Building 300CI six.Non efi head ,ported/polished,bigger valves,roller rockers,.020 overbore,reworked rods[shotpeened,polished beams,etc.] EFI exhaust manifolds ported/polished.....now have to decide on reworked,hotrodded factory EFI or 4bbl carb.I am well aware of pros/cons of each system .What I really hope for is to find someone with similar engine in similar chassis with 4bbl induction for some REAL mileage figures.My chassis is `81 fullsize bronco[same as F150] with 4inch lift and lots of suspension mods.Trans is LENTECH RV2000 AOD,so .67 o/d.Does anyone have something similar for real mileage figures?I would really rather have a carb if I can get acceptable mileage.Diffs are 4.56 but I have 37inch tires.Please no wild guesses[Ican already do that].Just please if someone has actual experience I would REALLY appreciate an informed response....MANY THANKS IN ADVANCE!

 

Hi and welcome to FTE

I've moved your question down to this forum for you. Hopefully you'll get some good answers here. Sounds like a fun project

 

No guess here. I have a Jasper rebuild with .030 over pistons and everting else is stock in the engine. I have Offy "C" and a 390 Holley on an F-250 4x4 with 3.54 gears and NP435 tranny. I get 15-16 MPG daily driving and 12-13 loaded with 1/2 ton of hay to 6000 # of horse trailer and horse.

P.S. I added a 1" spacer uder the carb and it seems to improved the loaded MPG but I have not checked the MPG. I have not towed very far after the spacer install.

 

MANY THANKS Just the kind of info I need ! Just wondering ,I know final drive on NP435 is 1 to 1 ,but any idea what size tires you have? That mileage would be a 40-50% increase over 400/c-6 combo I have now....THANKS AGAIN

 

The tires are 245 75 16 E and are close to OEM size of 7.50x16D. This makes the Odometer off by 4MPH and that is calculated in my ending MPG.

 

stewbronco....after using a mathematical formula i got off of a tire vs. gearing article on superlift.com's website, a rough estimate of your rpm at 65 mph is 1803 rpm in overdrive gear...the formula is as follows: rpm=mph x gear ratio x 336/tire size in inches thus:

rpm=65 x 4.56(multiply by .67 for OD gear) x 336/37
rpm=1803

i did look at the website, and they apparently no longer have the article available, and if they do, i don't know how to find it, but that formula will put you fairly close to your actual rpm at whatever given speed with whatever tire size and gear ratio you run...

MontanaFord

 

That is about the figure I get too.I think my custom torque converter will "slip " about 5-7%. So the .67 o/d will effectively become something less.