Supercharger Vs Turbocharger

Ok, we've seen it brought up a million and one times, so, I'm going to give my take on the whole turbo vs. supercharger argument

once and for all. Honestly, both devices ROCK. They essentially do the same thing (which is pressurize the intake) when it comes down to it. Argueing that one makes "more power" than the other is utterly redundant, as I re-iterate that they both essentially do the same thing. (Look up redundancy in the dictionary and it will say "See Redundant".) Anyways, I'm going to write this blurb based on the assumption that anyone reading it has grasped the basic concepts of how a turbocharger and supercharger work.

Typically, the argument

is that a turbo makes more power than a supercharger, which is not entirely true. For instance, the Lysolm (aka "screw-type" Supercharger, known as the PSI in Top Fuel) was the choice of forced induction for Top Fuel cars for years until they were banned for giving an unfair advantage to the cars using it. If it's good enough for Top Fuel, it's good enough to make some pretty good power on a street car. Now, don't get me wrong. I'm not telling anyone to run out and buy themselves a supercharger right now. In fact, I'm not even implying that it's better than a turbo. I'm just making a case for it. Just as I'll make a case against the idea that turbos are all about lag and disproporational power curves. That's not entirely true. A turbo compressor that is well matched to the motor and tuned properly can result in a car that makes power smoothly over a broad powerband. Per a conversation with Texan, the Audi R8, a LeMans car running in the LMP900 class, is a good example of a turbo car that drives like a very powerful all motor car.

Admittingly, both Top Fuel cars and LeMans cars are not the best examples of your everyday street turbocharged/supercharged car, but it's to make a case that either device can be good IF the car is properly tuned with it. Most of the myths about turbochargers and superchargers come from people that buy "kits" and slap them on their cars without any real tuning.

So how about Honda cars? Why does the turbocharger seem to be the definite forced induction of choice for these small inline fours that barely have enough displacement to hold a two litre bottle of soda? Because current turbo kits have more options and more room for expansion. Currently, the almost limitless availability of different sized turbos and intercoolers allows for a great deal of very detailed tuning. There are turbochargers galore that can be matched to suit an engine's flow pattern and needs, with a plethera of intercoolers available to compliment the compressor of choice. Most superchargers just don't have that option. (I'm mainly talking about Roots based superchargers. I've touched on the reason why I feel that centrifugal superchargers are poorly matched to the small displacement motor in an article in the Supercharger Forum.) Adiabatic efficiency is supreme when it comes to a boosted intake charge, and there's no getting around the benefits of an intercooled setup. In fact, other than a motor's limitations regarding the amount of power it can hold, the only other limiting factor when it comes to boost is the amount of boost you can make before the intake charge is heated so much that you see a loss in power. An intercooler allows for a cooler charge after the air is compressed, which allows for more compression, which, in turn, allows for more cfm of flow from the

compressor. More air being moved is always a good thing. Why?

(Air + proportional fuel) x being burned = Heat/3 = Power produced

So the more air that goes in, the more fuel you can burn, and the more power you can make. In that respect, it doesn't matter if that 150 extra cfm at 4000 rpm comes from a supercharger or turbocharger. 150 cfm at 4000 rpm is 150 cfm at 4000 rpm. However, the real important stuff happens somewhere along the way between the turbo/supercharger and the head. Boost is that cfm of air being compressed in the plenum, and how dense that intake charge can be is very dependent on how cool you can keep it. So we understand how an intercooled turbo setup is beneficial, right? Good. With that said, provided that both the turbocharger and supercharger producing the same cfm of flow that isn't intercooled, you'll see similar performance out of either. (Admittingly, the draw from the crank by the supercharger will show a slight drop in power in the end.)

Let's look at another factor we should take into consideration. Altitude. As everyone knows, the higher the altitude, the lower the air pressure. How does that relate to choosing between a supercharger and turbocharger? Taken into account that the devices relies on a supply of ambient air being fed through it, the relative air pressure can make a gross difference. As a general rule, turbos aren't affected much by altitude, provided that the wastegate is venting well below surge limit. The wastegate is controlled