Why Aren't Headers Standard Equipment?

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I was perusing a Toyota Tacoma site and noticed that some guys upgraded their 4-Cyl by purchasing after-market exhaust headers (HERE) . They claim to get more power and better mpg.

So, other than the obvious issue of $450, I am wondering why these wouldn't be standard equipment, or at least optional? I know there is a downside (reduced filtration) to putting on a K&N racing filter on the intake side, but is there any cost (other than dollars) to putting headers on the exhaust side?

Auto manufacturers seem to go to great lengths to increase their CAFE mileage. Why not use headers?
 
Noise.Tinny headers don't insulate valvetrain sounds like cast iron or thicker designs do.
 
Headers dissipate heat more quickly than iron manifolds, and that can lead to slow cat light off times. Also, that extra heat may harm things under the hood in a car not built for it.

Mazda found a way around this when they created the CX-5. Search for a picture, and you will see. They gained the advantage of 4-2-1 headers without comprising cat light off time.

Some cars left the factory with pipes that are similar to headers. The 2.2 and 2.3 engine found in Honda Accords are built that way.
 
Some compaines are incorporating the exhaust mainfold into the cylinder head, like the Chrysler Pentastar engine. I guess it cuts down on weight and costs. It would be impossible to install headers on that type of engine.
 
Some cars come with headers from the factory. Many don't. The 302HO in the 80's came equipped with factory headers (albeit, not very good ones) and many hi-po cars come with them factory like my M5 which has 4-2-1 headers stock.

As others have noted, cast iron is the most common manifold material because of its good heat retention, durability and low cost of manufacture.
 
Hi end cars do.

312-header1.jpg
 
Originally Posted By: hattaresguy
Hi end cars do.

312-header1.jpg





That's about 3 times the number of cylinders that I have....
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Why no headers?
Cost. Noise. Emissions. Durability.

Thin walled tube headers are more involved to produce and use more expensive metal than a cast header.

Tube headers make more noise under the hood as well as at the tailpipe end.
Most car buyers (especially over 30 y.o.) don't want all that noise.

Tube headers extract and cool the exhaust gases from the cylinder more quickly.
That increases HC emissions and makes the cat converter take more time to warm up.
They can also raise under hood temps.

Modern cast manifolds are far better than the "log" manifolds of yesteryear.
 
Amusing the interest in V8s with headers given that most high-volume V8 designs have 360 degree cranks and therefore uneven firing per bank. Same issue with V6s. Whatever good headers do, it's not going to be the same for every cylinder.

Not a problem with the in-line three, four or six however, and many smaller naturally-aspirated fours do have nicely-welded tubular designs.
 
2011+ 5.0 Mustang also have stainless headers. Quad cam heads are too wide tho, can't really see the headers. Dang...
 
If one is talking about full length, tuned, scavenging LONG TUBE headers, then the OEMs will NEVER use them now, since they do NOT allow the catcon(s) to be placed close enough to the exhaust ports in order to 'light off' properly, and STAY hot enough to function once the engine is running for a while.
They would never pass a 49 state sniffer test, let alone the crazy C.A.R.B standards.

If one is talking about factory/OEM length 'shorties', yes, they do allow the catcons to be placed close enough for light off and proper function (despite their worse heat retention than cast iron manifolds), BUT the OEMS would be VERY hesitant to use them due to; cost of 304/321/inconel stainless tubing material, the brittleness of this material, the aforementioned higher under hood noise issues, and the potential warping of the thinner mounting flanges and all of the exhaust/vacuum leak emissions/ECM problems that come with those leaks.
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Stock M5 exhaust (foreground):

ssheadee39comp2.jpg


You'll note the cats are a fair ways back from the headers, which I would categorize as "mid length", as they aren't shorties and they aren't long-tubes either.
 
Every SRT8 you see has a nifty pair of factory shorties wrapped in a sheet metal shroud. Flow well all the way to 600 crank hp or so. Quiet as a mouse!

Since many new engine designs have no exhaust manifold at all these days expect fewer headers!
 
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