connect the actuator directly to manifold vac, so it will only be in the long runner position when theres manifold vacuum.

This is something I'll probably play around with once I get the Raptor fitted. On the AU the short runners open at 3800rpm... with the mixer-ring LPG system in place the engine chokes briefly from about 3600 until the butterflies open... the manifold is designed to be "dry" & the LPG increases the volume passing through.

I'm inclined to think that the short runners should be used until about 3000rpm when the boost starts to kick in so as not to lose low-end torque. I'll be getting my tune tweaked to find the ideal RPM to open the butterflies. Easy enough on the AU with a flash tuner, which comes with the Raptor kit anyway.

You could probably do the same with the Eliminator chip, but 66 Coupe's suggestion "connect the actuator directly to manifold vac, so it will only be in the long runner position when theres manifold vacuum" has an appealing elegant simplicity to it.

wide open throttle you have no manifold vacuum ( anywhere along the manifold runners after the throttle body.

on forced induction engines ( ie positive manifold pressure ) at wide open throttle again no manifold vacuum you above atmosphere pressure

Ill post some pics later but i have setup a bracket with a spring to hold the butterflys closed untill the turbo pressure reaches 7psi, then the pressure from the manifold (ive hooked the line direct up to the manifold) over rides the spring tention and opens the butterflys. so not only do you have the benefits of long intake runners for torque off the line but a decent size (yeah i know not huge) plenum for top end performance.

Exactly, thats the point, so it goes to short runners under WOT.

Thanks... I wasn't sure how to respond to his post, other than to suggest that maybe he hadn't read the whole thread... or the title... LOL!

I just tested this with my vacuum gauge. There is steady vacuum from the HVAC vacuum reservoir (20 - 24 inHg) to the BBM actuator when the long runners are open, then atmospheric pressure when it switches over to the short runners at 3800rpm. So yes, connecting the actuator to manifold vac would work the right way around. It's then just a matter of how much vacuum is needed to keep the short runners open when you're off boost and at low rpm...