Q: Can you explain the difference between “4-1” and “Tri-Y” collectors?

A: The collector is where the primary tubes merge together. 4-1 and Tri-Y are the two main types of collector design.

The 4-1 design brings all four primary tubes into one collector at the same point.

(Image/Summit Racing)

The Tri-Y design (or 4-2-1) merges the four primary tubes into two secondary tubes. Then, the secondary tubes are merged into a single collector.

(Image/Summit Racing)

How is it measured?

The two dimensions that affect the collector are length and diameter.

  • Collector length is measured from where the primary tubes end, to the flange where it meets the rest of the exhaust system.
  • Collector diameter is the inside diameter of the collector tube.

How does collector design affect performance?

The scavenging effect created by the headers is what makes power.

Scavenging is created by maintaining the speed of exhaust flow. When the high-speed pulse of exhaust from the primary tube reaches the larger collector, it slows down.

Changing the size of the collector will affect how much the exhaust slows. The collector diameter is based on the primary tube diameter. Larger primaries require a larger collector. The collector can be tuned by changing its length.

Just like the primary tubes, the size of the collector will affect the torque curve:

  • Larger collectors will make more torque below the peak torque rpm.
  • Smaller collectors will make more torque above the peak torque rpm.

Tri-Y style headers do a good job maintaining flow velocity. Exhaust from one tube rushing past the “Y” can help scavenge air from the other tube. 

Tri-Y headers often make better low-end torque than similar 4-1 headers. If you need headers for a tow rig or engines that run mostly under 8,000 rpm, Tri-Y headers could be a good option.

Changing collectors can be difficult and time consuming. Racing vehicles with an open exhaust sometimes run collector extensions. They start long and are cut down until the power band is perfected. This should be done under controlled conditions like a dyno or measured trap speed.

Close up of engine headers
(Image/Richard Holdener)