dual exhaust pipes ? any downfall?

[Susuki_Jah]

will dual exhaust pipes cause any problems? it will reduce back pressure I am assuming and I know for some engines this may be an issue and could cause a loss of HP.

just wondering some opinions on it as far as that goes.

[Weston]

The issue is keeping exhaust velosity. Lack of backpressure isnt a problem. If your dual exhaust pipes are the same diameter as the header pipe runners I would say your good to go.

[Danny500]

I would say to maintain a balance of backpressure you'd have to run both downtubes parallel under the motor  to a little after the oil drain bolt and then put in an "X" pipe. Then continue on with the rest of the exhaust setup.

If you're going to run an under-tail or something shorter than a regular can, you may want to use something before the oil bolt right after the bend under the motor...

Basically this is INSTEAD of using the stock crossover and trying to keep everything balanced before the tail pipe.

Dan

[makenzie71]

Well the backpressure change in the backpressure will cause your backpressure bearings to backpressure and your motor will backpressure causing all kinds of backpressure in the backpressure backpressure backpressure backpressure.

Let's cover two things right quick:

First, "back pressure" is two f%$king words.

Second, if the first thing you think when it comes to exhaust modification is "back pressure" then you really need to just go out and ride/drive the way the thing sits.

Now, to the OP, there's a lot of options out there for stabbing a set of duals on the GS500 but very few that are straight bolt on deals.  Probably about the easiest thing to do is go pick you up a set of EX500 headers.  The cylinder spacing is slightly different between the two bikes, so you WILL have to cut the balance pipe and shorten it or remove it all together, and you may have to modify the flange rings to make her fit, depending on the year headers, but it does work quite well.  With a couple Sarachu (sp?) slip-ons it will sound pretty decent, too.  I've also seen people use the EX500 exhaust with the GS500's upper headers, but it doesn't look as clean.

There's very few bikes out there that offer the kind of flow per displacement that the GS500 has, so pretty much any route you go will require re-jetting your carburetors, which is a relatively mild task.

[Susuki_Jah]

 I was planning on creating a whole new system from scratch and testing a few different mock ups on a dyno over at my friends shop. The carbs were re-jetted when the vance & hines exhaust was installed and I have since then modified that with a can I made out of c17 alloy, although still haveing the same basic vance & hines design. The exhuast that is on it is fine but I wanted to swap over to a stainless exhaust considering mine rust no matter how many times I paint it. it was just an idea mainly to tinker around with.  I know with certain newer automobiles the engine has been engineered to except a certain amount of back pressure and a varience could cause certain undesirable outcomes. I will do some more reading on the engine though before I jump into it. I don't know if dual pipes is what I will end up with but my plan is to get rid of the can hanging from the side and gain some performance from it if at all possible.


I have a question that some of you may or may not know the answer to... other than a noise issue why would someone not cut the pipe at an angle and just run it the way it is under the frame? or would the only issue be noise and raspiness ?

[ohgood]

I was planning on creating a whole new system from scratch and testing a few different mock ups on a dyno over at my friends shop. The carbs were re-jetted when the vance & hines exhaust was installed and I have since then modified that with a can I made out of c17 alloy, although still haveing the same basic vance & hines design. The exhuast that is on it is fine but I wanted to swap over to a stainless exhaust considering mine rust no matter how many times I paint it. it was just an idea mainly to tinker around with.  I know with certain newer automobiles the engine has been engineered to except a certain amount of back pressure and a varience could cause certain undesirable outcomes. I will do some more reading on the engine though before I jump into it. I don't know if dual pipes is what I will end up with but my plan is to get rid of the can hanging from the side and gain some performance from it if at all possible.


I have a question that some of you may or may not know the answer to... other than a noise issue why would someone not cut the pipe at an angle and just run it the way it is under the frame? or would the only issue be noise and raspiness ?

