zenjoe

I have an intake manifold that if for a weber IDF downdroft carb. I'm not sure who makes the manifold, but I have heard that it is from redline performance.

Anyways, the design of this manifold confuses me. The intake ports for the intermediate housing are connected. As in, the 2 barrels from the carb get split up 3 ways and there is basically one runner for the intermediate housings intake ports, and a runner for the front and rear intake ports. That center runner is not divided and where the intake bolts to the engine, there is a big rectangle port.

kinda like this:



What kind of performance loss do you guys think I am losing because of this? All the IDA style manifolds I have seen keep the #1 and #2 rotor runners separate (seems to make more sence). There has to be a massive amount of intake reversion going on in that center runner.

Any thoughts?

Rx7carl

Notice you dont get any input here huh? 11 lookers but no takers!

No7Yet

Because of the fact that the intake port never really closes, and since the other port is right at its point of highest flow velocity when the first is "closed", I'd imagine that the design you've described is very workable, and probably never "reverts" like a boinger head with siamesed intake ports would.

Brandon

Scalliwag

The design was definately not made with performance in mind. They saved some money this way. But I am not sure how much loss is involved.
I would like to see some close pics of the actual manifold if possible.
You are correct that there will be a reverberation from windage created by the offset of the two rotors.

nimrodTT

Might be fun to do some experimenting with your manifold and the more conventional design. I would suspect that the large tube would act as a sort of plenum for the primary side and shift the powerband up, but that would be in the first half of the circuit in a four-barrel system. I don't know how the two-barrel carb would handle it.

zenjoe

Thanks for the responces guys, I'll let you have the manifold if you give me a good weber IDA manifold for a 12a....

That way you can play with it, make fun of it, test it, or do whatever you want to do with it...

Another design problem that I see is that when this big port is connected to the block, the port is split very abruptly by the division in the intermediate housing ports, that cant be good for flow or port velocity. The more I think about this thing, the more I am wondering why I ever got it in the first place.

Anyone have a Weber IDA manifolod for a 12a for sale?

KiyoKix

I fully agree that the design does save money for machining time/tooling. But if you or someone else (it's crossed my mind, but I don't have the finances to bother right now...) did I'm sure you would more than anything gain some torque because of the increased velocity of the air. I have more ideas, but I wanna save something for myself when I get everything worked out (I've got a huge intake idea, but I wanna save it) financially which should be soon.

fdracer

knife edge the center divider on the intake port inlet. if it's sharp enough you should have no problem w/ airflow. air will should flow smoothly around it.

Scalliwag

That would be a good idea if the motor was apart (less risk of filings) and if you really wanted to use this manifold that badly.
Before I did that though I would build a divider into the manifold as far as I could get it. You could make a plaster of paris casting of the first few inches of the runner. Pop the casting out and split it in half vertically down the middle. Lay it on it's side over a piece of cardboard and mark it. Cut it out and test fit/trim to size.
Take some aluminum plate and cut it to the fitted pattern except leave some REALLY small "ears" at the exposed end. Lightly file the center of the runner to accomidate the ears for centering the plate in the manifold.
Use the knife edge method FD mentioned on the inner end of the plate.
Drill a very small hole from the top and the bottom of the manifold into the plate to insert small locater pins.
Epoxy the holes after the pins are in.
Of course that is a shitload of work and depending on the casting of the manifold itself it could be easier or harder.
But the further into the intake that these two passages meet the less impact the windage from the offset rotors will have.
I will admit that I am probably the only one dumb enough on the whole forum that would attempt this just to show it could be done though

Scalliwag

Damn, my first double post!

zenjoe

If you want to try it, go ahead! I'll give you the manifold so you can see this thing up close. All I ask is that you send me a weber 48IDA manifold for a 12a in return! j/k

Anyways, I think that I will buy a new manifold that is correctly designed. I think it would be much easier to buy one than to modify this one. Thanks for all the info though.

Zenjoe