high end of the range. \\
+With good chamber turbulence and dual plugs, you can even run it higher, up to 9.5:1 is not unusual. \\
+This is a free tool, independently developed in-house by aswracing of the XLForum (Hammer Performance). \\
+Feel free to use it and distribute it as you please. \\
+It's virus-free. \\
+It collects no information about you or phones, home or anything like that. \\
+All it does is perform the calculations and give you the answer. \\
+{{:techtalk:ref:svcproc:compression_calculator_screeenshot_1_by_aswracing.jpg?direct&400|}} ((screenshot by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1441757)) {{:techtalk:ref:svcproc:compression_calculator_screeenshot_2_by_aswracing.jpg?direct&400|}} ((screenshot by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1441757)) \\

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