I'm at the bolt-on level and notice shifting at 5700 my car runs the best trap and ET but when shifting at 6000 it falls off.I want to exeriment with using 918s on the stock cam after reading the popular hot rod article about the carbed LS1.Anyone notice the carbed ad on made the same horse but picked up 25 horse into the 6k range with the spring addition?I wonder if some LS6 cam installers are really picking up HP in the upper range from keeping the valves from bouncing or the carb just shines better at RPM.I know it seems dumb to try the springs first but I would like to bring the car to low 12s after a spec 3 to hold the slipping clutch and a spring change before going cam for high 11s.Do springs make it a "non" stock internal?Any input?

 

You are running up to the limits of your stock cam,not enough duration mostly.Putting on the Comp. 918 springs will stop valve float to probably past 6600 maybe a little more on a stock cam with barely over .500 lift. The more lilft you have the harder it is to make the valvetrain stay on the cam lobe.You possibly are experiencing some valve float, either way the 918,s would be a good addition plus you"ll be ready for that bigger cam when you get it.

 

Upgrade the Springs on a stock cam?
I would use the Z06 springs; good for 100k miles and alot cheaper than the Comp 918's.

 

I found that shifting at 6150-6200 with stock springs returned best ET/mph for me (stock cam, torque converter, etc). I installed 918s & lost about 1 mph. I then bumped up the shift point to around 6300 and regained that lost mph. The stock springs were probably going into float at 6200 rpm. I figured that the lost mph was due to the higher frictional forces that the stronger springs created.

If the stock springs are old & weak, then I could see how a spring swap could gain a good amount of power at those rpms. If not, don't expect too much out of the swap.