The basic formula for creating power is pretty simple. The basic elements are air, fuel, heat and efficiency.
Some of these are easy to change and affect, while other elements are quite expensive and require some extensive trial and error or engineering. The efficiency of an engine is hard to affect. There are good synthetic oils like Royal Purple that reduce friction, which reduces the amount of energy needed to turn everything over, but all in all, the efficiency of the engine is pretty much whatever the OEM designed it to be.
Air, fuel and heat are three basic elements that are more easily changeable. Changing the air can be as simple as changing to a good air cleaner that flows more freely or it can be more difficult like changing the intake elbow or even changing the turbocharger to get more air into the engine.
Fuel is one of the first elements that most people change. Programmers and power modules change the fuel tables and add more power to the engine. They also adjust the injection timing-but that's another topic of discussion for a different time.
Heat can be good or bad. There needs to be heat to have everything working properly, but too much heat and things start breaking. So there is a fine line. Heat is an element caused by a few different factors. First and foremost, heat is what ignites the diesel fuel. So diesel engines have a very high compression ratio to generate the heat needed to ignite the fuel. A naturally aspirated diesel will have a compression ratio anywhere from as low as 18:1 to as high as 23:1, while a turbocharged diesel engine's compression ratio can be anywhere from 16:1 to 20:1 as a general rule of thumb.
Now, before you start writing to the magazine saying, "I have a diesel engine that's compression is . " there are exceptions to this rule. In fact, I have two engines in my garage that are turbocharged and their compression is 22:1. So there are engines that are outside of this range, but this is a good basic rule of thumb.
In addition to heat generated from the piston compressing the intake air, it is also generated from the turbocharger. As the turbo compresses the intake air, it too is heating it up. To combat this increase in temperature, today most diesel engines have intercoolers. Marine applications use a heat exchanger which cools the air with water, while over-the-road trucks and many generators use an air-to-air intercooler.
Anytime the turbocharger is working harder than designed, it starts to generate an increased amount of heat because the turbo is working outside of its efficiency range. Turbochargers start getting out of range when an increased amount of fuel is used, which creates hotter exhaust gases spinning the turbine wheel faster.
Many OEMs are now turning to variable geometry turbochargers to help reduce emissions by reducing the time it takes to spool. In the aftermarket world, some custom tuners think more boost is better and they are calling for higher boost pressures from these turbochargers. This increased boost pressure is at a very high temperature, which actually decreases the horsepower of the engine. Remember in science class when the teachers were talking about oxygen molecules and density? Well, if you were sleeping that day, here's the gist of it: the denser the air, the more oxygen per square inch it has. Air density comes from temperature. The colder the air, the more dense it is (let's not talk altitude).
The turbocharger is really the heart of the engine. Depending on how it is working effects the drivability, performance characteristics and usability of the vehicle. So how do you know which turbocharger to go with? Well, we went to some of the biggest names in turbochargers and discussed that very question with them.
There are some basic formulas to figure and calculate what size turbocharger you may need. BorgWarner Turbo and Emission Systems uses:
Engine size (cubic inches) x engine rpmx0.5 (for four-stroke engines) x volumetric efficiency (amount of air the engine actually ingests vs. the theoretical capacity)xpressure ratio. Then divide that by 1728 (to convert cubic inches to cubic feet) to get airflow rate (CFM).
The formula above is only designed to give you a rough estimate on what size turbocharger you need. In order to use the formula above, you will need to know or guess at some of the values, such as boost. When calculating boost, a general rule of thumb is that for every pound of boost, the engine will produce 10 hp. So, if you are making 50 lbs. of boost, the engine is probably making close to 500 hp to the ground. This rule isn't set in stone, but it is a good starting point.
"There are many other needed elements necessary, including ambient air temps, restrictions, compressor efficiency, etc.," said Kurt Henderson, technical sales representative for BorgWarner Turbo and Emissions Systems, when explaining how to calculate a turbocharger for a specific application.
Joel Gooch, partner of J&H Performance Diesel, said. "A customer should call and talk to whomever they are getting the turbocharger from. That way they can discuss the expectations, goals and costs."
Just about everyone we talked to said the same thing. Be realistic in your hopes and expectations. Before you call, decide on a couple of things:
What are you going to do with the truck? Tow? Race? Daily driver and/or weekend warrior?
How much are you willing to spend?
There are many different types of turbochargers in the market place and they all cost different amounts.
The answers to the above questions should help you determine what size turbocharger you should get. Of course, there are other factors that will determine the specific turbocharger needed, but you can discuss these with whomever you are purchasing the turbocharger from.
The experts take all of this into consideration and also use their experience to determine what turbocharger you need. The are things such as A/R ratio, which is defined by Garrett Turbochargers as the inlet cross-sectional area divided by the radius from the turbo centerline to the centroid of that area. The A/R ratio can be the difference between a competition-only turbocharger and street driven/weekend warrior turbo. The A/R ratio affects spoolability, egt and boost pressures.
With that said, matching the right turbocharger to your specific application is tricky and you need to discuss it with professionals.
So, how do you find the right professional and what should you look for?
"I always recommend people look for companies that specialize in their specific vehicle or brand," said Tadd Layton, owner of Elite Diesel Engineering.
Quality products, good fitment and products that have been tried and tested are always good indicators. Another good suggestion that Henderson had was to look for turbochargers that use common and easily available adapters and piping.
When you get ready to make the change, read the instructions prior to starting to make sure you have everything. "It's a good idea to make sure you have all necessary tools prior to the installation," said Rick Head, president of Exile Turbo Systems. "I also encourage replacing oil feed lines and air and fuel filters when installing a new turbocharger."
Layton added: "Be patient and leave yourself plenty of time to convert the turbocharger over." If the manufacturer says it will take four hours to complete, leave yourself 8-10 to complete the task. The manufacturer's time may be based off of someone with much more experience and better tools than you have.
Picking the right turbocharger for your vehicle can give you everything you want and more. Pick the wrong turbocharger and not only will your truck perform poorly but it may lead to major costly problems down the road.
So before you make that next purchase talk to a few of these guys and get all of your questions answered. Then you'll be ready to make a smart decision and move forward.
SOURCES:
BorgWarner Turbo and Emissions Systems
www.turbodriven.com
Elite Diesel Engineering
www.elitedieseleng.com
866-631-8518
Exile Turbo Systems
www.exileturbo.com
805-432-5582
Garrett Turbochargers
www.turbobygarrett.com
J&H Performance Diesel
www.jandhperformance.com
530-245-0176