So I've been contemplating what my dream drivetrain would be for an eventual down the road project and I've come up with what I think is a bulletproof and best-of-both-worlds setup.

Engine: mod'd 300
Trans: ZF 5 speed
Xfer case: NP205
Axles: 9in in back, built D44 in front
Gears: 4.10
Tires: 35's

Haven't decided what to put this in yet, but I know it's pre 1979.

This is just a dream right now. I know there's some sort of issue I'm missing that I haven't thought about that's going to throw a wrench in my plan. Like will a ZF5 even bolt to a NP205? If I wanted to use a 203/205 doubler, would I even be able to? Would this drivetrain work/fit in a pre '79 chassis/body without major fab work?
(*this forum specific questions*)
With the setup listed, RPMs/MPH would be 1800/60, and 2400/80. I have a lead foot, and do not like cruising slow (plus where I live the majority of the highway limit is 75). Is this too high for a 300 to return respectable mileage on the highway? I've thought about getting an overdrive unit to put on there, that would change the numbers to 1400/60 and 1850/80. (with the od unit I could jump up to 4.56 gears and improve my crawling ability, and the #s would be 1550/60 and 2050/80)

The end use for this truck would be to haul me, my wife, and our crap 150-200 miles to our vacation point, get decent mileage, and be able to have plenty of offroad fun, and not have to worry about anything breaking. And I'm not saying I'm some uber genius who has come up with a mythical drivetrain combo that nobody has ever thought about. I'm banking on someone having this setup in their truck so they can tell me the pros/cons of my plans.

 

Welcome to the forum, bigyellardawg1991! There is certainly nothing wrong with dreaming.

Regardless of how you gear it, these truck bodies are shaped somewhat like a brick and the air resistance at speed really hurts gas mileage [one of your stated goals]. Real world and time tested input from many forum members indicates that best mileage is obtained at speeds of less than or equal to 65 mph.

Have fun!

 

4x4 + 4.10 gears + 35 tires + "... I have a lead foot..." = MPG that sucks...big time.

 

I've had a 300 in a 91 F150 with an auto and I never got better than 12mpg, but I drove it hard all the time, especially stoplight to stoplight (the low end torque is quite addictive) and cruised regularly at 70+mph. But that was back in my younger days when gas was cheap and I hadn't a care in the world.

Yeah, I figured 4x4+4.10s+35s would be detrimental to mileage, but I figured I could offset that with the ZF 5 speed. I already knew not to expect decent mileage during city driving, but looking at the gear ratio calculator, all the rpms/mph seemed to point to a good possibility (should I keep my foot out of it and drive like a grampa) that it might get ok mileage, especially on the highway.

I'm not sure exactly how to word this, but is there an optimal rpm for cruising with a 300? Obviously I don't want to cruise at 3000rpm, but I've also heard that too low an RPM isn't exactly good, either.

 

Well you won't be banging through the gears like a hot rod with that ZF. They shift like a dump truck.

Cruising RPM will depend on the engine and cam. With most aftermarket cams you should be able to cruise comfortably from 2,000-3,000 rpm. Heavy tires, taller truck means more HP to hold 80. You'll have to hold your foot in it.

 

I plan on combating some of this by only lifting it high enough to clear the tires. And I plan on using the lightest wheel/tire combination I can find. I still have a bit of homework to do. I used to drive 18wheelers and 27' box trucks for a living...I'm good with the ZF shifting like a dump truck.

I don't plan on putting too hot of a cam in it, cause with the 4.10s, the granny 1st, and the 35s, I want all the low end (read: sub 1500rpm) I can get so I can crawl all over the place.

 

The NP205 will bolt to the ZF. But you will have to grind a little notch in the t-case mounting flange of the ZF for t-case shift linkage clearance.

The other issue you will have with swapping the ZF into an older truck chassis is you'll have to convert the older truck to an hydraulic clutch set up instead of the mechanical linkage. The 300/small block ZF doesn't have a clutch fork. It uses a hydraulic throw out bearing.

