[Alan Roehrich]

In order to gain the most from a tri-y or 4-2-1 header, the camshaft needs to be correct for the header. By the way, so does the firing order. The tri-y or 4-2-1 header allows you to do things with the camshaft that most 4 into 1 headers will not allow, due to sizing and tuning requirements.

If you have, for what ever reason, an exhaust lobe that is too small, the tri-y will improve scavenging. Of course, if your valve or port is so small that you cannot get enough cam lobe on the exhaust, the tri-y will help there, too.

For a Chevrolet V-8, the "A" firing order, 1-8-4-3-6-5-7-2, and the "C" firing order 1-8-7-2-6-5-4-3 (AKA 4/7-3/2 swap) will work on the same tri-y header. The "B" firing order, 1-8-7-3-6-5-4-2 (AKA 4/7 swap) requires a dedicated tr-y header. Some merge collectors, as well as the Flowmaster "scavenger" collectors are also firing order specific.