Combining Two to Make One
 

I have three S4 T2 engines and one S5 NA. Is it possible to use a S4 T2 to build a S5 T2?

no, but just built a nice S4 T2 engine, its almost the same thing...

Almost? Can you explain?

Some of the components could be swapped between the motors, but you would not have a S5 T2 motor with this combination of parts.

A better use of time and money would be to run more boost on a nice S4 T2 motor. The power difference between the factory S5 T2 and S4 T2 is very minimal in the grand scheme of things and could almost be attributed to the difference in factory boost.

Riddle me this? Eventually a person will reach a point power wise that the stock turbo needs to be modified( say BNR stage 1 or 2 for example) or replaced by a different turbo and moving to a standalone ecu. At this point does starting with a S5 really matter as much anymore?

meaning it's was built for turbocharging, and all things being equal, you will likely make roughly the same power with the S4. taking everything else out of the equation, your main differences are the rotors (compression and weight), spark plug locations and some block reinforcements from the factory.

i have a hankering feeling that this was all rhetorical, but i will offer my input anyway. :)

in theory, it does/should matter, but not much beyond your confidence in the parts you've chosen to build the car (as a whole) with, said factory reinforcements and the tuner's abilities. to put it another way, if you're just building a nice, fast car for the street, i honestly don't think it matters much which block you use. however, if you start out with specific goals in mind though (power, abuse, etc.) then it only makes sense to start with the latest series block you can get your hands on.

Somewhat rhetorical but looking for confirmation my thinking is correct in that if he builds a S4 because that's what he's got, when/if he upgrades the turbo and does supporting mods later it won't really matter that he didn't start with a S5. Spend some of the money that would've been spent on a S5 having the wastegate ported since that seems to be one of the benefits to the S5 turbo.

On a side note: how much more hp does the extra reinforcement on the S5 allow?

it doesn't seem to be as cut and dry as your question, but the number/range i would feel comfortable accepting is 100 to 150, stock for stock, at the wheels.

S4 Limit Thread

S5 Limit Thread