i hope you werent talking about me....


but your link proves absolutely nothing. Of course they are one of the best mods..... but that in no way proves that you can put a percentage increase and calculate the velocity and size of the chambers in your head.

i was thinking of making my own set up and the most logical way i could think of was to take sections of pipe that were pre-bent and weld them piece by piece. then when i lucked out and found a set i can say that its not worth the hassle. but they do give you a pretty big gain. its nice to pull away from other avengers. the only thing i didnt like was how raspy my exhaust got. im just going to have to get some resonators

look, the thing is, I already know all i need to know about rpms and all that, i was just explaining flow and the physical quantities. I really didnt think i needed to go THIS deep and explain the whole combustion process just to say how headers work and increase power. by the way, there are tons more ways to improve torque and hp that im sure isnt common knowledge to enthusiasts and even the best. headers decrease back pressure  which is a force pushing back on the engine via the exhaust system as it expels exhaust gases. less pressure equals less force which means less resistance for the engine. imagine pushing a light load vs a heavier load. you might be able to push both, but im sure tyhe lighter one makes life a lot easier. so this decrease in pressure means less energy is spent trying to expel gases and diverted toward making power..do i need to explain that? well this is because w/ every combustion , pressure is created in the combustion chamber causing movement of the cylinders...im pretty sure u know what that leads to...motion of the car. since there is a lower pressure, gases can exit faster creating somewhat of a vacuum as compared to stock allowing for higher engine speed and less engine stress. this increased speed however, does not change shift points directly as this is controlled in the transmission via sensors. however, you can get to those shift points quicker, creating better acceleration. of course this alone wouldnt give all the gains to be had. naturally, when air exits faster, it tends to enter faster due to the low pressure (u kno what im talking about). so we have more air = good right? well not entirely, the ecu via sensor has to send more fuel to compensate so that ur not running lean..as this will cause premature engine failure..which is why more air usually means more power. next..cylinders, they dont all fire at the same time for a number of reasons. for one the engine would be extremely inefficient as there would be too much of a time lapse between strokes. header pipes all have to be the same length b/c a difference in speed of gases causes turbulence which is what you DONT want. when each cylinder fires, it sends a pulse which appears continuous at high speeds at a higher frequency. these pulses cant all be at the same time for the reason stated above where all cylinders wont fire at the same time. another reason...exiting would be a pain having all those pulses.  there's a lot more sutff about timing/compression ration i just dont have the time to explain all that bs i got a class. exhaust/intake valves/ camshaft profile, cams that produce max torque at high/low rpm. also, its really TORQUE that matters as hp is just a product of torque at a certain rpm. The calculation of exact gains involves a lotta physics and unknowns which is why it is much easier to test instead of hypothesize all these unknowns. the way the stock exhaust manifolds are setup, are like vectors, and the losses can be calculated as i stated earlier. study vectors and u can calculate loss of speed due to angular impact...if u know the exhaust velocity. if not...a percentage loss can be calculated.

i wanna put one together..if i could get my hands on a stock exhaust manifold...

o i c...well tell u what...they'll probably be there for a while..im gonna try something, so ill let u kno if u should get those. i just have to check this thing out and find out if it'll work. ill keep updating.

There's a lot of people in this thread spouting a lot of crap, about things they partially grasp. I'm not even going to start to explain as i'd be writing PAGES.. I'll just comment that too much emphasis is put on peak velocity and pressure, and not enough emphasis is put on reversion and quality (not quantity) of flow.

*IF* you want the best header .. gather together your hard earned cash..

go here http://www.hytechexhaust.com and have them modify their eclipse header to fit the avenger.

These are the best headers $$ can buy.. also very expensive.. you get what you pay for however.

Their eclipse header made 40hp at the wheels, while turning DOWN the injectors.

avengers suffer from the same problems.. excess rich conditions, poor flowing exaust, bad merges, precats etc etc..

Exhaust gases could care less if your math doesn't make sense, most of the math i've seen on the net regarding hemholtz designs, tuned pipe designs are great if your designing a pipe organ, not so great for when your developing a non-steady state induction / exhaust system.