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techtalk:ref:svcproc26 [2019/08/06 15:03] hippysmack [Direct Method] |
techtalk:ref:svcproc26 [2020/02/27 00:32] hippysmack [Machined Squish Band] |
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| But it doesn't work well with heads that have angled domes. \\ | But it doesn't work well with heads that have angled domes. \\ | ||
| + | {{:techtalk:ref:svcproc:1200-1250_squish_band_measurement_by_hippysmack.jpg?direct&400|}} ((drawing by Hippysmack)) | ||
| ===== Direct Method ===== | ===== Direct Method ===== | ||
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| It takes more time than measuring the deck as in above because it requires an extra disassembly/reassembly cycle of the cylinder head. \\ | It takes more time than measuring the deck as in above because it requires an extra disassembly/reassembly cycle of the cylinder head. \\ | ||
| But this method works great with flat or angled head surfaces. The tools required are no more than if you are installing the heads. \\ | But this method works great with flat or angled head surfaces. The tools required are no more than if you are installing the heads. \\ | ||
| - | |||
| - | {{:techtalk:ref:svcproc:squish_band_1_by_aswracing.jpg?direct&300|}} ((photo by aswracing of the XLFORUM )) \\ | ||
| - | \\ | ||
| Place the solder in multiple places around the piston top. \\ | Place the solder in multiple places around the piston top. \\ | ||
| Grease works best to hold the solder but if using tape, keep it below the squish band. \\ | Grease works best to hold the solder but if using tape, keep it below the squish band. \\ | ||
| + | |||
| + | | Solder held with grease. ((photo by aswracing of the XLFORUM ))| | ||
| + | |{{:techtalk:ref:svcproc:squish_band_1_by_aswracing.jpg?direct&300|}}| | ||
| Install the head gaskets and heads then follow the torque procedure to full torque spec. \\ | Install the head gaskets and heads then follow the torque procedure to full torque spec. \\ | ||
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| Check with your engine builder / supplier for further assistance if you're looking for a complete performance package. \\ | Check with your engine builder / supplier for further assistance if you're looking for a complete performance package. \\ | ||
| + | ====== Compression Ratio ====== | ||
| + | |||
| + | <blockquote>Three tenths of a point in compression isn't really worth your time to tear it down. What's more, just the tolerance is greater than that. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1230012)) \\ | ||
| + | In other words it's entirely possible your motor is already 10:1 or higher and likewise it's possible it's already 9.4:1 or lower. \\ | ||
| + | There's variation in every one of the dimensions and volumes that determines compression ratio. \\ | ||
| + | And the 9.7:1 etc. they advertise is just a nominal number, it's somewhere around there. \\ | ||
| + | Measuring it really accurately involves several measurements, or alternatively, a volume measurement while the piston sits at TDC which is actually the most accurate way to do it. But it involves sealing the rings, typically with grease, so the liquid used to make the measurement doesn't just flow into the crankcase, and you'll also need a burrette to control and measure the volume of liquid introduced. | ||
| + | |||
| + | My advice would be to not worry about the exact CR so much (few people do). \\ | ||
| + | But if you want a worthy reason to go into it and make it better, look at optimizing your squish clearance instead. \\ | ||
| + | That will increase chamber turbulence (and thus efficiency) and bump up your compression a bit and actually reduce detonation in the process. \\ | ||
| + | Thin gaskets are an excellent way to do that. \\ | ||
| + | With N4's, stock pistons and dropping the top the typical .030" or so to get a real good squish clearance, you most likely will not cause yourself a clearance issue. \\ | ||
| + | Personally I'd check it anyway. \\ | ||
| + | |||
| + | If you want to understand the relationship between gasket thickness and compression ratio, it's not that hard to do. \\ | ||
| + | Let's say for example that your motor is 10:1 and each cylinder is 600cc (round numbers just to keep it simple). \\ | ||
| + | That means that at BDC, there's 667cc above the piston and at TDC, there's 67cc above the piston: \\ | ||
| + | * 667 minus 67 = 600cc of displacement | ||
| + | * 667 divided by 67 = 10:1 compression ratio | ||
| + | |||
| + | Now let's say you've got a .050" head gasket in there, and it's I.D. is 3.550". \\ | ||
| + | You can calculate it's contribution to the volume using the formula for cylindrical displacement, pi x r squared x h: \\ | ||
| + | * 3.14 x 1.775 x 1.775 x .050" = .495ci, multiply by 2.54 cubed to get 8.11cc | ||
| + | |||
| + | So let's say you go to a .025" head gasket. That 8.11cc will be cut in half to 4.06cc, right? \\ | ||
| + | So what does that do to the CR? \\ | ||
| + | * 667cc at BDC minus 4cc = 663cc | ||
| + | * 67cc at TDC minus 4cc = 63cc | ||
| + | * 663cc divided by 63cc = 10.52:1 | ||
| + | |||
| + | So in this example, taking .025" of thickness out of the head gasket bumped the cr about half a point. \\</blockquote> | ||
| \\ | \\ | ||
