Project Acura NSX Fujitsubo Exhaust - More With Less

Burns Stainless took our DC Sports headers and cut off the original collectors to be replaced with their merge collectors. The small expansion cone after the merge is also critical in increasing exhaust scavenging. Each collector is custom-built and designed for a specific engine's parameters to optimize flow.

Burns Stainless took our DC Sports headers and cut off the original collectors to be repla

The idea behind a proper merge collector is to not only smoothly merge the exhaust pulses from each cylinder, but also to take advantage of these exhaust pulses to help the engine breathe better through exhaust scavenging. Long story short, the merge collector can increase the amount of fresh air sucked into the combustion chamber by reflecting a negative pressure exhaust pulse back from the collector to the exhaust port. The negative pressure wave is essentially a vacuum that helps suck fresh air into the combustion chamber during valve overlap. There are two critical parts to building a header so that the reflected wave hits the exhaust valve right when both intake and exhaust valves are slightly open: the length of each primary and the dimensions of the collector. Since every engine is different, primary length and the merge collector dimensions have to be designed based on the engine (and user’s) target rpm, valve dimensions and cam specs. Burns Stainless does this using their 30 years of experience and their proprietary X-Design software that models an engine based on the exact specs that you send them. So if you just bought some random merge collector to put onto your car, chances are it won’t work as well.

In our case, the DC headers already come with fairly equal-length primaries, ranging between 30–33 inches each. According to the team at Burns, this is pretty much on the dot for a Honda engine that’s running on the big VTEC cam lobe. This means that we didn’t have to adjust the primary lengths and could just cut off the original DC collector and replace it with a Burns custom fabricated merge collector. In addition to the smooth merge, the Burns collector has one additional trait. It pinches the merge diameter down first before expanding the pipe diameter again. It’s counter-intuitive, but this pinch and its precise dimensions are actually what helps reflect the exhaust wave to increase scavenging.

At Burns’ suggestion, we did just a bit of fine fuel tuning with an old A’PEXi S-AFC to make sure the new headers were optimized. We only ended up taking out a few percent of fuel above 7000 rpm.

With just the intake, exhaust, original headers and high-flow cats, we took the NSX from its 249-whp baseline (already with headers) to 255 hp. We retested the car with the new collectors and tuning and saw only a 1hp peak gain. We expected this since we asked them to optimize the collector for more midrange torque which is what we got. In the case of a high-revving NA motor, midrange torque will actually help the car get out of corners faster than just a few more horses at redline. From 3000 rpm up, the torque gain is maintained all the way through redline. At its best, we almost picked up 10 ft-lbs of torque.

By Jay Chen

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