Well, I’m back.
I don’t know how much traffic this site gets anymore, but I thought I’d share my most recent project if for no other reason than to document it for posterity.
I’ve put together a truck: I’m calling it “the eco-cheapo-franken-F350.” The goals were to (a) build a “one ton” (350/3500 series) truck with upgrades for significant towing and hauling capacity, (b) make it as efficient as possible, (c) do everything as inexpensively as possible, using mostly factory/junkyard parts, and (d) end up with a final product that doesn’t “look weird.” This final goal has a practical purpose. Many people over the years have admired what I’ve achieved with our Metros (90 MPG avg.) and the Caprice wagon (45 MPG avg.), but have thought (or even said) “I’d never drive something that looks that weird.” I wanted to build something that my friends and neighbors wouldn’t be embarrassed to drive, and in so doing hopefully prompt more serious reflection.
Admittedly, this final goal puts a major limit on what I can achieve with this truck, as it rules out most aerodynamic modifications. The mileage I’m getting would be at least 20-30% higher if I made the same sort of aerodynamic modifications to this truck that I made to the Metros and the Caprice wagon. Nevertheless, this project has shown that a vehicle put together with mostly factory/stock parts, driven carefully, can still nearly double the EPA MPG.
The body and frame are from a 1990 F250 HD 4wd (same frame as an F350) with a 5.8L V8. The truck is now 2wd with a 4.9L I6, and every other drivetrain and suspension component has been swapped out as well (as you can read about below). Here's what the final product looks like:
I’ve measured three tanks so far. The first two had pretty mixed driving, including some trailer towing (an 18ft tandem axle box trailer with marching band instruments and gear), and were
26.72 MPG (348.6 mi/13.048 gal) and
23.28 MPG (167.4 mi/7.191 gal). My most recent fillup was for a long road trip, out and back, empty:
34.67 MPG (389.3 mi/11.229 gal).
I’ll start by summarizing all of the modifications, and then give a more detailed description of several key parts. If you have any questions, please don’t hesitate to ask. I think this project is at least as interesting as the Caprice wagon was, and I hope you do, too!
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Mods Summary
Drivetrain- 4.9L (300 ci) I6 engine from a 1987 truck; mechanically stock except for advancing the cam timing 8 degrees
- Engine tuning, using a “TwEECer” (mainly changes to the air/fuel ratio and ignition timing)
- Eliminated several engine parasitic losses:
- Manual steering conversion, using a steering box from a Ford Ranger
- No A/C or smog pump
- Electric cooling fan conversion, using a fan from a Ford Crown Victoria
- Two manual transmissions (from early ‘80s trucks) mated together: NP435 granny gear four speed and a modified T170 with overdrive; provides nine distinct, nicely-spaced forward ratios and three reverse ratios
- Dana 61-1 rear axle (heavy duty 61/70 hybrid) with a rare 3.07:1 ratio from a 1984 diesel model; upgraded with 35-spline Dana 70 axle shafts and a heavy duty “girdle” rear cover
- Heavy duty 4" aluminum driveshaft from a police-model Chevy Tahoe
- Forged 1350 u-joints, forged slip yoke, and forged pinion yoke
- Continental VanContact A/S tires (low rolling resistance) purchased used (for even less rolling resistance)
- Front are LT215/85R16
- Rear are 285/65R16C; these are “super single” tires, with a 4300 lb. capacity per tire (like a set of duals)
- 16x7” front and 16x10” rear steel wheels; rear wheels were custom made to fit the super single tires and handle their weight capacity
- “Poor man’s 4wd”: independent parking brake levers, one for each rear wheel, mounted in the opening where the transfercase shifter used to be
Suspension - Solid I-beam leaf-sprung 2wd front axle from a 1994 F-Superduty (F450); includes the F450 brakes
- Stock F250 front leaf springs; these are twice as stiff as F350 front leaf springs and almost as stiff as the F450 springs, but without the F450’s 4” of lift
- Rear leaf springs (including overload springs) from a 1990 F350 dually
- Timbren SES on rear axle (progressive rate rubber overload/leveling springs)
- Heavy-duty Ford sway bars front and rear
Towing- Draw-Tite class III/IV receiver hitch
- B&W Turnoverball gooseneck hitch
- Tekonsha Primus IQ trailer brake controller
