There's a lot of theory about plenum design out there, and on some engine designs it can be critical to performance.

But I think I heard Jake say something about the volume and shape on the Djet plenum not being that great, or maybe that it didn't matter so much or something?

I'm asking because mine had a crack in it. I patched it, but I got to thinking about replacing it with something different. I've eliminated a lot of the stuff that needed vacuum taps (emissions stuff, aar, decel valve, etc.) and would like to make a cleaner, nicer looking intake setup.

So, what do you have to say about the effects of messing with the plenum shape and size on a Djet TIV?

it's been a while since i had a /4 ( ) but there's an old thread here somewhere where i was looking into a custom plenum.

i even did all the math, for a 2056 with bigger valves, headers etc.

my idea was to take a 3.2L /6 plenum and cut off two runners. the spacing of the remaining 4 runners is almost exactly the spacing of the two intake manifolds that i had made to be used with fuel injection (note the injector bungs) ...

Andy

PS: i still have them manifolds ...

Click to view attachment

Click to view attachment

Design has proven to trump volume in my research on the topic.. On the STF there are pages and pages on the topic with some 2006 findings of mine...

Jake has some thoughts on it on the Shoptalk forums back about 3-4 years sgo.

Bottom line, the 2L 914 plenum with the top mounted TB is less efficient than the 2L bus plenum with the end mount TB.

What the 914 plenum needs is some guides to curl the air 90 degrees towards the intake pipes.....

Testing it to see if it made a positive change would probably involve a dyno.

Ken

so, is the /6 plenum design from the 3.2L and 3.6L a good design or not?
Andy

I had already been wondering if some of the single carb plenums might not be able to be made into something as good or better than the goofy-shaped stock box?

Anybody have one of these things laying around that I could experiment with?

sorry I didn't get any pictures for you guys
there are a pair of racing 1.7 djet vintage cars out here run by brothers.

last year they took 2 throttle boddies from a 2.0 and ran one on each bank... they had a ton of flat spots and not great running in general.

so this year (about 2 weeks ago I ran with them at our opening race of the season) They took 4 throttle bodies (all from 2.0's) and ran one throttle body per cylinder

these cars are still djet with stock (or was it 2.0 stock?) injectors
they are running the tps from one tb, and linkage to connect the 4
each throttle body has a k/n style cone filter individually
and each throttle body is running a custom plenum

these are relatively mild-ish motors with light cams.

they couldn't get the idle down (makes sense with 4 seperate idle screws)
but otherwise the cars ran much much better
they pulled up to 7K reportedly with no internal modifications
brothers claimed they would run out of steam above 6K prior to 4x TB modification.

wish I had gotten pics for you guys

I know somewhere a year ago I posted pictures of the 2xtb versions
in june I'll do it.
brant

Found the Shoptalk thread I was looking for (thanks to piledriver on Jake's forum).

http://www.shoptalkforums.com/viewtopic.php?t=102542

So anybody know of a single carb intake manifold/plenum, or a bus plenum laying around?

Tried thesamba?

They gots lotsa bus and porsche parts...

Ken

Thanks Ken, I'll post an ad over there. So there are a couple of bus models... Anybody know which plenum would be the easiest to adapt? (Looks like 1968 was the year of change... Before or after?)