My 82 Camaro rolled off the lot with cast manifolds and a single 2 1/4 exhaust. I swapped in a 350 when it was ten years old, and it was faster, but really lacked top end. A nice set of short Edelbrock headers and a 3 inch pipe took a full second off the quarter mile, and gave me 1500 more usable rpm.
So, yes, sometimes.
pointofdeparture said:Even if true long tube headers are overkill for most engines it's clear that the OEMs are reaping the benefits of more thorough and calculated manifold design. Today's manifolds look more like the aftermarket shorty headers of 20 years ago. For example:
This is the factory manifold from a new Mazda SkyActiv engine.
Here is the manifold from a ~20 year old Protege.
That's not the manifold from a 20 year old Protege. It doesn't have a giant crack between 2 and 3.
fidelity101 said:¯\_(ツ)_/¯ said:To pile on to whatever gets said here- what about on a rotary?
yes they are needed.
Not until you get crazy.
A well tuned stock port 12A is worth 150-160 horsepower (crank) whether you have a box manifold on it or a header.
Similar goes for a 6 port 13B... I vividly recall a dyno plot on Nopistons of an IT engine that made 174hp (wheel) with the manifold, and 175hp with a header, or something silly. Dyno plots looked identical to within testing error. The funny was the plot was posted to show how important headers were.
Most gains with a rotary before you port are in leaning them out, Mazda made them stupid rich from the factory to either feed the thermal reactor or to keep the catalysts from melting.
That said, I'll be doing dyno testing to see what exhaust setup makes the most torque at 4000rpm or so on my stockport 12A. Because reasons.
On on my dads 69 427 corvette hooker side pipe headers resulted in a 1/4 mile time a full second quicker and lower engine temps. Lower temps are especially great with big blocks as they tend to run a bit hot. That and with c3 with sidepipes have better ground clearance then the factory x pipe.
Ofcourse headers aren't needed just like turbos,super chargers,or any other non stock performance parts aren't needed.
Keith Tanner said:The problem is that this is all tough packaging. On my 2.0 Miata engine, I built a header with 31" primaries to get the frequencies I wanted. Four 31" tubes that are 1.75" in diameter is a tough fit.
That is pretty long, what was the designed rpm? Guessing around 6000?
We've got some shortys on our challenge destined sbc400, partially for weight (25lbs!) and partially for power. Car doesn't run yet so I can't really say if it's fast or not. Hope so.
The Audi 7A 5-cylinder 20V had a very cool stock header. People call it the "bag of snakes".
The 190E 16V had a nice header too. And the primaries are huge at 1.875" OD.
My answer as a hotrodder... you always benefit from proper exhaust engineering that matches the engine combo. Headers are one of the easiest ways to do that. OEMs don't use headers because they represent more R&D, warranty headaches, heat headaches, and they are nearly impossible to get the actual proper engineering and still comply with emissions.
In reply to Curtis73 :
You mentioned "heat headaches". I was always under the assumption that headers helped reduce under hood temps when compared to traditional cast manifolds. Is that not the case?
Paul_VR6 said:Keith Tanner said:The problem is that this is all tough packaging. On my 2.0 Miata engine, I built a header with 31" primaries to get the frequencies I wanted. Four 31" tubes that are 1.75" in diameter is a tough fit.
That is pretty long, what was the designed rpm? Guessing around 6000?
Check the dyno chart, that's right where the gains were :) It was actually based on EP Miata headers. Header design is like suspension geometry design, you can go crazy trying to take every possible factor into account or you can realize that being in the ballpark is honestly just as good.
Had I gone shorter, it would have been optimized for higher RPM. But I needed a rally engine, not a dyno queen. The engine eventually ended up around 175 rwhp with a lot of area under the curve - more than the turbo 1.6 that also lived in my garage at the time that had a similar power peak.
Rocambolesque said:The Audi 7A 5-cylinder 20V had a very cool stock header. People call it the "bag of snakes".
Only in 1990. In 1991, they went to a more conventional manifold, and power output stayed the same.
Hungary Bill said:In reply to Curtis73 :
You mentioned "heat headaches". I was always under the assumption that headers helped reduce under hood temps when compared to traditional cast manifolds. Is that not the case?
Oh my no, it is the opposite. Headers have a lot more surface area to transfer heat from. They are also a lot bulkier, so they run a lot closer to things like hoses and valve cover gaskets and spark plug wires and other stuff.
Chevy spent a good amount of time developing a double wall "shorty header" for the Corvette because of this, and because heat lost to the engine bay is heat not warming up the catalyst, and getting the cat warm is #1 priority for emissions.
In reply to Knurled. :
Thus the need to use coatings such as jethot or similar to keep the temps down
In reply to dherr :
I've found that those mainly serve to not look ugly compared to rusty tubes. You still need to heat-sleeve the wiring harnesses and the spark plug boots and, for GMs with plastic heater plenums, cover the whole thing with heat reflective tape.
