Intake Bellmouth / Horn Supply

[pillowmeto]

I am planning on making some bellmouth intakes for FVs based on research done by Gordon P. Blair. Originally I was only going to make a few for my friends and myself, but now I might want to make a few more to sell. As far as I am aware there are no companies that simply sell them. If that is true than I might make quite a few, if not, then I will only make a few more than I need. How available are bell mouths?

How interested would people be in them? (dimensions are ~2" tall x ~2" wide[at top] when installed on carb)

I will have someone run one on a dyno so HP gains can be quantified. (not my dyno, it is not complete yet)

[brian]

Who's Gordon P Blair? Most of the bells I've seen for the 28pic are home made.

[jpetillo]

He's a British professor that has a lot of experience in engine flow, including empirical models and writing software models, and has published a lot. He might be "the man" for this sort of stuff!

John

[clubford00]

And how is this airflow effected once you put an air filter on it? If you can .

[SR Racing]

We have Horn intakes for the 28PCI. They are spun aluminum and are quite nice.

[jpetillo]

And how is this airflow effected once you put an air filter on it? If you can .

I don't think it will work if you put an air filter too close to it. I'd say you'd need to keep at least two radii of the bellmouth away from the opening it to minimize flow disturbance. Just a guess.
John

[clubford00]

And running without an air filter helps meeee.....................How?

[SR Racing]

A race prepped 28PCI carb flows in the area of 105 to 115 CFM, from bad to good. (flowed at 28" of water)

ADDING a K&N filter from 4" to 6" in height will; INCREASE flow about 1 CFM (maybe 2 on some carbs).

ANy air horn I have ever tried got somewhere from 1 to 3 CFM of increase. (Usually the worse the carb, the better the increase)

Depending upon how air is ducted to your carb a horn may be better or worse than the above. On big bore carbs an air horn is much more helpfull. (Due to how short the carb is compared to the venturi diamter.) But the 28PCI surprisingly has a decent throat design for it's size.
You do want a filter or flat plate of some sort installed near the top of the carb. That in itself will increase flow a couple CFM. It creates a high pressure area right near the lip of the throat. This high pressure area helps to feed the carb. (That is why a filter will actually improve flow. ) In those rare cases where a air horn increases flow, a nylon stocking can be used as a filter to keep chunks of rubber etc. out. But I don't think I would use it all the time.

[jpetillo]

Jim,

Did you ever experiment with different combinations on the dyno, and did you see similar gains?

John

[SR Racing]

We did a lot of testing about 3 years ago, and found the same kinds of gains in HP. (IE/ Maybe from 0 to 2% max depending upon the carb. ) We will still often pop on a horn during a run just to see what happens since intuitively it looks like it should do something significant. But is is seldom that you see any real gains.
There is certainly something there, but is it worth the lack of air cleaner? ANd if you do plumb in an a/c, does the horn still do anything?

It is possible that significant pumping losses on a vee don't show till 8500 RPM. Maybe at 8500 RPM you will get 3% HP..

[jpetillo]

I don't think the standard air cleaner that we put on these will work with a horn, but if the air cleaner element is far enough away, then it could work.

[brian]

There is a lot of variability in carbs once they have been modified. In stock condition, flow varies less than 1%. Modified carbs display the same variability to air cleaners, bells and scoops. It's like running a carb backwards: some like it others don't. Frankly, it's my gut feeling that this variability is due to poor or inconsistant modifications. The improvements seen sometimes are simply a result of making up for poor preparation. As Jim mentioned, you can try something on the dyno and see what happens, but there is no hard set rule regarding any of the accessories.

[pillowmeto]

Anything I create would function with an air filter, in fact, an air filter may become part of the package.

Jim, your comments and testing results are very helpful. I have been wondering if the inflow to the mouth of the carb creates a low pressure region near the walls and a high pressure high velocity region near the center of the carb (over the choke). If so, smoothing the air coming into the mouth and then impacting it against the "step" before the choke and decreasing the pressure above the choke would not be good and could be the reason why most bell mouths / velocity stacks do not give the expected results when compared to most other engines that use an inlet without a large step in it.

Out of curiosity, what do you sell your velocity stacks for?

[SR Racing]

Here is the store index to them. With linked photos.

http://sracing.com/Store/FV_Stuff/FV_St ... #induction

[pillowmeto]

I had thought you sold them, but for some reason I did not see them when I looked there earlier. Do they fit inside or outside of the carb?

[SR Racing]

I just put them on the web site after this thread started.

Actually, they are the exact ID as the carb's ID. So they don't go in or outside. You need to use a piece of radiator hose (etc.) and a hose clamp to hold them on. This way they are aligned perfectly with no turbulence at the seam.

[hardingfv32-1]

I use a velocity stack that is internal, in the choke bowl, and is a perfect match to the venturi upper opening. Barely a visible seam. What could be sleeker, no interaction with choke bowl. ABSOLUTELY no extra power when compared to a carb properly prepared to the current rules. This class is 45 years old and this is a very easy area of the car to experiment on. Don't you think we would have gravitated to the correct answer by now, IF it existed.

Brian