Another item on the engine compartment clean-up, how important are the air horns?

[Healey Z]

Here is my engine bay with it's carbed L28 as it sits today:

Two issues, there are no air filters to the carbs and it has the aftermarket do-dad on the valve cover. Here is a picture of an original Austin Healey motor:

I have a set of Austin Healey air cleaners heading my way; $5 ebay win Getting them to fit as is shouldn't take too much work and note the inlet for the valve cover.

Getting them to fit with the stock air horns (I have an original 240Z air cleaner) will take quite a bit more work and I think I have the space to get them to fit.

The car runs great right now and when I plant my foot, the car really gets up and goes. Does anyone know how much the air horns effect and what RPM range it effects the performance of the motor?

Edited November 2, 2011 by Healey Z
added pic

[Zedyone_kenobi]

The SU's on the Z's really do need a horn on them for proper function. consider it an air smoother if you will. I would wager an original healy would run better with air horns as well. I know it will be more work, but I would strongly suggest finding a way to get them to work with air horns installed. When I tried my ITG's on my Datsun for a while before I refinished the air box, I put air horns in there as well. Yes, it was a pain, but it was worth it.

[Zedyone_kenobi]

just a thought, how much space do you have in front of your carbs. I wonder if my ITG filters would fit?

[LeonV]

Air horns have absolutely nothing to do with making the airflow "smoother". What the air horn does do is increase the overall intake length as well as reflect harmonic pressure waves in the intake over a larger rpm range. A longer intake length shifts the torque curve down (moves toward midrange) and the shape of the air horn will dictate the "bandwidth" of the intake's tuned length (width of torque peak). Air horns are definitely beneficial, it just has nothing to do with "smoothing" out airflow.

The air horn will also slightly decrease entrance losses since the SU's mouth is squared off, however, any radiused feature at the carb throat entrance will help that.

[Zedyone_kenobi]

I disagree to some point. It allows the air to enter over a smoother taper rather than a knife edge. Like a CdA calculation for compressible flow through any orifice. The Discharge coefficient matters as it alters the location and size of the Vena Contracta. But this is not an engineering pissing match as it does not help his situation. It is good to know how much information to give sometimes.

bottom line, the SU's need those air horns.

[Healey Z]

I like the theory (I'm an engineer too) and I know the air horns will help, but my question is to what extent.

A practical approach would be to take my air horns that I have on there now off and see if the butt dyno can feel the difference. I drove the car to work and take it home at lunch, so perhaps I will do a few 2nd gear bursts going home, take the air cleaners off and do the same going back to work after filling my stomach and see if I notice a difference.

I'll report back later

[jmortensen]

The air horn will also slightly decrease entrance losses since the SU's mouth is squared off, however, any radiused feature at the carb throat entrance will help that.

I think that is what is meant by "smoothing airflow".

For my money, I'd rather have no airhorn and a non restrictive filter than an airhorn with mesh on the end of it as is shown in the first picture. Also not good are the airhorn "socks" that slide over the airhorn. Getting the airhorn away from filters and screens is beneficial.

[Healey Z]

The butt dyno says that the car goes like hell and revs to 5500 too fast in either case to tell if there is a significant difference.

[LeonV]

I disagree to some point. It allows the air to enter over a smoother taper rather than a knife edge. Like a CdA calculation for compressible flow through any orifice. The Discharge coefficient matters as it alters the location and size of the Vena Contracta. But this is not an engineering pissing match as it does not help his situation. It is good to know how much information to give sometimes.

bottom line, the SU's need those air horns.

What you're talking about is entrance losses, as I mentioned.

I try to give the kind of information that will educate someone as to why something happens, instead of telling them "SUs need air horns". I think the proper knowledge in fact does help his situation! I prefer cause and effect to groupthink reasoning.

This is your quote (bold for emphasis):

The SU's on the Z's really do need a horn on them for proper function. consider it an air smoother if you will

What you said was incorrect, so I corrected it in order to not perpetuate further myths. SUs will work just fine without air horns, or any carb/intake for that matter. It is clear though that air horns do improve performance, but for the reasons previously mentioned.

I like the theory (I'm an engineer too) and I know the air horns will help, but my question is to what extent.

A practical approach would be to take my air horns that I have on there now off and see if the butt dyno can feel the difference. I drove the car to work and take it home at lunch, so perhaps I will do a few 2nd gear bursts going home, take the air cleaners off and do the same going back to work after filling my stomach and see if I notice a difference.

I'll report back later

I'm glad someone appreciates it!

They will make a difference. I don't know how noticeable the difference will be but it's enough to show up on a dyno.

I think that is what is meant by "smoothing airflow".

For my money, I'd rather have no airhorn and a non restrictive filter than an airhorn with mesh on the end of it as is shown in the first picture. Also not good are the airhorn "socks" that slide over the airhorn. Getting the airhorn away from filters and screens is beneficial.

I just don't like the term "smoothing airflow". It's one of those internet/old mechanic's terms, like "backpressure". It's not what the airhorn does, and I'll leave it at that.

I completely agree with your point about the filters, Jon, and I don't think that one would come to that conclusion if they thought that SUs need an air horn for "proper function". This is where understanding how the part functions helps make the proper decisions.

[LeonV]

The butt dyno says that the car goes like hell and revs to 5500 too fast in either case to tell if there is a significant difference.

Well there you go!

[Zedyone_kenobi]

Your arguing completeness ...

In your attempt to educate or just look smart on the intewebs you can confuse most people.

No, what I said was correct. They do that function exactly. However, it is not ALL they do, but they definitely do make the air flow entering the carb less turbulent. I will admit to leaving out the whole tuning the rpm range aspect of it, as that is an intake velocity discussion, which admittedly the air horns do influence. I just did not feel like getting into that.

Also, it depends on what your definition of proper is I suppose. Datsun though enough of them to integrate them into the stock intake manifold. They were needed then as well. Proper has many meanings depending on who you talk to. If you want your L series to run as Datun intended. You NEED air horns.

Edited November 2, 2011 by Zedyone_kenobi

[jmortensen]

If you want your L series to run as Datun intended. You NEED air horns.

As Datsun intended? Really? That's overstating the case just a bit. Ever driven a Z with K&N's and no air horns? I have. It drives just like a Z. Probably makes a couple hp less than with stacks. Of course, the one I drove had an L28 in a 240, so that was already not the way Datsun intended. And what if you get the super badass TWM airhorns? Aren't they also "not as Datsun intended" since they are really a lot better design?