- Removable backup camera, for hooking up receiver-hitch trailers
- Ford swing-out towing mirrors mounted on swing-away frames, and auxiliary aftermarket convex mirrors
Aero mods- Cover on rear half of bed (not pictured above), made of plywood painted black; for more information read this thread
- Factory front air dam from an F150
- Rear bumper delete; roll pan installed
- Antenna delete
Instrumentation and Controls- UTCOMP trip/MPG computer
- Innovate Motorsports LC-2 wideband oxygen sensor (connected to UTCOMP)
- Kill switch on each shifter (momentarily cuts power to the fuel injectors)
Fluids- Amsoil full synthetic in engine, transmissions, and axle
- Ethanol free gas
Other mods- LED headlights, exterior lights, and interior lights
- Auxiliary brake vacuum reservoir and electric vacuum pump, to allow for indefinite engine off coasting
- Engine coolant/block heaters
- Auxiliary coolant pump in heater circuit (to provide heat during EOC in winter)
- CTEK MXS 5.0 battery charger
- Cheap roll-on paint job (Sherwin Williams industrial enamel)
- Rust preventative oil undercoating
- Junkyard Chevy hubcaps and wheel trim rings…but with Ford stickers
Planned future mods- Deep cycle battery (when the conventional battery dies)
- Two removable rear-facing bucket seats in the bed, for hauling more people if needed
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Mods Details
How it all started
I’ve thought for years about how I would build a truck for towing and efficiency were I to build one, but for a long time I haven’t really needed a truck. We had the Caprice wagon for a while, and that functioned as a “truck” for us, but we sold that car several years ago when our work/life situation changed and we didn’t really need it either. However, my work has changed again and I’m spending a lot of time now helping on our family’s farm (I’m the fifth generation to farm it). Given that farming sometimes involves hauling loads and pulling gooseneck trailers, and given that the trucks that are available for me to use aren’t really suitable for hypermiling (they have automatics!), I now had a good excuse to commence a truck project.
I grew up around Chevy and GMC trucks, and “in my heart” that’s what I’d still prefer. However, I went with a Ford for several reasons. I wanted a straight six engine with fuel injection, but Ford was the only one of the “big three” to make a straight six into the FI era in their trucks. (Yes, there’s the GM 4.2L Atlas engine, which I’d LOVE to swap into a Chevy or GMC truck, but such a swap would far too complicated and expensive for a budget project like this one.) I wanted a straight six partly because I think they’re a superior design, mechanically speaking, compared to a V8, and partly because they tend to be of smaller displacement with peak torque at a lower RPM. And I wanted fuel injection because it offers greater efficiency, durability, and reliability than a carburetor.
1980-1996/7 Ford trucks also have, compared to GM trucks, (a) manual transmissions with better ratios, (b) factory made full-floating rear axles with higher final-drive gearing, and (c) much greater interchangeability of parts across different models. For example, I was able to bolt into an F250 both a manual steering gearbox from a Ford Ranger and a front axle from an F450. I couldn’t have done either with a Chevy.
So, the search began for a 1987 to 1997 F250 HD or F350 with a 4.9L engine. In this era of Ford trucks, the F250 HD had the same frame as an F350; for the 4wd trucks, the major difference was that the F250 HD had an independent front suspension while the F350 had a solid front axle (both with leaf springs), but for the 2wd trucks they were essentially the same except for the sticker (both having coil springs on the front). In January of 2024 I found a 1987 F250 2wd with the 4.9 and a T18 4 speed transmission in PA, which the seller said was a HD model when I asked. However, when I made the road trip to buy it, I discovered that it was a regular duty F250 and that both the cab and the bed were rotted out. Here’s what it looked like:
Despite the rust, though, the truck had low original miles (54,000) and the engine and transmission worked great. I negotiated the price down to $2200, and the seller also agreed to throw in a barely-used gooseneck hitch that would fit it. Once I got it home, I immediately sold the dump bed insert for $1800, so I essentially got the truck and hitch for $400.
