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MPG was not a consideration when I rebuilt my motor from "race ready" to street use. I simply wanted a more reasonable power band than the solid roller lifter monster cam and massive jet dual carbs with 12.5 to 1 compression had to give. Heck it wouldn't even make decent power below 3,000 rpm! Got 6 mpg.
Solid lifter flat tappet with a nice "lumpy idle", vacuum secondary smaller carbs with reasonable jets and the right power valve combined with lower compression and more quench achieved that goal. Before it was 660 some h.p., flywheel. It is estimated I gave up 150 h.p. with the rebuild. 1/4 mile E.T. went from 11.90 to 11.99. So close you can't "feel" the difference, but street manners have improved tremendously. Essentially, I didn't give up anything, I gained a bunch! Mpg and thus the RANGE on a tank of gas is more than double. A pleasant surprise.
You CAN have good power AND good mpg, with a carb (or two in my case). Look at the new cars with terrific horse power and great cruising mpg. It's because the engines are more efficient. Efficient means more horses and more mpg at the same time! You can have your cake and eat it to. Timing and carb settings are the key components. Typically Cobras run much richer than they need to be, that's #1. Typically they don't utilize enough advance in cruise conditions. Like I said, when you get it right (timing and carb) it is sweet. Throw in some combustion chamber tricks, like adding quench, and the pay back can be significant in terms of drivability, mpg AND horse power!
I went for a geared starter as well, $250 or so, still broke the drive gear on the starter in time. Eventually I just backed off the base timing until a STOCK starter would crank it and then added enough mechanical advance to come in a little quicker and that solved the problem. Still, I WOULD like more base timing than the 17-18 or so I'm running now to eliminate a slight stumble when conditions are just right. I'd have to buy an electronic MSD control to retard the timing for a hot start, which I'm not crazy about buying. But I would prefer that over a geared starter. The other problem is the dang MSD cannot be limited enough with how much mechanical advance it provides. Leaving me with TO much mechanical and base timing before the vacuum even kicks in. To limit the mech advance MORE than MSD allows I went with a custom bushing to further reduce the max allowed mechanical advance. Got it from some shop in Cottage Grove, Oregon, via the internet, can't recall the fellows name now...
Last edited by Excaliber; 03-16-2010 at 09:48 AM..
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