Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision Next revision Both sides next revision | ||
|
techtalk:ref:svcproc26 [2019/08/06 15:05] hippysmack [Direct Method] |
techtalk:ref:svcproc26 [2020/02/27 00:32] hippysmack [Machined Squish Band] |
||
|---|---|---|---|
| Line 27: | Line 27: | ||
| 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 ===== | ||
| Line 120: | Line 121: | ||
| 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> | ||
| \\ | \\ | ||
