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post #1 of (permalink) Old 03-03-2004, 08:02 PM Thread Starter
 
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exhausted...what\'s the diff?

ok...exhaust 101...what is the difference between headers and an exhaust manifold (besides cost)?

i'm not doing any work, just trying to get some learnin'...
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post #2 of (permalink) Old 03-03-2004, 08:46 PM
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Re: exhausted...what\'s the diff?

For most people, it's headers look cooler.

In reality, it's about the scavenge effect. The exhaust gas from one cylinder, moving through the system, puts a drag on the next cylinder to fire behind it. By being equal length and tuned, headers do a better job of creating the effect but only in the upper rpm range they are tuned to. You will actually loose power at low rpm.

Unless you are running high RPM for sand or mud pit drag racing, you are better off without going to headers.
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post #3 of (permalink) Old 03-03-2004, 08:57 PM
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Re: exhausted...what\'s the diff?

</font><blockquote><font class="small">In reply to:</font><hr />
exhaust gas from one cylinder, moving through the system, puts a drag on the next cylinder to fire behind it.

[/ QUOTE ]

Actually, it is to create a vacuum for the next time the same cylinder fires. The idea is the pulse is still in the individual tube moving toward the collector when the next pulse starts. There is a low pressure created between the pulses which scavenges the cylinder at the next pulse.
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post #4 of (permalink) Old 03-04-2004, 10:24 AM
 
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Re: exhausted...what\'s the diff?

Headers: Reduces pressure of exhaust coming out of the engine. Allows the engine to "breathe more free". Gives more power at higher RPM's. Welded tube construction.

Exhaust manifold: Stock setup usually, keep a little more backpressure, better for low RPM power. Cast iron construction.

Personally on a 4.2L engine, I like to run a stock exhaust manifold because the 4.2 has most power at low RPM's, where the stock manifold is strongest. Headers are for high RPM breathing, this is where my 4.2L does not often rev.

Also, the Header causes higher underhood temperatures (fact). Stock manifold is cheaper. Headers often cause clearance problems to steering shafts, auto transmissions, linkages, etc. This was also a problem for me. Finally, it is often harder to get a good seal with aftermarket header flanges in my experience.

I bought my used exhaust manifold for $15, had it resurfaced for $20 (required) at a machine shop, and then used a high temp bake on coating which looks like raw cast iron.
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post #5 of (permalink) Old 03-04-2004, 11:19 AM Thread Starter
 
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Re: exhausted...what\'s the diff?

thanks guys...i'm officially better informed than i was yesterday...as for smarter, well, you guys are good, but you're not magicians [img]images/graemlins/grin.gif[/img]
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post #6 of (permalink) Old 03-04-2004, 11:55 AM
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Re: exhausted...what\'s the diff?

</font><blockquote><font class="small">In reply to:</font><hr />
but you're not magicians

[/ QUOTE ]
Now why do you say that? I've been an amateur magician for 35 years. My favorite way to tip a waitress is to take a dollar bill from her and turn it into a five before her eyes. Besides she remembers that I tipped her five dollars but it only cost me four.
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