At 14psi mine made 40whp over a millenia intake manifold with the vris tied open at the same boost. I never got to test it vs my gutted millenia IM. On motor, mine showed effectively zero gains and a loss of about 20tq. Went from 193/170 to 193/150, but it sounded really mean.
The problem with short runner intakes is they have to flow A LOT of air to make power. So if you're running a lot of boost or a motor car revving out real high you'll see power gains. Another issue with short runner IMs is loss of low end tq. In my particular case my powerband was very off/on and it caused bad wheelspin issues.
Personally I very much prefer my gutted out millenia IM over my old custom IM and my track times show it.
I have a local fabricator guy interested in making me one that uses stock runners but a custom plenum. Essentially a wide open plenum design that will maintain the stock runner lengths and hopefully provide better low end power, maintain stock injector mounting locations and be very easy to install. It's a super back burner project though, I have to go drop him off an engine a stock IM to play with one day so he can screw around with it when business is slow.
92 MX3 Turbo ($100 junkyard KLG4) 11.904 @ 124.3mph, 14psi, DOT approved Hoosier drags, pump gas.
NSCRA 2009 FWD Drag Radial Finalist
HIN/NOPI Supershow Class Winner - Miami 2010 - Street-Sport Compact-Mazda
Links: Pretty Pic, GoFast Pic, Timeslip, Track Video As of July 2011 the MX3 has been retired and sold.