Here’s some data from my brother’s bike, which aftermarket pipe would you suggest and what gains would he see? FWIW he has since blocked off the left side and says it feels a little better but hasn’t taken it back to the tuner.

 

Stepped head pipes would be better. Short of that I couldn't say either way where decatted stock pipes rate. Where and how they bend is a factor.
Blocking one side and still using the crossover? I don't see how that could be an improvement. It might make the low end feel better by causing more of a restriction. Just my opinion.

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your dyno graph is not a valid data point,,,it is comparing 2 different bikes with LARGE amounts of perfromance enhancements.
it not a back to back run with just a differetn pipe and tune, that is the type of run you need to look at in order to make the assesment about the pipe, back to back on the same bike with only the once change and properly tuned up for it.
all that said, the graph with the engine work for your bros bike looks about where it should for the list on the sheet....I woud rather see engine RPM and AFR graphs, helps to make better choices having the data.
m

 

Checkout ThoseDynoGuys(Matt Smith), he has dyno graphs on his social media as well as a few video’s claiming the stock head pipe on the M8 de-catted is among the best. He’s mentioned it more then once. And a very reputable tuner in the industry. Now this is more then likely assuming 2-1-2 systems, he has commented before on the Khrome Werks conversion kit I mentioned at the beginning as well but since it’s not available anymore it’s not worth trying to find a graph. My original post was about people that might have mimicked this kit on a stock head pipe, but rather then just plugging off the crossover stub actually removing and welding it to prevent turbulence.

 

i kind of think that its wrong to think that someone is well known in the industry, i've beeen a professional tuner for 20 years and never heard of him. that doesn't mean much and I am by no means trying to talk bad about the guy as I dont know him or his work.
what i DO know is that from my experience gutting the cats out of headpipes usually does NOT work as well as WELL DESIGNED 2-1 header system...As Gunner mentions, stepped head pipes and lots of other design features go into a quality pipe. The Stock pipe was designed to flow with the cat in place, if you change the design it ususally doesn't improve things with factory headpipes.....Back in the days (TC88, pre cat converter) we coud still get over 100hp out of the old style factory touring model head pipes and good slip on mufflers, if the engine design was good. The factory head pipes in those days worked very well. things changed when the factory went to the under the frame designs. That has been my experience on my dyno.. One thing to remember is the HD spends MILLIONS in R&D work, and the better exhaust companies spend a lot as well....there are lots of flow characteristics and design features that make up a good pipe.
m

 

Yes I supposed it’s fair to say opinions on business’s and known names in any industry is subjective, and be clear I’m not advertising them nor do I speak on their behalf’s with anything I say on these forums. Just referencing. The only reason I mentioned his business being “known” at-least from my perspective is Wes Brown/Cyclerama. This may sound contradictory but I would argue that his products and business are pretty well known in the tuning/performance world for HD’s. And TDG(Matt Smith) and Cyclerama in the past couple years have mentioned each other a lot on social media and other platforms, so it’s likely that if you paid attention to one recently you’d come across the other I suppose.

Back to exhaust, I agree, R&D on any product is huge, and yes any WELL DESIGNED 2-1 exhaust system(especially with the M8) is going to work better then a 2-1-2 system with a decatted stock head. To compare that to say a HPI 2-1 system is not apples to apples. BUT for the average street build or rider that’s wants a typical cam, exhaust and tune setup… that 2-1-2 system or even a trial 2-1 or more financially attainable 2-1 system could be more then adequate.

 

I'd have to disagree on a 2in1 necessarily being better in this case. There are several 212 systems that work extremely well, maybe better than any 2in1, when it comes to M8s. More so than twin cams it seems.
Some of the nicest BB builds putting up the best numbers anyway have been with 212s. Especially Khromewerks full 212 systems. Or FM X pipe with Khromewerks cans. I've seen 128s doing north of 150/150.
Its no secret I don't care for 2in1s but this is honestly what I've seen and I'm not trying to discourage you from trying but I think you will be disappointed. At the very least I think it will take some trial and error to get this to really perform. I think you'd be further ahead with the stock decatted head pipes and a good set of cans. Just my opinion.
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Sometimes the decatted head pipe works ok