88 E350 Gearing 4:10 or 4:56?

[mtnparty]

Hello all.

I am new and just purchased a 1988 E350 extended 4x4 van. It has the 5.8L efi motor, C6 tranny, D60 LS rear, D44 front, 3:55's, and 285/75-16 cooper ATP tires. It's an awesome van I plan on using this for camping and pulling my raft and trailer around the mountains and right now that is not going to happen.

I searched and read as many posts as I can about re-gearing and think it's going to be the best option. I want the van to be happy at cruising 65mph as I don't really want to go much faster and most mountain roads are 65mph tops anyhow. From the research on this forum it seems like 4:10 or 4:56 are the best options. I have 4:56's in my Bronco with 35" and it's revving pretty high (2800-3000rpm i have a hard time remembering it's been in pieces for a while) at 65 so I am leaning towards 4:10's. I know the C6 is tough but pulls some HP from the engine but I don't want to mess with the tranny till I can do a manual swap (after the bronco is finished).

I know it will never be a viper-van. Anyone have 4:10's and pull a small trailer around the mountains? Or will I regret the 4:10's with a trailer and should have got 4:56's?

Thanks this site is awesome. I will post pictures once I take some... she's a looker.

 

[rockbender]

with 33's and a C6 tranny, 4.10's are as low as I would go. Alternatively, you could leave the 3.55's in and drop in a 460!

I wouldn't be expecting big gains in MPG - what you will be getting is a rig that is a bit more driveable.

 

[djbonsu]

Try this website --> http://www.grimmjeeper.com/gears.html

Should give you a good idea on what to expect with different gear ratios and tire size specific to your drivetrain. Not sure what engine speed that 351W would like to cruise at but maybe find out that info and aim the optimum engine speed at 65 mph? Or you could find out the ballpark optimum speed the motor would be happy at using stock gearing and tire sizes, find out that engine speed at 65 mph and shoot for that number with the 33s. Are 4.30 gears an option for your axles?

 

[mtnparty]

Thanks for the replies.

yeah I don't expect the mpg to go up much.
I guess I figured 410 and 4:56s were the only option I will have to do some research is they make 4:30s for D60 and HP-D44. Thanks for the gear calculator site. gear calculator shows 4:10's would be 69mph at 3000rpm and with 4:56 it would drop to 67mph at 3000rpm. for the 2mph maybe 4:56's are the way to go if I am planning to tow a small trailer over the passes on a regular basis. Thanks again for the replies I am super new to vans but I already love the big bastard.

 

[derjack]

This question has never been answered in this forum before.

 

[Mickey Bitsko]

mtnparty, don't fear the gear. I live and play in Colorado, in the big picture your mpg isn't going to change but you'll surely ease the work load on the drivetrain.

Mickey

 

[BajaSportsmobile]

With the C6 (no overdrive) I would go with the 4.10's. With an OD transmission I would go with the 4.56's.

 

[tgreening]

This question has never been answered in this forum before.

I think the first thing I'd do is make sure my engine is up to snuff. Unless your van is really really heavy, I don't see any reason why it should be struggling just to pull itself, anywhere. Your current gearing/tire combo has you pretty much right at a general cruising rpm for a gas rig of that vintage. Your 4.10s will put you at the upper end of that and I agree with Baja. You won't like 4.56 with those tires and at 65 mph. Been there/done that and a constant 3k rpm on the highway gets old really fast.


Around here a gear change will set you back around $1,000 per axle, assuming it's gears only and no lockers. I think for $2k I'd see what I could do in the engine compartment. I think in the long run you'll be happier with an engine that has the grunt to pull through the gears/tires you have, rather than gearing to make up for a weak engine.

 

[350outrage]

Either ratio (4:10 or 4:56) will be a Huge improvement over your 3:55's. If I remember right, a C6 doesn't have a positive lockup in 3d, so yours is probably making up for the too tall ratio with lots of slip. Your van will be so much happier, and run like a champ in the mtns once you drop the ratios.

 

[350outrage]

With the C6 (no overdrive) I would go with the 4.10's. With an OD transmission I would go with the 4.56's.

I agree with Baja: I have 4:10's with 33's and 4 sp OD tranny, but always lock out 4th gear (overdrive) when I get to the mtns. 4.56 seems mighty low for a non OD tranny, unless you really never want to hit the super slab.

 

[charlieaarons]

You mentioned a manual conversion. Do it at the same time, use something like ZF S5-47 with 0.76 5th gear, and think about 4.88 or 5.13 which will give you 3.70 or 3.90 in 5th gear. Or even steeper, like 5.38 which will give 4.085 in 5th. You will have tremendous get-up-and-go in the lower gears. Your tires turn about 645 times per mile. Multiply that by final drive ratio (diff times top gear) to come up with rpms at 60mph in top gear.

Charlie