How Exhaust Works

[Jason]

I was just wonder how you work out an exhaust system, and how you will know what kind of range it has? Or how to make it resonate at certain frequencies (RPM)

 

give me all the technical stuff... the knowledge its fill me :P :)

Edited January 10, 2005 by Jason

[Super Jamie]

most of this is controlled by the exhaust manifold. a stock one doesn't do much, it gets the gases out so you don't choke, and is quiet so manufacturers can sell cars

 

a tuned-length exhaust manifold (called headers or extractors) times the exhaust pulses into a collector so they help each other get out of the manifold quicker at a certain rpm, or more generally in a certain rpm rev range

 

shorter manifolds are designed for high rpm applications, they give little torque as there is less backpressure in the exhaust manifold before the collector (into the rest of the exhaust). longer extractors are designed for torque, but they can restrict top end as there is alot of gas in the exhaust manifold (too much backpressure) at higher rpm

[Super Jamie]

depending on who you talk to, backpressure is a good thing or a bad thing. david vizard (and old v8 and mini tuner, god of head porting) say the best exhaust is one with NO back pressure

 

realistically, the hotter an exhaust can run, the better it will flow, as higher temperature particles move quicker than lower temperature particles. you make temperature higher by making the exhaust small, so the particles of air don't fly too far inside the pipe (instead of out of it) and maintain speed. but if you make your exhaust too small, it won't have enough volume to flow the maximum amount of air your engine can draw in, so you'll restrict the power

[Medicine_Man]

don't know if this is any help to your question, but have a read anyway..

 

http://auto.howstuffworks.com/question172.htm

[Super Jamie]

one exhaust guy i talked to reckons the best thing you can do for your exhaust is to heat wrap the whole thing, this will keep temperature in the pipe and allow it to expel gases quicker, hence it will flow better

 

bends are also a big no-no for exhaust. it's said that a T pipe in an exhaust (such as at the back of a mazda6) is as restrictive as THREE METERS of straight pipe

 

as a general rule, "an exhaust is only as good as its first 4 feet". so spend your money on things like good extractors, dump pipes, catalytic converters, bends to under the floorpan, and the first muffler, don't worry about the rest of it so much, and things like exhaust tips

[Jason]

Ahhh cool thanks made it a bit clearer :)

 

yeah could of done with this before i got my extra long extractors :P silly me

Edited January 10, 2005 by Jason

[irokin]

http://66.90.77.237/images/brands/thermo-tec/TT11002.jpg

 

Exhaust insulation wrap. Ive got it on my celica. Have had for about 3 months now. Alot of people are going to go on about how your manifolds gonna crack blah blah blah. Its total bullshit. If you drive hard (like a turbo car) let your exhaust cool down for a minute or so before you turn it off. They don't hold all the heat in but if you turn the car off and within about a minute the wrap cools down enough so your able to touch it. Stainless tends to have the same effect because it tends to "repel" heat, but it depends on the type of stainless.

 

 

The position of your first resonator changes something too. I think it has to do with torque.

 

If youve got the $$$ get a set of ajustable headers made up :P

 

http://www.burnsstainless.com/TechArticles...ory/theory.html

 

those guys know their stuff.....

[Teddy]

think about it, the 4agze isnt going to be REVING incredebly high, and besides, they cost $100 for a good set with o2 hole... if i was u i would be really happy with them. :P

[Jason]

There big and beffy 2 1/2 out :P

 

How do you go about making it resonate is there a formula. But i would think making a pipe wider lets the gas expand more traveling less down the pipe before the next bang making the cycle shorter (high rpm ) thus letting the gas out easy?

 

This is just what i think, how far am i off by?? :)

[Super Jamie]

there's no general formula. because every engine has different flow characteristics. the intake is different, the manifold is different. the head is different. the combustion chamber and pistons and bores are different, the valves are different, so there's no exacting way at all you can say "this is how exhaust gas exits an engine". this is why getting tuned-length extractors made is somewhat of an artform, and expensive to have it done right, and to your requirements

 

your "making a pipe wider" comment is correct, to a certain extent. if you put a 4" exhaust on your corolla, the gas would expand and cool and slow down and the engine would actually be working against all the slow dense gas sitting in the exhaust pipe, and your exhaust would flow like a pile of crap

 

the trick is to find an exhaust size that allows the gas to flow freely throughout your rev range without making it too big to hurt power at low rpm or too small to hurt power at high rpm

 

have a read of this

http://autos.groups.yahoo.com/group/oldcor...xhaustsizes.jpg

[Super Jamie]

and as i have stated elsewhere, mufflers make an exhaust quiet, not the size of the pipe. i have a 2" press bent exhaust that is noisy as a motherf@$ker, and fook has a 2.25" mandrel exhaust that's actually very quiet, probably within ADR-compliant levels. my mufflers are probably empty

[Super Jamie]

aaand from what i can find, turbo engines are totally different. the larger the exhaust the better, as the turbo wants as little backpressure as possible, so it spools up quicker. the way most people talk, it will make little to no difference if you hang a 3" or 4" exhaust off the end of a small turbo

 

a supercharged engine is just to be treated as a larger capacity n/a engine. say a 2" pipe is good for a given size n/a engine, supercharge it and you could be looking at a step up to 2.5" or 3" (depending on the amount of boost you're running and the size of the engine in the first place)

 

and they're hot when you touch them, so don't do it

 

thats most of what i think about exhausts. google "exhaust theory" and draw your own conclusions :P

[wyldephyre]

....don't worry about the rest of it so much, and things like exhaust tips

Awww.... and I went through all that Milo for nothing? :P

[Super Jamie]

oh, and "extra long" extractors aren't so bad for a little K motor, i mean you're probably going to be restricting a few hp at most. maybe if you had a fully worked v8 where you're sacrificing 50+hp it might matter

 

rotary extractors tuned for torque (keep in mind each housing only has one exhaust port) often join far far under the floorpan, sometimes just before the diff

[Super Jamie]

lol haikal :P