....none of the board member have claimed to be an engineer that has positive knowledge of exhaust gas stuff....

imho - the noise would suck, and sound really poor. most likely it would hurt performance, ridability, and possibly burn valves/kill things.

as far as making your own exhaust, that's fine. you'll want to re jet the carbs, and skip the dyno. all you're going to do on a dyno with a gs is destroy an engine.

things known about gs engines:

1) they make a decent (for 500 cc's) power / torque curve up to 8,000 rpm or so, then trickle off fast.
2) valve float happens around 11,000 or so (and the power is gone anyway)
3) without modifying the head heavily, you're not going to increase the power
4) edit #3 to read "and adding a turbo, with intercooler and fuel injection"
5) a dual exhaust means you've just doubled the weight of the exhaust system. ok, one part of the system anyway.



if you really want something different, just try a re jet and an ignition advancer. heck, toss a 15t front sprocket on. you'll be happy, i promise.

the gs really is about as powerful as you want to try to make it (hellllllo reliability!) already.

good luck

[makenzie71]

blah blah blah blah blah I know with certain newer automobiles the engine has been engineered to except a certain amount of back pressure and a varience could cause certain undesirable outcomes blah blah blah

Yeah?  Name one.

I have a question that some of you may or may not know the answer to... other than a noise issue why would someone not cut the pipe at an angle and just run it the way it is under the frame? or would the only issue be noise and raspiness ?

Because it sounds like ass.  Parallel twins just don't sound good with straight pipes, but that's only an issue if you're concerned with sound.  There's pros and cons to everything.  Technically you could cut every thing off just before the bend under the front of the engine and blast the ground with your exhaust pulses...you'd lose weight and stand the potential for more power but it'd sound poor, require a complicate jetting configuration, and carburetor balance would be interesting to say the least.  Technically, if you really wanted, you could just vent the exhaust ports to atmosphere.

Like ohgood said...you're not going to make a lot of power...however, a dual exhaust doesn't need to be any heavier than the factory exhaust, and while it won't net you any kind of substantial boost in horsepower it can change the characteristics of the power delivery.

[Hawk996]

There are some opinions  about exhaust that has been infecting forums and motor head conversations since the internal combustion engine and the internet were invented.

The greatest Myth that I hear time and time again is that an engine needs "Back Pressure" to run properly, I have even herd to run at all.  Well in fact as with most myths there is a hint of truth under all the BS.  So, what is back pressure?   When most people that I hear talk about back pressure they are referring to a percentage of the exhaust gasses that are trapped in the exhaust system by the collector or the muffler. The misconception is that this old trapped gas is helping to pull the newly made exhaust gasses away from the exhaust valves and you run the potential of burning your valves with out this effect.  This is simply not true, the only time that "back pressure" is beneficial is when you are intentionally creating loads of it and this can only be accomplished with a turbo charger and this is more of a vacuum effect than back pressure.  The only truth to the back pressure myth is that most engines will not run properly and some (very few) will not run at all with the stock exhaust tampered with.  The only reason that this is semi-true is that by modifying the exhaust flow you are all so modifying the air / fuel mixture.  This is all so the reason why valves may become burnt, the mixture is to lean...   

Well then, What are the facts?  Without getting to complex and going into laws of thermal dynamics, displacement and bla bla bla more boring oh my goodness, the plain simple truth is that temperature and flow  of the exhaust pipe and headers are the biggest factors in high performance exhaust systems.  There is "FREE" energy to be had there, yes, "FREE".

Lets look at the first variable, Temperature:  The first thing that happens when the exhaust valve opens is that a sonic wave (fuel air mixture explosion) travels through your header and down the exhaust pipe at about 1600 feet per second.  Secondly the actual exhaust follows at about 300 feet per second.  As the exhaust cools this speed slows down considerably, of course the temperature of the pipe is highest closest to the head.  As the pipe cools so does the exhaust gas and this speed slows a considerable amount.  Some people go to great lengths to minimize the cooling effect and wrap the exhaust with heat tape.   If your main concern is power you want the exhaust to exit as quickly as possible, all so know as exhaust velocity.

Second variable, Flow:  This is the interesting part that led to the "Back Pressure"  misconception in the first place.  So many people come from the bigger is better camp, when in fact bigger is often bad especially that far down from the head pipe.  Why the megaphone muffler was invented, I'll never know.  To keep this simple, as hot gas travels down the head pipe it is expanding,  so if you give it more room to expand the faster it will flow out of the system right.  WRONG... Actually the larger the tube, the slower the speeds. For the expanding, hot gases a slower speed means a higher pressure and, conversely, a higher speed is a lower pressure.  BERNOULLI explained this mathematically for us a long, long, time ago.  Generally we want a lower pressure and a higher speed in the exhaust. Having a highly negative pressure in the exhaust during the overlap period when both inlet and exhaust valves are open, is the key to making power.  Design will influence this but, in regards to the primary tube size, we can simplify things a bit.  The primary tube size will go up in relation to engine size, but the size of the tube should be slightly larger than the exhaust port are.

