Well as many of you know, I am considering dumping my exhaust under the bike and getting rid of my undertail exhaust. This has obviously led to some questions about how this would impact the performance of the bike.
One of the biggest issues I have come up against is the issue of backpressure, is it or is it not needed? Well thanks to various posts from Wavex over time, I have learned that I should probably investigate a little bit before I do anything to rash
Over the course of the past several months, I have fabbed up a system that I wanted to try (kept the cost under $100 so far), before actually installing it on the bike, I decided to do some research on backpressure and exhaust in general.
Talk about your 'Dark Art'! Well, I read several internet articles on the subject and not surprisingly they all managed to contradict each other. So...I got off of my butt and visited a couple of local mom and pop mechanics shops (auto and motorcycle).
The Fiction Camp:
All of the conversations pretty much provided the same information, basically that if I did not have an EGR Valve (Exhaust Gas Recirculation) then reducing the back pressure would make the engine perform better and get better gas mileage, as long as I get the engine tuned when I was done.
I asked them why there was so much missinformation about backpressure and they essentially said that the problems that people have experienced by increasing exhaust flow are often blamed on a lack of backpressure, when the real culprit is either, they did not tune the engine correctly after the modification, or they increased the size of their exhaust pipes, which reduces the exhaust gas velocity and causes positive pressure near the end of the pipes, messing up the exhaust pulses.
I asked them why some people think that backpressure increases torque, they said because it does, a little bit, but it does it in the wrong way, it makes the engine work against itself.
The Fact Camp:
I then turned to Jett Tuning in Camarillo, CA: JETT Tuning - Welcome to JETT Tuning - performance for what you ride (very close to where I live), I sent them an email with a picture of the design I was contemplating, and the questions I had about backpressure. I also visited the shop and had the pleasure of a more in-depth discussion with John Ethell the owner. John has worked with some of the best racers around. The likes of Reg Pridmore, Jason Pridmore, Fritz Kling, Gerald Rothman, Jake Zemke, Nicky Hayden, Roger Lee Hayden, Miguel DuHamel, Alex Gobert, Aaron Gobert, Josh Hayes, Andrew Short, Davi Millsaps, Kevin Windham, Ernesto Fonseca, and Jeremy McGrath.
After giving the disclaimer that, exhaust is both a science and an art and that their are probably only 2 people on the planet that truly understand it (both of whom he has worked with), John said yes, the engines need the backpressure, they also need to have the exhaust designed in such away that the exhaust pulses will keep the exhaust from pipes 1 and 4 from trying to back flow into pipes 1 and 3 and vice-versa, that he says is why the in-line 4's use a 4-2-1 system with varying lengths of pipe.
Upon further discussion of my design John said that while it was aesthetically pleasing, he would not recommend it as it would most likely cost me performance. We then discussed the possibility of an R6 shorty and agreed that I could probably get the look I wanted without sacrificing performance by going this route, naturally I would still need to dyno tune it when done.
So, given John Ethell's credentials, I am convinced thatBackpressure is Fact. What are your thoughts?
One of the biggest issues I have come up against is the issue of backpressure, is it or is it not needed? Well thanks to various posts from Wavex over time, I have learned that I should probably investigate a little bit before I do anything to rash
Over the course of the past several months, I have fabbed up a system that I wanted to try (kept the cost under $100 so far), before actually installing it on the bike, I decided to do some research on backpressure and exhaust in general.
Talk about your 'Dark Art'! Well, I read several internet articles on the subject and not surprisingly they all managed to contradict each other. So...I got off of my butt and visited a couple of local mom and pop mechanics shops (auto and motorcycle).
The Fiction Camp:
All of the conversations pretty much provided the same information, basically that if I did not have an EGR Valve (Exhaust Gas Recirculation) then reducing the back pressure would make the engine perform better and get better gas mileage, as long as I get the engine tuned when I was done.
I asked them why there was so much missinformation about backpressure and they essentially said that the problems that people have experienced by increasing exhaust flow are often blamed on a lack of backpressure, when the real culprit is either, they did not tune the engine correctly after the modification, or they increased the size of their exhaust pipes, which reduces the exhaust gas velocity and causes positive pressure near the end of the pipes, messing up the exhaust pulses.
I asked them why some people think that backpressure increases torque, they said because it does, a little bit, but it does it in the wrong way, it makes the engine work against itself.
The Fact Camp:
I then turned to Jett Tuning in Camarillo, CA: JETT Tuning - Welcome to JETT Tuning - performance for what you ride (very close to where I live
), I sent them an email with a picture of the design I was contemplating, and the questions I had about backpressure. I also visited the shop and had the pleasure of a more in-depth discussion with John Ethell the owner. John has worked with some of the best racers around. The likes of Reg Pridmore, Jason Pridmore, Fritz Kling, Gerald Rothman, Jake Zemke, Nicky Hayden, Roger Lee Hayden, Miguel DuHamel, Alex Gobert, Aaron Gobert, Josh Hayes, Andrew Short, Davi Millsaps, Kevin Windham, Ernesto Fonseca, and Jeremy McGrath.After giving the disclaimer that, exhaust is both a science and an art and that their are probably only 2 people on the planet that truly understand it (both of whom he has worked with), John said yes, the engines need the backpressure, they also need to have the exhaust designed in such away that the exhaust pulses will keep the exhaust from pipes 1 and 4 from trying to back flow into pipes 1 and 3 and vice-versa, that he says is why the in-line 4's use a 4-2-1 system with varying lengths of pipe.
Upon further discussion of my design John said that while it was aesthetically pleasing, he would not recommend it as it would most likely cost me performance. We then discussed the possibility of an R6 shorty and agreed that I could probably get the look I wanted without sacrificing performance by going this route, naturally I would still need to dyno tune it when done.
So, given John Ethell's credentials, I am convinced thatBackpressure is Fact. What are your thoughts?
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