Letters and Emails

Published in the December 2009 Issue December 2009 Column

Dear DT,
I just sold an F-250 Super Duty V10 that I purchased new in 2000 and the truck was fantastic. I put 258,000 miles on it without so much as a single issue. I've owned four Ford F-250s and two F-350 Power Stroke 7.3L trucks and all were impressive.

Last week, I went and purchased a new 2009 F-250 Super Duty with the new 6.4L diesel engine and was shocked beyond belief that the best fuel mileage I can obtain is 12.5 mpg average. I am so disappointed in my Ford product . any suggestions?

Duane Davis
Aerospace engineer
Commercial Pilot/CFI

Welcome to the backwards world of the diesel particulate filter (DPF). We have done extensive testing with several different 6.4 aftermarket configurations (Diesel Tech February, 2009, "6.4L Power Stroke 4-way Tuner Test" page 38). The best combination we've found while leaving the exhaust system in stock condition with the DPF in place is the DiabloSport Predator tuner with an air intake (any aftermarket intake is vastly better than stock). This gained a mere 2 mpg increase.

The other alternative is to remove the factory exhaust system completely (the DPF is what's causing the mileage problem) and replace it with a DPF-delete "competition-only" exhaust system and then use either SCT or Spartan tuning software to program the truck to run without the DPF unit. This has shown mileage gains anywhere from 5 to 9 mpg, depending on tuning software. The downside is that it's technically a race-only modification. EPA emissions regulations require 2008 and newer diesel pickups to have the DPF in place. Good luck. Let us know what you wind up doing and what your results are. -Ed.


Dear DT,
Great magazine. I just recently caught the diesel bug. I'm 16 and I'm wanting to purchase a diesel. I'm kinda stuck on what I should go for. It's between a 7.3L-equipped F-250 4x4 or a 1998-2002 Dodge 2500 4x4. I'm eventually going to boost it way up and try to make it magazine worthy. If you could I'd appreciate the advice on what to pick as far as the reliability aspect and the power potential.

Ethan Marquis

Both are great trucks with reliable engines. The Ford makes good power, has a great transmission (for stock power levels) and you can get some decent power out of a few minor upgrades, like an intake, exhaust system and programmer/ chip. However, the 7.3L (and 6.0L) Power Strokes can only make so much power before you need to jump into injectors, high-pressure oil pumps and turbo upgrades. At that point, you don't get as much horsepower out of the modifications as you would on the Cummins.

The `98-2002 24-valve Cummins engines are good power plants, although given the choice, we would take the 2001 or 2002 model. They also respond well to an intake and exhaust system and there are dozens of programmer options. You will get more horsepower per dollar spent out of the Cummins in the long run, but that also means you will be rebuilding a transmission sooner, too. Cummins turbos are easy to change, as are the injectors. The Cummins is probably an easier engine to work on if you plan on doing most of the mods yourself.

If you're looking for a reliable diesel that you can add a little extra power to without compromising reliability or spending a ton of money, either truck has its pros and cons. If you're after big horsepower numbers, go with the Cummins. Most high-horsepower streetable 7.3L Power Strokes top out at around 470-530 rear-wheel horsepower. There are several 24-valve Cummins trucks out there that are close to 1,000 horsepower. -Ed.


Dear DT,
I bought a 2008 F-350 King Ranch with the 6.4L diesel and am getting around 13 to 15 mpg around town, pretty good I think. I just did a run around the Puget Sound and ended up with 17.7 mpg, best yet. I hope it keeps up-this is not towing. It only has 7,800 miles on the engine. I bought the Banks Big Air Filter and the 4.5-inch DPF-back pipe. The question is, how can the air box and exhaust get more air and exhaust in and out to the tail pipe if the cat and DPF are still there? It makes no sense to me because I will only be increasing the exhaust from 3.5 inches to 4.5 inches, but it is still being restricted by the DPF and the cat. I haven't installed the items yet.

Can you guys explain this to me? Why would I even want to install the above items?

Dave Hobbs
Silverdale, WA

The air intake will make a noticeable difference in your truck's performance (we've dyno'd intakes on the 6.4L that have shown gains of up to 35 horsepower). As for the DPF-back tail pipe, the only benefit there is a cooler gas temp at the tip of the tailpipe. There are no power or fuel economy benefits from running a DPF-back aftermarket tail pipe since, as you stated, there is no back pressure from that point on. -Ed.

Dear DT,
I am not trying to get into the magazine or get an article right now or anything. I am just having tons of trouble trying to find the things I need to build my dream truck. It's going to be my little present to myself for having been in Iraq for the last seven months. What I would like to do is take my 1965 K20 and put a 6.6L Duramax with a ZF S6-650 transmission, good transfer case, Dana 60 front axle and a Dana 70 rear axle in it. I will spare you all the details so this isn't too long. I would love to apply for an article in a few years when everything on it is all finished, but right now I just can't find these parts: a rebuilt or crate Duramax, the 6-speed manual ZF and the axles. If you can help me at all I would really appreciate it.

Jonathan Heim

While we don't necessarily know where to start looking, we'd bet a few of our readers would. If anyone has suggestions for Jonathan, send them to dteditor@dieseltechmag.com and we'll forward them on to Jonathan. -Ed.

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