why are superchargers more popular with v8s and you never hear of any 4 cylinder or 6 cylinders with them?

 

There are a lot out there, so not sure where you are getting your info from.

4 cyl usually go turbo... the 2.3T was a great motor to play around with.

As for the V6 crowd... I'd say power adder choice is equally split between SC, turbo and N2O.

 

There were quite a few roots supercharged 4 & 6 cylinder cars produced. A lot of the 4/6 cylinder crowd didn't buy the car for high power vs a lot of the v8 crowd. The ones that did get a 4 or 6 usually go turbo because the highest power gain can be had from a turbo vs. a s/c lb for lb of boost.

Car factories typically go with a roots because it's cheapest, most reliable, & has least effect on fuel economy vs the centri, turbo, or twin screw. It also requires very little attention.

 

Lots of cars have them, even from the factory (Think of the millions of Grand Prix's with M90's on the V6).

But the thing about a roots blower is that it will rob power from the engine to spin the supercharger. On cars that don't produce much torque they aren't nearly as effective as a turbo. EX: look at how terrible the aftermarket superchargers work on Honda's compared to a turbo system.

 

I hate it when people say that. It's all about the application and design.
The M112 on the V6 Mustang makes the same or better hp per psi as any turbo kit offered for the same motor. It also has a wider power band and tq climbs a lot faster.

 

It is all about application and design, but a good turbo set up will have almost the same power band as a roots car and have much more potential. Especially with the new billet impeller designs. Or awesome little turbo's like the Aerochargers.

 

Every supercharger will rob power from the engine. Turbos do as well. Superchargers do exactly what they're supposed to do & they do it well on any brand or cylinder engine. Turbos are more efficient at higher rpm where you would be making peak power. Roots superchargers are designed to offer a broad powerband and great low/mid range without sacrificing fuel economy. It's not designed for maximum power.
The M112 will make less power than a turbo kit at the same psi if both are designed equally
A good turbo setup will not have the same powerband as a roots. Roots are geared toward low & mid range, turbos are geared toward mid & high.

 

foxgt explained it best. I figure most 4 cyls go with turbos because 4 cyls want to rev. Superchargers don't do as well as turbos in the higher rpm rangers due to parasitic drag on the engine. Turbos spool off of exhaust gas instead, it takes longer to get it going, but once it's spooling, it's essentially "free" power.

most v6s and v8s do most of their work in the lower rpm ranges, so a supercharger is a pretty natural choice. Some still use turbos, but many people like getting all that extra power right away instead of waiting for a turbo to hit boost. And then there's the people who don't really care either way and they just buy whichever kit will get them a lot of power the easiest and the cheapest, which is usually a supercharger.

 

Turbos are not free power. You have an impeller blocking your exhaust which causes a restriction & would definitely lower power output if the compressor were not hooked up. You don't see that power loss because of the gain. Think of it in terms of: A supercharger may cost me -30hp, but I gain +100hp so I see a +70hp gain. At that same pressure ratio with a turbo the restriction may cost me -15hp, but I gain +100hp so I see a +85hp gain. What rpm the engine turns has little to do with which you should pick. Diesels run turbos all the time, some with a 3000rpm redline. It's more a matter of WHERE you want the power and what you're willing to sacrifice. Turbos, centrifugal, & twin screw superchargers compress air internally meaning they are ALWAYS producing a drag on the engine even if you don't see positive boost. Roots superchargers don't compress it internally so a bypass valve can be used to let it essentially freewheel, meaning very very little (a fraction of a hp) drain on the engine. They also have less tolerance requirements and a low operating speed, making them the most reliable, cheapest to produce, and most economical of the common forms of belt and/or exhaust driven forced induction. Combine that with the low end power that most people want for a fun car & you get the reason most car companies choose a roots over every other type. I personally prefer the feel of a positive displacement car in terms of fun factor, but they can't compete in terms of max power & speed vs. turbos.