[Here is a copy and paste from another guy that asked the same question...some of it might not makes sense like the refrence to the procharger but it still all applies]
Hmmm…. one of the most difficult decisions I still have to make as well. Let me start out with the supercharger. I’ve just recently seriously started thinking about a turbo setup but have been reading and researching superchargers for some time now.
Superchargers
Procharger as you well know is a centrifugal supercharger. Don’t get me wrong they are great power adders but if you’re going to be spending the money I highly suggest a twin-screw setup and here is why. Centrifugal superchargers are great but lack bottom end boost. Meaning your not going to have as much bottom end power in the low RPMs. Roots on the opposite end like the Eaton S/C have great low end boost but lack in top end and to be honest really aren’t in the S/C market anymore just because of the twin-screw application blowing up. Now this takes me to twin screws…. they combine the best of both worlds and give you great consistent boost throughout your band. Another advantage to twin screws is they are self-lubricated so you don’t have to tap your oil pan.
Brands
As far as suggestions for companies with twin screws I would say FRPP Whipple is the best choice IMO. Second would be KB and third Saleen.
Turbos
As for turbos. Ill start off with some stuff about gas mileage just because I know its something to consider with the gas prices now days. Superchargers because they are belt driven off your motor take HP to run and in that case lower your cars MPG. Turbos on the other hand are well known for being much more efficient because they run off exhaust and heat expansion using none of your engines HP and actually on an average boost your MPG by 5 miles or so.
In addition to being more efficient turbos are also known for their durability. They work great and last forever.
Boost
Also superchargers to change boost need to have there pulleys swapped…turbos can have controllers manual or electronic to very boost. Personally I would go with an electronic one that toggles between two boost pressures with the bush of a button. That way I can run 5 PSI or so while driving around casually and when I want to do a bit more spirited driving hit a button and have 10 or 11 PSI at the petal.
Man I forgot how many options there are with turbos.
Single or Twin
There is also the decision on whether to go with single or twin turbos. I think I'm going to go with a twin turbo setup just because running two smaller turbos is more efficient than one big one. They also will have a higher output if one day I decide to build my engine and want some more boost.
Mounting
There are two ways to mount turbos. STS has a system called a squire system that has the turbos at the rear of the car. A lot of people say that this is less effective because there is a loss of pressure due to the air traveling through so much piping. This is true but only about 1 PSI. Now what they left out is that all that traveling cools the air about 100 degrees which is about 45-50 horsepower. Now the loss of 1PSI is only a 10 HP loss.
The other choice is under the hood near the exhaust manifolds/headers. Some like this better because it looks cooler with turbos under the hood but in reality they create a lot of heat. Either way you’re getting the same effect.
here is a good example of why most people end up wishing they went with a turbo. Compare the red lines from the top two graphs [top HP bottom TQ] with the kenne bell. What i think is funny is the kenne bell graph is at 8 PSI and the turbo is at 7 and look at the results.
So the twin screw has an advantage in hp till a little before 3500 RPMs and after that its history. As you can see though the max HP output with the S/C is 400 hp and the turbo is 450 and thats with the extra PSI on the s/c. That means the superchargers drag on the engine from the belt that drives it costs the engine 60hp.
Now for torque the twin screw is putting out a pretty stable 350 to 380 ft-lbs of torque....and the turbo again with 1 psi less is hitting a peak of 480 ft-lbs of torque....almost 100 more ft-lbs.
something youve got to think of as well is like someone else said how are you going to be using it. Superchargers will give you the headstart from a dead stop but after 1st gear it wont because when your shifting through your gears at 6000 rpms your not shifting down and starting back at 1000 rpms....so when you shift into second and are at 3000 or so that disadvantage of bottom end is completely gone because the turbos going to head straight for its peak again.
hope this helped and good luck =]
***here is a picture of a squires type turbo setup....those are the turbos at the exhaust tips***
). At the moment i'm undecided about what to get, which is why i need yalls help! It would help out a lot if I could hear some of yalls opinions on what i should possibly buy. Thanks!
That won't be happening anytime soon, Sport. 
You mock me so. hahahahahaha (deserved at that)
