I can get stock exhausts from other bikes pretty cheaply thanks to a somewhat local motorcycle salvage yard. Im thinking of doing this as an alternative to buying a several hundred dollar yoshi or V&H, but I have some questions first.

As far as performance/power is convcerned, all that performance exhausts do is allow air to flow faster and more freely due to larger pipes or a less restrictive muffler correct?

A 1000cc bike's exhaust would allow for more airflow than a 500cc bike's exhaust right? Since it's trying to pump out twice as much air (assuming both are fourstrokes, with some give and take for tuning, power vs tame design/tuning etc)

If I'm wrong on any of this or missing anything then please explain. A search on the finer details of how exactly this all works did not yeild great results so anyone with any insight please share.

Er...confusing.
Do you mean muffler rather than exhaust ( ie the whole, head/headers/tail and collector/ and muffler.)
Once the exhaust gases have expanded as far as the muffler, they no longer need an outlet as big as the inside diameter of the individual exhaust headers.  So same size will cause no restriction. Please don't go on about "back pressure" myth.
With the headers and tail, what matters if the RIGHT size not just bigger. A rule of thumb is the header needs to be about 15% bigger crossectional area than area directly behind the exhaust valve/s . It isn't that straight forward for peak HP/torque, but it will do.

Way back in 03 or 04 there was a ZX10 whose exhaust can I modded for someone.
That can along with the connector pipe looked like it would fit a 89-00 GS header. I never tried to fit it though, so take it for what its worth.
That can had a scroll in the tail pipe which was a catalytic converter, I had to punch through it and twist it out till it had a nice pass through hole and when we were happy with its sound and performance we had to sort of stuff a sleeve to keep it from fluttering.
Anyway looked like a good option, best option was that it was a Titanium can and a titanium mid pipe. Looked cool as the dickens and light as a feather.

Cool.
Buddha,

Quote from: gregjet on February 21, 2018, 07:24:17 PM
Er...confusing.
Do you mean muffler rather than exhaust ( ie the whole, head/headers/tail and collector/ and muffler.)
...

With the headers and tail, what matters if the RIGHT size not just bigger.

Yes probably just the muffler. So what exactly makes aftermarket exhausts give more hp or torque?

If by "aftermarket exhaust" you mean "muffler" (aka "slip on" etc.), then the only thing that makes them give "more horsepower or torque" is marketing spin.

That said my "butt dyno" tells me that my own GS500 with the big/cut-down Yoshi muffler wants to rev more >9K without the baffle in the muffler than it does with the baffle, but to rev >9K is past the HP peak and doesn't actually add power. Sound and psychology, not real measurable differences.

Quote from: MotoSig on February 22, 2018, 10:07:59 AM
...
So what exactly makes aftermarket exhausts give more hp or torque?

By themselves, nothing. A good aftermarket exhaust (and I mean a full exhaust system, not just a new muffler) is less restrictive with regards to the flow of exhaust gasses. This alone doesn't really give any benefit to the power the engine produces, and can actually cause problems like burnt exhaust valves if nothing else is done to the vehicle. Where the performance gains are found is when the vehicle's fueling is adjusted to better take advantage of the less restrictive exhaust. With an exhaust capable of flowing more exhaust gas out of the combustion chamber, you can increase the amount of fuel and air being burnt at any given time, which is where your increased power comes from.

Quote from: MotoSig on February 21, 2018, 06:05:58 PM
As far as performance/power is convcerned, all that performance exhausts do is allow air to flow faster and more freely due to larger pipes or a less restrictive muffler correct?

Incorrect.

I'm not the most knowledgeable about exhaust theory but essentially the big name of the game is exhaust velocity.  If you hook a drain pipe to the head you're basically letting the engine handle waste management 100% and it's physically incapable of doing so.  The exhaust gas gets pushed out of the engine by the piston but since "top dead center" isn't flush with the the head there is always a pocket where gases can remain.  So, it doesn't all make it out, and based on engine timing it can possibly get sucked back in as the piston begins it's intake stroke while the exhaust valve is closing.  Exhaust remaining in the cylinder during intake stroke means less fuel and clean air can be drawn in, which in turn means less engine power and less engine efficiency.

