Three tube vs. Four tube headers
 
 

The most significant advantage of tube headers (with a common collector) is their ability to lower the atmospheric pressure within the collector. This provides scavenging of the combustion chamber, which more effectively removes the exhaust gases and tends to "suck" the intake charge into the chamber during overlap. The effectiveness of the scavenging is dependent on proper matching (tuning) of the header pipe sizes to the engine RPM and application. All street Pontiacs run best with 1 5/8 or 1 ¾ inch primary tubes into a 3 inch collector. The primary tubes length should average 30 inches or longer. A race engine that never sees a load under 4500 RPM may run slightly better with larger diameter primary and secondary sizes. The "tuning" ability of 4 tube headers make them slightly more effective than 3 tube units. The 2 inch center tube simply will not "tune" in the operating range of the engine. Most three tube units have very short primary tubes, which again tune above the normal operating RPM of our Pontiacs.

How much difference in performance is there? We recently substituted a set of "Blackjack" aluminized three tube headers in place of "Hooker" four tube 1 ¾ inch primaries, 9 inch secondaries, on our 11 second ’67 Le Mans, and it lost .2 seconds and 2 MPH in the ¼. The three tube units were tried on our 12.5 second ’71 Le Mans in the place of four tube "Hookers", and it lost. 1 second and 1 MPH. Although there is a small, measurable difference in performance at the dragstrip, it is unlikely that this difference could be detected on the street. Accordingly, use the headers that fit best, are easiest to install, and are the most reasonably priced commensurate with their quality.

We have performed a similar test with the Pontiac GTO cast headers (Ram Air series) on the 12.5 second car, and they performed identically to the three tube units. The cast units are easier to install and maintain in comparison to the tube type headers, and are an excellent choice for street and street/strip applications.