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Message started by wrd17 on 11/01/08 at 21:15:26

Title: No backpressure?
Post by wrd17 on 11/01/08 at 21:15:26

How does an open exhaust effect an engines performance? I have heard that an engine needs some backpressure to perform properly but I was wondering if there is anything to back this up. Does it hurt a motor to just have an open pipe (no baffle, muffler, etc...)?

Title: Re: No backpressure?
Post by Chong Kim on 11/02/08 at 00:38:12

I am running an open pipe on mine now, just the header and a nine inch exhaust extension. Sounds obnoxious and I love it. I have noticed less backfiring (though the little I have remaining is MUCH louder!) and an increase in acceleration. I'm riding at 7000 feet, so someone else's experience may be different.

We have several other bikes in our family and all but one are running open pipes. Even our old Naked Goldwing. Been doing it for years, with no problems.

My son rides a 2003 Kawasaki Z1000, and it's Power Commander is programmed for his Scorpion exhaust. That's the only one of nine that has so much as a muffler. All the rest are basically headers. Our neighbors are also bikers, so we don't bother them any more than they bother us.

Loud pipes DO get you noticed more in heavy traffic in town. In my book that's a good thing. I have noticed less propensity for them to cut me off since I went over to the Dark Side and made my bike LOUD! Always a good thing if it keeps them from changing lanes into you.

Oh, one more thing...when I do occasionally have a backfire, it sounds like a .38 Special going off! Good or bad - you decide. Like I said, I like it.

Title: Re: No backpressure?
Post by EssForty on 11/02/08 at 03:37:41

Lower backpressure would logically improve engine performance to a point, since it means that the engine is not fighting against the pressure on the outlet side.

However, I would think that a level of backpressure is important to prevent air from going the wrong way in a carbureted system, creating a true backfire situation (not an afterfire in the exhaust). Backpressure might also retain some of the spent combustion gases within the system so that nitrous oxide emissions are lower. It's a dynamic system so there are going to be give & takes.

My concerns would be the possibility of reverse air flow, excessively lean running conditions, serious backfire, increased NOx pollution, and of course the noise pollution. I'm not an exhaust systems expert, just trying to figure it out based on the physics of the situation.

Title: Re: No backpressure?
Post by Chong Kim on 11/02/08 at 07:10:19

Lean running conditions are easy to solve with a re-jet if necessary. It has not been necessary on any of our bikes except the Vulcan, judging fromthe plugs. On our VN800 we went fromstock 155s to 180s and problem was solved.

Length of the pipe is a consideration in a true backfire. That's why I have the 9 inch extension. I have been told by several qualified folks that 3 feet of pipe is safe. So far so good after tens of thousands of miles. Have a look at the custom Harleys. Most of those run unbaffled pipes that are MUCH shorter than standard.

One man's Noise Pollution is another man's safety equipment and is music to another. No noise regs in New Mexico, so we fortunately don't have to worry about breaking any laws here.

As for increased emissions, possible. But no emissions tests in Santa Fe, and I figure I pollute less than any car from the same year, even in my staright pipe configuration. So I have no guilty feelings.

For me, the increased awareness I got is worth the other tradeoffs. Not trying to convert anyone here, just relaying our experiences in our family.

Title: Re: No backpressure?
Post by wrd17 on 11/02/08 at 10:34:10

thanks to everybody for the input. i am running an open pipe that extends about 3 feet from the end of the header. its just a truck exhaust tip welded on but actually looks pretty good. just a lot of bluing. I just wanted to make sure I wouldn't be hurting the engine. i have just heard a few different things and wanted to get some input. thanks for the help.

Title: Re: No backpressure?
Post by Chong Kim on 11/02/08 at 22:22:47

3D382E7B7D4A0 wrote:

I looked at a Vance & Hines tip: about $50.

Got the one I have at Pep Boys for $6.95. Looks just as good, and my husband had fun using the SawsAll to cut away the unused portion of the original hanger. Darn that thing cuts fast!!! We hammered it on with a rubber hammer for a really tight fit, and then installed two screws and lock washers under the pipe so they don't show. Four thousand miles later and there is no leak, and they are still secure. The predecessors of our Savages (British Singles) were run without baffles, and with no problems until the government Beureaucrats got involved in designing motorcycles. Our carbs are much better than the ones those old Brit bikes had, so I very much doubt that a fire is much of a danger in case of a backfire on starting. If you're running unbaffled, I know you already appreciate the performance difference that an open filter and an open pipe can give.

When somebody complains about the noise (usually couched as a joke), I usually take the time to explain to them that it is primarily a safety issue with me. I used to be cut off in traffic AT LEAST once or twice a week. SOmetimes it was once or twice a day! Now it is once or twice a month. No matter what other people say, I am going with my personal experience on this. I don't have to kiss up to an exhaust manufacturer to get ad revenues like I see some writers do in the MC mags. For $6.95 and 15 minutes of work, I have an exhaust system that makes my bike truly sound like the 1948 Norton 500 Single that shows up here locally on Sundays, and has reliability that he can only dream of.

By the way, the chrome on the side of my tank reads "Roadqueen". My little dig at the Harleys who show up there. Those guys get a kick out of that. Or so they say...