Why Install Headers?

See the Exhaust_Theory section of the FAQ for a lengthy technical discussion of this topic.
[KP] Most passenger cars will have an exhaust manifold whose job it is to collect the exhaust gases from each of the exhaust ports of the head to which it is attached. These manifolds are typically cast iron to reduce noise and provide some longevity. In a typical exhaust mainfold, the individul “runner” for an exhaust port is virtually non-existent and the exhaust gases from all cylinders (on the same bank) merges within just a few inches – at most.
A header, OTOH, is composed of dedicated “runners” (tubes) for each exhaust port. In nearly all header designs, there is an intent to keep the length of each tube identical and the same as tubes attached to the other head (if any). There is a great deal of science around header design and like most other engine designer choices – it is an issue of compromises. Length of the tubes and diameter of the tubes as well as the collector can be varied to optimize torque and HP at different RPM ranges. Of course all of this extra *plumbing* usually has to fit in a rather confined space – which presents additional challenges. Headers are typically not made from cast iron – though BMW has used cast iron headers on their older M5 and M6 cars. Recently the material of chice for headers is stainless steel. Mid-80’s Mustang GT’s (5.0L) even came with ss headers from the factory.
The NSX *finally* went from cast iron *manifolds* to stainless steel headers with the advent of the 3.2L engine in 1997. Even this NSX factory header is compromised (though a big improvement over the manifold) IMO because the engineers did not want the three header tubes off of the front head to pass under the engine where presumably they could be more susceptible to being scraped, bent or broken. Instead, the factory 97+ headers are comprised of very short tubes that are brought into a collector so that only a single exhaust pipe must pass under the engine. If damaged, this exhaust pipe can be repaired or replaced more easily than a header. It’s my belief that even the 97+ cars will benefit from an RM/CT/DC header since all of these designs use longer header tubes which the NSX seems to thrive on. I think that anyone who has seen a stock 3.0L exhaust manifold would have to agree that is is the least elegant part of the entire NSX. In fact, it looks just like the unrefined manifolds on the first 283 cu in chevys where I first perfected ways to burn my forearms while fiddling with these motors.
From reliable sources, it appears that Honda considered but opted against headers on the car due to their unfamiliarity with the longevity of headers and potential header material. Keep in mind that both performance and everyday reliability were the chief design goals for this car. The risk of using headers – and their *unknown to Honda* potential for wear, cracking, etc. was too much of a risk. Cast iron manifolds, while reducing HP a bit, were a known quantity and a very safe bet.
In Honda’s defense, they probably made the right decision. Will the aftermarket headers we’re all installing stand up to 100K miles of road salt, hard driving, splashed water from deep puddles, etc, etc.? I have my doubts. However, that’s not to say that enthusiast such as those found on this list aren’t ready to make the trade-off. If I have to replace my headers *every* 50K miles, well, no problem at all. *To me*, the trade-off is worth it.
Even today, there are few cars on the road that come with good, free flowing headers. I suspect for the same reason that Honda didn’t use them… and we’re 8 years more knowledgeable!
Yes, the 3.2L motors (1997 +) now have factory headers but even these are pretty conservative. IOW, they are very compact, and I’d bet that that don’t flow as well as the aftermarket ones. However, there’s probably not as much to gain from swapping these guys out as their was with the 91-96 cast iron manifolds.
The bottom line is that if you want solid, 100K mile reliability, stay with the cast iron. OTOH, if you’re willing to trade some noticeable HP improvement for, IMO, a small decrease in *potential* reliability, then go for the headers.

What Headers Are Available?

Comptech

Stainless steel, available for all years. MSRP about $1600.
[BM] I have had a problem with header cracking, but Comptech stood behind it and sent it off to DC Sports to get it fixed, installing one of the headers on my car until it came back repaired. No problem since.
[SA] Just to clarify on the issue with CompTech headers cracking. I talked with Gary at CompTech and he told me that the cracking problem was actually a problem with the joint between the header and the exhaust. The unit he sold me is a new design that is suppose to be improved and fixes the problem. Talk to CompTech for more details.

