Header Dyno Testing & Comparison, Tri-Y and 4 -Into-1

We needed a suitable test mule to properly conduct our testing. We built an otherwise stock B16A short-block using Probe Racing forged pistons. The block was topped off with a ported B16A head, Crane Stage 1 camshafts and a Holley 68mm throttle body.

First up was Airmass' tri-Y design. The first thing we noticed about the Airmass header was its significantly lighter weight when compared to the stock manifold. Our handy dandy shipping scale told us that we just saved 15 pounds by replacing the bulky cast-iron piece with the lighter Airmass tri-Y header. After comparing the stock manifold to the tri-Y we began to wonder how much power the header had to offer, after all, the two designs were so similar. Our fears were soon put to rest after the first pull showed power readings exceeding 200 hp. Equipped with the tri-Y the B16A produced 201 hp at 7,700 rpm and 141 lb-ft of torque at 7,200 rpm. Note that both the stock manifold and the tri-Y header produced horsepower and torque peaks at equal engine speeds, 7,700 rpm and 7,200 rpm respectively. Though camshaft timing and intake design play a major part in shaping the overall power curve, identical peak power engine speeds demonstrate, at the very least, consistency in exhaust design. The similarity in design didn't stop Airmass' tri-Y from bettering Honda's setup though, especially once engine speeds reached 6,000 rpm. From 7,500 rpm to 8,100 rpm, the Airmass one-upped Honda by a good 5 to 7 hp. It's also worth noting that nowhere in the rev range did the tri-Y lose out to the stock exhaust manifold.

Our fuel system consists of an AEM fuel rail, 30 lb/hr injectors and an Aeromotive adjustable fuel pressure regulator.

After seeing the gains offered by the tri-Y, we were anxious to see how well the 4-into-1 header would perform. Performing a header swap is no big deal, even installing a single piece 4-into-1 header is not terribly difficult. A skilled enthusiast with only two thumbs should be able to knock it out in roughly an hour. On the engine dyno, a header swap takes all of five minutes or so, which is why we chose to conduct testing on such a dyno in the first place. The 4-into-1 header was well worth the time it took to install because it posted the highest peak power figures of the afternoon. Our 4-into-1-fitted B16A produced 204 hp at 7,700 rpm and 143 lb-ft of torque at 7,200 rpm. The 4-into-1 was good for 10 hp compared to the stock exhaust manifold but this additional peak power came at a price, a slight penalty near our 5,200rpm VTEC engagement point. The 4-into-1 design was down roughly 3 to 4 hp across a 600rpm spread (between 5,300-5,900 rpm) when compared to the stock exhaust manifold but, by 6,000 rpm, things quickly turned around and, by 7,000 rpm, the 4-into-1 pulled away with a vengeance.

Frankly, the fact that the 4-into-1 got the best of the tri-Y up top didn't surprise us but how close the tri-Y followed in the 4-into-1's footsteps-even at the top end-and bettering it by 1 or 2 hp down low, as well as supplying more peak torque, did. This alone should be enough to knock the textbooks out of at least one or two bench racer's hands.

All three headers were run through this dyno exhaust system. The system consists of a 2.5-inch pipe running from the header flange to a 3-inch section of tubing and finally out to 6-inch evacuation tubes.

Equipped with the stock exhaust manifold, the B16A produced 194 hp and 139 lb-ft of torque.

After installing the tri-Y, peak power jumped to 201 hp. Since the majority of power gains occurred after 6,100 rpm, the peak torque reading was up just 2 to 141 lb-ft. Given their similar designs, it wasn't surprising then that peak power and torque values occurred at equal engine speeds when comparing the tri-Y and the stock manifold.