Speed & Sound: Performance – Nitrous for Diesels
Who says you can’t have fun in a diesel.
Story by Budd Stanley
As regular readers may have gathered, I do not go into much detail about power-increasing modifications in these performance pieces. I am of the firm belief that power is the last facet of performance modification to be explored when looking to gain a faster time at a track day, or to give your ride a little more excitement. Therefore, I’ve concentrated on suspension, brake and chassis tuning to get the most out of what the factory has given you. However, this month, I will finally be diving into the engine, but it won’t be something that the majority of you may think. I’m talkin’ diesel power tuning!
As an Auto Journalist, I have the good fortune to test out the latest vehicles each manufacturer has on tap, and a popular segment that has recently caught my attention is that of the modern diesel. The recent introduction of the BMW 335d and X5d, VW Jetta TDI, and Mercedes E-Class BlueTEC are good examples, as well as some great potential sleepers in older VW, Mercedes and Volvo diesels that were available in the ‘80s and ‘90s. These modern-day diesels have given me an entirely new outlook on the performance potential of these cars, while being economically cheaper to run and more eco-friendly.
So, we are going the diesel route. I expect the other three aspects (chassis, suspension, brakes) to be worked on first, but there is not a lot of info out there to get power out of these torque-oriented diesels. Personally, I am one of those people who hates the bang-for-buck modification of simply slapping a nitrous oxide kit on a performance car. It just seems amateur to me, almost cheating. I believe in getting your hands dirty, getting inside an engine and machining a better performance. However, I recently discovered an interesting mod out there for the diesels that intrigued me.
While NOS works great with petrol engines, it is detrimental to diesels. This modification I talk about is popular in the trucking community as well as with Europeans, to whom 50 percent of the vehicles sold are diesels. The injection of propane into the fuel mixture in the same way NOS is injected into petrol engines yields some impressive figures. But first, why propane and not NOS? Pretty simple, it all has to do with compression. Petrol engines use a spark to fire the fuel mixture, while diesels use heat from compression. Because of this, NOS would pre-fire, essentially stopping the piston before the diesel was supposed to ignite. Propane, on the other hand, is a compression-friendly substance that burns slower, better suiting the operational characteristics of a diesel engine. By adding a propane mixture, power can be increased from 25-60 percent, depending on mixture ratio, while fuel economy can also be increased as much as 10 percent. Propane’s cleaner burn has also been known to help clean carbon and soot from the combustion chamber and runners.
The typical system is rather simple, including lines, fittings, clamps, a pressure regulator (usually adjustable) and a solenoid valve to turn on and off the gas. It works by properly mounting a propane tank (BBQ units do work) to a solid surface, ideally in the trunk of the vehicle. Connect lines with a solenoid and a pressure regulator, then plumb a feed line into either the airbox, bypass valve or tapping the intake pipe to the intercooler. It is important to start on the lowest mixture so as not to ping the engine. To find maximum efficiency, slowly increase pressure until the engine starts to ping, then back it off slightly. While this will give you the biggest increase in power without damaging the engine, it is recommended to back the propane off an additional 25 percent to decrease the risk of damaging pistons under hard driving conditions.
The nice thing is that there are already several system kits on the market for turbo-diesel trucks. This makes adding this system to a diesel-injected car fairly simple and straightforward. Costs usually run between $700-1,200. However, the systems are quite simple, and fabricating a homemade unit shouldn’t pose a problem to those who are comfortable working on fuel systems. Materials needed usually run in the $100-200 range.[PSGallery=kqqorrf9k]
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