"Power Mods" - Worthwhile or Waste of Time?

[jonahv]

I've read about some mods to get more HP from the engine, such as the K&N lunchbox air filter, re-jetting the carbs, and an aftermarket exhaust. I wouldn't mind getting a little more kick from my trusty GS, but I don't want to waste my time and money doing mods for insignificant power gains. Looking for some feedback from those who have tried these mods and/or have more experience with the GS than me. Are any of these mods worth it?


On a separate note, if an aftermarket exhaust is worth it, does anyone know a good one? Looking for more of a "hum" than a "thump" tone, should I get one. (I actually don't mind the stock one at all. In fact I kind of like its tone, although it could be a touch louder.)

[J_Walker]

more HP, not by much, we're talking maybe .1 numbers here.. if not like .05. more efficient and responsive possibly.

moral of the story, just buy a faster bike. skip chasing the 1HP mods.

stock exhaust is the best sounding exhaust the GS has.

[Watcher]

No matter how you mod it, the GS will never perform like nor sound like a 600cc 4cyl.

That being said, the GS is already jetted poorly from the factory.  A simple rejet will make it feel a little stronger, though an exhaust will only really be a few pounds lighter and more then a few decibels louder.  You won't notice much if any performance increase from an exhaust.

But at the end of the day, if you like it go for it!  I like a louder exhaust, and a K&N isn't really all that expensive and is easy to care for, and can end up saving you money over the life of the bike.  That will depend greatly on how long you plan to own the bike.

[mr72]

Rejetting is really needed for adequate running, but not really power.

The other mods won't net you any meaningful improvement in power. The biggest benefit of aftermarket exhaust is weight, second is that it's likely stainless steel and won't rust.

The lunchbox will likely make it much harder to tune and may make it more difficult to start and idle especially when cold even if you get it tuned correctly. It won't increase power.

The reality is that getting 50ish HP from a 2-valve/cylinder 487cc air cooled carbureted twin like this is really pretty good. Even modern CBR500R with FI and water cooled and 4 valves/cyl and all that gets just about the same power and weighs more and is much more complicated. There's just not really much power left on the table with this engine. The exhaust, carbs, intake (air filter) are not inadequate to supply the engine. You might be able to eek out a little bit of extra power or improved low end torque with careful camshaft regrind but who knows.

I say it's a waste of time and money and may even be counterproductive.

BTW you can probably drill around the silencer/baffle in the end of the stock muffler and get it to sound a bit louder without changing the overall tone. My dad did that on his Shadow 750 and it is now nearly as loud as my shortened Yoshi on my GS.

[jonahv]

BTW you can probably drill around the silencer/baffle in the end of the stock muffler and get it to sound a bit louder without changing the overall tone. My dad did that on his Shadow 750 and it is now nearly as loud as my shortened Yoshi on my GS.

Thanks everybody for the input. I will not be selling the GS ever. I love how light and agile it is! I think I might rejet the carbs as it sounds like the bike runs kind of lean from the factory, but I'll probably keep the airbox and exhaust stock. However, send a picture or explain how to drill out the silencer? I may try that.

[mr72]

If your muffler looks like this:



... then you likely have a smaller diameter outlet inside of what looks like a larger outlet, right?

IDK specifically because I don't have a stock GS500 muffler here. But presuming it's like many others I've seen then there should be a sort of steel "donut" between the outer and inner outlets. You can drill holes in this donut and it'll get louder. Drill a 3/16" hole or so and you can then put a machine screw in it if you don't like the result to plug it back up. Want louder? drill more holes or use a unibit to enlarge the one hole.

This won't change performance at all, it'll just make it louder. It may wind up being buzzy or have more of a "whistle" to it. Depends on a lot of factors.

Easier is to just replace with a slip on of some kind that'll be a lot louder and maybe have a removable "baffle" or "silencer" (sort of a tube-plug that goes in the end) so you can adjust the nose level.

[Endopotential]

I totally agree with all the above.  Hard to squeeze more horsepower out of a 10+ yo bike, though rejetting and air filter are simple enough.

As mr72 said, the cheapest and easiest way to change your exhaust note is to drill out the baffle.
My first bike was a Yamaha R3 and this is what I did (check halfway down)  http://www.r3-forums.com/forum/546-exhaust-fuel-delivery/15001-yoshimura-thread-13.html

Though to tweak the equation a bit, it's more about power to weight ratio.   I did a lot of changes to my bike, and think I may have shaved off 30lbs or so.   I don't have another stock GS500 to compare directly, but I do love how mine rides.  An extra 25hp and 20ftlb torque would make it the perfect bike...

To derail the conversation, I wonder how removing the fairings would help.  You would shave off a few pounds for low speed riding, but wonder at what speed aerodynamics would kick in and make the fairings worthwhile?

[The Buddha]

IMHO, slip on if you get one cheap enough and a rejet as spec-ed in the manual for non epa countries gets you the best bang for the $$$ without losing much in terms of longevity or much of anything else.
After 17 GS'es and countless hand made parts that have either ended in the trash pile or been used to a "meeeh" effect, I now have a bike with more suspension and cosmetic and tank coating etc etc mods than performance.
I have a 95 (weirdo me I like naked 89-00 style) with yosh Tri oval slip on (hey I am not above the cool sheite) with stock airbox and correct jetting (non epa spec as laid out in suzuki manual). Its a great bike to ride, reliable and will be till it wears the duck out (anticipated @ 40-50K miles)
It also has Bandit 400 rear wheel, Kat 600 suspencion RF600 shock, corbin seat etc etc.
For fun factor, improve the suspension and "correct" the jetting.
To waste $$$ chasing an elusive horse power number - yea do mods out the wazoo.
Seriously. lots of people think I conjured up a jetting formula out of thin air, with an OR sensor screwed to the exhaust and running down an empty highway @ full throttle.
OK OK I did that, but only for K&N and pipe.
The correct jetting is listed in the manual under "Canada".
Cool.
Buddha.

