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Many vehicles on the road today come equipped with a turbocharger or supercharger on their engines. Given the number of queries in my inbox asking about them, it’s safe to say that an explanation of their purpose and the differences between the two might serve you well during your next conversation with your mechanic.

Firstly, it’s helpful to know that within an internal-combustion engine, the ideal air-to-fuel ratio is 14.7:1. Simply put: For every single part of fuel, there should also be 14.7 parts of air. This stoichiometric ratio creates the ideal circumstances for efficient combustion. The ratio must always be maintained, which means as you add more fuel, the corresponding amount of air must be added. While the former is easy, the latter is tricky. The go-to method in the muscle-car generation was to use fuel-thirsty, larger-displacement engines. A larger engine equals a larger amount of air. By contrast, contemporary engineers now have to design engines that achieve maximum horsepower using the least amount of fuel. The time-tested method of bigger-is-better is no longer the only answer.

Because the regular barometric pressure of Earth’s atmosphere is 760 mm Hg (14.7 psi), it goes without saying that only 14.7 psi of air pressure is available to a normally aspirated engine. Enter forced induction. If more air can be forced into an engine than what atmospheric pressure allows, it is labelled as forced induction. Turbochargers and superchargers have been around since the early 1900s, but they were typically used as power-boosting devices without regard to fuel economy. Now they are used in both sports cars and smaller econo-boxes with differing objectives.

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Essentially, both turbochargers and superchargers do the exact same job. They are turbine compressors that increase air pressure, thereby improving overall efficiency and increasing the engine’s performance. The difference between the two is in what drives each unit. A turbocharger uses the engine’s escaping exhaust to spin the turbine, while a supercharger uses a belt-drive system connected to the engine’s rotating crankshaft. They each have their advantages. The turbocharger’s use of unused exhaust energy causes very little net loss of horsepower, but it takes time to build up significant pressure as there is no direct connection. A supercharger, on the other hand, has a fixed mechanical connection to the crankshaft, which makes turbine speed consistent. Therefore, the power boost occurs immediately but at the cost of a small amount of horsepower to drive the unit.

But how do they save fuel? When an automotive manufacturer adds a turbocharger or supercharger to an engine without decreasing engine displacement, that is usually a performance-oriented design. However, using forced induction, the manufacturer can decrease engine size significantly. The power boost from the forced induction system is used to make up for lost power due to the smaller displacement. Most drivers don’t require all their available horsepower all the time, so the smaller engine will use far less fuel most of the time, leading to better overall fuel economy.

Turbochargers are far more common than superchargers in today’s market due to the fact that superchargers rob engines of a small amount of horsepower, while turbochargers generate boost with little cost to fuel economy. The turbocharger is not going away any time soon and, in fact, will likely increase in use. Get used to the idea, as vehicles without turbochargers will soon go the way of the manual transmission.


Your automotive questions, answered

Hi,

I took my ’09 Focus to Halfords for a wheel alignment and brake check as it was free. I had a call saying the calipers had seized, the pads were too low, the discs were cracked and shattering metal fragments - also, the drums needed doing. I was quoted £550+, but they’ll refund me for the alignment because it was fine. I simply couldn’t afford it but managed to get financial help from a friend, who paid £500 total. The car was delivered to me from Halfords by a mechanic on his way home. After taking it around the block, I was satisfied with how it felt, but I noticed the clocks were wrong. I’m unsure as to why they’d disconnect the battery, but I’m told some garages do. Because I was curious, I lifted the bonnet and found brake fluid everywhere due to the cap not being replaced properly. I managed to twist it a few times before it was shut tight! I’m petrified to drive it. What problems could it cause, and what else should I look out for?

Emma E

First off, chances are the battery was not unhooked and likely something far simpler occurred. When a brake job is being completed by the technician, they typically turn the front wheels back and forth to make it easier to access the front caliper bolts. In order to do this, the key has to be in the ignition and turned forward to the point where the steering wheel will be unlocked. Unfortunately, this means that the car may have been inadvertently left in the run position, using an elevated amount of energy from the battery. Unless the battery is brand new, it may have become depleted in that time on the hoist, to the point where the technician had to boost the car, hence the reset clock.

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The brake-fluid cap being left off was carelessness on the part of the technician. While minor, I can understand why you would question the safety of the remainder of the job. Take the car back to the repair facility and insist they recheck the complete job.

I’m really happy with my 2006 Ram 1500 Crew Cab 4x4 with about 280,000 km on a 4.7-litre engine. The truck works well and is well maintained but has one reoccurring problem. The dash lights up with warning codes for brakes, air bags and lamps. The engine runs well, heater works, the signal-light indicator works on the dash, but there are no lights working outside. The headlights, windshield wipers, brake lights and signal lights do not work. The problem comes and goes, often starting after hitting a pothole. The problem goes away after the truck is shut off for a while. The signal light and high-beam steering-column switch have been replaced. The ignition switch is also new. The truck has an LED driving light slaved to high beams. Any ideas of where to look next to solve this intermittent problem? Thank you.

Juha, Fort St. James, B C.

I am not a Chrysler expert, but I believe this was the first year that Ram trucks came with a Controller Area Network (CAN) bus system. This means that previous vehicles would have had an analog communication system, while yours is digital. This may be significant, as any electrical disturbance to this circuit will yield the most peculiar results. I am going to assume, since you have had several pieces replaced in your quest to solve this problem, that all the various computers and control modules have been checked for any applicable codes. After that assumption is verified, I would immediately start by looking at your aftermarket LED lighting system. And I would completely remove it temporarily and restore it back to the original settings. If any of the added LED headlight wiring is shorting to ground, this will cause mayhem and perhaps be the cause of the erratic behaviour. If that proves fruitless, then I would next look at the instrument cluster itself and the body-control module (BCM).

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.

Shopping for a new car? Check out the new Globe Drive Build and Price Tool to see the latest discounts, rebates and rates on new cars, trucks and SUVs. Click here to get your price.

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