My 63 has a 302 and a C4 tranny and a 9in rear. Right now it has plenty of power but at about 65 its really wound out and gets crappy gas milage. Does anyone know what the ideal gear ratio for this combination is? my driving is about half freeway half surface streets.

 

3.25 is as high as i would go with that combo. It will keep the engine in the meat and potatoes, whereas a set of 3.00's will be too low and kill the bottom end.

Garbz

 

been wanting to this as well.. but unsettled on the ratio... I've got a beefy 5.0 with a tci c6 and 3.50 I believe.

Im turning 4kis at 65 3kis at 55..

Just waiting to get my wheel and tire combo so I can get it all right.

Garbz you think the 3.25 would be good for me as well?

 

My 351 cleveland with c4 and 28 or 29 inch tires, 4.11 rearend was running 3K at 55. I'm dropping back down to 3.50, so it has some drivability. Spinning through all 3 gears was fun, but not practical to drive around.

 

whats the best place to get the gears or rear end to swap out?
my 3.89 with inline 6 and 3 speed is horrible on highway.

 

If you go to the "Articles/Specs" dropdown menu at the top of this page, you will find some very helpful "Automotive Calculators". I think you will find them useful; I did.

What I haven't found is a source that tells what the "best" RPM for power and efficiency is for the different Ford engines. I suspect there are just too many variables related to specific engine setups.

 

I have a 3.00 in the rear. 65 mph is about 2300-2400 rpm. It is a good highway gear and does fairly well in a light truck/vehicle. Agree with one of the above posts that 3.25 would generally be as high as you want to go.

With a mildly hopped up 292 with Mustang 2bbl, mpg is 18. Hope to get better this summer by backing off to a 1.08 venturi and 48 jets.

 

Guys, More than ratios, things must be kept in perspective. Faber if your engine is a 240 the 3.89 is about right, if it is a FE it is way too high.

Remember this, big horse up front little gears in the back, little horse up front big gears in back.

I currently run 3.00 behind my FE, and think it is more all around good, I have run 2.75 in it got better mpg but it was a dog with my big trailer behind it.

Dave these trucks get crappy gas mileage, when designed & built about 50 mph was the top projected use speed. Back then before 4 lanes there were two speed limit signs on every road SL 55mph under it trucks 45 mph. Times have changed, aero designs have improved but they are still big boxes.

The beauty of the 9" is the ratio can be changed in about an hour from the time you pull out the jack til you drive off. You lift the rear, drop the ds, loosen the chunk bolts and start the fluid draining, pop the axles out a couple-three inches, swap the chunk and reverse the process.

46 a 292 that's saying 18, likely has a mismatch speedo gear giving a false reading. While possible, not very likely without OD. IMHO




John

 

3.25 seem to be the better gear to keep the smaller displacement motors in the right power area. They do not like to lug like larger displacement big blocks.

If you want to jackrabbit from stop light to stoplight nothing beats a set of 4.11s but regular driving in freeway traffic and speeds the 3.25 will do and still have a bit of oomph.

Garbz

 

What was the original rear axle ratio?

The AXLE code is listed on the Warranty Plate.

If y'all want to know, post what it is.

1959 thru today:

If the AXLE code begins with a letter: Limited Slip.

If the AXLE code begins with a number: No Limited Slip.

 

I'm running a hi perf 460 with C-6 Shift kit and 3.00 in the rear all highway around here, She still goes no question but I would like to drive to show n shines so I'll probably stick with the 3.00 as I don't want my truck to be a trailer queen. Also my frame was a 460 C-6 with 3.00 from factory(1975 f150 frame).

 

I run 2.75s in Christine with the 472 EFI. It lazes along at 1100 rpm at 50 and at 65 it is about 1800.... I have a lot of motor left...LOL 4000 RPM in third is down righ scary hairy...

I hauled a fairly overweight trailer across the county to get here and the truck never noticed it had a trailer behind it. Pulled a good 16 MPG average across too.

GarbZ

 

mine was 09 or O9

I need to crawl under and take the tag off... the head of the nut covers half the number.

I've got another 9inch from the 64 ... but no tag on it... I know there is a method for determining what it is..any ideas? The 64 had a v8 originally... where as mine had a 240... hoping it is a lighter rear end.

if not I'll be rebuilding my rear end.

 

Jowilker, my speedometer reads 13.2% low. So it is an easy mathematical correction when figuring mileage. Truck is very light weight so that helps too. When I built the motor mileage was a main objective, therefore tried to get the CR up as high as possible. It is a true 9.2 static, which also helps the mpg.

 

thanks guys....thread has been helpful.
appreciate it....