4.56 Gears and 31's Question, I know it's been covered before, BUT! (kinda long)

[needabronco]

Alright I've searched and read the threads, but I'm not convinced.

I've got a fresh 302 with the Perfomer cam that makes decent power (up to around 4400 rpms is pretty good), stock 3spd, stock suspension, 3.50 gears and damn near new 31's. The gearing sucks...

Since my frame off plans are now in the toilet, I'm building my rig in stages and I think axles and gears are going to be next. I've already done the engine, trans, and d20.

I will be using Explorer EFI, 4R70W (which has a .7 overdrive), 2" BL, 3.5 suspension and 35's. Blah blah blah.

Here's what I'm thinking of doing now: 4.56 gears, detroit rear, open front (for now), 31 spline axles, and 4340 front axles.

I hope to have the suspension and tires done within 1-1.5 years, but what kind of drivability will I have with the 31's and 4.56 gears. I only plan to drive it around town and on level 2 and 3 trails in AZ, NM, and CO until it's done. I do plan to eventually drive it on the highways at around 70 MPH. I don't drive it very much now anyway and I'm considering buying a trailer to get it places until I get bigger tires and the overdrive.

Any input is appreciated. Thanks Casey

 

[Broncobowsher]

I'll guess that 4.56 and 31's will be very close to 4.88 and 33's, which is what I have now. Just that I already have the 4R70W in it and I run the overdrive.

With that in mind, I don't think that the 4.56 gears, 31" tires and no overdrive would be drivable at 70 MPH. It could do it, up hill, down hill, it would never notice the hill. But 4000 RPM cruising speed is a bit high.

Now the downfall is that 4.56 gears will probably not be enough once you get the 35's and the overdrive. You will be needing something more like a 5.13 gear. This is from someone running a very torquey 351, 4.88 and 33's and done several long highway cruises in it.

Now if you only drive it around town, forget about highway. 4.56 gears and 31's would be rather fun.

Hear is another thought. Instead of gears right now do the 4R70W. I know the overdrive will be worthless with the 3.50 gears. But just set the computer to not use it. Just make it a 3 speed for now. you get the 2.84 first gear and the torque convertor for low speed stuff. You can still lock the converter in 3rd gear for highway use. It will make it much more drivable then the stock 3 speed and even better then the C4 by having the lower first gear and lock up convertor.
Detroit in the back with the stock 3.50 gears for now and 31 spline axles can be a seperate upgrade before or after the transmission. Later you can change ratios without throwing away any "new" parts. At that time start using the overdrive.

 

[broncnaz]

Not quite sure of what you need to be convinced of. But with 31's and 4.56's hiway driving will drive the RPM's up when ae you doing the OD swap? I'd consider that about the same time as the gearing swap although I'd also consider going with 4.88's instead of 4.56's with the OD.
Driving around town and some trails with 31's and 4.56's will bo ok probably even fun as it will probably light the tires up at will. But out on the hiway the RPM's and mileage will probably suck.
Your current gearing shouldnt be all that bad I run 33's with 3.50 gears never had a problem with it amybe a little lacking on the low end but not much. heck when I had 31's it would light the tires from the stoplight easily. while I do run a NP435 I rarely use first unless offroad and the second gear is about the same as the stock 3 speed so I dont know where your power problem comes from although my engine is a little more built than yours.
Are you running headers? how about intake? Headers/good exhuast system is really needed on SBF's to gain any power the cam you have may be making more power but is being restricted by the ill flowing stock exhuast. a good exhaust system can allow that engine to make full use of that cam.

 

[needabronco]

I already have the 4R70W, but I still need the computer and harness to run it, adapter, shifter, and all the little stuff. I understand I'll need driveshafts as well, and I'd like to complete that swap with the suspension cause I'll need driveshafts then also...

I'm trying to build stuff so that I don't have to do it a gain, i.e. change out gears, lockers, axles more than once.

My 302 has the edelbrock cam intake, msd ignition, and carb, so it is pretty good on the low end. It'll do 75-80 on the open road, but as soon as I hit a hill I'm looking at 40-45!. I do still have some 'tuning' to do.

I'm really trying to get it ready for the Stampede in March and trying to have a reliable drivetrain over anything else. I honestly don't know the condition of my u-joints but I don't want to waste money on stuff that will be replaced soon. I don't want to break stuff on it's first real off road trip.

 

[Broncobowsher]

If you only can do 45 up a hill with that combo then there is an engine problem (tune?).
My first Bronco would do 88 MPH downhill towing a trailer in the rain but slow to about 80 going up the next hill. That was a 302, 3.50 gears, stock 3 speed, 31" tires and an engine so tired that I had to give up on it when trying to rebuild it because the cylinder wear was so bad they didn't have enough mater left to bore it out. After the rebuild and without the empty trailer it had no problem zipping up to 100 before I chickened out (it was still pulling at 100).

 

[needabronco]

I did just change jets and rods for the carb, and springs in the msd, but haven't been able to run it to get everything adjusted, hopefully it'll make the difference. Before I know it was running pretty rich and I don't really think the distributor was advancing all the way.

 

[DonsBolt]

35's 456 gears and a overdrive will be just about perfect.

I agree with the others getting the engine tuned right is important. I see your from NM so I would guess your not even close to sea level. In which case you have to lean out the carb.

I have 35's 456 gears and a NV3550 so I think the overdrive is close to the 4R70W. Even in overdrive I don't loose any speed up long steep hills, though I am at sea level. Once you go to fuel injection the comuter will compensate for alltitude.

When you go to 456 gears make sure you upgrade to 31 spline axles.

 

[needabronco]

Considering I can go from 3500 feet to almost 13000 in a matter of hours around here, efi is the way to go, but before knew better I bought an edelbrock 650, and I need to lean it way down, I did put smaller jets in and swapped the rods, we'll see if it helps.

As far as OD goes I do know others running an OD trans w/ 35's and 4.11's. So I know I'll be able to utilize 4th a little bit more(hopefully).