I recently discovered how a turbocharger works on howstuffworks.com and it made me curious about a few things. I also learned how a supercharger works as well. I used to falsely believe that a turbo charger worked by ‘sucking’ the exhaust out- I thought it was the reverse of a supercharger. While I found out that wasn’t the case, is it possible for such a device to be installed? Some sort of impeller which can increase the rate in which the exhaust leaves the cylinders?
Also, I was curious if it were possible to install both a supercharger AND a turbocharger on a car? Everything I’ve seen only seems to suggest one or the other. However, in theory it would seem like having a vehicle with a twin turbo and a supercharger would be maximizing the amount of air it can cram into the engines (assuming the ECU could be adjusted to optimize it).
And finally, what is better, a supercharger or a turbocharger? It seems like a supercharger is better, since there is no lag, and it doesn’t need to be attached to the oil system or needing an intercooler.
Answering your questions in reverse, or thereabouts:
Intercoolers are needed because compressing air heats it, and at any given pressure hot air is less massive than cold air. The idea is to get a mass of air into the engine, not a given volume. So cooling the air after it had been compressed delivers a greater mass of air to the combustion chamber.
There are turbocharger designs that have a very small time lag. They operate by utilizing variable incidence vanes on the rotor. The rotor spins at a near constant speed in the exhaust stream, but the air compression is regulated by the vanes. When power demand is transmitted to the turbocharger the vanes increase their angle of incidence to the breeze, as it were, and more air is delivered.
The question of putting both on a powerplant is sort of pointless. They both have their bonuses and drawbacks. Putting a combination probably isn’t going to get you anywhere a bigger one of either wouldn’t have…
At one point I had a book from the 1960’s where several experiments were done with exhaust scavenging using such methods as a belt-driven exhaust pump, electric-driven pump, and even a venturi which operated on the airstream passing by the car. They found that the belt driven and electric pump both took more power than they added, and that the venturi device seemed to create more wind resistance than it created power. Thus, they declared it a failure. I do not know, however, if that makes the concept a failure for all cases per se.
It can be done, and I have seen a couple of heavily modified race cars where it has been done. Sizing of the turbo is key. If you can balance out the airflow issues you can get some outrageous power, but balancing and tuning is very difficult.
Generally a turbocharger is more efficient at producing power, although there is the turbo lag. A turbo also (generally) has a much higher reliabiity than a supercharger due to fewer moving parts and smaller moving mass. Some superchargers need to be attached to the oil system as well, or else have their own separate lubrication system - all those moving parts and bearings need oil as well. And it’s been a while since I’ve seen a production supercharged car that didn’t have an intercooler. However, an intercooler is not required for either a turbo or a supercharger, and many of the Chrysler turbos of the mid-1980’s did not come with intercoolers.
A well designed exhaust system, from headers back to mufflers and tailpipes, will scavenge exhaust, actually creating a sucking action. One important aspect of this sucking action is to have it ‘tuned’ in frequency more or less to give the engine a desirable power curve - or to affect the power curve and power in a way that suits the application.
Just sucking out the exhaust might not be beneficial and might not work in synch with the combustion process.
Tuned to the application, you can gain high end peak power for maximum acceleration and horsepower (at the cost of drivability and economy), or it can focus on low end power, for towing, drivability, but at the cost of all out HP and performance. Or it can be a setup good for a combo of things, but not excelling at any one thing in particular.
Also, take notice to premium automakers and their push to keep engines naturally aspirated. Turbos and Superchargers are falling out of favor a bit.
I would add that a supercharger increases boost as the engine rpm’s increase - it is belt driven off the engine. Turbos have some lag but they often build boost faster than the SC.
Superchargers have lag too.
Since a turbo uses energy already created (exhaust) it is more efficient than the SC - but a big 10-71 blower sticking out of the hood looks soooo cool.
I have seen diesel marine engines with both blowers.