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Old 05-25-2011, 09:05 PM
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Default 2-1-2 exhaust. Do they enhance performance?

I've been reading a lot about performance, and the general consensus seems to be that a 2-1 exhaust is better for torque than a 2-2.

Since I'm planning to stick with my stock "tommy gun" head-pipes, I'm wondering if the collector provides the same benefit, even though it then splits into two again.

I have yet to remove the cats, because I've yet to see the downside of having them (I had originally planned to remove the catalyst), but I'm also considering fabbing up a single pipe from the collector and doing away with the duals. I just don't see the purpose in splitting the exhaust after it's already entered the collector.

Thoughts?
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Old 05-26-2011, 01:47 AM
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I've read and read again the design ideals for bike exhausts systems and it still seems a lot of black magic to me. Here's a pretty good description: http://www.rbracing-rsr.com/exhausttech.htm.

From what I make of it, the 2-1 system works because you get a push/pull thing going on between the two headers connected to a single expansion area. Whether it means the two cans on the back of a 2-1-2 can be considered a single chamber and so its close to being a 2-1 I dunno.

If you figure it out then let me know .
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Old 05-26-2011, 02:24 AM
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Check with forum member 8541hog. He did some customization with the stock tommy gun exhaust.
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Old 05-26-2011, 02:44 AM
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Yeah, I saw another guy who did that by making the stock tommy gun exhaust a true 2-1 system. I tend to think that the collector would provide enough of a balance point between the cylinders' exhaust pulses, regardless of how many exits there are from the collector, but I really don't know.

I have two sets of the stock pipes, so I may try one with the cat material intact, and the other with it removed, just to see if there's a noticeable difference between the two set-ups.
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Old 05-26-2011, 08:27 AM
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Not really sure about performance difference, to me the main priority in making my pipes was sound quality. The larger the exit diameter, the lower the tone.

My pipes are actually quieter than my Big Radius I had, by about 2 dB, but yet they sound much better due to the large pipe. I think they measure a lower dB due to lower pitch.

I hate pipes that have a high pitch or sound tinny so my current setup solved that and for me give the best sound I could get with an EFI bike with such a high idle speed.

I also like the fact that I only have 1 baffle. The one I have in there now is a car exhaust baffle, not many 3" motorcycle baffles.

You could do several different types of ends on these pipes, whether it is a slash cut, turned out, turned down, or whatever to get the look you really like. I may make another set of these and make it a few inches longer, but will keep the straight end like I have.

It is a very easy build, and if you already have a set of pipes, can be done for less than $50.00 if you do your own welding.
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Old 05-26-2011, 08:49 AM
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Quote:
Originally Posted by 8541hog View Post
Not really sure about performance difference, to me the main priority in making my pipes was sound quality. The larger the exit diameter, the lower the tone.

My pipes are actually quieter than my Big Radius I had, by about 2 dB, but yet they sound much better due to the large pipe. I think they measure a lower dB due to lower pitch.

I hate pipes that have a high pitch or sound tinny so my current setup solved that and for me give the best sound I could get with an EFI bike with such a high idle speed.

I also like the fact that I only have 1 baffle. The one I have in there now is a car exhaust baffle, not many 3" motorcycle baffles.

You could do several different types of ends on these pipes, whether it is a slash cut, turned out, turned down, or whatever to get the look you really like. I may make another set of these and make it a few inches longer, but will keep the straight end like I have.

It is a very easy build, and if you already have a set of pipes, can be done for less than $50.00 if you do your own welding.
Thanks. I checked out your webpage a while back. Good stuff!

Welding isn't a problem. If I don't want to do it, I have a buddy who welds a bit better than I do. He does it for a living, where it's just an occasional hobby for me. He's always looking to make an extra buck, and he loves his work, especially anything custom.

I also recall, a while back, one of our friends from across the Atlantic posting how he made his 2-1 setup. I think he made his with a 2-1/2" pipe. I think I'd probably stick to that size, if I go this route. I already have plenty of 2.5" mufflers, and I also like the added ground clearance, as I tend to scrape the pavement occasionally with the lower pipe on my bike. Every little bit makes a difference there.
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Old 05-26-2011, 09:00 AM
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Quote:
Originally Posted by cjlandry View Post
Thanks. I checked out your webpage a while back. Good stuff!

Welding isn't a problem. If I don't want to do it, I have a buddy who welds a bit better than I do. He does it for a living, where it's just an occasional hobby for me. He's always looking to make an extra buck, and he loves his work, especially anything custom.

I also recall, a while back, one of our friends from across the Atlantic posting how he made his 2-1 setup. I think he made his with a 2-1/2" pipe. I think I'd probably stick to that size, if I go this route. I already have plenty of 2.5" mufflers, and I also like the added ground clearance, as I tend to scrape the pavement occasionally with the lower pipe on my bike. Every little bit makes a difference there.
If you can find 2-3/4" pipe that would actually fit the best on the collector. I would buy a short piece and do some test fitting, cheap at any auto parts store.
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Old 05-28-2011, 07:29 AM
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I read all of Foxster's link, and several other pages on the subject this morning, and a few of them recommended either 2-1 or 2-1-2 for the best performance. They don't differentiate between them, because the theory seems to be that the vacuum signal created by one cylinder's exhaust velocity will increase flow in the other cylinder as that exhaust valve opens.

It seems that the important thing is that the exhaust velocity is maintained, when it comes to performance. It seems that larger pipes slow exhaust velocity, within limits, of course.

I have to consider all these things, because I plan on some engine upgrades in the near future. I'm thinking some nice aftermarket heads and a torquey street cam. I ultimately want one of those flat torque curves that starts just above 2K and stays flat to about the time the HP catches up to it at 5252.

I believe the Tommy Gun head pipes will work fine for this. Now I have to decide whether to stay with 2-1-2, or go to 2-1.
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Old 05-28-2011, 08:25 AM
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My vance and hines big shots are also a 2 into 1 into 2 pipe. Both pipes connect in the flat area. So esecially these are like the tommy gun without the cat. THese are not 2 individual pipes.
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Old 05-28-2011, 01:01 PM
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a 2 into 1 is the most noticeable (feel able)bolt on mod I have ever done to my bike... I had top of the line 2 into 2 (rineharts) before, but I was amazed at the differance the moment i took off down the road with my 2 into 1... i will never go back to a 2 into 2
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Old 05-28-2011, 01:01 PM
 
 
 
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