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Patriot Guard Rider
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(From the Vulcan Verses)

http://www.vn750.com/forum/verses.php

It is the catalytic converter (pre-muffler) that connects the two exhaust pipes under the the frame just in front of the rear tire.

The goat's belly is that ugly chamber thing right in the middle on the bottom of the bike that connects the two sides of the exhaust together. It looks like a goat's belly. Just above the GB, and under the battery case, is the R/R. Because of its location, we believe that the heat from the GB combined with the lack of air flow (since it is pretty much "enclosed") causes the R/R to get too warm, which can cause it to fail, which can cause your stator to blow, which is a very expensive fix. Therefore, the second thing we recommend you do (after getting the sealed battery), is to lose the GB and/or relocate the R/R out in the open air. Scootworks has a kit for bypassing the GB, or you can get aftermarket pipes from Vance & Hines or Cobra or Jardine which also eliminate the GB.
 

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It is NOT a catalytic converter, and removing it is a BAD idea. It is an essential part of the exhaust system. Removing it will reduce engine power, adversely affect carburetion, and make a horrible noise. A v-twin needs a crossover in the exhaust to help equalize backpressure. The "goats belly" is a "tuned" crossover, designed to get max power out of the stock system.

Modifying any part of the stock exhaust system will change backpressure of the exhaust beyond the operational range of the carbs. No matter how you rejet, the mixture will be right only between a very narrow part of the engines operational rpm. (from idle to redline). It will either be too rich or too lean everywhere else.

If you want a loud noise, you can safely get one with an aftermarket exhaust system and rejetting, but you will lose some power. Most likely not enough to notice. An aftermarket exhaust has less backpressure than stock, but unlike a butchered stock system, it remains fairly constant over the engines entire usable rpm range. No exhaust system known will beat the stock system for power however.
 

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and removing it is a BAD idea. It is an essential part of the exhaust system. Removing it will reduce engine power, adversely affect carburetion, and make a horrible noise. A v-twin needs a crossover in the exhaust to help equalize backpressure
True only in part. If you use muffs after a degoat with more backpressure than stock, no need to re-jet, etc.
I degoated, mounted stock Sportster muffs, and use very near stock carb settings (earshave as well) w/o changing jets. More power than stock, smoother response.
And V-twins DO NOT need a crossover. Dunno where you got that from. The only thing required for equal backpressure are 2 pipes of equal lengths from the cyl head, with equal ends or muffs. Ask any custom builder.
 

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V-twins DO need a crossover, even Harley uses one. Aftermarket systems don't usually have them, but some very precise engineering went into them, and they still cause a power loss. Why do you think a set of aftermarket pipes are so expensive? They are not plumbing pipes. Most likely more than half the cost of an aftermarket exhaust system is in research and development. You must have some backpressure, or else carbs will not be tunable. Many engines have met an early death because someone put short open pipes on them.

There is a way around that problem. It's called fuel injection, and it can be mapped to change the air/fuel mixture up and down over the entire usable rpm range. Many Harley riders who actually understood how an engine works welcomed it, because it allowed them to use short open pipes without frying their engines. But you can't do that with carbs. They have a very narrow tuning range, so you need consistant back pressure.

Removing the goats belly will cause your back pressure to be all over the place, and with carbs, you air/fuel mixture will be too. Carbs are adjusted for a certain backpressure, and they don not automatically compensate for changes.
 

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V-twins DO need a crossover, even Harley uses one.
Wrong again. Harley only began experimenting with a crossover after 1984. Before that Sports had none and the big twins generally ran a 2 into 1 (I had 4 Harleys, so I "think" I know"). Even most of the 2011 models DO NOT have a crossover, only a few select models do. Also, around '86 or so, Harley began playing with matching pipe lengths to balance by adding a forward loop to the rear pipe.

Most likely more than half the cost of an aftermarket exhaust system is in research and development.
Most likely, the cost goes into the CEO's pockets. There was a guy named Ted from Ted's Cycle Shed in Newburgh (google him, he's famous) thats been building systems since the 60's at 2/3 the cost or less of the "fancy brands". His pipes are much sought after, and although retired now, his designs live on. Im sure in his early days was much trial and error (R and D, lol), but actually, pipe in bulk is cheap, and he had his own warehouse full.

And I dont see where anyone mentioned running straight pipes w/o extensions :confused:. I fully agree that backpressure is necessary, the amount is a varying factor to suit the situation (carb, compression, intake, etc).
Ballancing the 2 pipes is mostly important for performance, but can also be achieved in different ways.
1)Both pipes of equal length and diameter.
2)Varrying lengths with ballancing achieved through a varried diameter.
3)2 into 1 "almost works as well as a crossover.
4)Modifying one baffle over the other, or even making an adjustible baffle on one will do it as well. I did the first on mine so that I could keep the ends at an equal length.

