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  • Diesel Gelling Concerns, Diesel Motorhomes and Twin Turbos - Top Diesel Tech Questions

Diesel Gelling Concerns, Diesel Motorhomes and Twin Turbos - Top Diesel Tech Questions

You've Got Questions? We've Got Answers!

Jason Sands
Jul 5, 2015
Photographers: Jason Sands
Gelling Concerns
I own an ’11 Ford F-350 with the 6.7L diesel. Whenever the temperature drops below 0 degrees, the fuel filter will clog with gelled fuel. I treat the fuel with anti-gel at every fill-up starting at the beginning of colder weather, usually around November. Even with the anti-gel treatment, my truck has gelled five times this winter. I also have two Volkswagen diesels and two pieces of off-road diesel equipment that get their fuel from the same source as the Ford, and these have never gelled. The re-liquefiers can work, but I've had the truck gel again the next day without adding more fuel to the tank. In cold weather, I can't depend on the truck to run without problems. Do you have a solution to my problem?
Jim Redman
Mill River, Massachusetts
Photo 2/4   |   We’ve seen FASS lift pump and filter systems around the industry for years, but some newer versions have optional provisions for a fuel heater, which can be a lifesaver during cold winter driving.
The stock fuel filter isn’t in the best location on new Ford trucks. It’s exposed to the environment and away from any residual heat that might keep it somewhat warm. We’ll assume you already tried replacing the stock filter with a new one, as after the fuel in the filter gels for the first time, it usually leaves some pretty nasty buildup.
There are a number of simple things you can try first, like insulating the filter or parking the truck in a garage. There are also heating blankets or patches from auto parts stores you can put on the filter. Even though it will only keep the outside warm (but it can’t get too warm, as the housing is plastic), it will help keep the fuel from gelling.
If you’re looking for a fix-it-for-good-and-walk-away-type solution, we suggest adding one of the new FASS Titanium series lift pumps. These pumps come complete with a filter assembly and can be ordered with an optional heater. The filters are also rated for diesel fuel and the correct micron filtration, so you won’t have to worry about contaminating your fuel or improper filtration. If the fuel does start to gel, these types of powerful electric pumps can usually push through a partially clogged filter, although we still recommend checking from time to time.
Diesel Motorhome Questions
My friend is having problems with the 400ci V-8 gas engine in his ’83 Chevy C30 step van motorhome. A compression test, conducted after eliminating the possibility of bad ignition wires, bad coil, bad spark plug, and so on, confirmed my suspicions that the engine is on its way out. The 400 V-8 in his motorhome still spins the original and venerable TH400 three-speed automatic transmission. Since my friend makes cross-country trips in this "rolling museum," which has a customized interior and a lot of time and money in it, the appeal of an overdrive transmission and diesel fuel economy is high. His trip costs are now measured in gallons of gas and quarts of oil, which isn't good!
Despite the need to beef up the front suspension to carry the heavier diesel engine, to fabricate new engine mounts and redesign the engine compartment, and even probably redesign the vehicle’s snub-nose front end, this diesel-swap project has appeal. The Cummins 6BT 6.7L, mated perhaps to a 68RFE automatic transmission, sprang to mind as one possible swap. But, are there other promising options?
Maynard McKillen
Milwaukee, Wisconsin
Photo 3/4   |   Although the 4BT Cummins engines are often thought of as too small to make power, they’re actually quite capable and can fit in nearly any place a small-block Chevy used to sit (like in this ’32 Ford).
Your thoughts about swapping a diesel into your friend’s vehicle are on point. A 400ci small-block and TH400 transmission usually don’t combine to offer good fuel economy, and pushing a rolling brick down the road makes the issue even worse. Since it sounds as though space is limited—and since you didn’t mention that he’s looking for more power—we'd shy away from the 6.7L/68RFE combination, simply because of the high level of fabrication needed for the swap. Cost is another factor, as a used 6.7L core engine can cost $5,000 to $6,000, and that’s without any guarantee that it even runs. The transmission would be around $2,500, and the cost of controlling it all would require tons of time in wiring.
So, what do we suggest? Consider swapping a 4BT Cummins into that RV. The famous 6BT’s smaller counterpart, the four-cylinder powerplant, was available as an option in step vans, so placing one where a small-block Chevy normally resides shouldn’t be that hard. And, with the proper adapter, it should even bolt to the TH400 transmission. With a bit of luck, 4BTs can still be found for about $2,000 to $3,000—ready to run. Although they’re turbocharged, these engines aren’t powerhouses. However, with inexpensive injector, turbo, and pump upgrades, even the VE-pump versions can make about 200 hp, which should be enough to power a small motorhome. If you’re looking for more power, a P-pump, larger injectors, and compound turbos can make 4BTs 400hp-capable and beyond.
We recommend actually keeping the TH400, installing a low-stall torque converter, and adding a Gear Vendors electronic Overdrive. While the Gear Vendors units aren’t cheap, finding a good diesel transmission core can cost much more than $1,000 before it’s even rebuilt. While a newer automatic transmission like the 68RFE might sound good on paper, the $4,500-plus price tag for a transmission that may or may not last is usually too much for people. We’ve seen many instances of 68RFEs failing at 150,000 miles or less at stock power levels, so we’d be wary to install one in a hopped-up or heavier vehicle. If your buddy just has to have a modern transmission, we suggest a six-speed Allison 1000 automatic, although going that route will take a considerable amount of wiring and fabrication.
True Twin Turbos
I’m in the middle of swapping a Duramax engine into an older Ford F-100, and I had some questions about turbochargers. The truck is going to sit low, and I don't really like the location of the stock turbo in the engine valley. I was looking at going to true twin turbos (one on each side of the engine), but I am lost when it comes to how to size them. I would also like to know what size exhaust I should run (3-inch? 3.5-inch?) and what kind of turbine housings I'll need to spool things quick. I'm not looking for crazy power, maybe 400 to 500 hp. Any help would be greatly appreciated.
Rick Grant
-via email
Photo 4/4   |   Parallel twin turbochargers must be sized much smaller than a normal single turbo, thanks to each turbo only supporting one half of the engine. Still, a properly sized combination can spool very quickly and make plenty of power.
We probably see more sets of parallel twin-turbocharger setups on Duramaxes than we do on any other diesel engines, and most of them are sized a bit too large. If you think of it in terms of having a turbo for each bank, then you’ll basically need to size the turbo for a 3.3L four-cylinder that makes about 300hp at the crank. Sizing the turbos to give you a total of 600 hp means a little more than 500 hp should make it to the wheels, which will be right at your power goal.
That means turbos as small as the 42mm Garrett GTX2860 (rated for 200 to 300 hp each) could be used, although if you're going to spend the dough, we might suggest a little horsepower wiggle room, like stepping up to the 47mm GTX2863R series. Rated at 250 to 430 hp each, the 2863 also has the advantage of wastegated turbine housings to limit boost.
If you’re looking for the same type of performance using offerings from BorgWarner, we suggest the S200 series. Twin 51mm S200s can flow enough air to make some serious power, yet they can handle the higher pressure ratios diesels need to make power. As turbine housings go, step down to the 0.60-0.70 A/R range to keep spool time to a minimum. On exhaust, twin 3-inch pipes should offer plenty of flow, as the total area is more than a single 4-inch exhaust, and we’ve seen a 4-inch setup support more than 1,000 hp. As a final thought, whenever you build your own turbo setup, tuning, wastegating, or housing changes are always a possibility—so don’t expect everything to be perfect right out of the box…but it will be close.

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