3.73 or keep the 4.10?

[cancow]

My 67 F250 has a 4.10 rear end but i would like to get more mpg. Seems the 3.73 would still be a good puller (I dont pull stuff that often) Anyone have an idea what kind of improvement this would be? My truck will cruise at 75mph all day long no problem but i am getting 10 mpg. I have an fmx or mx trans that need to be replaced as well.

[FORDification]

You didn't mention what size engine you have, but I'd guess it's a 360. I don't think I've heard of anyone getting more than about 12-13 mpg with those, almost regardless of what you do. However, your engine RPMs out on the highway are definitely going to be high with those gears...dropping down to something in the high 3's will drop your engine's RPMs and should definitely help with mileage by a point or two. I don't think it would have any kind of detrimental effect on your towing abilities.

Adding a good full-flow dual exhaust system is one of the best add-ons you can make to these trucks. Not only will it help with your mileage, but will give it a bit more pep too.

[cancow]

I have the 352 engine. I need a new trans and have been toying with the idea of using a 700r4 and an FE mounting kit. Do you know anyone who has done this? The idea of an OD is nice... I had been looking for headers and a dual exhaust but i am unable to find a manufacturer. All the big makers Hedman etc say there headers work for 67s but not the campers specials. Some say it is a sway bar issue, others the bendix, others the HD MX trans cooler lines. Any ideas? Thanks!

[FORDification]

From what I understand, the headers will not work with a Bendix box, or the Camper Specials equipped with the swaybar that goes between the radius arms. I've never heard of problems with cooler lines, but I would think those could be easily rerouted to work.

[cancow]

What about with manual steering? What if i hit the headers with a hammer? I dont have the sway bar if i remember correctly.

[cobraF100]

I've also been kicking around the Idea of putting a 700R4 (Chevy Trans) behind my FE so I can run alittle Bigger Gear and Have the 30% reduction 4th OD Gear of the 700R4.

FE's are Torq. Monster's and the 700R4 is not known to take alot of Torq. and have been known to break "Input Shafts"

So when and if you do this (still on my Drawing board) You need to have the Hardened Input Shafts installed and it will push your Trans Price up a Bit about another $300-$450 Bucks.

The Adapter Kits can be bought for around $700-$850 whitch will include everything other than the Trans. and Converter.
http://www.transmissioncenter.net/Fe_to_Chevkit.jpeg

And after I'm done with the New Motor and done a few things to the Truck I'll start saveing up to do this myself and maybe they'll come down in price when I'm ready to this in about yr.

[FORDification]

Headers will fit just fine with manual steering or with the Ford/Saginaw power steering box, used from about '69 on up. I doubt you have the sway bar...in fact, I've never even seen one, but they do exist.

[bumt72]

Ok on a related note, was the dual exhaust ever an option? Da BUMT has dual exhaust and after the "Exhaust System" on my build sheet it got me wondering.


Kep

[morganater]

MY c6 sucks on the highway. I don't even know what my rearend gears are, but with my 295/50/15s I am at 3,000 RPMs @ 70mph on the highway. I dont mind this too much but is it because of the tires? and do you guys suspect I have a 3.50 rear end, becuase it is stock ( or is it¿)

[willowbilly3]

3.50 was the most common rear end on the F-100
On the F-250 with a 31 inch tall tire I like the 3.73 gear. It seems to pull good and the engine isn't twisting too hard. I doubt if you will see much difference in milage going from a 4.10 to a 3.73 though. Headers should give you another 1 1/2-2 mpg at highway speeds. And while the 700 R-4 has several inherent weaknesses, a good builder can eliminate them. It would be the best bet. For about the same price you can put a gear venders o/d behind your C6 but remember that C6 robs a bunch of horse power. It can have as much as 30 horsepower parasitic drain. Another thing I have noticed with FE motors is they really aren't too bad on gas while cruising but are horrible in stop and go situations like traffic.
I put headers on a stock 74 highboy with 4.10 gears and ran 13 pretty consistent and got 15 1/2 a couple times driving 55 with the tailgate down. My tired 390 in the crewcab just consistenly pulled 10-10 1/2 all the way home pulling a 16 foot trailer with my 96 F-150 on it. It is a 4 speed with 3.73 gears. I haven't driven it empty yet to see how it does.

[cancow]

remember that C6 robs a bunch of horse power. It can have as much as 30 horsepower parasitic drain. .

I have heard that and more. Does this mean my milage would be worse than with my MX-HD?

[willowbilly3]

I have no experience with the MX/FMX transmission.

[Comet]

Although this won't help you figure out your fuel mileage delta with a gear change, the following formula will find the new RPM your motor will run at a given MPH. This, in turn, should help you get a better idea on the impact to your fuel consumption:
RPM = (mph x gear ratio x 336) divided by (tire diameter)

[jreb333]

What if i hit the headers with a hammer?

ROTMFFLMMFAO!!!!!!