I never said tri Y's don't work. I recommend 4-1's. Sound better, go better. Darren DiFilippo is a manufacturer, he pushes what he makes. Street Machine are a commercial enterprise, they push whichever advertiser pays the most. As I said, there is very little difference on a dyno between tri Y's and 4-1's, just torque delivery. 4-1's will have a longer torque curve due to the way the exhaust gases collect. Tri Y's are also called "interference" design, because the gases collect sooner and the pulses interfer with each other. I'm not saying I am 100% right, exhaust design and theory is all over the place. What works on one engine may not work as well on another. The best exhaust for power is none at all. One pipe off each exhaust port, tuned to the correct length for the application will see the most power produced on a dyno. Why do top fuel and funny cars run this type? Most exhaust design on race engines, you will find are the way they are because of regulations more than optimisation. They have to run the best that they can and still be within the rules. Noise is probably the biggest deciding factor. If you Google enough, you will find supporting arguments for all theories. To have the best exhaust header design for your particular application, all sorts of things have to be taken into consideration, intake size, runner length, valve size, duration, exhaust port size and length, valve overlap, compression ratio, exact displacement. Millimeters either way in some measurements can make as much as 1-2kW difference in the final result. Does all this matter on the street? Probably not, but you will sound like a genius at the pub.