A properly sized exhaust (not just diameter but also length) allows for good exhaust velocity where with the piston's push the gas will want to evacuate the system, and often can create a vacuum that will pull any remaining exhaust gas out of the cylinder that the piston could not force out.  That's what the little connecting pipe is in the front of the GS header, the pulse from one side creates a vacuum in the other which helps the exhaust system "scavenge".

That's why aftermarket exhaust systems can be so expensive, a lot of time, effort, and engineering goes into making them specific to each bike.



Now if you're talking about mufflers specifically(or silencers depending on what world you live in), often, but not in all cases, those are "universal" and just need X or Y "mid-pipe" to be adapted onto any other header.  But there are still many things to consider.  A muffler for a GSXR1000 is going to be way larger than what you'll need for a GS500, just as a muffler from a Ninja250 will be way too small.  It's better to go too big than too small, but it's all just going to be added weight and bulk you don't need.
If you're feeling cheap and just want to pick a muffler off some random other bike, get as close to cc as you can.

Hey qcbaker, I'm not sure that's entirely true.

The size of the exhaust primaries, diameter and length, affect the acoustics of the pipe more than anything, due to gas expansion and exhaust temperature (caused by velocity) it changes the resonant frequency and will likely screw up scavenging, which probably results in lower engine vacuum, which is why you have to put a bigger jet to keep the bike from running lean, there's less vacuum and lower velocity of airflow. It's not because you need more fuel because it flows "better". It doesn't flow "better", it flows slower, and scavenges less, or scavenges at a lower rpm, or both.

The net result is that on a bike that's restricted by the head/valves, bigger exhaust primaries will result in reduced torque, if there was any exhaust tuning in the design to begin with.

EDIT: Watcher is correct, the scavenging is a result of acoustics. There's a pressure wave and a low pressure tail behind the pressure wave, you want to get that low pressure tail to align with the time when the valves overlap, which will only happen at a very narrow range of rpms. The crossover pipe actually just adds a node to tune the acoustics, like taking your finger off of a hole in a recorder, makes the resonant frequency much higher.

Thanks mr 72, You saved me the trouble.
BTW a source of cheap(ish), light weight and well made muffler/silencers is TYGA in Thailand ( they actually are making some exhausts for Moto3 and Moto2 now I was lead to believe.) I have been useing them for years for my race bikes. NOTE THEY HAVE NOT CAT CONVERTERS ( you cats will stay the same).
The valves on the GS500 aint gonna restrict much, nor will the cams. Old style big valves , ports and cam timing. You could make is punchier, but not a lot of point on a road air coooled motor.
The whole point with the GS500 is because it is a 180deg crank  and big cam overlap, making a proper 2 into one exhaust si somewhat problematic. A nice flowing not over loud muffler/silencer with an outlet ID of 28-32mm will do the job perfectly well with a muffler with a reasonable  effective volume. Smaller and it will be a bit restrictive and bigger makes no difference. Forget back pressure myths. You will probably have to rejet though as they are a bit lean to start with. If you are going to rejet get an aftermarket air filter from a GS1400 Suzi . Fits straight in and much bigger flow with more filtering.

Quote from: qcbakerWhere the performance gains are found is when the vehicle's fueling is adjusted to better take advantage of the less restrictive exhaust.

I got that I'll need to rejet/tune. I'm just trying to get my exhaust option sorted out and an K&N airfilter in before I do so I only have to rejet once.

Quote from: gregjetWith the headers and tail, what matters if the RIGHT size not just bigger.

So then what do aftermarket full exhaust systems do? Just get closer to the "right" size than the suzuki engineers did? (and also reduce weight?)

Quote from: qcbakerA good aftermarket exhaust (and I mean a full exhaust system, not just a new muffler) is less restrictive with regards to the flow of exhaust gasses.

So wouldnt you want a muffler that also was less restrictive? Or does it not matter at that point as I think gregjet was saying? Even if it wasn't a 1000cc (that was just for an example) Is there anyway using a larger (550, 600, whichever) muffler would add any benefit after being properly rejetted?

I dont care about the sound, I'm just looking for power increases. As I understood it the name of the game was, in simplicity, to get more air in, more air out, and then a proper fuel/air mix to match. That's what I'm trying to do without dropping 400$ on an exhaust for a bike I bought for 1500$ (and then proceeded to scrape more value off of with some low-grit asphalt ).