Crossover mods and goats bellies (etc) ie attempts at ballancing were more an effort to combat the low grades of gas that started in the 80's, to reduce ping, and satisfy the EPA bs.
What used to be Sunoco high test (98 octane, with 102 avail), has now become 91 octane with all kinds of junk mixed in. Luckily, companies like Harley arent taking the "easy" way out by just adding a crossover. They balance their OEM exhausts properly. Thats one of the reasons that many stock Harley muffs have either front/rear stamped on them, or left/right.
 

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Harleys no longer need crossovers because they now have fuel injection, which can be mapped to compensate for changes in backpressure. Just for the record, I also own a Harley, a '97 Road King with a carbed EVO. It has a nightmare of an exhaust on it. It starts out normal enough, with the typical Harley 2 into one used on FLH series bikes, then splits up again into two pipes, just so it has the appearance from the rear that it has a dual exhaust. But both header pipes do connect together.

And yes, you can design an exhaust system without a crossover. The V&H cruisers have no crossover. But they are not just straight pipes either. They have used all kinds of tricks in there to keep the backpressure consistant. It is lower overall than a stock system, but it does not change much with engine speed, so carbs can be tuned to match it.

Doing things to the carefully designed stock system, such as removing the goats belly, or punching out the baffles destroys the consistency of the back pressure over the engines rpm range. Carbs simply cannot properly compensate for that. While I am not a fan of fuel injection and it's complex, expensive, and failure prone electronics, when it works like it should, it WILL compensate for drastic changes in backpressure.

Unfortunately, Harley has mapped their fuel injection all wrong, causing the engines to run lean across the board. That's why they overheat. Remapping the FI will fix that. And if you have the right exhaust system, rejetting a carb will fix it too.

But the point is, you can't simply bolt on some open pipes, or cut up the stock system, and expect it to work. Designing an exhaust system is a job for engineer.

I just converted a V6 pickup from a single exhaust with a crossover and a catalytic converter, to headers on the engine, and 2 straight pipes out the back, with no mufflers. but it was not quite that simple. I had to make sure the pipes were the same length, and since I was using 2 1/2" pipes on a 4.3 liter engine, I has to put restrictors in the pipes to get back some of the back pressure I lost by using larger pipes, and eliminating the cat con and muffler. I required information from an engineer to design this system, I didn't just start bolting pipes together. I would have never gotten the backpressure right on my own. And a twin is a lot more sensitive to backpressure than a six cylinder.
 

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I also own a Harley, a '97 Road King with a carbed EVO
Thats a sweet ride ! Except that I dont like EVOs much. All my Harleys were '72 and older. Dont know much about AMF and after (dont care either).

And, believe as you will, Im not going to debate it anymore, but Ive built both bike exhasts and car (musclecar) exhausts since the late 70's. Sure, a lil trial and error at times, but we didnt have the luxury of hiring engineers or purchasing "name brand" bike systems. Our shovels, pans and knucks all ran like tops, and our cars always ran great times at the dragstrip. And we fabbed em all in our garages. Maybe higher compressions and higher octanes helped that. (What are "emissions controls" ?)...

But...question for you since you seem to know so much about backpressure (serious question)...its easy not to have enough, but how do you know when its "too much" backpressure (by engine performance) ?...example : when I mounted the baffled Sportster muffs on my 700, I felt with my hand that one side was pushing a lil more exhaust that the other...so, I drilled a 3/8" hole in the baffle plate in the one which was lacking (seemed to be running slightly rich as well). Now its fine, and was out for a few hours today.
 

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Too much back pressure with a carbed engine will result in a loss of power, a rich mixture, and engine overheating.
 

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Thanks....thats what I thought and why I released some backpressure. Only had one "too much" backpressure prob before (1975 ?), and that was when a neighborhood punk jammed a potato in my Chevy's single exhaust. Was a '65 6 cyl Impala...wish I still had it !
 

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Oh, kinda like the banana in the tailpipe thing from the original Beverly Hills Cop.
 

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Thank you for this discussion. You've helped more than one newb.
I haven't even looked at the underside of the exhaust yet. The bake came with shorter mufflers installed, as well as the stock ones should I decide to switch back. I'll admit that the ones on it sound pretty good.
It sounds like if the goat still exists, then I'll relocate the R/R only. If the goat is gone, I'll just carry on with it as is.
 
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