Don Terrill’s Speed-Talk

I've run DCOE's, on my Formula Atlantic so, I'm familiar with the jetting (main, air corrector and emulation tubes). In my racing, the tubes, once selected for the application, didn't change in the jetting, for A/F ratio. The tubes, became standard, in those engines, since they were run for a number of years and here, 50 years later, they still are.

I haven't read much, regarding Webbers, on this forum but, I thought I'd ask here first. I'm considering installing four either, 48 IDA or IDF's on my 7400+ rpm, 306 Ford. My questions are:

1. Is there any difference in HP, potential between the IDA & IDF? I know the IDF has a cold engine enrichment and cost less.
2. Is there any particular emulation tube, that works better in that application of 7400+ rpm?
3. What would be a good size, air and main jets, to start with?

I know the jet is best done on a dyno and this engine, will be done that way. It's a dyno mule but, I would like a good starting point, to work from.

This will be a little different application, in that they will be mounted on a Holley 300-275 tunnel ram, rather than a IR manifold. IR jetting would be appreciated, too.

I'm basically in same boat as you. Only i'm doing inline 6. Idf on plenum intake. Still pondering on maybe trying a dual or tripple at a later stage. Still need to get to start up and then deal with tuning.
Harry aka enigma57 advised jetting on mine to start with. Much gratefull for his help as i'm still learning on these carbs. More used to dcd and dgv type downdrafts.

From all the reading i did most say the idf is more streetable than ida.

Chevyfreak.

The IDA was a race carb & had a very basic transition cct [ idle to main cct ]. The IDF was designed for street use & has a better transition cct. Think of one as having coarse adjustment, other fine adjustment. The IDA is also taller if bonnet clearance is an issue. Both carbs take the same E tube, air jets & main jets. IDF has plastic float, IDA has brass. IDF float adjustment is easier, like any Carter 4bbl.

Impossible to give E tube & jets #s, as every combo is different. Weber had over 20 E tubes originally, now only a few available. The new carbs come jetted with the main jets sized for an IR set up, ie one barrel feeds one cyl. When you add cyls, main jet needs to be bigger, all else being equal.

Genuine Weber manual is still available & worth the $$ if you are working with Ws.

Your going to install a carburetor meant for IR, on a plenum... so... ..
Yeah
You will end up with some odd jetting.

"that they will be mounted on a Holley 300-275 tunnel ram"

That's not a good idea. Why would you even do that. I really want to know

Why not webers??? Anything goes in my world. A downside is a more complex linkage than with 2 fours. But may be bæ drive better with the webers?

When I bought my 2. Hand set of IDF’s, they sat on top of a supercharger, a 8-71 if I’m not mistaken.
Personally I might never had done such a thing, unless I had money in large excess, and because I wanted to...

The lid for the cherger for 4 IDF’s are still for sale if someone is interested...

I can supply the jetting these carbs came with if any interest.

modok wrote: ↑Wed Sep 16, 2020 12:58 am "that they will be mounted on a Holley 300-275 tunnel ram"

That's not a good idea. Why would you even do that. I really want to know

There are five reasons I want to run them:
1. They are more tuneable than Holley's
2. They (a set of 4) will flow more than any pair of 4150's
3. They will set over the manifold runners, evenly
4. You can swap out the venturi sizes
5. I personally believe there boosters are superior.

My question now is, what possible reason is there not to run them, other than expense?

All the Webers discussed in this thread are designed to work in IR configurations, AFAIK, so will likely be problematic on the tunnel ram due to wide digression of pulsing from normal.

chimpvalet wrote: ↑Wed Sep 16, 2020 1:09 pm All the Webers discussed in this thread are designed to work in IR configurations, AFAIK, so will likely be problematic on the tunnel ram due to wide digression of pulsing from normal.

Can you explain this in more detail?

Tunnel rams need a bunch of accelerator pump, the kind that is hard to get out of webers. Tunnel ram fuel distribution is very sensitive to how straight the air enters the carburetor as well as how straight it leaves the carburetor. Adjustment of fuel mixture doesn't mean much if the air is coming off the bottom of the carburetor poorly.
You will most likely need some small air correcters on the low speed jets to make up for weak accelarator pumps, it will be crappy at part throttle but thats just the animal.
I would run the engine with a good set of Holleys first and get some sort of baseline before taking off on the Weber thing

4 IDA carbs on an IR intake would be sized right for somewhere around 500hp

4 IDA carbs on a plenum would be sized for around 1500hp
Not enough velocity to function
You would need to use two IDAs, not four. Or four of the smallest IDFs

Not sure about the IDA, but IDF acc pump nozzles can be drilled out to suit the application, just like other carbs. The total fuel delivery & delivery rate is also adjustable.

I bought this manifold (300-275) because I had 3, 4412's, on hand (I just got a 4th, last week) and the manifold lends itself to many configurations. It also has straighter, separated ports that I thought might be a advantage with the 7-8 or 6-5 firing order (it would be easy to add a separator plate between them), following through with that idea, I suppose I could separate all ports for the Webers?

The Weber idea came about, because I have a chance to get 4, 48mm IDF's very cheap but, the opportunity won't last long so, I have to make a decision soon. I can make a sub plates, for the top plate (large 4 bolt pattern), to mount both 4412's and the IDF's.

I thank all who have posted, for their input.

I'm familiar with jetting for DCOE's after the emulation is selected but, know nothing about testing and selecting the E tube. Any input on that?

If you can 'jet' DCOEs, then you can jet IDF carbs. Think of the IDF as being a downdraft version of the sidedraft DCOE. Both take the same E-tube, main & air corrector jets. The same E-tube selection criteria applies for the IDF as for the DCOE.

modok wrote: ↑Wed Sep 16, 2020 7:32 pm 4 IDA carbs on an IR intake would be sized right for somewhere around 500hp

4 IDA carbs on a plenum would be sized for around 1500hp
Not enough velocity to function
You would need to use two IDAs, not four. Or four of the smallest IDFs

I see what you mean- however, wouldn’t smaller aux venturis?
I seem to remember my idfs had 36 or. 38 aux- and they sat on a plenum. Now i have 41mm