[rkreigh]

I remember some of the early 415 had the drop plenum mod that was supposed to be worth 10-15 hp on the big 415. I believe raising the runners and adding more volume will help and is a better way to go, but not enough to be worth much more than 15-20 hp

kirchoffer spent a ton on a box ram on his big 421 and it didn't seem to work nearly as well as I would have thought. it had a pretty big "plenum box"

with the "s turn" in the LT5 intake, I prefer the the ITB option. now that OBX has a 1300 setup for the LS1, use that as a starting point and cast up or fab some new base plates for the LT5

I spoke to graham about this and much like the lotus "caliope" stacks they used on the race car this a 4500 up mod, and low rpm thottle response can be a bit abrupt and hard to control the big "stacks" can really kill low end torq so you need some gears to get it rolling

my LPE has the crazy "bifurcation" manifold where they saw in half to do a better job of porting

they did a nice job of dressing the welds and keeping it straight

so, if we "scrap" the manifold and go ITB why not go the extra mile and raise the port? I saw an old ford where they filled the bottom of the port with epoxy and ground away the port roof and used thick billet "plates" recessed into the head

this provides a very high velocity straight shot with a low profile crab style ITB

tuning would be a challenge to be sure as you get LOTS of airflow with little throttle movement and the car will really jump!!

I thought about putting an ITB on the old LS1 in a C3 for sex appeal

the OBX stuff is beyond cheap and looks to be of good quality

nothing like the inglese but still very nice! borla does this stuff too

as small as it is, you could 3d print" the adapter manifold to make the ITB work with the LT5 head and it would likely be strong enough to work just fine

sounds like fun!!