Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
techtalk:ref:svcproc20 [2019/10/16 22:18]
ixl2relax [Test Each Cylinder for Compression]
techtalk:ref:svcproc20 [2020/03/02 05:55] (current)
hippysmack [Compression Calculator]
Line 91: Line 91:
 **Pics of the Damage**: ((Photos by sep69 of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1567509&​page=2)) **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|}}| \\ |{{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 ======
 +Article by aswracing of the XLFORUM ((http://​xlforum.net/​forums/​showthread.php?​t=1441757)) and Hammer Performance site. (( http://​hammerperf.com/​ttcompression.shtml)) \\
 +
 +[[http://​hammerperf.com/​ttcompression.shtml|Click here to download a free copy of the HAMMER PERFORMANCE 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 just download the 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 Hammer Performance ((aswracing of the XLForum)). \\
 +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. \\
 +
 +Note that results given by this program are intended as a guideline only. \\
 +HAMMER PERFORMANCE assumes no responsibility for what you do with the information presented. \\
 +
 +{{:​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)) \\
 +
 +