[cbrfxr67]

some doofus did an engine swap in his GS for more hp,...what a huuuuge waste of time!

[mr72]

haha!

I thought for a half a minute about a chopped down GSX 1000 head...

And I thought a whole minute about microsquirt.

Then I thought much more seriously about a different bike with more power and FI and 70+ hp.

Then I decided the GS500 is really fast enough and it gets the job done.

Now I'm in a loop between different bike and GS500 is good enough.

[gregjet]

This isn't a 10year old design it is a motor designed in the mid eighties. Now before you go jumping to conclusions, the mid eighties was towards the end of performance AIR cooled motors. Although this bike was never meant to be a supersports ( at the stage this bike actually came out, the NSR and RGV 250's made it look like a lump), It does have quite a solid performance/reliability profile for an aircooled 500. The cams are quite spritely, decent sized valves, 34mm "flat slide" CV carbs on a a 250cc fourstroke cyl. TYher IS stuff you can do to get more HP out of it but you are going to run into reliablity problems that will remove the MOST important point of this bike. I have seen just under 70HP gs500's that weighed less than 140kg, but you couldn't ride them on the street ( and certainly not for long).
Having said that two places where you can get more "performance" besides cleaning up the through flow. One is weight. The GS500 is full of heavy 80's designed stuff ( footpeg assemblies weigh kilograms) that can be lightened which is the basis of my project. The other is suspension. Almost every bike will increase it useable performance envelope by refining the shocks and forks especially the GS500. Decent suspension will allow you to ride faster AND safer. Won't help your straight line accelleration, but if yoiu want that, buy a megabike.
Despite the mega-cc-aphiles the gs500 will take you across any continent reasonable comfortably,  reliable, and with equal performance MINIMIUM to the vast majority of cars with the possible exception of Germany's Autobahns.

[gregjet]

I will add one other place the gs500 won't be much good. Across Siberia...the roads are bloody aweful and even modded the GS suspension ain't up to it. The word "roads" is used with a touch of sarcasm when refering to the aforementioned ...

[elbiancho]

No matter how you mod it, the GS will never perform like nor sound like a 600cc 4cyl.

That being said, the GS is already jetted poorly from the factory.  A simple rejet will make it feel a little stronger, though an exhaust will only really be a few pounds lighter and more then a few decibels louder.  You won't notice much if any performance increase from an exhaust.

But at the end of the day, if you like it go for it!  I like a louder exhaust, and a K&N isn't really all that expensive and is easy to care for, and can end up saving you money over the life of the bike.  That will depend greatly on how long you plan to own the bike.

What jet size will improve the factory settings? Thanks

[Watcher]

What jet size will improve the factory settings? Thanks

What year is your GS?

[Endopotential]

I will add one other place the gs500 won't be much good. Across Siberia...the roads are bloody aweful and even modded the GS suspension ain't up to it. The word "roads" is used with a touch of sarcasm when refering to the aforementioned ...

Greg, no way you rode your GS across Siberia!  That's balls out crazy and impressive.  Please post some pics so the rest of us can couch surf and travel vicariously.

[elbiancho]

What jet size will improve the factory settings? Thanks

What year is your GS?

1999. It´s main jets are 122.5

[gregjet]

"reg, no way you rode your GS across Siberia!  That's balls out crazy and impressive.  Please post some pics so the rest of us can couch surf and travel vicariously."
I haven't. But I watched the "Long way round". I am a mad bastard but not that mad...
https://en.wikipedia.org/wiki/Long_Way_Round

[The Buddha]

What jet size will improve the factory settings? Thanks

What year is your GS?

1999. It´s main jets are 122.5

Yea you need 40/125, sadly wont make a lick of more power. It will make it run a lot better, especially when cold, and will warm up and ride better 30 sec after start on a cold day, but will not make much diff on a dyno.
Rideability yes, power no.
Cool.
Buddha.

[elbiancho]

Thanks a lot 

[mr72]

FWIW in case you get the inkling to go one size bigger, I am running 40/127.5 jets with a chopped Yoshi muffler and I'm considering going back to the 125s next time the carbs are off because it seems to be running rich on main, reflected mostly in poor fuel economy (high 30s, low 40s).

To get a meaningful amount more power you'd have to get more air through the head which essentially requires a 4 valve/cylinder head, then you could choose cams that make use of higher revs and ride it >9K rpm and you'd make more power. HP = torque*rpm/5252... GS500 w/stock heads power peak is under 9K. Doing nothing else but increasing airflow so you can move the power peak to 11K will increase power by 22% all by itself. But that's an expensive change and also remember the stress on the rods, bearings, etc. increases with the cube of rpm so moving the RPM up by 22% will put over 1.8x as much stress on the bottom end so your engine durability will be radically reduced.

Again, way easier to swap the entire motor. WAY easier to swap the entire bike.