benefits of air horn extension

[zhopeful]

I have a '72 240z, and am considering getting extrudabody air horns. Is there any benefit to getting the extension? if so longer or shorter? Also, what is the bore i should use 40, 45, or 50 mm (for the horn)?

[gjc5500]

Air horns basically create a huge venturi that causes the air to pick up speed. high velocity air is better to have than high volume(genraly speaking). I have never used them on the z car so i cant help you there. I did however run one on a sbc on the dyno, picked up like 5hp using it.

[Zmanco]

You didn't say what carbs you're using, but I'll assume they're SUs. From what I've read, the stock air horns on the air cleaner are pretty good already and unless you've heavily modified the engine (in which case you probably wouldn't still have the SUs), there's little to be gained with other horns. FWIW, I had notably less power at high revs when I tried running without them.

[JMortensen]

I think he's using the extrudabody individual throttle bodies and calling them air horns, then asking what extensions to use with them. Please correct me if that is wrong.

 

The ITBs can be fairly large, larger than carbs because the injector will atomize fuel better at low rpms than carbs do. If you're building a full on high rpm engine get the big ones. If you want a lower end motor I'd go with the 45s. I would not bother with 40s.

 

The "extension" you're referring to is what most people call an air horn. As stated is smooths the flow and increases velocity in the intake manifold. I've only seen the extrudabody ITBs with a very short air horn and I would suggest that you run one, as it will make a difference vs not having one.

[brokebolt]

Interesting read from Extrudabody's webpage:

 

http://www.extrudabody.com/TechInfo/FlowInfo.html

 

Shorter overall length has a tat higher flow rate according to his independent testing. Not affiliated with them in anyway. Doesn't state who the competitor is but knowing a bit about the company I can take a guess.