WildBill, there are plenty of mid to low-11 second 03 Cobras. I've read many of your posts on LS1.com. I think you know enough about what an 03 will do. There's more than enough info, posts and topics without questioning one sig.
Back on topic:
A friend of mine has a six upper and six lower. I've lost count of how many belts he's shredded along with his hood liner and a few hoses. It developed a knocking noise after we sprayed it on the dyno a few weeks ago. I thought for for sure the engine was hurt. After we left, the noise became intermittent. I figured then the motor was fine. He left it with me and I drove it for two days and it never knocked. Just when I was about to give up, it started to knock. I popped the hood and you could hear a knock on the driver's side head. I revved the engine by the throttle cable and I could hear a pop when I would let off. I moved to the front of the engine where I could look down when I revved the engine and the belt was riding up on the crank pulley and when I let off it would snap back down in the pulley. I figured either the alternator was bad or an idler pulley was bad. On the way home I drove the car easy. Just before I got home I pushed it a little to see how it felt. The car had no power and I looked and there was no boost. I pulled in and popped the hood. The belt was hanging loose over the blower pulley. I figured it broke. I decided I would swap out my idler pulleys with my buddies so I went and took mine off. I walked over to my buddies 03 and grabbed the belt to rip it out and it wouldn't come out. I looked down and it wasn't broke. I thought that maybe it had walked off the crank pulley. I was looking it over and that's when it caught my eye, the alternator pulley was gone. That was what was knocking. It probably was spinning on the shaft for awhile before it finally fell off. I think that a few of the belts he broke probably wrapped around the alternator pulley and when it broke and probably grabbed the pulley enough to break the nut loose. My buddy beats the mortal piss out of his car. He's into boost 75% of the time he's behind the wheel. If you are the same way, this is a bad combo. You are asking for trouble. Make sure to carry a backup belt or two and a pull handle. Mark does. You can drive it about 30 miles before the battery will be dead at night with the lights without the belt ont he alternator. Mark can tell you.
I don't drive mine too hard. I run a 2.93 upper for the street with a four pound lower. When I go to the track I swap in a 2.80 upper which and eventually ended up staying on the car. I have never broken a belt. I don't street race and I am basically easy on the car. Now on the track, I beat on it about as hard as anyone. I think this is about the best combo you can run if you have driving habits like mine. I milled 1/8" wide slots in my upper pulley at 45 degree intervals similar to S. Fla. Pulley's non slip pulley and I also bead blasted it. I made my own idler pulley bracket. With this combo it made 503 rwhp SAE and 550 rwt with very little belt slip. I live in the foothills of the Blue Ridge and it's pretty cold here. The other day it was in the low 30's on my way home from work. I decided to rip off a run to see how the car felt and how much boost I was making. I run 3.90 gears. I ran it up in second to about 40 and stomped on it. It immediately broke loose and I caught my needle crossing 19 psi before I let out. I went into third and the car got loose again but I made 20 psi. That was a first for me. If I could get down to Rockingham today, I know this sucker will hit 10's. But, I'm working 7 days a week and it will be a miracle if I can get on a track again while it's still cold.
I wouldn't go over four on the bottom. But, if you are like Mark, I would go ahead and get a KB or ProCharger if you want the big time, trouble-free power.
with the 6lb upper pulley. I am going to Get the stock supercharger ported and also port my T/B intake i am at 18lbs of boost now i want more.... Let me know if anyone has done that if so what were the results 
