With these mods we're seeing well over 200 lbs-ft of torque peak and around 300 hp.
You can also get by with a Comptech Icebox intake and a stock exhaust without sacrificing more than 10-15 hp.
The real key is the race header and cams/valvetrain. Spend about $3000 on those parts and get a Kpro and you'll have a ripping setup.
On a side note we recently did a K24 (not the new 190 hp engine) from an Accord in an 07 Civic Si (salvage car, funny story). With a cold air intake and exhaust (and flashpro) it put down 210 whp and 175 lbs-ft of torque. The torque was nearly flat from 2000 to 6000 rpm. I was totally shocked, but even the intake VTEC only K24 makes some serious hp. It used to be we'd see 150 whp max from an Accord K24, and maybe 175 whp with a couple bolt ons, but the newer motors are really good. By comparison, my S2000 only put down 212 whp and 138 lbs-ft stock.
Do you remember if your K24 civic SI was a K24Z2 or a K24A8?