Compression test
From Crankshaft Coalition Wiki
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==To check compression:== | ==To check compression:== | ||
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'''Disable spark and fuel''' | '''Disable spark and fuel''' | ||
| + | Ideally, warm up the engine first. Piston and rings are designed to provide optimum sealing at operating temperature. | ||
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On a vehicle with a electric fuel pump pull the fuel pump relay, let engine idle until it stalls out. For mechanical fuel pump, I think using a vise grip and 2 thin blocks of wood (to avoid crimping the soft line) on the rubber fuel line will work. This prevents fire hazard. | On a vehicle with a electric fuel pump pull the fuel pump relay, let engine idle until it stalls out. For mechanical fuel pump, I think using a vise grip and 2 thin blocks of wood (to avoid crimping the soft line) on the rubber fuel line will work. This prevents fire hazard. | ||
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Move onto the next cylinder, repeat the compression test, and when you're done they should not be more than 10% off from each other, and none should be really low (0). If they are, you have some problems. | Move onto the next cylinder, repeat the compression test, and when you're done they should not be more than 10% off from each other, and none should be really low (0). If they are, you have some problems. | ||
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| + | ==Static compression ratio== | ||
| + | *[http://www.wheelspin.net/calc/calc2.html SCR] | ||
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| + | ==Dynamic compression ratio== | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator] | ||
| + | *[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| + | Some dynamic compression rtatio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate. | ||
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| + | If the intake valve closing (IVC) point isn't known, it can be calculated: | ||
| + | # Divide the intake duration by 2 | ||
| + | # Add the results to the lobe separation angle (LSA) | ||
| + | # Subtract any ground-in advance | ||
| + | # Subtract 180 | ||
| + | This result does not need to have any amount added to the IVC point, like the KB calculator calls for. | ||
==Resources== | ==Resources== | ||
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