You are talkin about two different things.
Just because you need to keep boost down on a forced induction system does not mean that because you can get 50-60% from a quad throttle body setup you have to worry about your internals.
A F.I. System is simply that it forces air into your engine. With a quad throttle body set up, you have no increase in air pressure going in your engine(maybe a marginal increase but not like a turbo). You simple can get a bit more air into your engine heaps quicker and more efficiently.
Say you get like 150kw from a quad set up, it will not be the same as turboing your engine etc... the internal pressure will not get as high, the air is still being sucked into your engine not forced or blown in.
Turbo's have like 6-7 psi (pounds per square inch) being forced into the engine increasing the internal pressure, and since the ka24e is not designed for a turbo then the pressure is going to be pretty high.
If you raised the compression on your engine a bit to get more power then this would kindof have a similiar effect to a turbo in a sense.
The engine may be under more strain with a quad throttle body set up because it is reving out quicker and getting more fuel in, but not like a turbo.
Oh well thats my input...