sorry
but if you intend to operate this Stude at widely varying altitudes, keep in mind that each 1000 ft will change your cylinder pressure by about 5 psi. This is about the same pressure difference as one cam size.
Since you mentioned fuel economy, I jumped in with the cam-talk. A loss of cylinder-pressure directly leads to a loss in fuel economy.
Whereas, in steady-state use, the intake, any common intake you chose, will make very little difference.
And NO intake you can install,without other engine changes, can touch the EFI-keg, for low-rpm torque and fuel economy. That Keg is like a folded long-ram. Look on this graph and see how that Keg, at low-rpm (say 3200 and down), makes the 5.2 engine feel and act like a much bigger engine than it is. On this graph you can see nearly 300ftlbs available at 3200 rpm. That is a pretty big number for an engine of it's size. And you can see the oddball kink in the power curve that the torque is generating. But take a look further down! The available torque at 1200 is ridiculously high.
When you swap that keg intake off, you will lose a sizeable chunk off that, also losing some of the fuel economy it was helping to generate.
Is it a big deal?
Yeah I think it is. I might be willing to bet that the combination of Keg and SEFI might easily be worth 20% fuel economy, in steady state. And we haven't even talked about the ignition timing problems you will have, trying to achieve advance with the overdrive trans, at the low-cruise rpm it offers. The lack of cruise-timing could easily cost you another 10% in steady-state use. When you add those two together. it comes to 90% of 80% so a left over of maybe 72%, So now you are back to 318LA type economy.
Could I be wrong?
Sure, but my experience is this; for steady state fuel economy, your engine needs to be in a sweetspot that you create with pressure, valve-events, rpm, and ignition timing. In the case of the engine in question, that sweetspot was created for you by the factory, using the Keg, the SEFI, and the computer controlled timing. Once those are gone, then so is the cruise fuel economy that the Magnum is known for.
Furthermore, the Sequential Port EFI is able, to some degree, to compensate for changes in elevation, whereas without the computer, the carb/dizzy is hopelessly over whelmed, especially a vacuum-secondary carb, which for fuel-economy, is the better choice.
I'm just trying to help.
BTW, other tips
you don't have to use the factory ECU, there are programmable stand-alone systems out there. But if possible I would install a scanner on the current combo, and get a feel for what the factory ECU is doing, before pitching it,........... cuz you won't believe what the factory timing is doing.
At one time, you could buy a tool to "redrill" LA intakes to fit Magnum heads. Then weld on some small spacers to get the angle right, under the bolt heads. That opens up your intake choices drastically.
Today, you can buy heads with Magnum ports and LA intake bolt angles, which totally solves the problem.
