240zip Posted November 2, 2006 Share Posted November 2, 2006 I believe the LEngine.exe application has errors, but perhaps folks can help. L28 (F54) block, .5mm overbore, flattop pistons, std gasket, E31 head, L28 rods, and L28 crank. It claims I have a CR of 10.32:1 ... but it also claims I have a deck height of .030" (mine appears to be -.020"). Given I drive this car on weekends and infrequently, using 91 octane gas is no issue. I'm also OK with grabbing some aviation gas if that's needed. I'm just worried that I'm looking at an 11:1 CR or something like that with my set-up. I'm at 5,400 feet (Colorado), so I've been told a 11:1 CR is like a 10:1 CR at sea-level. Perhaps this is also another myth from my time spent on the ZCAR forum. From what little I know about quench, it seems I should have a decent set-up with a nice 'squish', but the CR is of great concern. If I was doing this from scratch, I'd likely select a different head / block combo, but all the work has already been done. I'm just at the assembly point now. I just want to see if I'm totally screwed. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 2, 2006 Share Posted November 2, 2006 I have basically that same configuration but I shaved the head a bit and I have about 11:1 and at sea level I need about 95 or 96 octane with a .490/280 cam. It is true that you don't need as much octane at altitude. Some stations that I filled up at in CO had 85, 87, and 89 instead of the sea level 87, 89, and 91 octane that we have here. I don't think you're screwed. If you have problems with pinging, I'd go to a bigger camshaft to fix. I bet you wouldn't have any trouble with a cam as big as the one I'm running. Quote Link to comment Share on other sites More sharing options...
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