I've also seen claims of 12 hp gains...but none of the claims I have ever seen have been verified.
Bottom line is that there are so many better places to spend money on go-fast parts than the raised top. Especially when someone is starting to mod their car. The raised top is definitely not the place to start.
With the M90 pressurizing the entire intake system, a raised top is of little value. For a system that blows through the top (i.e. cetrifigual supercharger) instead of pressurizing it, the benefit would be much greater. But since our superchargers are positive displacement, the raised top is really not for anything more than show.
There have been a host of parts listed that will give you better bang for the buck for performance parts. I suggest going with some parts that are listed here already. You will be much happier than the performance you will (not) get from a raised top.
the raised top does make hp and increases flow but only on well modified blowers. stock top is a restriction on overdriven blowers ....it in itself makes no hp but in a system of high flow parts its integral no one component is going to make big hp .
ported blower with out the other mods like raised top, bigger inlet ,
bigger TB , maf, ic unit, is not going to be a big deal ,
same with steigmire heads probably spelled wrong> but heads with out good exh is a waste you need to improve all areas of air flow .
so to benefit from any part you must have the partner parts ,
a good SC has all the high flow stuff to perform at its best , aka
big maf ,,inlet tube,, TB unit,, inlet plenum,, ported blower,, of any configuration S port D port , MP III, or A/R ,, good IC,, bigger return plenum ,,and matching lower ,, raised roof?????, ported heads ,, exh headers,, free flowing exh pipes,
also a cam change is needed to really get it moving, rockers , etc.
but any of this without the others is not going to make a big difference,
its a complete system from air filter to exh tip at rear of car