Quote from: gregjetIf you are going to rejet get an aftermarket air filter from a GS1400 Suzi . Fits straight in and much bigger flow with more filtering.

Huh, haven't heard of doing that. So will the increased air from better flowing air filter change the scavenging dynamics that Watcher was talking about? Or will a properly sized exhaust properly scavenge the exhaust gasses regardless of how much air you're putting in with different air filters? (again, rejetting being a given).

Quote from: gregjetBTW a source of cheap(ish), light weight and well made muffler/silencers is TYGA in Thailand

Thanks, I'll check them out. 

In my opinion the main thing you can achieve with aftermerket exhaust system is weight saving. Increase power to weight equals faster acc. and better handling.

The physically bigger filter of the GS1400 will restrict the air flow less. ALL filters will restrict airflow. Some less than others.  It is in one of the performance FAQs on this forum somewhere. That's where I got the idea. Bought an aftermarket hi flow cleanable GS1400  filter and dropped it straight in. The airbox itslef isn't that restrictive , though resonances may change it's performance.

Quote from: mr72 on February 22, 2018, 11:24:34 AM
Hey qcbaker, I'm not sure that's entirely true.

The size of the exhaust primaries, diameter and length, affect the acoustics of the pipe more than anything, due to gas expansion and exhaust temperature (caused by velocity) it changes the resonant frequency and will likely screw up scavenging, which probably results in lower engine vacuum, which is why you have to put a bigger jet to keep the bike from running lean, there's less vacuum and lower velocity of airflow. It's not because you need more fuel because it flows "better". It doesn't flow "better", it flows slower, and scavenges less, or scavenges at a lower rpm, or both.

The net result is that on a bike that's restricted by the head/valves, bigger exhaust primaries will result in reduced torque, if there was any exhaust tuning in the design to begin with.

EDIT: Watcher is correct, the scavenging is a result of acoustics. There's a pressure wave and a low pressure tail behind the pressure wave, you want to get that low pressure tail to align with the time when the valves overlap, which will only happen at a very narrow range of rpms. The crossover pipe actually just adds a node to tune the acoustics, like taking your finger off of a hole in a recorder, makes the resonant frequency much higher.

Yes, you're right in that I failed to mention wave tuning or scavenging which are also important to performance, and Watcher is indeed correct about how the crosspipes function with regard to that.

But I think you're getting a bit hung on semantics here. When I say it "flows better", I simply mean that a performance exhaust is capable of evacuating greater overall volume of exhaust gases from the cylinders per unit time. If you have the same volume of gas per unit time flowing through a larger diameter pipe, yes the velocity is reduced, resulting in a lower flow rate. But if you add more fuel and air to any given combustion cycle (increasing power), a larger volume of exhaust gases is produced, and a performance exhaust is better able to evacuate those gases from the combustion chamber (better flow in that the overall flow rate is increased). Larger diameter piping is obviously not the only reason a performance exhaust is better able to evacuate those gases and increase the flow rate, and I should have mentioned that, I just didn't think it was necessary to go into the minutia of it. Because at the end of the day, no matter the mechanisms for it, the reason that a performance exhaust allows for engine performance increases is because the overall flow rate of gases going through the pipes is able to be increased.

Quote from: MotoSig on February 22, 2018, 05:13:50 PM
So then what do aftermarket full exhaust systems do? Just get closer to the "right" size than the suzuki engineers did? (and also reduce weight?)

Yes, but it isn't really limited to that. The Suzuki engineers had to strike a balance between fuel efficiency, emissions, cost of manufacturing, and performance. As I said in my reply to mr72, and as Watcher explained, the size of the pipes isn't the only thing that contributes to the gains that can be made with a performance exhaust system.

Quote
So wouldnt you want a muffler that also was less restrictive? Or does it not matter at that point as I think gregjet was saying? Even if it wasn't a 1000cc (that was just for an example) Is there anyway using a larger (550, 600, whichever) muffler would add any benefit after being properly rejetted?

A muffler on its own wont really increase the overall abilities of the exhaust system as much as people think. A less restrictive muffler is indeed "better" but without headers and everything else to match, it can't really do much.

