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| compression ratio https://www.slantsix.org/forum/viewtopic.php?t=8736 |
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| Author: | leaningtowerofpower [ Tue Mar 16, 2004 3:41 pm ] |
| Post subject: | compression ratio |
so what is the highest compession ratio that i can run (say in a long rod engine) on gas from the pump.....whats the best compression you can run on good ol cheap 87? |
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| Author: | 70valiant [ Tue Mar 16, 2004 4:18 pm ] |
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I had 0.100" taken off of my slant's head and I can't run less than 92 octane with my inital advance set to 2* |
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| Author: | leaningtowerofpower [ Tue Mar 16, 2004 4:25 pm ] |
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where did you get your machine work done? I've been looking for a shop I can trust here in PA. |
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| Author: | Doc [ Tue Mar 16, 2004 4:34 pm ] |
| Post subject: | |
It is better to think about this question in terms of cylinder pressure instead of calculated compression ratio. Calculated compression ratio is simply the volume ratio between a full cylinder and a fully compressed cylinder. Cylinder pressure is the cranking pressure (in psi) that the cylinder sees during a compression check. The cam profile and cylinder "leak-down" has a big influance on this number. This is why big cam profiles are combined with higher compression ratios, the cam "bleed-off" is off-set by the higher C/R to yield a desired cylinder pressure. Here is my opinion on cranking cylinder pressure readings and the fuel you need to use: Anything under 100 psi = rebuild the engine. 100 to 140 psi use 87 octane 140 to 170 psi use Premium (92 octane) 170 to 200 psi use Race gas (100+ octane) 200 to 240 psi use Super Race Gas (114) 240+ alcohol Finding the true cranking cylinder pressure for a new combination is difficult to do, you really have to build the engine and check it. That is why it is nice to find a "proven" combination of parts which is already known to produce the proper cylinder pressure for you application. DD |
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| Author: | 70valiant [ Tue Mar 16, 2004 8:01 pm ] |
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I had my head done at ABC automotive in souderton PA. they got me for almost $500 for cleaning, testing for cracks, shaving 0.100" off the mating surface, new guides, an intake valve, valve and seat resurfacing and a gasket set. This place has had a good reputation since I was a kid working at a GMC truck shop(I'm 35 now). I think I must be in the 160 PSI range now. My brother-in-law si going to let me borrow his compression tester this weekend when we get back from the MOPAR get together near king of prussia. |
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