Header Dyno Testing & Comparison, Tri Y vs. 4 Into 1 - Performance By Design

When it comes to performance there is but one steadfast rule: All the good air that goes into making horsepower must eventually find its way out. This means that the addition of everything from camshafts to intake manifolds, even superchargers to help improve airflow into the engine, will be useless (OK, maybe not useless but certainly much less effective) if the engine is not able to rid itself of its exhaust. Cork up a serious performance engine and watch it struggle and gag on its own fumes. Adding the right header can add some much needed exhaust flow as well as additional power by means of the scavenging process because a header is much more than a simple set of tubes welded together in hopes of directing exhaust flow. A true header provides not just a path for the exhaust but can also help draw spent gases out of the combustion chamber. The effectiveness of this so-called scavenging process is determined by a number of design criteria, some of which we'll examine and test.

When it comes to long-tube Honda headers-or headers in general for that matter-there are basically two primary designs: the tri-Y and the 4-into-1. As the name implies, the tri-Y refers to a group of three Y sections created by joining the primary tube of runner one with runner four and runner two with runner three. Once the four runners converge into two tubes these two eventually merge to form the final Y section to complete the tri-Y design. In the case of many tri-Y headers, like our test piece from Airmass, the final Y section merges to form a short collector. By contrast, 4-into-1 headers feature no such Y sections, instead merging its four runners into one short common collector. We've also seen short versions of the 4-into-1 design but the Airmass version features long primary runners to help enhance low-speed and midrange power production. The commonly accepted theory is that the 4-into-1 header offers more top end power, while the tri-Y header is designed to bolster midrange torque. Though there is a great deal more to the performance of a header than simply its overall design (4-into-1 versus tri-Y), our testing indicates that the basic layout makes for a strong indicator as to what to expect performance-wise-no matter what brand you might be considering.

Before we get to our test engine and comparison results we should take a closer look at additional header design criteria that might affect power output. A number of variables can be changed within both designs, most of which affects performance. With either the tri-Y or the 4-into-1, it's possible to change both primary and collector tubing diameters and with the tri-Y, add to that the secondary tubing's diameter, which can also be altered. In addition to tubing diameters, it's also possible to change the primary pipes' length, prior to their merging, to form the secondaries (or collector in the 4-into-1). The same is true of the secondary pipes' length and even the collector for that matter. Speaking of collectors, it isn't just lengths and diameters that can be tailored but also shapes. Collectors can be tapered, converging or even diverging at the exit. The exit diameter can be altered as well. By now the many great possibilities when it comes to header design should be obvious. Throw in the near infinite number of engine combinations, even within just one engine family-like the B-series, for instance-and it isn't hard to imagine how difficult (if not impossible) it is to build a header that works best for all applications. It is for this reason that many companies offer both tri-Y and 4-into-1 designs since both have their strengths and weaknesses, although a custom header designed specifically for any given engine combination (and operating rpm) will always provide the best performance.