But an exhaust system designed for a larger engine is most likely going to be too large. The GS500's engine wont be able to produce a high enough volume of exhaust gases, no matter the tuning, to be able to fully take advantage of an exhaust designed for a larger bike, and could possibly end up being harmful.

Quote
I dont care about the sound, I'm just looking for power increases. As I understood it the name of the game was, in simplicity, to get more air in, more air out, and then a proper fuel/air mix to match. That's what I'm trying to do without dropping 400$ on an exhaust for a bike I bought for 1500$ (and then proceeded to scrape more value off of with some low-grit asphalt ).

On a basic level yes, but a muffler alone isn't really going to do much for you. If you're after performance increases, you should go with a full exhaust system. However, it is going to be much more expensive, unfortunately.

Quote
Huh, haven't heard of doing that. So will the increased air from better flowing air filter change the scavenging dynamics that Watcher was talking about? Or will a properly sized exhaust properly scavenge the exhaust gasses regardless of how much air you're putting in with different air filters? (again, rejetting being a given).

The air filter shouldn't have any effect on the exhaust, directly. The air filter just allows more air to be pulled into the combustion chamber, which means that you can add more fuel, etc., etc.. All the parts need to work together.

Quote from: qcbaker on February 23, 2018, 07:24:19 AM
Yes, you're right in that I failed to mention wave tuning or scavenging which are also important to performance, and Watcher is indeed correct about how the crosspipes function with regard to that.

it happens to be the only thing that matters in this case, though.

Quote
But I think you're getting a bit hung on semantics here. When I say it "flows better", I simply mean that a performance exhaust is capable of evacuating greater overall volume of exhaust gases from the cylinders per unit time....

Well that's a confusion of cause and effect. Because the pipe diameter is larger, the exhaust gases flow more slowly and at a lower pressure. Putting bigger exhaust doesn't CAUSE a higher volume of exhaust to flow, or even enable it. The rate of flow is critical, and it is not true that the ideal is the lowest possible rate of flow (bigger pipes). The acoustical tuning to produce scavenging is way, way more important than flow rate.

Quote
Yes, but it isn't really limited to that. The Suzuki engineers had to strike a balance between fuel efficiency, emissions, cost of manufacturing, and performance. As I said in my reply to mr72, and as Watcher explained, the size of the pipes isn't the only thing that contributes to the gains that can be made with a performance exhaust system.

Increasing the size of the primaries will likely reduce the performance of the GS500, at least where it matters. Bigger pipes can only be beneficial if you can add more volume of exhaust. To do that means a different cylinder head or much higher rpms.

Quote
A less restrictive muffler is indeed "better" but without headers and everything else to match, it can't really do much.

It won't do anything, fortunately, because with bigger headers you will just lose torque.

The big advantage to an aftermarket exhaust system (head to tail) is that you can get better materials (stainless), and as gregjet pointed out, weight. But these aftermarket systems are generally going to be tuned very similarly if not identically to the Suzuki factory parts.

QuoteThe GS500's engine wont be able to produce a high enough volume of exhaust gases, no matter the tuning, to be able to fully take advantage of an exhaust designed for a larger bike, and could possibly end up being harmful.

It will definitely end up being harmful. But it'll be louder and you will think it's faster. Or more fun, or whatever. That's the big reason to change. The truth is, unless you are racing, a GS500 is plenty fast bone stock. I mean, when do you really need to accelerate from 0-60 in under 4.5 seconds? Or when do you really need to go >100 mph? A racetrack, maybe. But the stock exhaust does sound pretty wimpy.

Quote
As I understood it the name of the game was, in simplicity, to get more air in, more air out, and then a proper fuel/air mix to match.

Yes but  to get more air in and out you need larger displacement or a different cylinder head. You need 4 valves per cylinder. You can chop down a GSXR cylinder head and fit it and then retune probably with different carbs and make 70 hp or so with a GS500 bottom end. Then you might have some advantage to different exhaust but you'll be on your own for tuning, and it's really very difficult to do. But you can't just bolt on power outside of the head, short of adding a turbo. Stock exhaust and carbs are both more than capable of supplying all of the air and fuel that the cylinder head can move through a normally-aspirated GS500 head.

