exhaust air horn outlet

[Shrek]

I've been thinking what if you add an air horn outlet to the exhaust, kind of like a diffuser for the exhaust, would that work?

[mx_tifoso]

You're on quite a posting rampage!

[Ciro Pabón]

The exhaust is dimensioned quite precisely to take advantage of the compression waves reflected in the exit. Read here: Trumpet diameter

[riff_raff]

Shrek,

When you ask "would it work?", what is it suppose to work for?

Would the engine run? Yes.

Would it make noise? Yes.

Would it make more power than a straight tube section? Not likely.

Would it look cool if it was chrome-plated, sticking out of the engine cover of an F1 car, and belching flames? Yes, definitely.

Does that help?

[Shrek]

Ok riff raff

[riff_raff]

Shrek,

I'm glad you appreciated my feeble attempt at humor.

The reason a tuned header system works is due to the abrupt change in cross section of the various tubes, at critical points in the system. It's this abrupt change in flow passage cross section that creates the acoustic reversion pressure wave effect. The reversion wave is what makes headers work.

If you replace the cross section geometry of a cut-off, straight-walled tube with that of a long, gradually tapered cone, the reversion effect would be greatly diminished. This is both good and bad.

Tuned headers are good for racing engines because they increase VE at specific firing frequencies. But they also hurt VE at off-design firing frequencies. Since a racing engine operates at a very narrow range of firing frequencies, this is normally not a problem. However, with a road car engine that must operate a wide range of firing frequencies, it can be a big problem.

Take a close look at this picture. If you look closely, you can see the change in diameter of the primary tubes about half-way along their length:



Regards,
Terry

[Touring23]

An "air horn" isn't a bad idea, but suggests a sudden transition in diameter. Better would be a gradual expansion of the collector:

For Drag Racing and similar applications where a tailpipe is not required, megaphones fitted with reverse cones are invariably the best option. They make the the most horsepower, maintain the highest and smoothest torque curve, and, on well developed engine combinations with optimally short header tube lengths and a well chosen collector outlet diameter, offer the highest potential power past the peak without compromising the lower end of the power band.

http://www.burnsstainless.com/MergeColl ... ctors.html

[DaveKillens]

Riff raff is 100% correct.

[Touring23]

Okay, prove it 100%.

[PlatinumZealot]

A cone is suppose to lessen the pressure in the exhaust.
I can see It working wonderfully in a turbo application, For NA I don't know how it be an improvement at all rpms.

???

[Touring23]

Now that's not a very nice thing to say: If you just throw in some kind of reverse cone, you really don't know what you're doing. No more condescending posts please.

I've been thinking what if you add an air horn outlet to the exhaust, kind of like a diffuser for the exhaust, would that work?

I see a diffuser cone in the link that you provided.
I would like to hear your technical rebuttal of the burns stainless link that I provided.
Let's look at these:

[Carlos]

I was the very last... to notice my double post

[Carlos]

Every few months curiosity raises this subject again, and , each time from a different title ... exhaust header merge pipe, exhaust cone, trumpet. In my mind ( a strange place to spend time) the specific subject is megahone design. There is absolutely nothing on the web about the design specifics of 4 stroke megahones.

I used to have a book:
http://www.bentleypublishers.com/automo ... stems.html

Which I lent out. Not wanting a deleted post twice in a week, I'll reserve discription of that individual.

I do remember a section on megaphone design, having read it in '72
Burns Stainless refers to it as the basis of much of their expertise in the field. The only other information source would be Dr Blair's books or SAE papers. Anyone have the source material? Believe me , If I can't find megaphone design specifics on the web ... no one can; although I would enjoy being proven wrong.

So I think the grail we are all searching for ... is the 4 stroke megaphone.

It's off topic of course, but because it's the best material on 2 stroke expansion chamber design, a link here, to a PDF of the 3 part series the legendary Gordon Jennings wrote on that subject:
http://www.vintagesleds.com/library/man ... really.pdf


This is the Honda RC-166 250cc 6 cylinder of 1966
Honda thought megaphones were so effective they put 6 on it.
They might have been right. Honda knew and knows something about 4 stroke engine design.
Then again they might have put 'em on 'cause they looked so damn cool.

EDIT AUG 7TH - Post a picture of the Honda 250-6 and it's certain an article about Mike Hailwood surfaces in the press:
http://newsnow.co.uk/h/Sport/Formula+One

[Touring23]

I suspect (but have no data to support it) that the teams change the collector from track to track,
for example that Monza has different collector requirements from Monte Carlo.
I wish I had the time to do a good, proper photo study, from track to track.

Thanks for the post, Carlos. I'm headed off to read the links now. For megaphone physics, I turned here, but haven't had the time to devote to a thorough study.

Six megaphones. Wow.

This discussion reminded me of this old Vizard article.

Here's a question: Are movable pieces allowed on the F1 exhaust (like a trombone slide)?

[Paul]

Code: Select all

5.6.2 Variable geometry exhaust systems are not permitted.