mileage on built six
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Junior User
Joined: Aug 2003
Posts: 69
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From: Burlington, West Virginia
mileage on built six
I have a freshly rebuilt 300 in my '86 F-150 4x4 stepside. It has a crane cam, punched .030 over, a 500cfm Holley 2bbl, and straight exhaust, no cats. I have a C6 auto and 3.55 gears and am running 30x9.50s. I am getting 7mpg. Is this normal? If not, What can I do to get a little better. This thing is breaking me up driving 36 miles a day to work. 
Senior User
Joined: Dec 2003
Posts: 215
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Well, with your tranny/gears/tire size combo you'd never get out of the mid-teens anyway. The combo is excellent for work or performance but not mileage. Your biggest problem, though, is probably the way your engine is set-up. You have a 500cfm carb on one end, a cam with at least moderate duration in the middle, and almost no back pressure at the end. So, unless the carb is tuned perfectly, it's throwing out too much fuel. The cam has both valves open at the same time longer than stock, and no back pressure from the open exhaust gives the mixture the perfect place to go on the compression stroke. If you fine -tune the carb and install high flow cats and mufflers you will probably run stronger and nearly double your mileage. Good luck with it.
