The Cal-look Lounge

As a train of thought, in positioning carburetors, which is the better preference-to have the butterfly's open towards the head side of the manifold or to the outside? Or does it matter?
Installing my dcnf's and know there is a thought of others with more knowledge on the subject.
Thanks, Steve

I have always wondered this!!

Of course full throttle would be the same either way, but I would be curious to know if the flow was different at part throttle. It would be easy to check on a flow bench with a manifold that mounts the carb either direction.

Look at DDS manifolds for IDAs, compared to other intakes of the era. Dean Lowry had his view on this subject, but others, liked turning the IDAs around (Skat Trak for example).

its thinking relative to fluid dynamics really isn't it?






*people far smarter then I can continue that!!

So there has been nobody who has done any study to this other than Dean Lowery?

Porsche mounted most of their stuff with the butterfly's opening inboard.   Shelby mounted the IDA to to open outboard.   I don't think it matters.

Still, it would be very easy to verify. Set up from carb to cylinder. Lock the throttle in different positions, maybe every 20% or so all the way up to full open. Flip the carb back and forth and repeat tests. I would be very interested to see the results.

Hmmm interesting..... I know when I used DCN's they were MENT to be mounted in the direction of travel and this did effect how they worked but I have never thought about the fact that I also "Reversed" them  :-\

I am guessin someone like Johanas/JPM might be able to give us more info on this.......

maybe one way it better for atomisation then the other also?

My guess is microscopic differences, and that it's easier to have the adjustment screws on the outside.

I was messing with the flow bench last night, and I remembered this thread, so I thought I would throw a carb on and try it facing both ways. 

For the test I used a stock 35x32 040 head with a Berg DCNF manifold and a 40 DCNF w/32mm vent, no stack.  My super technical test process involved different height nuts, and 2 different bolts.  I used each of these between the throttle arm, and the adjuster screw to hold the throttle shaft open.  Not super scientific, but very repeatable.  The intake valve was held open at .500" lift for the whole test. 

I am still learning the software, so I don't have a super cool printout and screen shot of the graph.  A pic with my phone was the best I could do. 

The numbers were almost identical for everything but right at 3/4 throttle, and only then they were about 3-4cfm different.  The higher number was with the mix screws facing in. 

I will do a little more extensive testing next time I have a real good head on the bench.  I will figure some way to test IDF's and IDA's facing both ways. 

(http://images.thesamba.com/vw/gallery/pix/1256907.jpg)

Although it's cool that you tested it, I don't think that is what needs to be tested.  I think you would have to test the pull on the jet stack or pressure difference between the jet stack and the barrel.  Either way it's mostly about how the air and fuel travel down the intake manifold that would be the difference.   A dyno would be the best way to find out I'm afraid.

I agree with you 100%. 

I was thinking maybe it would help set the air up better to make the turn into the port, but the difference was nil.  I will have to wait a while till I am able to get my own dyno at the house.  I will test it then, and report back.  I figure at least 20 years..... :D