DEI probably has headers to thank for 90% of its business selling heat protection products 
In reply to Knurled. :
iiiiiiiinteresting! Thanks for that!
When the E55 went from shorties to longtubes, the amount of work the radiator fan had to do dropped so dramatically that I am sold on that basis alone. Went ahead and put blankets on them as well and yeah engine bay temps are a fraction of what they were. The idle to redline giddyup gains are icing on the cake.
Hungary Bill said:In reply to Curtis73 :
You mentioned "heat headaches". I was always under the assumption that headers helped reduce under hood temps when compared to traditional cast manifolds. Is that not the case?
They have thinner walls and the heat transfers to the surrounding air more quickly. Think of it like a a cast iron griddle versus a baking sheet. Both will get to the same temp, eventually, but the cast griddle will take longer to get there and stay there longer and more consistently. The baking sheet will be all over the place and change temp quite quickly.
On my 924, I had all sorts of underhood heat issues with my switch to a long tube header, if my cast manifold hadn't cracked I'd have used that. Ceramic coating the header helped quite a bit.
Knurled. said:In reply to dherr :
I've found that those mainly serve to not look ugly compared to rusty tubes. You still need to heat-sleeve the wiring harnesses and the spark plug boots and, for GMs with plastic heater plenums, cover the whole thing with heat reflective tape.
DEI probably has headers to thank for 90% of its business selling heat protection products
You're wrong, but you're welcome to your opinion. I had an uncoated header melt poly control arm bushings and plug wire boots on my 924 (spark plugs are nestled between the exhaust flange like many V8s). Coated it with a proper ceramic coating (inside and out) and the heat problems went away.
Actually thin wall tubing transfers less heat to the bay... counterintuitive but true.
"Header" (Exhaust manifold) and Intake Manifold design principles are very similar. Like Keith mentioned using the helmholtz frequency to determine primary/runner lengths. Intake manifold tuning is a bit different in that you have the plenum volume to consider, along with fuel injector positioning, and runner distribution, but the general runner tuning is similar if not the same. Exhaust manifold tuning also gets complicated with primary/secondary tuning and collector design, so I'm probably oversimplifying things.
If you want to experiment without having to weld up a bunch of different parts, 1D engine modeling software can be very helpful. You can change manifold design on the fly and run dyno charts to see a quick visible difference. But its like any simulation, garbage in = garbage out.
Stefan said:Knurled. said:In reply to dherr :
I've found that those mainly serve to not look ugly compared to rusty tubes. You still need to heat-sleeve the wiring harnesses and the spark plug boots and, for GMs with plastic heater plenums, cover the whole thing with heat reflective tape.
DEI probably has headers to thank for 90% of its business selling heat protection products
You're wrong, but you're welcome to your opinion. I had an uncoated header melt poly control arm bushings and plug wire boots on my 924 (spark plugs are nestled between the exhaust flange like many V8s). Coated it with a proper ceramic coating (inside and out) and the heat problems went away.
My experience is with shorty headers on F-bodies. They glow red and orange just fine despite the coating.
In reply to Paul_VR6 :
Eh, not quite. Cast holds heat longer compared to tubing, but that's about all. The Cast Iron griddle analogy posted above is an apt description...
Paul_VR6 said:Keith Tanner said:The problem is that this is all tough packaging. On my 2.0 Miata engine, I built a header with 31" primaries to get the frequencies I wanted. Four 31" tubes that are 1.75" in diameter is a tough fit.
That is pretty long, what was the designed rpm? Guessing around 6000?
the primaries on my 13b are 6' long lol
In reply to Keith Tanner :
Only 4 tubes? A mere 31 inches long? That's onlya shade over 10 feet! All that room?
Try stuffing 27 feet of 1&5/8 tubing in a Jaguar V12 engine compartment that's so tight a dime won't fall all the way through.
Paul_VR6 said:Actually thin wall tubing transfers less heat to the bay... counterintuitive but true.
Ok, you are all simultaneously right and wrong about the heat stuff.
Cast iron manifolds soak with heat, but at a much slower rate. More heat makes it out the tailpipe with cast iron. Tubular headers soak very fast and have lots of surface area to shed heat, but have a lower overall SHC.
The result: Manifolds hold more heat with less actual temperature. They convect most of their heat which means it rises and gets blown away. Headers hold less heat at higher temperatures. They radiate tons of heat which is why things like suspension bushings and wires melt even through they aren't above the heat source.
The boiled-down version of the story is this: EGTs with headers are almost always lower at the collector than manifolds are at the flange... regardless of how long the primaries are. You could cast full-length iron headers and compare them to shorty tubular headers, and the shorties will still probably have cooler EGTs.
tubular headers put more heat into the engine bay. It's just that it is far more biased toward radiant heat instead of convected heat.
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