Now that I knew I had a good 4.9 engine, I needed to find another truck to put it in. While this increased the amount of work that the project would require, it also opened up my options considerably, since there weren’t too many F250HDs and F350s that came with the 4.9 from the factory. So, in February of 2024 I brought home another truck (this time from MD): a 1990 F250 HD 4wd with a 5.8L V8 and a ZF5 five-speed manual transmission. This truck had an engine that wasn’t running (it had been parked for 6 years and wouldn’t start) and it didn’t have a title, but the seller said that the transmission was good, and the body and frame had remarkably little rust. Here’s what it looked like (the camper shell and aftermarket wheels weren’t included):
I got it for $1000, and once I got it home I started the title recovery process and eventually got a title for it too. Now that I had two trucks, I had to figure out the best way to put them together!
F450 front axle swap
I wanted the truck to be 2wd (for a number of reasons), but swapping the 2wd front suspension into the 4wd truck wouldn’t have been easy: it would have required exchanging the front crossmember, which is both welded and riveted to the frame rails, and drilling some pretty precise holes for mounting brackets. But then around the time that I was thinking about this a 1989 F-Superduty (F450) came up for sale along the route that I took to work each day, so one day I stopped and looked at it. The F450 of this generation was 2wd, but it had a sold front axle with leaf springs. I took some measurements from that truck, compared them to the 4wd truck that I had at home, and came to the conclusion that the F450 axle would essentially bolt into my truck. I soon found an ad online from someone who was parting out a 1994 F-Superduty and I bought its front axle and related parts.
There were two issues that had to be sorted out before I could install it. The first issue was the springs. The F450 springs had about 4” of lift built in, which for aerodynamic reasons I wanted to avoid. Using the F250 4wd springs gave me essentially a stock 2wd ride height, but the front crossmember had to be trimmed a little to clear the axle and Panhard bar under full compression. As a side note, the stock F250 4wd springs are almost as stiff as the F450 springs. The F250 springs are 842 lbs./inch of deflection, the F450 springs are 950 lbs./inch, while the stock F350 springs are 464 lbs./inch. This is because the F250 springs get twice as much compressive force due to the lever action of the independent suspension. In my case, though, they let me lower the F450 axle while keeping almost the same spring rate.
The second issue with the F450 front axle was the hub/rotor. The F450 had 10 lug wheels, and only came as a dually. I needed to be able to use 8 lug wheels with single rear wheel offset, while hopefully keeping the F450-sized brakes (which are a significant upgrade). The F450 spindle is the same size as the spindle on a 2wd F250 or F350, so an F250/350 hub/rotor would bolt on. However, the F450 rotors are much thicker and of a different diameter, so the F450 calipers won’t work with the F250/F350 rotor, and unfortunately the calipers are not interchangeable. So, I did some research and determined that a hub/rotor from an early ‘90s single rear wheel Chevy P30 step van had the correct 8 lug bolt pattern, the correct rotor thickness and diameter, and used the same bearings as the Ford rotor. The only problem was that the inner bearing was spaced differently. I ordered two of these P30 rotors, had a machinist cut the bore for the inner bearing race a little deeper, and they bolted on. I now had an F450 front axle and brakes with standard 8-lug wheels.
Rear axle swap
To finish the suspension, the next step was to swap the rear axle. I found a full-floating Dana 61-1 axle with 3.07:1 gears from a 1984 diesel truck in a local junkyard. These are pretty rare—they were only used for a couple of years on 2wd diesel F250HDs and F350s before the Sterling axles and overdrive transmissions came along. This version of the Dana 61 has the standard 61 gears, carrier, and 30-spline axle shafts, but everything else is beefed up: the housing has extra webbing and reinforcements for more weight-carrying capacity, and the tubes, spindles, hubs, bearings, and brakes are the same as what you’d find on a Dana 70. According to Dana parts books, the Dana 61-1 (or “heavy duty 61”) was even used on Ford vans with dual rear wheels.
Because I knew that the higher gearing would place more stress on the driveline, I swapped the factory cast 1330 pinion yoke for a forged 1350 yoke. And because I knew that one way or another I’d have extra low gearing in the transmission for pulling heavy loads (and thus extra torque output), I installed a heavy-duty rear cover with carrier bearing load support bolts (i.e., a “girdle”), and I swapped out the side gears in the carrier for used ones with 35 splines and installed 35-spline axle shafts from a junkyard Dana 70.
