The SVO intake and cylinder heads are no longer in production and no longer appear n the Ford Racing Catalog. The heads and intake were released in 1998 and were to be used on the poor breathing non- PI '96 thru '98 2 valve 4.6. The intake was a long runner intake made of cast aluminum rather than the composite material of the production 4.6. It utilized a two throat throttle body and closely resembles the cast aluminum intake used on the 2001 Bullitt Mustang. THE SVO INTAKE WILL NOT WORK WITH THE PI HEADS USED ON THE '99 THRU '04 MUSTANG DUE TO AN INTAKE PORT MISMATCH.
The SVO heads are best flowing production 2-valve head with better flow numbers than the PI heads. Again these heads are no longer available. The non PI heads had the valves moved to the outer extreme of the combustion chambers creating shrouding by the cylinder walls when the valves were opened. There was also a small finger like wall cast into the combustion chamber surrounding the intake valve to induce swirl. This was further reduced intake flow. The non PI heads flowed poorly both on the exhaust and intake side.
The SVO heads moved both valves closer to the center of the combustion chamber and the wall in front of the intake valve was removed to un-shround the valves and increase flow. Both valves in the SVO heads were larger than in the Non PI head. Intakes were 46.83 mm and the exhaust were 35.88. The combustion chamber size was 51 CC non PI, 42 CC PI, and 53 CC SVO.
The SVO head out flowed both the non PI and PI heads at all levels of valve lift. Intake valve lift at .05" lift was 25 cfm non PI; 25 cfm PI and 27 cfm SVO. Flow at .600" was 166 cfm non PI; 160 cfm PI; and 206 cfm SVO
The exhaust flow numbers at .05" were 22 cfm non PI; 24 cfm PI and 23 cfm SVO . Flow at .600" was 117 cfm non PI; 138 cfm PI; and 143 CFM SVO.
The Trick Flow 2-valve heads flow much better than the SVO head, but the SVO heads were the best available until the advent of aftermarket heads. FYI the flow numbers for the Trick Flow Twisted Wedge heads for the 4.6 2 valve are 252 cfm intake and 188 cfm exhaust at .600" lift. (figures from Trick Flow's website).
The information about the SVO intake and heads comes from Sean Hyland's book "How to Build Max Performance 4.6 Liter Ford Engines". ISBN 1-884089-78-X from Car Tech Books.
Here is a link to Trick Flow's website and their intake manifold that resembles the SVO and Bullitt intakes.