Why not a decrease?

 

On my 2016, you could slow cook a pot roast on the right passenger footboard until the cat was removed.

On my 2021, I have the 131 and the HD high-flow cats; absolutely no heat issue whatsoever, and my warranty is whole.

 

Did not retune after the mod. My service guy told me because it was the only thing I changed that the ECM would be able to adjust to it, which seemed to be the case for me (no popping, no gurggling, no pingging) none of the stuff you would normally associate with out a retune. No, I didn't consider the fan option as doing the decat was just time to me (I have cutting tools and a welder).

 

This is a myth. Engines do not require back pressure to create torque. In fact, they have backpressure limits to prevent excessive loss of torque, and overheating.

Harley doesn't have a magic combustion process different from any other hydrocarbon burning engine. My experience is with development of turbocharged diesel engines, but a number of exhaust suppliers here I've talked to have derided this myth as misinformation.

 

recall reading up on back pressure in this context, and it being a bit of a misnomer, where really the performance is about velocity, scavenging, baffle diameters..whole bunch of tech stuff I can't fully comprehend..maybe some subject matter experts can expound on it more

 

It's not a myth. Talk to Fuel moto.. With M8 they even see a HP / TQ gain by adding back pressure with certain cams..

I've seen torque go down and HP go up with baffle removal some bikes and the opposite on others.. I have examples of both..

The thing is that it really pretty much depends on everything but mostly cam, compression and exhaust design. If all you are only looking at flow you'll fail.. You have to look at exhaust tuning.

When you turbo charge, it's a whole different ball game..

 

First, FM has some issues, ok? Like an "expert" advising you should only shift above 4,000 rpm. A muffler vendor expert on here said it is bunk, as did my own pro builder. There has to be enough backpressure to not encounter reversion, but that is dependent on the diameter and length of each pipe.

Of course you have to look at the system. But increasing exhaust backpressure in general terms does NOT increase engine power output. Period.

 

I thought we were all pro builders here.. So you dis FM because he said something you disagree with? and I supposed to take your word for it?

What about over exhausting? One of the things to note is that you can build a pipe that works perfect but 90% of the time that pipe won't fit..

 

I think I'll trust the guys that are on the forefront of developing tuners, maps, performance upgrades and big bore to racing engines as the go to expert.

I've witnessed firsthand what just removing the noise reduction inserts do to backpressure and reduced low end torque.

 

I know its wrong. Not only after talking with other sponsors and builders on here, but personal experience hearing epm shifts on the road. The guy was talk ok ang about street racing, not street driving. There is an FM cult on here that believes anything they're told.
and I wouldn't call a single company a sole leader wither.
I've been in engineering 32 years. It's not true. You guys "believe" what you want to.
I'll listen to those on here talking physics and have test data.