I wanted 3.07 gears for several reasons. Manufacturers often recommend against towing in overdrive with a manual transmission; this is because overdrive gears tend to be the weakest gear in the transmission, and towing in any gear other than direct puts more stress on the transmission and creates more heat. 3.07 is about the same ratio as a 4.10-equipped truck in overdrive, so it allows you to tow “in overdrive” with the transmission actually in direct.
Another reason I wanted 3.07 gears was for hypermiling. With the tires I’m running, a 3.07 rear puts me at about 1000-1900 RPM from 30-55 MPH in direct. This is ideal for my engine, since it’s right around peak torque (and thus peak volumetric efficiency) with the camshaft advanced, and it’s also ideal for transmission efficiency, since direct uses about 5% less energy and fuel than any other speed (as no power is being transmitted through the gears).
A 3.07 rear also slows down the driveshaft, for less wear and parasitic loss, and numerically lower ring and pinion gears (according to what I’ve read from the “high performance” crowd online) tend to rob less horsepower than numerically higher gears and tend to be stronger, too (since the pinion gear is larger in diameter).
A final point regarding this axle that’s worth mentioning is that it has an open differential, and I wanted to install some sort of traction aid. On the Caprice wagon’s 14-bolt rear axle I was able to install an Eaton E-locker differential inexpensively by sourcing a junkyard unit from a Hummer H2. There are Eaton (and other manufacturers’) E-locker differentials available for the Dana 60/61, but they never came in a factory application and are thus impossible to get inexpensively (since they can’t be found in a junkyard). I really liked the E-locker in the Caprice because it had all of the advantages of an open differential most of the time but 100% lockup at the flip of a switch. Clutch-type limited slip differentials and mechanical locking differentials can be found for the Dana 60/61 inexpensively, but they have serious disadvantages in wet, snowy, and icy conditions.
What I ended up doing was installing two parking brake levers, one for each rear wheel—which I call “the poor man’s 4wd.” I removed the factory parking brake pedal and installed the levers in the opening where the transfercase shifter used to be. With this setup, if one wheel is spinning you can pull the lever for only that wheel and (hopefully) transfer torque to the wheel that isn’t spinning. It’s the same concept behind the independent brakes on most farm tractors. While it doesn’t work as well as a selectable locking differential, it was much, much less expensive (about $100 in parts vs. $1500 plus installation for a new E-locker), and it should nevertheless help in some low-traction situations.
Transmissions
Another question that needed answering was which transmission I was going to run. I had two transmissions already from the two trucks that I purchased: a 2wd T18 four speed, and a 4wd ZF5 five speed with a BW1356 transfercase. Neither one of these options seemed to be ideal. The T18 only has four gears, with fourth being direct and first being a “granny low.” While I was planning to do most of my driving at speeds of 55 MPH and below in direct, I knew it would be nice to have an overdrive gear on the interstate when travelling unloaded. I could also envision scenarios in which the granny-low first and reverse gears wouldn’t be low enough for starting or backing big loads. And, the gaps between the gears in the T18 are really, really wide, which also isn’t ideal for towing: you have to rev really high before shifting to avoid lugging in the next gear, and downshifting can make the engine scream.
I seriously considered using the ZF5 and transfercase with the internal chain removed. This setup would give me both an overdrive gear and extra-low forward and reverse gears. However, the gaps between the gears would still be pretty wide, the shift between low and high in the transferase is unsynchronized, and the ZF5 is difficult and expensive to rebuild (unlike the four speeds). I also knew that the ZF5 and transfercase would be worth a lot of money were I to sell them.
Another option would have been to find a “Ranger Overdrive” to use with the T18. This is an aftermarket auxiliary overdrive unit that bolts between the bellhousing and transmission, giving you direct and over in each gear and thus turning the four speed into an eight speed. This would solve both the overdrive problem and the gear spacing problem, but it wouldn’t address the low gearing problem. These Ranger Overdrive units are also out of production, hard to find, and tend to be expensive when you do find them.
