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Madman’s guide to forced induction

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Posted: Friday, April 6, 2012 2:57 am

There is no replacement for displacement. I have heard this well known saying my entire life. Everybody from drag race veterans to my eleventh grade auto shop instructor.

Displacement, displacement, displacement … there is apparently no replacement. I will agree that the overused adage has a strong foothold in physics, but it is misleading. While there may not be a replacement for displacement, there is an alternative for displacement. Forced induction in the form of turbo or super charging is the cool whip to displacement’s whipped cream.

Displacement is, of course, the size of an engine. Displacement is not the amount of space the engine takes up under the hood, but how much volume is in its collective cylinders. For example … if you were to fill every cylinder of a Corvette Z06 with chocolate milk you would need seven liters of delicious moo juice. In comparison my Honda Civic will hold one and a half liters of milk, much better considering the price of chocolate milk these days. While a class of first graders would be thrilled to have a Corvette portion of chocolaty milk, the car requires fuel and lots of it.

While there may be no replacement for displacement, there is absolutely no escape from it. The hefty Corvette Z06 seven liter V8 must be filled with lots of gas in order to run properly. While proponents of muscular engines will argue it takes a large engine to make copious power, they overlook the Corvette ZR1. Okay, stay with me here … the Z06 has a huge 7 liter while the ZR1 has a smaller more powerful 6.2 liter. The smaller ZR1 engine produces 133 more horsepower and manages almost the same fuel economy. The relatively small 6.2 liter engine uses a supercharger to level the playing field. A supercharger uses a belt driven compressor to force pressurized air into the cylinder making a more powerful explosion and more power.

Clearly a supercharger can significantly boost the power of a smaller engine. This is interesting to a very small segment of the population. I realize that many of the Lodi News Sentinel readers are not looking to blow the doors off of a Corvette Z06. Even if you do not have the need for speed, forced induction has its advantages in the form of fuel economy.

Turbo charging is a form of supercharging that uses exhaust gas to make extra power. In turbo charging, exhaust gas is run through a manifold which houses an impeller. This impeller looks like a convoluted propeller sitting inside of a chamber with an entrance and an exit. In order for the hot exhaust gases to reach the tailpipe, they must pass the impeller, spinning it furiously. Connected by a shaft, there is a similar impeller in a chamber of its own spinning with the energy from its twin on the hot side of the housing. The cold side impeller sits in a housing that resembles a hair dryer and it blows air like one. This blowing air is force fed to the engine making a bigger bang and lots of power. The great thing about turbo charging is when the extra power is not needed the turbo is bypassed making extra fuel enrichment unnecessary.

No, I don’t blame you for speed reading the last paragraph. Turbo charging uses exhaust gas to make power while a supercharger uses engine rotation via a belt. They both make smaller engines more efficient than their bigger counterparts. Take the Ford F150 truck for example. For the first time in history the best selling truck in America is rocking a twin turbo V6 that is more powerful and fuel efficient than its standard V8. The Ecoboost V6 manages 40 more feet pounds - of - torque than the much larger V8 and it manages slightly better fuel mileage. That is a significant power increase from a smaller engine using less fuel to do it.

While rebutting old automotive thinking is something I can always get into, I had good reason for writing on this subject. Automotive design is changing rapidly to satisfy consumers that want power and efficiency. The turbo charged Ford truck was a real wake up call to car guys everywhere. If Ford is willing to replace displacement in a pickup … then times are changing. The next time you are car shopping, please remember the biggest engine may not be the best and it’s going to take a lot more chocolate milk to run.




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