Car Corner
Electronic-Turbo for maximum fuel economy

January 1, 2008
By Scott Lewis

A few years ago I talked about an idea I had for a Continuously Variable Boost Supercharger. This month I have a new idea for an electronically controlled turbocharger, the Electronic-Turbo.

What is different about the Electronic-Turbo from the Continuously Variable Boost Supercharger is that everything (and I mean everything) needed to create this system exists and is in use today in many cars. They just haven't been put together like this.

Most cars use turbocharging to increase horsepower. For those of you that don't know what turbocharging is... a turbocharger (or turbo) is basically two propellers on a single shaft separated by a housing. One side of the propellers has the exhaust pumped into it. This spins the turbo. The other side is connected to the incoming air supply of the engine. When the exhaust gasses spin the turbo it forces the incoming air into the engine. This forced air is the boost, hence the term turbo-boost. By forcing more air into the engine you allow the engine to burn more fuel (fuel will not burn without air). More fuel to burn means more power.

Turbocharging cars has been done mostly for performance, you have heard of the Porsche 911 Turbo, right? But it is also done on economy cars such as the VW Turbo Diesel Golf/Rabbit or whatever they call it today. The economy idea comes from the theory that you can fit a car with a smaller engine to get better gas mileage and the turbocharger will provide the power of a larger engine.

And this works. However, the problem with this is that you can't turn the turbocharger off. If you keep driving your turbo car like a Mario Andretti you are going to be forcing all that air into it, and the on-board computer is going to be supplying the appropriate fuel. So you don't get as much benefit as you would like.

Let's look at an apples to apples comparison. My beloved Mini Cooper is already outdated. They have change from using a supercharger (driven by a belt as opposed to exhaust gases) to a turbocharger for the Mini Cooper S. This gives us a great chance to compare two nearly identical vehicles with and without a turbocharger.

The 2007 Mini Cooper has a 1.6 liter engine that puts out 120 hp. The 2007 Mini Cooper S has a turbocharged 1.6 liter engine that puts out 172 hp. The EPA rates the Mini Cooper with 30/40 mpg city/highway, and rates the Mini Cooper S with 27/36 mpg. The turbo in the S model costs you 4 mpg on the highway. Wait a minute. On the highway, in normal driving condition, you are mostly going at a steady speed. It is no trouble for all cars to maintain a speed within approximately 5 mph of the speed limit, well maybe not the Smart.

So why doesn't the turbocharged S get the same highway mileage? Simple, at 3000 RPM on the highway you are going to be generating boost, and with that boost comes extra fuel. You have to maintain the air/fuel ratio for your engine to run properly.

The question them becomes, why can't we eliminate the boost from the turbocharger when we are cruising on the highway at a steady state?

I think we can. Now we are going to mention all the pieces of technology that already exists to make the Electronic-Turbo work. For starters I need to explain what a wastegate is. A wastegate is a device used on almost all turbocharged applications (in production vehicles anyway). This device sits between the exhaust and the turbocharger. The exhaust goes through it before the turbocharger. The wastegate will bypass the turbocharger when the amount of boost the turbo provides reaches a certain limit. This is how you prevent the turbo from supplying unlimited boost and blowing your engine through the hood of your car.

Most cars with turbos have an electronically controlled wastegate. Many aftermarket tuners will adjust the amount of boost the turbo will make before the wastegate kicks in. For instance, let's say a production car has a turbo and the computer opens the wastegate a 11 p.s.i. of boost. You add an aftermarket programming device to tell the on-board computer to open the wastegate at 15 p.s.i. of boost. As long as the computer provides the appropriate extra fuel to go with that 4 extra pounds of boost you will get an increase in horsepower. Granted, you can only increase boost so much before you put too much strain on the engine and disaster strikes.

How will this help us with mileage? Why couldn't we program the computer to open the wastegate all the way, in essence creating no boost at all, when driving on the highway at a steady state. This is no different than the programming the aftermarket does today, just with different results. Then we should be able to match the highway mileage of the non-turbo car. There may be a slight lose of efficiency in the exhaust plumbing of the turbo car that may cost us 1 mpg over the non turbo car. Beyond that all should be possible.

Of course, you would not have the passing power on the highway this way. So we need a way to get back that power. I have two possibilities. First is to program the computer to turn off the wastegate when you press down on the throttle. This would not be any different than when an electric hybrid kicks in its electric motor to assist its gasoline companion.

However, the better approach would be to put it on a switch. Some cars have adjustable suspensions. You set a switch in the passenger compartment to sport, normal and/or luxury. On sport the suspension is tightened up to provide crisper handling. On luxury the opposite happens to provide a more pleasant ride.

Our Electronic-Turbo car would have performance and economy labels. Under economy the wastegate would bypass the turbocharger all the time, providing no boost. Without the boost we should get very close to the fuel economy of the non-turbo car all the time. When we need the extra power we simply flip the switch to performance and we have all the power the turbo normally provides and the accompanying loss in mileage.

BMW puts just such a switch in its M5 super sedan. The switch in its normal position allows the engine to provide 400 hp. Flip the switch and suddenly you have 500 hp on tap. If they can go from 400 to 500 horsepower at the flip of a switch, why can't they go from 120 to 172 hp with the same switch. What's really cool about this idea is that it would cost almost nothing. You add a switch to the car that cost about a $1 and you just have to spend the time to program the computer to open the wastegate and adjust the fuel curve. Simple.

I want one. This is one of those ideas that is sorely missing in the age of imported oil and gas prices over $3/gal. Every turbocharged car could be equipped with this for a few dollars and people would have the option to get better gas mileage or better performance on demand. I rarely use the full power of my Mini Cooper S' supercharger. Traffic and those pesky police won't let me. So why shouldn't I get the advantage of the cheaper, non-turbocharged car when I want it.

Conclusion

Well, there is another one of those great ideas I just need funding to make happen. What bothers me is that nobody has had this idea before. It seems pretty simple to use modern technology that is already in use to go that extra mile... or should I say that extra mile per gallon.

I guess I will just have to wait until I win the lottery to make this happen myself. Along with the Continuously Variable Boost Supercharger, and the right way to build a hybrid.