well... from the stand point of doing rearmount twins.... you are going to need to do ALLOT of cutom piping for it, the two turbos, oil pump for the turbos, boost controler, waaste gate, and all that is on top of the fuel system mods needed but i think they are the same for both builds.
On a side note, I am working on a twin turbo set up. Its a matter of not wanting to cheap out on the turbos and buy something readily available like the t25BB of the eclipses. There is allot of math involved in getting the turbo sized propperly. its not just a close enough type thing. you have to have the right size turbine and compressor, as well as the right size housings. One that people dont think about is the size of the piping you can run to and from the turbo. Turbos are 100% about pressure/temp changes. thats what powers them. if you can only run some 1" pipes out of it (yeah i know its exadurated) then your not going to spool properly and get some crappy performance out of it. I have been looking at different ways to do twin turbos for a while now. I have two ideas left that are still remotely possible. and I got new ideas everytime i looked at the car for a while. its just SOOOOO hard to fit stuff in these cars.
The other issue is answering why. These cars havent been proven over 7.5psi or so. Internals are going to be pretty pricey too. It can be done, but almost everything needs to be custom made. At the power levels you can get out of those internals, your tranny will need to be beefed up. figure this.... 20-25hp/lb of boost.... complete internals = 1.5 BAR or 21-22psi. 22x25=550..... thats ontop of your 215 for a stock first gen. 22x20=440. 655-765 RWHP out of an LS would be great, but you would already be close to 10k into your build and the car can not handle the power yet. tranny rebuild wise, the Level 10 animal kit is said to the be the best for the 5r55 right now and after everything (may as well have them do your custom stall at this point) your looking at another 10k. You're also going to need to swap to a 31spline and 8.8. So ok another 1-2k for the rear end, and 2 more for the wheels and tires to be able to put that power to the ground. Your at 24k, but havent done any head work, manifold work, chassis work, etc. Plus at this level of boost you need to further upgrade your fuel system. You need bigger injectors and a bigger MAF at the very least. With this much in mods to take the power, why buy cheap turbos?
People shy away from ILLS turbo kit due to the price, but fail to see what they are getting. Garret is one of the very top names in tubos. The turbo you get is custom built for the propper sizing. The engine vs turbo math isnt close enough, its dead on. The needed upgrades are found erring on the side of safety. errrr..... let me explain that real quick. The fuel injectors for example are upgraded instead of to just big enough they are a touch bigger so that you dont make em out. When I built the turbo on my civic I originally bought a turbo kit for 2k. and after getting it on and running, it need more upgrades and such to really make that 2k kit work. I would have been better off spending the 5500 to do it right. That being said, there is no cheap kit out there for these cars. The only option available for buy and install is the 5k done right kit. People dont see that side of things though, they only the price tag. The other thing people are worried about is that these arent stangs or camaros where everything has been done before. You dont fall into that category, but your also not the only whos going to read this.
All that being said, I'm not the end of all of resources for this as I am still studying and doing my research, nor am i a pricing dictionary. I am basing everything in this post off my research and quotes and such. Anyone reading this who is interested in actual pricing on ILLS' kit, should contact him and not go off my post since he offers a few different kits that vary in price and inclusiveness.
