Is backpressure important?

It looks like the backpressure issue is handled with whatever size pipe is used on the header. Is it important to tune the pipe for the pressure coming out? I know on the HDs this was extremely important. You could tell a significant torque difference from running with or without the muffler.
I get a good laugh out of the folks who pull the baffles out of the stock pipes just so it is louder. especially on Harley's. Hard to beat a quality exhaust system such as Vance and Hines.
 
Really struggled with how to write this answer up, the short answer is: Back Pressure is the devil, on ALL 4 stroke motors, the long answer is linked below:

exhaustbackpressure
Thank you for that explanation. So pretty much you need to pick an exhaust system that works best with the rpm range you want to spend most of your time in. This article makes sense. If you want to flow more air/rpms you would need a bigger system. More low end torque run a smaller pipe which is more efficient in the lower range. I wonder how hard it would be to run a duel exhaust with a butterfly valve for the second pipe and have the valve open gradually as engine rpms increase. I'll bet you could run it off of engine vacuum. Have it run with spring tension that the vacuum can close at idle. As the vacuum decreases with acceleration the valve would open up more. Someone has had to have done this. I mean other than Ferrari. :)
 
Yes, that is a very good approach, if you can't use other technology due to packaging constraints, or noise, or emissions.

The best way, and one we are lucky to have available is a tuned length exhaust. By having the diameter right for high rpm flow, paired with the right length before the merge collector, combined with the right diameter and length after the merge collector, you can create a best of both worlds pipe.
The length assists low rpm and the diameter supports high rpm, it literally is a science, and the few companies that make them for rocket's have nailed it, mainly Reband/CES.

When you look at their dyno ploys you'll see a kind of double hump in the shape of the torque curve. The first hump is where the head and cam flow best, right around 2500-3500RPM, the second hump at around 4500-5000 is a result of the exhaust tuning.

This is how those pipes create so much more up top without losing much on the bottom, and why, unlike so many vehicles we can simply bolt on a good 35hp with just an exhaust. The Coyote powered mustangs also see immense gains from long tube headers, for the same reasons, very restrictive stock exhaust.

Carpenters pipe is a bit of a different animal, it trades more power from the bottom for even more up top. Short primary length and larger primary diameter are how it's achieved, just a different take and different power band.

Very, very few cars or motorcycles, have enough aftermarket support to be able to pick a power band like we can by selecting the right manufacturer for where you want to make power.


HARLEY: Harley's are a world full of misconception. Those very common individual pipe exhaust, 1 per cylinder, are actually terrible for power. By not combining the exhaust they leave a large time gap between pulses, and that time is enough in some cases to allow fresh air to flow all the way back up to the valve, leading people to the conclusion that back pressure is needed to prevent that.

In reality if they would use a 2 into 1 with proper primary length, they could use larger diameter pipes for high end power with no risk to the motor, and it would make more power :)
 
I agree with you there. I had a Rinehart 2 into 1 on my 103. Rinehart got it's start making Nascar headers and know there stuff. It was a very good pipe for what it was. You got me thinking of those two brands now. I've heard Viking is pretty good too. He's been at it a while right? It's crazy we can make as much power as a turbo naturally aspirated. I love playing with all this stuff but I think I'll ride it awhile to get used to the power. It took me a week to get used to the new power when I put cams in the Harley and it left me wanting more. I found it in a stock R3. Once I'm used to it (hopefully it takes awhile) I can do the steps one at a time.
 
Yeah I think slow, deliberate increases in power is a good idea on the R3. The difference between a stock and piped bike is pretty big, and its easy to get in over your head, I imagine the step from intake/exhaust/tune to carpenter is even more drastic, and is probably super easy to write a check with the power that the chassis can't handle.
 
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