Drive train suggestion

[MikeKC130J]

I'm wanting to build a 351w efi and want to run 33-35 in tires what automatic transmission and gears should I run, I would like to have overdrive so I'm not running 3500 Rpms down the road.

 

[bronconut73]

4R70W
Auto

Or

NV3500
Or
ZF-5

May be even the MOD5 ? out of the 90's Broncos


Gears for 35's would be around 4.88....maybe a little more.....5.13....

 

[Digger556]

I'm wanting to build a 351w efi and want to run 33-35 in tires what automatic transmission and gears should I run, I would like to have overdrive so I'm not running 3500 Rpms down the road.

EFI 351 with a 4R70W. 4.10 gears for 33-35s.

I turn 37s with 4.56's and tow no problem.

 

[68ford]

With overdrive 4.56 for 33s and 4.88 for 35s minimum. Buddy has 4.88 with 35s and a warm 351 and he wishes he had 5.13. the overdrive puts the rpm too low on the freeway he says and he wishes 1st was quicker to take off from a start.

 

[sanndmann3]

I'm running the 4R with 5.13s. Had 4.56 but had to regear...

 

[MikeKC130J]

I'm running the 4R with 5.13s. Had 4.56 but had to regear...

Why did you have to re gear?

 

[DirtDonk]

What gear ratio and tire size are you running now Mike?
I think the overdrive autos are the best choice too, but just for comparison's (or argument's!) sake, with stock 3.50 gears, a non-overdrive C4 trans and a 33.5" tire (a typical 35) your engine would be turning over at a leisurely 2300-2400 rpm.
It would be "a tad sluggish" off the line to say the least. Not a good combo, but I was using it to compare the highway rpm level.

With 4.11's (also a stock ratio) you would run at about 2700-2800 rpm. Probably a bit high for an EFI'd 351, but not over-revving by any stretch and would be a lot more peppy off the line.

But both are compromises. With the 4R70W trans, you have a lower first gear, a tighter torque converter, and an overdrive to help out.
With the same 4.11 gear, it puts you at about 1800-1900rpm at 65mph.

But as always, we need more info. Because it all comes down to what you want in the way of performance with your Bronco. And are you going to be running 35's for sure? Or more likely leaning towards the smaller 33's instead?
And what will your engine be built like? You said EFI, but what kind of cam? A hot rodded motor, or a stock, to stock-ish version? How is the Bronco going to be set up?
Stockish and light, or fully outfitted with all the coolest (and heaviest) off-road gear?
And lastly, but not leastly, how will you drive it and in what conditions?

We really need to know all that before we can narrow down the ratio you'd be happiest with. Otherwise you're going to get the range you already have. From 4.11 to 5.13.
And none of those recommendations are out of line either. All fall within the sweet spot for certain uses. The overdrive auto gives you that much leeway, but narrows considerably based on exactly what you expect and want.

Paul

 

[chuck1022]

4lo.com ,you can plug in different scenarios

 

[DirtDonk]

I like this one too: Yukon Gear Calculators

Paul

 

[nvrstuk]

What Paul said...if this was a Mustang forum we could help ya out a bit more with what ya gave us but ....

- do you use the Bronco off road?

- what type of driving style are you looking for besides just reducing rpm's on the freeway

- do you have a doubler? If you do then some of the answers above about not having a low enough first gear can be tossed out...

tell us more about driving habits, style, where do you want to drive it (like off road)


I ran a 351W w/OD, with gear doubler and 4.56 gears with 35"s and 37"s for 15 + years. GREAT on hills (we have an abundance of 7% inclines here) and about 2K at 70mph... I wheel a lot so low gears were important but I also drove 1,000 miles at a time and not spinng at high rpms on the highway were/are important.

 

[rguest3]

Mike - How often are you driving on the highway? Is the OD a Want to have or more of a Need to have?

351w, C4, 4.11 gears and 33-35s may be great for you (Up to 60 mph comfortably) if mostly driving around town and back roads.

 

[MikeKC130J]

What gear ratio and tire size are you running now Mike?
I think the overdrive autos are the best choice too, but just for comparison's (or argument's!) sake, with stock 3.50 gears, a non-overdrive C4 trans and a 33.5" tire (a typical 35) your engine would be turning over at a leisurely 2300-2400 rpm.
It would be "a tad sluggish" off the line to say the least. Not a good combo, but I was using it to compare the highway rpm level.

With 4.11's (also a stock ratio) you would run at about 2700-2800 rpm. Probably a bit high for an EFI'd 351, but not over-revving by any stretch and would be a lot more peppy off the line.

But both are compromises. With the 4R70W trans, you have a lower first gear, a tighter torque converter, and an overdrive to help out.
With the same 4.11 gear, it puts you at about 1800-1900rpm at 65mph.

But as always, we need more info. Because it all comes down to what you want in the way of performance with your Bronco. And are you going to be running 35's for sure? Or more likely leaning towards the smaller 33's instead?
And what will your engine be built like? You said EFI, but what kind of cam? A hot rodded motor, or a stock, to stock-ish version? How is the Bronco going to be set up?
Stockish and light, or fully outfitted with all the coolest (and heaviest) off-road gear?
And lastly, but not leastly, how will you drive it and in what conditions?

We really need to know all that before we can narrow down the ratio you'd be happiest with. Otherwise you're going to get the range you already have. From 4.11 to 5.13.
And none of those recommendations are out of line either. All fall within the sweet spot for certain uses. The overdrive auto gives you that much leeway, but narrows considerably based on exactly what you expect and want.