If anyone wants a real lesson on exhaust look at F1 race cars.  These guys are making 4-6 HP per cubic inch.  If I could convert this to my wife's little GS500E: 500cc = 30.5ci X 5 hp = 152.5 horse power.  Wow, I could pull up to a brand new GSXR1000 and rip it in half.  Granted these numbers are not the result of a super phenomenal exhaust system alone, but I guarantee that pain staking detail, research and a couple million dollars were put into it.

[Susuki_Jah]

Carbs have been re-jetted and 15t front sprocket has been installed and it currently has a vance & hines design exhaust on it. and how would I destroy the engine on a dyno? I push the little engine to its limits every time I ride it. I don't see where puting it on the dyno would cause any problems. as far as reliability goes the motorcycle is something fun to ride when I get the chance, I do not use it as any main form of transportation. I don't expect any major gain if any at all, but if something could be pushed out of it while make a more pleasing to the eye exhaust system, it can only be a plus . don't get me wrong the one I have in fine now. just looking for another project on the bike.

Hawk... that was a great response and I really enjoyed reading it! I am going to look into this even more before doing anything because it is very interesting.

and as far as sound goes I really dont care lol. my 83 volvo turbo wagon sounded like a tractor but was still fun to drive with 15lbs of boost .

I know I have talked about this on here before many years ago, but as far as it goes I am just trying to learn. I am not going to slap junk on there I would actually like to learn about what works the best . So I am just taking it all in from you more knowledgable guys in this area. so thank you

[makenzie71]

^(Hawk's post)That's little different than the uneducated people claiming your valves will burn if you remove the muffler...and thinking about it way too much.

Like the turbocharger comment, for example.  There's a big reason why turbocharged race cars...and even the odd turbo busa and such...dump right after the turbine.  ANY resistance on the combustion chamber's ability to evacuate will greatly reduce the flow.  Be assured, back pressure exists, and you want absolutely none of it past the turbine for maximum potential power.  The only type of unnatural aspiration in which back pressure will play a more significant role is with superchargers, where delta wave assisted evacuation of the combustion chamber allows for even more atmosphere to be plugged into the combustion chamber the next time the intake valves open.

I also didn't think I'd ever get to say "Bernoulli's Principal doesn't apply to internal combustion engine exhaust design" again.

[Hawk996]

"Bernoulli's Principal doesn't apply to internal combustion engine exhaust design"

As a fluid passes through a pipe that narrows or widens, (collector, muffler, cat, stepped head pipe, etc. etc....) the velocity and pressure of the fluid vary. As the pipe narrows, the fluid flows more quickly.  Bernoulli's Principle tells us that as the fluid flows more quickly through the narrow sections, the pressure actually decreases rather than increases which would in effect allow exhaust gasses to escape more quickly.

How does this not apply to exhaust design and the internal combustion engine?  If I could answer this question I would be making Bill Gates money selling exhaust systems that mysteriously don't have to adhere to the laws of physics to Formula One.

[makenzie71]

Bernoulli's Principal applies to the velocity of a fluid in motion.  Where as an exhaust is a fluid in motion, it's velocity is moot except for a certain speed must be kept up in order to allow for a certain volume.  Point is, though, that volume is the import part of drawing the most power out of an exhaust system.  It doesn't matter how fast the fluid is moving, only that it's moving the greatest amounts possible between pulses.

[Hawk996]

Anyway, I really dont want to get into a pissing contest over the possibillities of quantum physics or any other topic.

In my opinion, if you want to build a custom dual exhaust system for your GS, Go for it.  Tons of motorcycles have custom exhausts and there are no ride-ability / reliability issues.   The bottom line is that if you have the time and the patience to build it and properly jet your carbs you will end up with something unique that you can be proud of.  Good luck and keep us informed of the progress and problems...

[GeeP]

I suggest a little reading from people who have actually studied the subject in-depth.

I would start with a few classic texts on the subject, such as:

Scientific Design of Exhaust and Intake Systems

The Internal Combustion Engine in Theory and Practice

If you read them, we can hold an intelligent discussion.   

BTW:  The Vance and Hines exhaust for the GS is a classic Morrison design.