kenne bell twin bore throttle body

[Tunning @ LMR]

I have an 07 saleen with a kenne bell blower that was brought to me to tune, I am having problems with the throttle body calibration. It surges at low throttle, and has a hanging idle when it first starts. Also its seems as thoght the throttle is real sensitive.I have gotten the wot stuff pretty much done. I think its a 2.8 kb with the mamoth mouth intake and 75mm twin bore tb. It has cams and has upgraded internals. I know the trims are off but I am worried about the tb calibration. I have read that the bypass valve causes problems with the trims from bank to bank, on cars with cams.

[3vsteed]

I've had similar issues with mine. When vacuum falls below10 in or so the bypass valve closes and starts to build boost, throttle demand is not there so pcm pulls throttle, vacuum increases, valve opens and the process starts all over again as seen in your log. My cams are still stock and the surging is very annoying to me. I found that locking the bypass open when doing part throttle tuning has helped a lot. I was able to get a much more stable tune. After unlocking the bp valve, the surging was much less but still there.

I ordered from KB a new bypass valve with external spring. The external spring valve stays open longer and doesn't surge at part throttle and light loads. KB warned me to be careful as the later closing of the valve builds boost later in the rpm range and power comes on hard and sudden. Can't tell you from experience as I haven't yanked the blower to swap valves yet. I'll let you know...