In general with a turbo you can get more power. However, there are also some drawbacks. If the turbo is too large, you risk turbo lag, which is the latency between you floor the gas pedal until it starts producing power. I think this engine is going to be especially suitable for turbos. This integrated header thing looks like it was made for a turbo. There is plenty of room back there for a turbo and the plumbing could be very short if you used an water-to-air intercooler. The shorter the plumbing, the less lag you will have and the better the drivability and that is what the water-to-air intercooler would provide. The long stroke is also going to produce some killer torque. I did some basic calculations with the engine simulation program Engine Analyzer Pro and it looks like it would be pretty easy to get over 300 HP with pretty low boost, like 7psi.
A supercharger generally starts building boost immediately so there is very little of no lag. This engine is really well suited to a roots type supercharger. This is what CT Engineering is doing. The placement of the supercharger would be easy considering where the intake manifold is located. I think this will be the best option for street driving. It should also be easier to get CARB certification. You could also do a centrifugal type supercharger like a vortech. These tend to be optimized for the higher rpm range. Since this engine is all about torque in the mid-rpm range, I don't think this will be the optimal solution.
With either option, I think it should be possible to get more power, with excellent reliability, than cars such as the Mazdaspeed3, the Volkswagen GTI, or even the WRX STI. Even with the price of the kit, they should be lower price. Throw a 300 hp supercharger with a good suspension kit and you should have one smokin' sport compact. I'm really looking forward to seeing what the CT Engineering kit produces and costs. It looks like a properly engineered kit where they use CAD/CAM and proper modeling software. I see alot of I-built-it-in-my-garage-and-am-totally-unqualified-to-be-designing-parts-for-an-engine kits on the market for a lot of cars and people end up destroying their engines in a short amount of time because they got fooled by the supposed big numbers they put out. Don't be fooled by high HP numbers. A properly designed system can have substantially less power on the dyno and still smoke these kits. Don't be a bench racer.
my Si.
cant wait for things to magically start coming up quick