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Message: <blockquote data-quote="Silver95bird" data-source="post: 1404363" data-attributes="member: 21743">I agree with what you're saying. Lean isn't really a problem in the conditions you're talking about - steady state cruise on a flatland - you can really lean it out and gain MPG that way. Heck, they've been experimenting with that since the advent of eec-iv. Too lean in those circumstances creates emissions problems, if nothing else. It seems that load plays a big factor in that equation though. Same timing, same A/F, but going up a big hill, and it'll knock like crazy. It's just that WOT is basically maximum load, and we're not just talking about 1200rpms worth of detonation under low load, but more like 6000 under maximum load. The engine just can't dissipate heat as well at that rpm. I get where you're going with the timing discussion. That's why diesels are so efficient. Unfortunately, it's not just purely combustion efficiency we have to deal with. There's also keeping temperatures low of things like exhaust valves and catalytic converters we have to deal with. That has a lot to do with setting the WOT A/F ratios, and ignition timing becomes the movable variable. That's more where I'm going. Whether I build an engine NA or SC, I'm not going to vary my A/F ratio because I changed my piston to head clearance, but I might be able to change the ignition timing and make a few hp more without blowing the dern thing up. Great discussion.</blockquote>