The Ranger Overdrive did give me another idea, however: using two transmissions in series. I spent a lot of time thinking about this, doing research, considering options, calculating ratios, and taking measurements. I’ll spare you most of my deliberations and simply describe what I settled on: a modified T170 bolted between the bellhousing and an NP435 four speed (another “granny low” transmission like the T18). The modified T170 has three speeds (since I physically removed both first and reverse gears from the case and modified the shifter to eliminate their respective shift locations): direct, .71:1 overdrive, and 1.92:1 “low range.” People like to complain that second gear in the T170 is too low, with a huge gap between it and third (direct). However, it works great as a low range! It’s very close to the low range ratio in an NP205 transfercase (1.96:1). These three ratios are also very close to the ratios in a Spicer 5831 auxiliary transmission, but unlike the Spicer the gears are fully synchronized, and the T170 is much smaller, lighter, and easier to install.
Once it was modified to bolt between the bellhousing and second transmission, the T170 now functions like a Ranger Overdrive but with an additional low range. This means that I have 9 distinct forward ratios: the four speeds of the NP435 in direct and overdrive, plus first gear low range (2nd, 3rd, and 4th low are essentially the same as 1st, 2nd, and 3rd in direct, so while there are technically 12 combinations there are only 9 distinct ratios); and three reverse ratios: direct, over, and low.
Here's how it using it works: in normal, unloaded, non-interstate driving, I leave the T170 in direct and drive using only the NP435, starting in second (as first is too low to use unloaded). If I get on the interstate, I’ll shift the T170 into overdrive. This essentially turns the NP435 into a 5 speed. However, if I’m pulling a trailer I can use the T170 to split the gears in the NP435, starting with the gear that’s the most appropriate for the size of the load, the grade, and the road surface. Despite having a relatively small engine and a relatively high final drive ratio, I’ll most likely never find myself needing more gearing to get a load started; with the NP435 in first and the T170 in low range I’m confident I could get a fully loaded gooseneck trailer started, even on a very steep hill.
Another advantage of this setup is the reverse gearing. One of the disadvantages of towing with a manual transmission is backing up. Especially in tight spaces and/or on a steep hill it’s necessary to creep with a trailer in reverse; an automatic transmission allows for this naturally, but with a manual it can be difficult to do without slipping the clutch excessively. With this setup, the NP435 already has the lowest reverse ratio (8.26:1) of any manual transmission ever put in a pickup in the US, but combined with the low range of the T170 it can become nearly twice as low (15.86:1). This is more than enough gearing to back even a very heavy trailer slowly without excessive clutch slippage. And, the overdrive gear in the T170 can speed up the NP435’s reverse gear (to 5.86:1) when that would be advantageous, too.
How did I bolt the two transmissions together? There were three parts that needed to be machined to make this happen. First, I had the main/output shaft of the T170 shortened and splined internally. The T170 uses the same input and output bearings as a T18, with a center bore that’s 1.575” in diameter. That means the shaft is 1.575” in diameter at that point, which is large enough to spline internally at a big enough diameter to transmit the output torque while still leaving the shaft with enough thickness to be sufficiently strong. The challenge was finding someone who could do such splining in a blind hole. After talking to all of the machinists in my local area and then making a bunch of phone calls nationally, I ended up speaking with Gabe Osten at Northern Drivetrain in Wisconsin who agreed to do the work. He shortened the output shaft and cut the splines internally to the same specifications as a Dana 44 pinion yoke (26 splines at a 1.146” major diameter).
The second part that had to be machined was the input shaft of the NP435, which needed to be shortened and splined to fit into the output shaft of the T170 after it was completed. The stock Ford NP435 input shaft wouldn’t work for this, as it was too small in diameter (1.0625”); instead, I bought a new NP435 input shaft from an International Harvester application on eBay that was 1.25” in diameter. Moser Engineering in Indiana did this work, as Gabe’s equipment wasn’t set up for cutting into hardened material like that of the input shaft.
