reg exhaust vs headers

[jamchico]

Hey there! Just looking to further my education. What is the difference between stock exhaust manifold and "headers"? The headers seem pricey so I assume there is some significant upgrade involved.
Thanks
Allen
69 wag
Dauntless 350

[ClarkGriswald]

One goal of headers is to provide an equal amount of tubing to each exhaust port before it gets to the collector, where it ties in with the rest of the exhaust. And the output is usually much larger in diameter than a stock manifold. I you look at your manifold, you will see that all the different exhaust ports join together rather soon and continue down to the exhuast sytem as one pipe.. .. Basically they are for increased flow capability

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88 Grand Wagoneer
D44's front\rear
Warn 20990 Lockouts
AMC 360
TF 727
NP 229 (Funky)
Custom Hacking Via S.P.A. (Standard Polish Archetecture)

[Narnian]

To add to that clarification, each cylinder has an exhaust valve. Exhaust valves take turns opening and closing as the cylinders fire. Older stock exhaust manifolds allow all the exhaust valves to open in one chamber. As more exhaust is released in this chamber, pressure forces it as a whole down the exhuast pipe. The problem you encounter is that as cylinder 1 is closing cylinder 2 may force some exhaust into it. The result is that you don't completely empty a chamber of exhaust before you fill it with gas and fresh air.

Headers give each cylinder it's own exhaust chamber and provides more room for the pressurization, thus allowing the cylinder to operate unhampered. Another item which helps in this category is a cross pipe. But that's another question.

Aftermarket headers tend to be noisy and rust prone until you spend lot$ of dollar$. They also take up a lot more engine compartment space and can be difficult to install if you are not replacing the entire exhaust system at the same time. However, they can provide a significant HP boost.

I read an article where a 300HP motor dyno'd at 325HP after putting on headers and sports mufflers.



[This message has been edited by Narnian (edited September 06, 2000).]

[Ralph]

Well said, guys.

On the issue of installation, I found my Edelbrock headers easier than the OEM manifolds, primarily because I didn't have to bolt on the AIR tubes afterward. Even so, there was not enough space to get a socket and torque wrench in on the header bolts, so I had to guess at how tight they were. I probably made up for any problems there with the type of gaskets I used.

But changing the spark plugs with these headers is a lot easier than before.

[Veepster]

to add to Narnians great explanation:

headers also assist in scavenging. what is scavenging? I will try and explain....

exhaust is not dispensed in a continuous flow, it is in pulses. W/O scavenging the exhaust pulses are pushed into the exhaust by the piston moving towards the top. With scavenging the previous pulse sucks the exhaust from the combustion chamber, this frees up HP!

each of these pulses as it flows down the exhaust tubes has a low pressure area behind it in the tube so as the exhaust valve opens the exhaust in the chamber will flow to the low pressure area behind the previous pulse....and another benefit to this is...due to the overlap in the cam(intake and exhaust valve open at same time)this scavenging will also help suck the intake charge into the combustion chamber.......!

so you can see how an exhaust manifold is not as good as a header because all these pulses from all the cylinders are dumped into the manifold and mixed up together so they can't help do the job of scavenging.....check out the Thorley Header website and they will explain how Tri-Y headers take this theory oone step further...

I hope this made sense to someone out there!



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Peace.............BartG

78 Chero
360 2v, 400 QT with low
almost drivable:
4" skyjacker
33x12.50 BFG KO's
Thorley headers, 3" exhaust
Infiniti power leather seats