QuoteThat's what I'm trying to do without dropping 400$ on an exhaust for a bike I bought for 1500$ (and then proceeded to scrape more value off of with some low-grit asphalt ).

Actually if you want more power you'll be a lot better off selling the GS500, get your $1500 back, put that $400 with your $1500 and scour craigslist for a ratted out SV650, Bandit Ninja 650, Katana 600, etc., which should be easy enough to find for around $2K. Or put another couple of hundred with your money and find a GSXR600 which will be really fast and you can probably find one for $2500. Fast is not an advantage of the GS500. Reliable, easy to work on, cheap to buy and keep up, simple and easy to use, those are the advantages.

Quote

Quote
Huh, haven't heard of doing that. So will the increased air from better flowing air filter change the scavenging dynamics that Watcher was talking about? Or will a properly sized exhaust properly scavenge the exhaust gasses regardless of how much air you're putting in with different air filters? (again, rejetting being a given).

The air filter shouldn't have any effect on the exhaust, directly. The air filter just allows more air to be pulled into the combustion chamber, which means that you can add more fuel, etc., etc.. All the parts need to work together.

The limiting factor is not the air filter or the exhaust. It's the head.

Changing the air filter and exhaust will just make the bike more difficult to tune. You will have to rejet because air velocity has been reduced and vacuum has been reduced. The same amount of air will be moving at all conditions besides idle, just slower. If you screw up the stock exhaust tuning then you will lose torque along with pulling your hair out trying to get it jetted correctly.

I can tell by what you are writing that you don't want to hear this, but it's the reality either way. Trying to get more power out of the GS500 is a fool's errand. If you want to accelerate quicker and wheelie every once in a while then change the front sprocket. The bike will feel quicker if you can knock 30-40 lb off of it, you know a 10% weight reduction is like a 10% power increase, at least for acceleration, and the exhaust may lose half of that weight. Getting that other 20lb off is going to be quite expensive.

There's a reason why the "Projects, Builds, Racing and Tech" section of this forum has virtually no racing talk and most "projects" are purely cosmetic or just getting a mothballed bike to run again. You have the wrong bike if you want to go fast on a racetrack.

You can make just about 4 hp from it, I have the dyno charts to prove it. Of course it sill is going to be the slowest bike with that 4 ... it just wont be as slow as without that extra 4.
Pipe alone probably wont net you any measurable hp. A K&N would get you 3.99, but its difficult to tune K&N without the pipe.
Pipe is a huge weight saver for sure, but that cross connect @ the head definitely messes up scavenging and hence tunability.
Cool.
Buddha.

So basically just a stock exaust+K&N filter for best power boost without being expensive? I know its not a fast bike, im just trying to crank out what i can. I just like wrenching on it. As far as speed/accelleration this bike is just tiding me over till i can afford a newer daytona 675.

Stock air filter & stock exhaust, +1 size on pilot and main jets, tune the carbs right, that's your best power boost.

K&N filter will cause you to wear the rings faster. Way too fast.

Please, just sell the bike now or leave it alone.

"K&N filter will cause you to wear the rings faster. Way too fast. "

Er ...no... Not appreciable difference in wear to the rings unless you fail to keep the filter clean. Most wear in an ICE comes from chemical reaction not mechanical wear. Something established a long time ago.  Even so,he size of any particulate getting through will be well within the film thickness and most likely about the same size as carbon engine generated particulate.
If you want to leave you bike alone , buy a car...

Gregjet - I used to have oil get dirty far faster with K&N's vs stock ... I even had pop socks put on em 2 layers thick soaked in oil and still had it get dirty very very fast. I got away from K&N's after that on all vehicles.
Cool.
Buddha.

Quote from: mr72 on February 23, 2018, 12:36:36 PM
Please, just sell the bike now or leave it alone.

Heck no. Half the fun is modding it. Im with gregjet on this one.

So are therr any aftermarket filters you all would reccommend other than K&N?

Quote from: MotoSig on February 23, 2018, 02:50:48 PM

Quote from: mr72 on February 23, 2018, 12:36:36 PM
Please, just sell the bike now or leave it alone.

Heck no. Half the fun is modding it. Im with gregjet on this one.

Knock yourself out. I'll tune out now.