Just how important are street headers, really?

[PackardV8]

Was looking at a core Ford DOHC V8 which had come in. This is/was Ford's state-of-the-art street engine, DOHC, four valve, beautiful EFI intake . . . and maybe the ugliest exhaust manifolds I've ever seen. Just an old-school log which looked to have been welded up from old tomato cans and had the least free-flowing profile I've ever seen. So, bottom line, do headers really matter on a fully muffled street engine?

[hoffman900]

Might be a good time to revisit this oldie:
viewtopic.php?t=8305

[Tom68]

Was looking at a core Ford DOHC V8 which had come in. This is/was Ford's state-of-the-art street engine, DOHC, four valve, beautiful EFI intake . . . and maybe the ugliest exhaust manifolds I've ever seen. Just an old-school log which looked to have been welded up from old tomato cans and had the least free-flowing profile I've ever seen. So, bottom line, do headers really matter on a fully muffled street engine?

Headers don't matter till you're at race car power levels and have a race to win.

Look at all the effort OEM go to with intake manifolds, that's obviously a big gain area, a big effort with the exhaust is rare and it's possible they only put in an effort for homologation purposes if they're vehicles are involved in a race series.

[BLSTIC]

Those horror manifolds are there primarily that crap to heat up the really close cat converter super fast. Long tube manifolds would be vastly superior in terms of power output, but not when you throw emissions, cost, longevity, and packaging on the table as well.

Many modern turbo manifolds are like that too. It hurts my brain to look at it but I'd rather cars be sold with a bad flowing manifold than not be turbocharged. Also one of my favourite engine swaps for no particular reason fits into a hole so small the only way to have boost is to "Lay back and think of England" while using a compact log with almost zero runner.

[allencr267]

WAG's
Maybe some prototype, proof-of-concept, engine & body & chassis swap combo, a limited production run quicky that needed more then a one-off.
Lower weight or clearance issues, or maybe just removing a big cast iron heatsink that was too close to another component.

[BOOT]

From what I've herd/read, it depends on the exhaust & cam. If so makes sense why oems don't bother.

[hoffman900]

I see you don’t know about harmonics, resonant tuning, compression and expansion waves or inertial scavenging. Yes, headers make a world of difference. I’ve witnessed a 70 lb torque difference between two great headers

Ironically, Calvin / Hendricks on an then open spec NASCAR Cup engine found a 8” stub exhaust into a log manifold to only be down like <2% over the full set up. One of his takeaways being that most headers do more harm than good.

[dannobee]

For reference, Calvin's "Log" header. IIRC, it only lost something like 10hp vs the best Cup car header setup. Calvin has a thread here if you're interested in going down that rabbit hole.

FWIW, there are far different criteria for "success" with respect to emissions testing than street performance. Because of they way emissions are tested, it is critical to get the cats heated up as quickly as possible, otherwise the engine will fail, even if it could actually blow zeros after warmup. The EPA tests with a big bag and analyzes the contents of the bag. A few extra seconds without the cats working will cause a failure.

[PackardV8]

I see you don’t know about harmonics, resonant tuning, compression and expansion waves or inertial scavenging. Yes, headers make a world of difference. I’ve witnessed a 70 lb torque difference between two great headers

Only been doing this for sixty years, so I do know a bit about all the above, but the question wasn't about great race headers, but about headers which fit within OEM engine compartments, running through a full exhaust and meeting emissions regs.

Those horror manifolds are there primarily that crap to heat up the really close cat converter super fast. Long tube manifolds would be vastly superior in terms of power output, but not when you throw emissions, cost, longevity, and packaging on the table as well.

For true. Seeing Ford make zero effort on their 4-valve engine brought the question to mind.

[juuhanaa]

I was responsible for this engine and it was the first time for me that someone else built it, and then drive it... This is what i call a street performance on a 90's hothatch using modified OEM parts.

Page 19:

viewtopic.php?f=15&t=55767&start=270

Notice how effort was taken to make room for the headers on the front fire wall... I dont know about the emissions, but the valves were about 0.5mm open @ TDC, and i doubt the extra mufflers would hurt it.

https://www.youtube.com/watch?v=297_XxbaTj0



-juhana

[Tom68]

I see you don’t know about harmonics, resonant tuning, compression and expansion waves or inertial scavenging. Yes, headers make a world of difference. I’ve witnessed a 70 lb torque difference between two great headers

Only been doing this for sixty years, so I do know a bit about all the above, but the question wasn't about great race headers, but about headers which fit within OEM engine compartments, running through a full exhaust and meeting emissions regs.

Okay. I guess I took a different read on the OPs question in general relating it more to high performance rather than emissions - with the title of this thread. I personally don’t see a difference between race headers and street headers other than rpm range, horsepower, and installation. I get the idea that firing off the cat quickly is necessary

Packard V8 is the OP.

[rebelyell]

* just as hoffman900 wrote above ---

very long but very good thread --- started by long-established exhaust pro (exhausted) --- lotsa credible, practical testing. Much to learn here.
viewtopic.php?t=8305

I came away with the following "generality" --- that below about 4K-4500, Headers demonstrate little to no performance advantage over Log. YMMV

[Tom68]

For true. Seeing Ford make zero effort on their 4-valve engine brought the question to mind.

Yet when it was about diminishing the flat plane crank sound, they put in a lot of effort, all for the acoustics I believe.

Screenshot 2022-10-29 095631.jpg

My Mk1 Zephyr had this Hockey Stick.

Five Stars.jpg

[rebelyell]

Also --- In our continuing era of efficiency, I am entirely convinced that Headers would be OE on every new ICE --- IF (within typical street rpm ranges) Headers provided any significant increase in efficiency or performance. Today, and in the face of weight-saving & fuel efficiency campaigns ---Relatively heavy cast iron remains the standard --- the OEMs KNOW more about the subject than most.

[Racer71]

Most engines now especially the 4 and 6 cylinder ones don’t even have a manifold at all, it’s part of the head casting with a single hole for an outlet, typically with a 4 stud mounting for a pipe to bolt up. Always made me curious about how you’d go about porting one if you could at all.