I think the key to merged collectors working well or not is the pipe timing in relation to the firing order and the placing of the pipes from each other based on the firing order. What little I remember about the theory is you do not want two pipes blowing into each other that are 90 degrees crankshaft firing order away from each, you shold have them side by side so the pulse from the first one helps suck the other out the collector, not blow against each other Maybe not I'll try and ask my Son tomorrow about what they did and the rules they followed when he made them for Rob Muzzy racing.