our 655 Predator headed engine with SV1's gained 65 h.p. over a set of stock carbs and 55 h.p. over a set of custom built four barrel carbs!
http://www.prosystemsracing.com/svseries.html
looks like you need to be over ~600 Hp to run the cheap one:
WIth cfm ratings as low as a REAL 1100 cfm, the SV1 is perfect for 650 horsepower on up engines
sorry if it's a repost, can't search for "SV1" because it's not a long enough word.
if i was racing with someone else's money, i would have one of these...

(Chris, can you REP me for that)