Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power? Send us an email at jason.sands@sorc.com and we’ll do our best to answer it.
Racked Barrels?
Question: I keep hearing people talking about “racking the barrels” on a 12-valve Cummins, but I have no idea what that means. I guess I’m just wondering if there’s actually a difference in performance, or if people are just blowing hot air.
James Moore
Chicago, Illinois
| Before we swap in the monster 13mm Scheid Diesel–built pump on our 12-valve Cummins project, we’ll rack the barrels on the pump—just to see how much horsepower it actually gives.
Answer: What folks are referring to is the Bosch P7100 inline pump that came on ’94 to ’98 Dodges. Mid year in 1998, Dodge switched to the VP44 rotary pump on a 24-valve Cummins engine, which didn’t offer the same amount of performance potential as the P-pumped 12-valves. This type of mechanical inline pump can basically be thought of as a tiny engine, with the plungers being analogous to pistons, the case being the block, and so on. Since these pumps have to be very accurate in their metering of fuel, adjustable barrels were built into the case to ensure the fuel levels could be controlled precisely enough to achieve a smooth running engine. This type of adjustment is usually performed with the pump on a test stand to make sure all the plungers are within a few cc of each other as far as pumping volume goes.
From the factory, none of these barrels are bottomed out to their full fuel position; rather they’re somewhere in the middle. So, racking the barrels involves loosening the nuts that lock the barrel in place and tapping the barrel clockwise until it bottoms out. This means that every barrel will now be giving all it can as far as fueling goes. The upside to this modification is that it does indeed give the pump greater fueling capabilities and, in many cases, can be worth a good deal of power (about 50 hp as far as the rumor mill goes).
But, there is a downside. If your pump is worn or out of balance, racking the barrels can cause a very rough, poor running truck—and it’s not all that easy to get the barrels back to where they started since the adjustments are so minute. If racking the barrels causes the truck to run bad or rough (which happens quite often) at that point, your only option is to send the pump to a shop to get it flowed. While it’s a virtually free modification, it’s one that probably shouldn’t be performed unless you’re ready to send the pump out anyway.
LML Power
Question: I’ve heard there’s almost nothing you can do to the ’11 and ’12 Duramax-powered trucks to add power. Is that true, or have folks cracked the code to unleash some more performance?
Mark James
Modesto, California
| Although dyno-proven horsepower is available for the LML, keep in mind that changes may be tracked by the ECM, which could cause future warranty issues, should problems arise.
Answer: Compared to earlier years, the new Duramaxes have been rather slow on the uptake as far as performance options go. H&S Performance does offer some performance tuning, as does Duramax Tuner. Most of the performance tuning for the LML Duramax has been focused on DPF-on applications (for emissions purposes), which isn’t as bad as one might think. At roughly 350 rwhp from the factory, they’re already at where a tuned, stock transmission ’01 GM would have been five years ago. Even with the DPF in place, recent testing (see “Emissions-Friendly Tuning,” August ’13) has proved that nearly 500 rwhp can be reached on the stock transmission, and with the DPF in place. Best of all, fuel economy is still very good, thanks to SCR. While there are only a few places offering tuning for the LML Duramaxes, the results these tuners have been able to achieve so far has been very impressive.
Ford Transmission Conversions
Question: I read all the time about Ford transmission swaps, as in a 4R100 behind a Cummins, or 5R110 behind a 7.3L. So my question is, how is this possible? Can the transmission be made to work with the factory computer? How about the Ford 6R140? Has that been swapped into anything yet? It would be cool to have a six-speed 7.3L tow rig.
Mitch Marshall
Tempe, Arizona
| If you’re looking for a killer transmission for a Ford truck, don’t dismiss the Allison 1000, as we’ve seen the Allison work rather well behind Cummins-powered Fords in the past.
Answer: The most common transmission swap we see really isn’t a swap at all. Rather, it involves installing a Cummins engine (either an earlier 12-valve or later common-rail) in an ’03 to ’07 Ford. In most cases, the owner of the truck wishes to retain the stock 5R110 transmission, which involves making a Cummins-to-TorqueShift adapter. These adapters are available from Destroked.com and a few other conversion sources.
To get the transmission to shift properly, a Powertrain Control Solutions (PCS) controller is normally employed, especially if the transmission is installed in a vehicle it normally didn’t come in (like a 4R100 behind a Cummins). With the PCS controller, shift points, line pressure, and many other transmission features can be custom tailored to an application to keep the engine that’s being used in its powerband. We did a little poking around PCS’ website, and it looks like Ford’s 6R140 is indeed supported, so with some custom parts, a six-speed, 7.3L-powered tow monster could actually be a possibility.