DC Sports

Mandrel bent polished T-304 stainless steel. 2-year warranty. MSRP about $1520

RM Racing

Fabricated by hand and built to order, the system is constructed entirely of high-grade T-304 stainless steel, offering great looks and a lifetime of performance. Starting off with the flange, a solid stainless steel billet is precisely machined on a CNC mill for accurate fit and seal. Primary header tubes are 1.75 inch diameter, .065 thickness and have soft radius mandrel bends throughout. Merging of the primary tubes is carried out through a long collector which gives more top-end performance than a short-type collector. Coming off of the collector is a short length of bellow tubing to relieve stress from the headers due to engine torqueing. Exit diameter of the header/collector is 2.5 inches. Price: $1,299.00 * LIFETIME GUARANTEE
[CA] Picked up the NSX from David McDavid Acura this morning. I started it up, it idled nicely, a little deeper tone with the new headers, but not much different, I am not so sure it is so much deeper as there is more tonal across the spectrum, there just seems to be “more” sound.
I took it to redline and shifted to 3rd, smooth consistent power all the way up, can definitely feel more pull. Looked over at Craig and he had perma-grin, the smile only a surgeon could remove.
There seems to be much more pull from the passenger seat…consistent, solid….very nice. I took the highway home, and experimented with sprint and drift, I found I don’t have to downshift to get the power I want, I am sure I will adjust and be back to downshifting again soon! : – )
I highly recommend the headers to anyone, especially as a first mod.

Are There Any Problems Installing Headers?

Some people have had rattling noises from their aftermarket headers. See Noises for more info.
A few people have experienced trouble with the “Check Engine” light coming on and uneven throttle after installing headers. This usually seems to be a result of getting some kind of contaminant (oil, etc.) on the O2 sensors, which must be removed during header installation.
[KP] When steady-state cruising, say in 3rd gear at 3500 rpm, you can *feel* the car acting a little herky-jerky. If you accelerate, it stumbles once or twice, clears itself, and then takes off. I guess I’m going to drive the car *carefully* for awhile to see if the situation passes. My theory is that the O2 sensors may be adversely affected from the WD-40 — (Randy warned me about this too late) or possibly other contaminates that might burn off after some additional miles.
UPDATE:
Well, how many knew of the self-healing qualities of the NSX? Fortunately, my hunch was right. I guess that whatever was bothering the O2 sensor finally cleared or more likely burned off. I drove the car about 50 miles today and it’s back to its perfect self again. No hesitations, no stumbles… very, very smooth.
The most difficult step in the header installation for me was removal of the O2 sensors. After trying several wrenches and techniques one night, I finally squirted the with WD-40 and went to bed. The next day I called Randy who told some tricks to get the manifold off without removing the O2 sensor. Then he added that under no circumstances should I subject them to WD-40… oh sh__!
After learning that the O2 sensors are $100 ea from Hoehn, I decided to “clean” them and see if they would work. To clean them, I sprayed them a lot with some electronic component spray that I had in the garage. It *seemed* to get all of the WD-40 off i.e., they no longer looked oily. After re-installing them and wrapping up the header install, I had the above described herky-jerkys for about the first 8-10 miles that I drove the car.
The check engine light came on which allegedly put the car into some default fuel mapping program. It ran better. I drove it another 10 miles or so on the freeway to try to heat up the O2 sensors before parking it for the night. This morning, everything is fine.
[CCA] The top O2 sensor on one cylinder bank apparently was the problem. I’ve put several hundred miles on the car since it’s return and all is way more than well. It goes like a scalded cat and howls like one too.
[RKB] To reset the ECU just pull the 7.5A fuse marked “clock” in the under-hood fuse box and leave it out for 15 seconds or so. This will reset your ECU and get you out of “limp mode”, but I’d wager your check engine light will come back on after awhile.
Performance