modified plenum?

[88lxi-shortram]

i was surfing through prelude power earlier and found this write up on how tb spacers arent worth buying but instead modifying the plenum is the key to increase volume. my question is has anyone ever done this?

quoted from the page:
adding volume to the plenum will usually produce gains in power.
but the location of where the volume is added is what gives it that bump in power, caused by less turbulence mainly. adding plenum volume at the TB mounting location really doesnt do anything at all.

the best way to add plenum volume and actually see a gain in power is to cut the webbing out of the plenum, then round off or knife-edge the edges of the ports in the top of the butterfly plate. then have a custom spacer made to go between the butterfly plate and the plenum to raise the plenum up a bit, making sure the spacer does not have webbing either of course; only the surrounding border.i hadn't fully finished yet when that pic was taken, but you get the idea. then make a spacer that is the same exact shape as the mating surface of whats left on the plenum.

the benefit of this is that the runners will now be able to gather air from a broader angle due to the plenum surface above the inlets being further from the actual inlets. remember, air has momentum, and it doesnt like taking sharp turns when there isnt something to physically guide it through those turns. so by raising the plenum further from the runner inlets, you are allowing the runners to gather air from a larger chamber, and in a more direct line of motion instead of being forced to suck from the side and making the air curve more than it wants to

[Clockworkz]

In the jeep and Dodge world we called it the kegger mod. I never did it to my jeep but I hear you get a REAL NICE power increase.

[88lxi-shortram]

im thinking about hitting the junkyard and pulling a manifold just to try it. but do you just do the upper plenum or should i do the sandwich runner plate to?

[Clockworkz]

In the jeep you do the whole upper intake on the 5.2.

Check this thread out to give you some ideas.

http://www.ramforumz.com/showthread.php?t=80192

I was gonna do it on my ZJ but I rolled the vehicle over before I could do anything with it lol.

[88lxi-shortram]

picking up a plenum from tim wednesday that way i can return to stock if i need to. ill post back on any gains i see since ive never seen anyone here do this mod.

[cygnus x-1]

Doing it this way would add a lot more volume than just a throttle body spacer. While it may give you a small boost in power, it may also reduce the throttle response a bit because now there is more volume to fill. A larger throttle body would help there.

C|

[chedda_jsauto]

You could also go with a whole new intake, I love making intakes. Its my favorite.

[Jedup]

Looking at the Rb20 plenum it looks better for a front facing mod than the rb25. Its slightly tapered at the rear 2 runners which would help even out the airflow.

[JohnBoy]

doing this mod will cause lang you will Increase the quiet throttle taps, but in short it will kick bog then take off like a scaled dog. think of it like a single plane plenum vs a dual on a chevy or ford. in less you got a/c/e and a higher c/r I think you be losing.

[Accordtheory]

i was surfing through prelude power earlier and found this

What did they say on prelude power? I wouldn't do it, a b series manifold bolts up with a few extra holes and port matching of the head. That, a header and a tune would probably be 20hp. obd-1, tuning is everything