Better-Than-Stock Emissions?
Question: I have an '07 Dodge 1-ton with a 6.7L Cummins and an automatic transmission. When I bought the truck, it had 41,000 miles on it and got 12 1/2 mpg (calculated by hand). I have modified the truck with an H&S Black Maxx programmer and about every other bolt-on and bolt-off modification imaginable. On my last trip, I got 21 1/2 mpg. So here's my question-could you call upon an expert to prove to me that I am harming the environment more by getting 21 1/2 mpg versus the stock 12 1/2 mpg?
Collin N.
Oklahoma City, Oklahoma
| Many people think this is where diesel particulate filters belong, but low smoke and horsepower can coexist. Remember, not many people complain about the air they breathe being "too clean." For those looking for horsepower and low emissions, the technology is there. BMW's 335d makes 260 hp and 420 lb-ft at the rear wheels with a 3.0L engine-while meeting the most restrictive diesel emissions standards in the world.
Answer: Oh boy, you've opened up a can of worms here. A lot of diesel enthusiasts assert that they're actually doing more good than harm by removing emissions devices, and they may be right-sort of. If you've been watching the news at all during your lifetime, you've probably heard the term "carbon footprint"-the amount of CO2 your vehicle (or for that matter, you) emits into the atmosphere. By removing all your emissions equipment, you're actually cutting your carbon footprint in half (according to your fuel economy figures, anyhow) and reducing pollution greatly. But, like everything else, there's a tradeoff. In larger cities, where NOx and particulate matter (soot) is looked upon as the boogieman of vehicle emissions, your carbon footprint may be of less concern. While there is research that suggests our increased carbon emissions could cause climate shifts after hundreds of years, particle emissions can have immediate health repercussions such as asthma, bronchitis, and other respiratory problems. In this case, the extra fuel sacrifice was looked upon as a necessary evil in order to reduce particle emissions to just 10 percent of what they were in 2003. New advancements such as urea injection and piezo injectors will hopefully allow the diesel fuel economy advantage to return to what it once was, while still retaining a lower emissions level. Better yet, if airborne particles are the enemy, give us a large DPF that is easily removed and cleaned without using excess fuel.
New To Nitrous
Question: I am new to nitrous, and I am looking to put together my first system. I bought a wet-nitrous kit from my cousin and a dry system from a local performance shop. The guy who sold me the dry system gave me a 0.047-inch jet and said it should be good for around 75 hp. I have three solenoids now, and I eventually hope to try something like a 0.095-inch jet in each one.
D.J. Steinwagner
New Athens, Illinois
| We've seen plenty of cobbled-together nitrous systems in our time, but most serious racers end up stepping up to a diesel-specific nitrous system that features larger lines and solenoids.
Answer: First off, throw everything you've learned about nitrous from the gasoline world out the window. Since a diesel can operate on such a wide range of air-to-fuel ratios, there is no given amount of horsepower a nitrous jet will give you. We've seen a 0.070-inch jet add anywhere from 50 to 150 hp, depending on the application. The more overfueled your engine is, the more gain you'll see from the same amount of nitrous. With most of the gasoline-based nitrous stuff (we're assuming it's all used), about a 0.080-inch jet is all you'll be able to support. After that, your solenoids, lines, and nozzles will become a restriction. But don't despair-if you have three solenoids and nozzles, three 0.080-inch jets will feel like a pretty good hit, although that's about all a normal bottle and -4 AN feed line will support. Bottle pressure is also a huge factor with diesels. Get some bottle heaters and run about 1,000 psi of bottle pressure to get the best results. Any lower pressure than that, and your power will drop. Any more pressure, and you might crack a nitrous line or your solenoids won't open. On Project Rust Bucket, we saw a 40hp gain with a one-stage system just by raising bottle pressure from 600 to 950 psi. If you have a few bucks to spend, Nitrous Express sells a diesel kit with two 0.157-inch solenoids, big lines, a -6 AN feed line with a high-flow bottle valve, and a programmable controller for less than $1,000. We've seen this kit add more than 400 hp on diesels that have plenty of fuel.
True Twins
Question: I was wondering if it was possible to run two stock turbos on my '97 Cummins 12-valve instead of the factory single turbo. It seems like the airflow would be a lot better than the factory single turbo, and the exhaust and intake piping would be a lot easier to make than a compound setup.
Jonathan James
Via email
| Banks Power once produced a 700hp, twin-turbo Cummins marine engine for the military. Although it worked, Banks' new single-supercharged, twin-turbocharged, 800hp Duramax works even better. To check out a full write-up on that engine, check out the Sept '10 issue of Diesel Power.
Answer: Yes, it is possible to run parallel twin turbos on a Cummins. In fact, Banks Power built an engine featuring true twins in 2002. Its twin-turbo 5.9L Cummins made 700 hp and was designed to run as a marine engine. The setup wasn't perfect, however, as the restrictive Cummins cylinder head caused the turbos to surge in the middle of the powerband. Earlier this year, Banks built another marine engine. This time around it was a 6.6L Duramax diesel that featured more displacement and less restrictive cylinder head flow. A supercharger was used at low engine speeds to spool a larger set of parallel turbos. This combination made the 800hp Duramax much more efficient than the earlier 700hp Cummins.
Now your 12-valve engine with two Holset HX35 turbos would flow about 1,200 cfm, which would be about the same amount of air produced by a single 66mm turbo. The twin Holsets would require a lot of engine speed to spool-remember there'd only be three cylinders feeding each turbo. The two Holsets would also require a header to be fabricated, two separate exhaust pipes, and two intake tracts. In the end, it's a lot easier to bolt on a single turbo that's larger than stock and be done with it. An aftermarket turbocharger will not only be able to flow more air, but it will be able to withstand much higher-pressure ratios (more boost) than the factory HX35. Remember, the HX35s were wastegated at about 20 psi from the factory and typically grenade somewhere between 35 to 45 psi. An S366 (66mm S300), for instance, will flow as much air as two HX35s, while being safe to about 50 psi of boost.
Oil Leak Laments Question: I just purchased an '03 Ford F-250 truck with a 7.3L diesel engine and have noticed it's left a few spots of oil in my driveway. When I got out and looked under the truck, I saw there was a leak between the oil pan and the transmission pan. Any ideas where this motor oil is coming from?
Julio Velasquez Via email
Answer: When there's an oil leak between the engine and transmission of your truck, most people assume the cause is the rear-main seal on the crankshaft. And if the truck is a Dodge or GM, that may in fact be the problem. Over time, the rear-main seal tends to get brittle, and oil will start to leak out the back of the engine at the crankshaft. This causes oil to drip from between the engine and the transmission bellhousing.
On Fords, the oil leak is caused by something else. The injection control pressure (ICP) sensor, oil lines for the high-pressure fuel system, or even the turbo pedestal can leak oil into the valley of the engine. Any leak on top of the engine will drain off the back of the block and seem like a rear-main seal leak. While a bad rear-main seal is common for a variety of different diesels, more often than not on the Power Stroke-powered Fords, the issue is on top of the engine. If you're headed to a repair shop, expect about a $300 to $500 repair bill if the leak is somewhere on the top of the engine, which is a lot cheaper than the $800 to $1,000 if it is the rear-main seal, since a rear-main involves pulling the transmission. If you're a do-it-yourself kind of guy, the hardest part will be tracking down the leak. But if it were us, we'd start by checking all your high-pressure lines for the HEUI oil system.
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