Intake and Exhaust suggestions for LZ9 3900?

[niceguy]

Hi guys, I'm a long time browser as there are few places to go for 3900 V6 performance besides the G6 and Impala forums.

I'm curious about intake and exhaust flow and options on the 3900 LZ9 engine. It seems from input from members here and elsewhere that the LZ9 is primarily limited by it's VVT cam setup so I'm wondering if there's much to be gained from basic intake and exhaust enhancements? BTW, don't laugh too hard but this is on a 2008 Chevrolet Uplander Cargo Minivan (work).
Currently I have an 87 octane engine and auto tranny tune by Overkill Motorsports.
On the intake side, I currently have an AFE drop in dry panel filter.

Does a drop in panel filter flow enough air for only basic intake/exhaust mods?

Also on the exhaust side I have the OEM 2.5" OD midpipe, 28" muffler, though the catback piping necks down to 2.25" OD at the small tailpipe/resonator can under the rear bumper.

I've been doing what research I can on various thoughts on an engine's flow needs and I've encountered 2 different camps: Those who say it doesn't matter what piping you run after the collector and those who say that proper piping and muffler selection (based on sufficient but not too much flow) are critical to improving on stock setups in power and throttle response and that certain mufflers may flow too much for a given setup (stating that a muffler must be able to be 'filled' sufficiently by exhaust to retain good tq/response).

The calculations regarding intake and exhaust flow needs are a little above my head so I'm wondering 1) the reason for having decent sized 2.5" piping and then necking down to 2.25" resonator can/tailpipe and,
2) would a straight through type muffler and resonator of sufficient size to muffle volume retain sufficient exhaust velocity and make more hp/tq without sacrificing off the line and low end response?

I just want to make smart decisions and most of my limited experience is dealing with DOHC Nissan 4cy engines.

Thanks guys and apologies for the rambling novel!

Jeremy

[caffeine]

Just throw on a turbocharger . But honestly if you just pick up a 'turbo' style muffler they typically flow well and are not too loud.

[caffeine]

And keep in mind that the transmission is probably the weakest link. I have no idea how much additional power they will handle.

[niceguy]

Yeah I'm just looking to first maximize what I have to work with NA...I guess I have to realize that despite having VVT, being coupled with an OHV engine design is simply limited in output despite the advantage in displacement. I still wouldn't mind picking up another 20-30hp/tq but aside from you turbocharging pioneers, it seems it's not worth it to most to maximize the 3900's NA efficiency and performance.

A rear mount turbo setup would be fairly easy with the huge amounts of spare room under the Uplander chassis but I'm going to tackle the suspension and braking before I consider slingshotting myself into a near death experience with this behemoth

I may just grab a large Dynomax Super Turbo to replace the huge stock muffler for now then consider what to do with the necked down rear resonator/tail pipe section. Being stuck with the variable intake setup which favors torque production, I don't want to lose any exhaust velocity and kill my low end.

Will at Overkill Motorsports mentioned that the 3900 downpipe off the rear bank manifold is a restrictive (how much so??) double walled unit but I can't find anything for the 3900 and no one locally will even bother to give a price or their time. And it's only about 9"-12" from the rear manifold flange to the converter. Wish I could find a new or used downpipe that would work!

Thanks for the input so far!

Jeremy

[1QUICKHATCH]

If you are staying N/A you might want to get a set of headers made up, or maybe see about swapping to the g6 exhaust manifolds if they are different.

[niceguy]

Yeah it's a consideration for sure....just trying to do what research I can between work, family and out of town non profit work and see what can possibly be retrofitted and mod intelligently.

I know with DOHC Nissans, we've found big gains (with tuning) using 3.5" intake setups but as I've read here already, with the variable intake LZ9, the engine may not even benefit from opening up the intake (and possibly) exhaust but with practically no modded NA dynos it's hard to know for sure.

There's always the option of going with the non variable 3900 intake down the road after I get to learn more about this particular engine/IM setup.

First up is the muffler and hopefully finding someone around Memphis that will fab up a downpipe for me!