Paul

Mostly back roads and highway, will to mild off roading, od is a want/ nice to have for me. I’ll probably stick to 33’s also have a Dana 20. The motor will be built stockish if it’s not too much more may stroke it not sure how all that will work with Efi. I’ll have to do some research as I’m not familiar with efi at all.
Thanks for the help every one.

I just sold my 75 with 351w carbureted 3.50 33 11.50 it was sluggish off the line.

 

[DirtDonk]

Over the years most people have reported an amazing improvement with your old setup, simply by changing to the 4.11 setup. Makes it just peppier enough to keep most happy.
The overdrive does let you go lower a bit more too, if you need to. Which is sounds like you might not need to.

A mild 351w with EFI should pull a mild-ish built Bronco around very nicely at under 2000 rpm on the highway. You could go even lower in the rpm, but I think that would start to return you to the old sluggish acceleration a bit too closely.
Which puts the 4.11 recommendation right in the running.

This also means that, if the engine is indeed a good runner with good low to mid-range torque, if you did up-size to 35's someday you would not be out of line on the highway.
This does mean 1900-ish rpm with the 4.11's and 1800-ish at 65mph with the 35's (approximately of course), if that seems acceptable to you.

So here's a "range recommendation" from me at least. If you want to bias it towards the highway a bit, the 4.11 is a good center point.
If you want quicker acceleration and a little better crawling ability (handy for pulling loads and hills without tasking the trans and building extra heat) then the 4.56 is a good choice. After all, 2000-2100 is still not a crazy high rpm to run a 351.

If you want to keep the rpm lower on the highway, at the expense of pulling power, slow-going trail power, and a bit of acceleration off the top, then there are always taller gears (lower numbers) to choose from.
But that kind of puts you back closer to where you started.
To that point though, what gear ratio do you have now? Remember you can always build the engine and Bronco first, then drive it around with your gear/tire combination as it sits. See how you like it and go from there.

In fact, that would give you a lot more date than we can by far.

Good luck!!!

Paul

 

[MikeKC130J]

Thank you for the information. I would like to pull my pontoon boat (2800lbs) to the lake and not have issues pulling it out of the water.

 

[DirtDonk]

Another good aspect of the 4R70w transmission that most of the time is not discussed, is that it's got a nicer way with compression braking than the other transmissions I've used.
Now, some of that could be overall differential gearing as well, with mushier tall gears having less perceptible compression braking, but the one I'm using sure does feel nice and solid. The lower the gear ratios in the diffs are though, the better any setup is with regard to compression braking.

How are the highway rules in TX? Just remember that 2800 (is that the boat and trailer together?), while not that much by today's standards, is WAY above the stated GVWR and two-rating of an Early Bronco.
It's not that you can't tow with it. You just can't do it legally in some states. The most important aspect from our standpoint (Bronco users that is) are the brakes. They were barely adequate for stock, much less lifted with larger tires AND towing a load.
So make sure that your brakes are top-notch and then some, before you go towing even that light of a load.
I'm guessing that boat probably tows like it's not even there behind most vehicles. Not gonna' be the same behind a Bronco. Just something to be mindful of.

Paul

 

[sanndmann3]

Why did you have to re gear?

I felt like it needed more gear to keep the engine in the power band...

 

[Broncobowsher]

General ballpark is aim for 2000 RPM at 60 MPH with an overdrive transmission.
4R70W is a great. The stock convertor is a lot looser then a stock C4, but the great part of the 4R70W is the convertor will lock up taking out the slip. With nice low gears the convertor will not be working hard even off the lockup.

For reference I ran for years with a warmed over 351, 4R70W, 4.88 gears and 33s. Road tripped it from Phoenix to Vegas several times as well as wheeled it on some fairly aggressive stuff. With only the 33s, it was a slight bit overgeared but not near enough to change. 4.56 gearing would have been better. OR stepping up to 35s would have fixed the gearing. OR the gearing would have been fine with a lesser engine. It is hard to think of 4.88s being a good highway gear, but they were.

 

[MikeKC130J]

Another good aspect of the 4R70w transmission that most of the time is not discussed, is that it's got a nicer way with compression braking than the other transmissions I've used.
Now, some of that could be overall differential gearing as well, with mushier tall gears having less perceptible compression braking, but the one I'm using sure does feel nice and solid. The lower the gear ratios in the diffs are though, the better any setup is with regard to compression braking.

How are the highway rules in TX? Just remember that 2800 (is that the boat and trailer together?), while not that much by today's standards, is WAY above the stated GVWR and two-rating of an Early Bronco.
It's not that you can't tow with it. You just can't do it legally in some states. The most important aspect from our standpoint (Bronco users that is) are the brakes. They were barely adequate for stock, much less lifted with larger tires AND towing a load.
So make sure that your brakes are top-notch and then some, before you go towing even that light of a load.
I'm guessing that boat probably tows like it's not even there behind most vehicles. Not gonna' be the same behind a Bronco. Just something to be mindful of.


Good point I'll just stick to towing with my pickup. I sure I won't be legal towing on the Texas roads.
Thanks for the info.
Mike

 

[DirtDonk]

Yeah, it's a shame sometimes because they'd be a lot of fun at the lake!
But with a tow rating of something like in the sub-1000lbs for some, and maybe as much as 1500(?) at the most for others, coupled with a minimal 92" wheelbase, it's not considered a very tow-friendly vehicle.

Lifting it up higher and mounting larger and heavier tires just reduces that even more.

Paul

 

[surfer-b]

try 4.30's, I really like these for 33 tires, the 4.10's were not really enough and the 4.56 were too much for my likes on the highway. setup is 2000 explorer an 4r70w