The third part that had to be machined was an adapter plate, which I had done locally using a 1.25” thick piece of aluminum. A machine shop cut the bores for the output bearing of the T170 and the input bearing retainer of the NP435, and milled both sides flat, and then I drilled all of the necessary bolt holes. I never took any pictures of the machined shafts or the disassembly and reassembly of the transmissions, but here’s what the two gearboxes look like bolted together with the adapter plate:
The T170 box with the adapter plate is 11.5” long, so the transmission crossmember had to be moved back 11.5”, I needed to find a driveshaft that was 11.5” shorter, and then cut a hole in the transmission tunnel for the second shifter and bend the two shifters to clear each other as well as the seat and the dash. I ended up finding a heavy-duty 4” diameter aluminum driveshaft that was the right length from a police model Chevy Tahoe in a junkyard, which also allowed me to upgrade to forged 1350 u-joints (instead of the stock 1330 joints) and a forged slip yoke. Here’s what it looks like in the cab with everything installed:
I went with an NP435 instead of the T18 for several reasons: (1) the NP435 ratios are better suited for splitting than the T18 ratios; (2) the NP435 has bigger, heavier-duty synchronizers than the T18, which is important considering that they need to spin up more gears and mass than normal in this setup; (3) the NP435 has a larger diameter 31-spline output shaft (the T18 is 28-spline) which is better suited to handling the extra torque output; and (4) it’s much easier to swap an input shaft on an NP435, as doing so on a T18 requires disassembly of the entire transmission. I removed first and reverse gear from the T170 for several reasons as well: (1) using first or reverse in the T170 in combination with first in the NP435 would be so low as to be impractical and unusable (I’m not rock crawling with it!); (2) using first or reverse in the T170 could multiply enough torque to well exceed the NP435’s input torque rating and thus possibly break it, and given that others may drive the truck from time to time I wanted to “idiot proof” it; (3) the reduced mass and drag from the removal of the first and reverse gears would put less strain on the NP435’s synchronizers; and (4) removing those parts lightened the transmission overall. The T170 weighed 83 lbs. with the shifter before being modified; after modification it weighed 70 lbs. with the shifter and adapter plate.
Another cool thing about this transmission setup: the total cost, including purchasing the two four-speed transmissions, buying the other needed parts, and having the machining work done, was less than what I ended up selling the ZF5 five-speed transmission for!
Wheels and tires
I knew from my experience with the Caprice wagon that I wanted to find low rolling resistance tires, if possible; I also knew that I wanted to buy used tires since I won’t be putting a lot of miles on this truck, and used tires are significantly cheaper and have less rolling resistance than new ones. I ended up settling on Continental VanContact A/S tires. From what I could tell from the European tire label ratings they have fairly low rolling resistance, and since they came from the factory on Sprinter vans, they’re readily available used. And, since they came from the factory on Sprinter vans, they include a “super single” model that was an option on the Sprinter 3500.
Once I learned about these “super single” tires, I knew I wanted to run them: they have all the advantages of a single rear wheel setup, but with dually weight capacity. However, the tricky part was finding an affordable wheel that would work with them. 16x10” is the ideal size, especially for maximum stability and minimal tread crowning, but none of the 8-lug 16x10” wheels that are commercially available have a high enough weight capacity to use on a 7400 lb. GAWR axle (which is the stock dually GAWR of this generation of Ford trucks). I ended up having the rear wheels custom made by Diamond Racing Wheels in Wisconsin, and for custom steel wheels they were pretty affordable.
Some final thoughts
As I mentioned earlier, one of my self-imposed rules for this project was to make sure that the truck didn’t “look weird” when I was done with it. But here’s the thing: if I were to make the same sort of aerodynamic modifications to this truck that I made to our Metros and Caprice wagon, I could probably improve the mileage I’m getting by at least 20-30%. That would include a large air dam under/around the front bumper, a partial grille block, full length side skirts, rear fender skirts, smooth wheel covers, gap sealing, and most importantly a full-length tapered bed cap. If I did all of those things and saw only a 20% improvement, that 34.7 MPG tank would have been 41.6 MPG. If they made a 30% improvement, it would have been nearly 49 MPG.
Nevertheless, I’ve shown with this project that focusing primarily on reducing drivetrain losses using inexpensive parts and optimizing driving technique can still nearly double a vehicle’s typical MPG.
There’s much more that I could say, but this post is already far too long. I welcome any questions, observations, or feedback that you have!
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) but not the Metro[s]. Can you post a pic?
