Tri-Y

It’s November of 2021 and I’m starting up on the headers again. Yeah, it’s been ten months since I stopped working on the 180 degree headers. I managed to drop 35 pounds and lower my blood pressure. I can feel the difference. Working under the car is so much easier.

Although it’s taken 10 months to get back to the exhaust, I haven’t been ignoring the rest of the car.

I did step away from the car for about 3 months but when I finally made it back to the Mustang, I took care of a few areas that really had me annoyed; The heater blower motor and fan, the brakes and the steering. You can read about the work done and why in their respective posts.

While making progress on other areas of the build, I was searching for anyone who could build some headers for me but wouldn’t cost me more than what I bought the car for. On one search I discovered a shop that had made headers for the 1969/70 Boss 429 Mustang. The design wasn’t the typical pavement scrapers that were offered for the Boss 9. These were similar to my design where the two front primaries on each side hugged the engine but instead of a 4 into 1 design, these were Tri-Y headers.

I scrutinized the pictures of the design and decided that these headers could probably be modified to work on the Cammer. Without going into detail, I emailed the shop and hit a dead end. I couldn’t get a set of the Boss 9 Tri-Y’s but taking what I learned from my previous attempts, I believe I can make my own Tri-Y’s.

The bottleneck that occurred when I tried to feed four 2-inch pipes through the restrictive areas through the car should be minimized by the use of two 2 1/2” pipes.

One major difference on the left header is how the primaries are grouped. Instead of cylinder 5 and 6 being joined by a Y and 7 and 8 combining to make the other Y, Cylinders 5 and 7 are joined while 6 and 8 are paired. It’s that pulses thing again. The right side is more conventional with a 1/2, 3/4 pairing.

Work in progress

To be honest, at this stage in the build, I’m pretty tired of working on this car. I haven’t lost interest, I’m just tired. If I could have gotten away with a set of log style exhaust manifolds, I would have gone with those.

I blew myself up by retaining the shock towers. Without the towers, it would have been so much easier to build proper headers and maybe come up with a design that could accommodate all of the go-fast theories like equal length primaries and smooth bends. If there is supposed to be a particular rule to follow in designing a Tri-Y, I missed that class. My whole aim now is to get the exhaust out of the engine and to the back of the car as best as I can. I have no idea how long the primaries are supposed to be. I can tell you they are not equal length. The secondaries are all over the place and different lengths to each other. I decided on 2-inch primaries that feed into 2 1/2-inch secondaries and a final 3-inch collector loosely based on other designs.

This is an engine that was designed to rev out to 8,000 rpm. Will I ever take it that high? My cams don’t go near that high. I’m not racing this thing so if I leave some horsepower on the table, that’s fine. If I get serious about building some real horsepower, the first things to go away will be the shock towers and then I can concentrate on designing a good set of performance headers.

As of this writing, I have one header nearly completely welded to its flange. After that, it’s just a matter of fitting and welding the collector.

I’ll go into a little more detail of what it took to build the headers, maybe dig up a few camera shots in the next post.