And since the ZF has an aluminum housing it's not a bad idea to fab up a second crossmember just to support the weight of the t-case. I personally wouldn't trust just the stock 205 side mount with it mated to the ZF. The crossmember is mandatory if you go with the 203/205 doubler.

And if you are going with 35's & the ZF I would probably go with the 4.56 gears. It will make driving it a lot more enjoyable. If you are thinking about double OD's ( the ZF already has OD ) just remember you need to have enough torque to pull it in double OD.

 

Funny thing. The more I research it, the more I like what I'm seeing with AB's setup (except for the 35s). I didn't know the NP435 had a lower granny than the ZF, and, *apparently*, the NP435, even without an overdrive, with the setup AB has, *almost* gives me the same low gear crawling ability that I'm looking for, and better cruising rpms.

Learn something new every day, 'specially when you look outside your box.

Although I am slightly dissapointed. I wanted to do something slightly different with my setup...something not many people have. Turns out what I've basically been looking for has been staring me in the face since the first time I read one of AB's posts.

 

That's basically what I'm doing with my project truck I'm mounting a 54 F100 body on a 78 F150 4x4 chassis. I'm going with the 300 with a NP435/NP205 combo. I'm going to be running either 33's or 35's with my stock 3.50 gears. I always start off in 1st gear anyways. And the 6.69:1 first gear will help make up for the 3.50's to get it moving. Between the tires and the 3.50 gears it's like a poor man's OD. I don't think my 300 will have any issues with it. But my engine is going to be a littler wilder then most 300's.


Hey man if you want different go with an Advance Adapter's Ranger OD box ( mounts between the bell housing and trans ) , NP435 and a 203/205 doubler and either 4.10 or 4.56 gears! That would give you an ultra low craw ratio but you would still have OD for highway use.

 

I plan on using a 203/205 doubler. On paper the 4:1 helps with the 3.00 gears, with a crawl speed of 87 feet/minute at idle. With the ZF/205/203/205 combo with 4.10s, the crawl speed is 75ft/min at idle, so there's not much difference there. The 80mph rpms for the NP435/3.00 combo is 2300, the ZF/4.10 combo is 2400. I like the way the 35s work with both of these combos rather than the 31s.

It looks like either combo is a good one to go with. Would be nice to find someone who's done the ZF combo, or something similar, to get some real world info on.

If I wanted to really go outside the box, I'd go with a ZF 6speed

 

Gear Ratio Calculator

Pretty cool site that lets you pick tranny and transfer case from dropdowns then input gear and tire info and calculate drive ratios, crawl speed, rpm at speed, etc. Side by side comparison too.

I second and reiterate the suggestion to go to 4.56:1 or even lower axle gears. I have 31" tires on the Bronco (ZF, NP208, 3.55 gears) and it will be happier with 3.92 or 4.10 gears. Not it in first/grannie - it's fine there. But I only use 1st off road (or theoretically if I were towing something very big). Even with a 2.94 second gear the engine has to work a lot harder to get the bigger tires rolling.

Of course, I'm into simplicity and the ZF/NP 208 combo in the Bronco fits that bill. 5.72:1 first gear plus 2.6:1 low range for crawl, .76:1 OD for highway.

Then again, a pre-1979 4x4 with 35" tires at 80 mph? That may be a pretty wild ride. The Bronco's pretty squirrelly once it gets too far north of those speeds.

Now don't get me wrong. The 300 is a great little truck engine. But it is a little truck engine. It has a better power band for a truck than a 302 but even a decently built 351 would push a lifted truck better. You're asking a lot. Something which will lug big tires at crawl speed that still has the guts to push a lifted 4x4 80 mph and get decent mileage.

I think a more aggressive cam, a higher power band, 4.56 gears and the ZF would give you a good compromise. More fun to drive, simpler, and at least decent economy. Anything over 10-12 mpg at 80 mpg in a lifted truck would be a gift from Zeus.