"TUNABLE EXHAUST"- A valid concept?

[Nashville Kat]

I'm always hearing about tuned exhausts here, and frankly I have my doubts.

How can an exhaust system really improve the motors performance? Doesn't all the motor's own internal workings occur before the exhaust, and isn't that just to carry away the by-products for the next ignition sequence?

Surely if anything impedes the exhaust flow to any degree, this will hinder performance- to that end I personally drilled some small extra holes in my endcap- because it was smaller coming out at the bottom than the exhaust manifold at the top. The idea of straight header pipes in loud hot rods is that then there isn't ANY muffler to impede flow in any way.

But how can any exhaust system really IMPROVE how your motor runs?

Don't get me wrong, I'm all for quieter running and I think the answer is a longer pipe and bigger chamber. I just don't think any real problems can be solved or improved worrying over exhaust, if it's not already restricted somehow.

[BarelyAWake]

I think SpookyTooth has a pretty good explanation here;
Spooky Tooth Cycles - Motorized Bicycles: Gas Powered and Electric Bikes - Expansion Chamber Exhaust

Or for a more comprehensive explanation here's the wiki for expansion chambers;
Expansion chamber - Wikipedia, the free encyclopedia

What it amounts to is those hot rods are four strokes, the "wave" created by a properly placed expansion chamber on a 2 stroke helps mimic the effects of valving.

Hope this helps

[Kevlarr]

Also, notice even dragsters run pipes off the head. The idea is to have the length correct (in other words tuned) so that the exhaust from the previous cycle is exiting the pipe causing a low pressure area inside the pipe to help pull the gasses out of the cylinder on the next exhaust stroke.

[jay sawdust]

Well...your gonna get alot of feedback on this one....On a four stroke engine little or no backpresure is best for racing (although this is also "tuneable" by varying the length of the collector pipe).....A 2-stroke engine is a differant animal altogeather...A "tuned"exaust system for a 2-stroke utilizes an expantion chamber that both draws unburnt air/fuel mixture through the motor and by use of pressure waves "reinserts" said air/fuel mixture on the next stroke....essentialy superchargeing the motor....thats the basics....Ill let the more knolageable members elaborate....J

[foureasy]

i wish i would have found this thread earlier. but jay pretty well summed it up

[Pablo]

Originally Posted by Nashville Kat

I'm always hearing about tuned exhausts here, and frankly I have my doubts......... I just don't think any real problems can be solved or improved worrying over exhaust.....

A two-stroke

Tuned Pipe Theory

How Two-Stroke Expansion Chambers Work, and Why You Should Care.

http://sickbikeparts.com/Manuals/Tun...structions.pdf

Sick Bike Parts

[Nashville Kat]

Haven't read the articles yet, but I'm remembering a fifth grade lesson in physics I had that might make this viable- My teacher then, Mr. Bryant, pointed out the phenomena of a showercurtain: how when you are in a shower that it wants to sorta blow over toward you and cling to your body.. he then explained it was due to the effect of the shower water itself- disturbing the air and creating a vacuum in that direction-and that air in movement has less air pressure

So I guess it could apply to an exhaust system somehow- actually sucking the exhaust out instead of it merely being forced out with it's own expanded pressure-

I'm not sure exactly what effect the temperature would have, or the sizes of the pipe or chamber- so I guess the concept is valid. All the variables are left to be proved in the pudding I suppose.

[foureasy]

he was showing you an example of bernoulli's principle. the same reason a carb draws fuel and a plane stays in the air. the higher the velocity the lower the pressure