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I think this question has been raised before but I want to discuss it again. My 3310 Holley has 72's up front. It's got a metering block so rear "jetting" is basically fixed. I'm just trying to guage if I need the 72's on a mild street big block. Holley and fuel mileage don't usually go hand-in-hand but every little bit helps. Right now I get 12-13 or so mpg cruising at 2400 rpm. If I could jet down to 70 or 71 and not hurt performance I'd do it. Is this a "try it and see" situation? This is on my 472 with Performer intake, 210/218 cam, mildly ported heads, PI exhaust manifold, and 8.5:1 compression.

What do the rest of you guys run for jetting in your carbs? Your combos?
 

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On my 347 I use 67 in the front, and 65 in the back. It works pretty well. I switched it to 63 up front for emissions testing, and the performance sucked.

As for fuel mileage, I'm not sure.
 

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I run 76`s in front and 86`s in back on my little 5.0 in my 650 speed Demon. 9.5 P/V. runs great, no stumbles, no black smoke, no plug fouling. This is an estimate but it gets between 15 and 20 mpg on the freeway.
 
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