I've been comparing 2 different engine build plans for my 1973 Bronco resto. I'm looking for opinions, and pros and cons on both. I'm building this Bronco to be easily trail capable, but also drivable, in some regard, on the road. I'll make a list of each plan with some basic specs.
Plan 1:
-Engine: Original 302 (rebuilt and stroked to 347ci, 350hp and about 350-400 ft/lbs of torque, Holley Sniper EFI)
-Trans: Tremec TR4050 5 speed manual
-Transfer case: Atlas II
-Axle gears: 4.56s, air lockers front and rear
-Tires: 35x12.5x15r
-Suspension: 3.5inch Duff lift with 2in body lift.
Plan 2:
-Engine: R2.8 Cummins turbo diesel crate engine (spec'd at 161hp and 310 ft/lbs of torque)
-Trans: Tremec TR4050 5 speed manual
-Transfer case: Atlas II
-Axle gears: 4.56s, air lockers front and rear
-Tires: 35x12.5x15r
-Suspension: 3.5inch Duff lift with 2in body lift.
I'm not comparing price right now, I'm mostly curious as to other benefits the Cummins would provide, other than improved fuel mileage, especially considering the torque and horsepower specs of both. Is there any reason to even consider the Cummins over the 347? My first judgement would be to go with the 347 because of the HP and torque, but I am definitely not an expert and would like to know more/other opinions.
I also found an R2.8 crate engine with the TR4050 already bolted on and ready to go from this site:
https://quickdrawbrand.com/.../cummins-r28-tremec-tr4050.../ Seems like a decent price for the package.
Thanks in advance for any knowledge/advice.
I've been down this road. My rig started out with a decent carb'd 351W, 375HP/400+lbft. When I first bought the Bronco, it made a whopping 9-10 mpg with questionable driveability. (poor cold starts, warm up, fueling control over rpm range) Made lots of power and burned lots of gas. With the OE 12 gal tank, I was filling up every 100 miles. ?:?
I changed cam, exhaust, intake and added a homebrewed TBI injection system. Driveability went way up, mileage climbed to 14mpg. Plugs showed the engine was running much cleaner. Switched to a 23 gal tank, but driving range was around 230 miles. Better, but not on par with current production vehicles. It got worse when towing.
Around this time Cummins re-tuned the R2.8 and bumped torque to 310 lbft. RPM and weight are comparable to a V8. Since I live in CO, mountain driving and altitude power loss are very real. Minus 15-30% hp and torque. This makes the R2.8 on par with the V8 power under certain, but critical conditions. (10,000ft passes) I pulled the trigger. The R2.8 is priced decent for what you get and ROI over the V8 is pretty good with the mileage improvements.
Here are the plus's of the diesel over the V8
- Brand new engine, alternator, PS pump , etc. All new
- Cummins reliability
- Very complete package. Computer, wiring, gas pedal, gauge, very good install manual
- Turbo power!
Here are the drawbacks:
- The Cummins takes a lot of ancillary equipment. Intercooler, PS reservoir, coolant expansion tank, remote oil and fuel filters, extra plumbing, etc The Bronco engine bay is small and it's hard to fit this all in. (Although I've figured most of this out, so skim my thread for ideas)
- Cummins will require frame mods. I had to make new engine mounts and modify the crossmember. There may be clearance issues with std width front axles. The oil pan is wider than a Windsor block. (With full widths, clearance is not really an issue and the pan doesn't hang down as far.)
- You will be largely on your own figuring out problems. Cummins has decent engine support, but no help with the rest of the integration. The RepowerOwners website is okay, but far from great for support.
For gearing, don't go deeper than 4.10s with 35s. I ran 4.56s and 37s with the V8 and will continue running them with the R2.8. There is an RPM calculator on the Cummins website. With my setup and for 4.10s/35s, you will be well into the diesel's power band. You will be beyond the optimal efficiency range. Remember that engine torque peaks at 1800 rpm.
Since I mentioned it, be careful comparing power and torque numbers between gas and diesel engines, they don't tell the whole story. My 7.3l diesel is old and only make around 190hp, but it would out-pull that 375hp V8 all day. Why? Diesel make much more drivable power. V8s with performance cams push peak torque up between 3500 and 4500 rpm. This is hardly where you want to be hanging out when towing or climbing a long grade. Diesel typically peak below 2000 rpm. Below 3500rpm, I bet the 2.8 feels more powerful or at least on par with a 347.
That Tremec transmission is a good choice for pulling and crawling. I stuck with the ZF5, , which is very similar.
For lift, you will need the 2" body lift to clear the R2.8. I still had to modify the hood to make it fit.
Final thoughts: The R2.8 modernizes a lot of things that most people spend weekends upgrading on the Windsor block engines (serp drive, modern electronic controls, cooling system, etc) Reliability is big factor. No matter how hard I worked on the 351W, certain aspects seem to undercut my efforts. The design is more than 50 years old. Engines have come a long ways since then. Aftermarket parts are another Achilles heal. I had issues with multiple aftermarket parts that sent the truck back to the garage. I've been in that industry and like it or not, the aftermarket does not build to the quality level of the OEMs. Add in the push to move manufacturing to "low cost regions", aka China and part quality falls further. Beyond fuel mileage and saving money, driving range was a huge consideration. I would rather go 400-500 miles between stops vs 250. Now I don't have to add Jerry cans to my bumper for long trips. That is safer than 10 gal of gas sitting on the bumper in an accident. (also diesel is not nearly as flammable)
I've talk to other owners with similar rigs (CJs, Broncos, D90s) and they all love the R2.8. Can't wait to finish mine.