Hey everyone.
I'm doing the engine in my little cafe fighter GS500 in a few weeks. Im going to upgrade the camshafts and valve springs while I'm at it. Port Polish as well.
My main question was pertaining to the megacycle catalog listing for what they offer for the GS.
They offer a mild cam that is to be used with no other mods. One that recommends upgraded valve springs and pistons and one that says the supporting mods are mandatory. Along with a shim under bucket full race profile.
I can get kibblewhite valve springs no problem but does anyone know what they mean by modified pistons? Hate to sound like a noob but I've never heard of aggressive cams having any effect on pistons.
If anyone has any experience with this or any insight I'd be very happy to hear it.

While I'm here. I've searched and searched to no avail but I remember reading something about these engines being capable of 12-13k rpm with only a valve spring swap due to the stock ones  failing to close fast enough above 10k or so. Is this even true?

I'm taking this engine as far as possible and I'd ideally like power from 8k rpm and upwards from there.
Right now I'm running pod filters and a vance and hines open header with jetted carbs on an otherwise stock engine. I realize timing modifications are going to be a good idea but I'll cross that bridge when I get to it.

Thanks in advance to anyone who can help. This is my first bike and I'll probably never stop adding to it.

upgraded pistons...  what do they mean by that? the pistons themselves? the rings? rods? bearings?

and mild isn't exactly mathematical.. they can change the compression ratio a bit, but without exact stats its hard to say, engines are all about math, and the perfect math optimizes the engine, both in terms of gas-mileage and performance.

as for the higher RPMs. the GS engine isnt.. umm.. very balanced machine to begin with, especially stock. I can see you getting 12-13k if you get the crankshaft, and flywheel balanced at a GOOD machine shop.

They mean pistons with reliefs cast into the tops so that the valves don't hit.

Consistently revving much beyond the stock redline is going to greatly shorten engine life.

Quote from: RichDesmond on February 25, 2017, 01:04:07 PM
They mean pistons with reliefs cast into the tops so that the valves don't hit.

what he said ^

Quote from: RichDesmond on February 25, 2017, 01:04:07 PM
They mean pistons with reliefs cast into the tops so that the valves don't hit.

Consistently revving much beyond the stock redline is going to greatly shorten engine life.

This makes sense to me. The catalog literally just says "modified" pistons and I never even thought about the valves getting driven down further towards the piston faces.

I know big bore kits and the like are basically impossible to come by so I'm gonna go ahead and assume I'm stuck with the stock pistons for whatever I do in the future.

Thanks for the info.

If/when I get some dyno time in I'll have to ask if they're capable of balancing the engine in such a way that I could remove the crank balancer without shaking the engine to death. I've heard of people removing it to Rev up quicker but from what I understand it's not even remotely worth it over time.

There isn't any way to balance a vertical twin so that it won't vibrate badly, short of using a balance shaft.

Quote from: RichDesmond on February 25, 2017, 02:19:02 PM
There isn't any way to balance a vertical twin so that it won't vibrate badly, short of using a balance shaft.

That's good to know. My knowledge is lacking in certain areas haha.
Since we're here I just thought of a few more questions if you or anyone else doesn't mind me rambling.

Short of cutting up a gsxr cylinder head are there any major mods I'm not thinking about?
And has anyone here had good results with cam/valve springs swaps at all? I know I could throw a few thousand bucks at this engine and still be under 70hp but it's still something I'll be pursuing regardless of numbers produced when it's all said and done. Just want to make sure I know the possible options.

Thanks again though. I know these bikes are only getting older every day.

There's no rational reason to try to get more power out of the GS500. Well, other than "I like messing with stuff.", which is certainly valid. 
From a cost/benefit perspective it makes far more sense to sell the GS and buy an SV650.
Not trying to dissuade you, just pointing out the reality.

The GS500 has never had much attention paid to it by racers, it was in the same lightweight classes as the EX500, which made a lot more power to start with. So there was never any significant demand for engine hop up parts.

Quote from: NighthawkNFLD on February 25, 2017, 04:05:51 PM
Short of cutting up a gsxr cylinder head are there any major mods I'm not thinking about?

Port/polish and bolt on an ebay turbah!

This is my first bike and like I said. It's getting just about everything over time regardless of the money to gains ratio. I'm probably going to end up with a 2018 gsxr 1000 in the somewhat near future so I'm well aware faster bikes are out there.

As far as I know the Broussard (sp?) guy is the only guy to hit 70+hp and obviously he went balls deep with his mods. I was just wondering if anyone here was familiar with any such similar setups.

Pod filters, Full exhaust, CR carbs, port/polish, aggressive cams with necessary valve springs and proper jetting/timing mods should get me past 60hp I'm thinking.

I've considered turbocharging but I'm pretty sure carbed turbo setups are only good for up to 8ish psi... and I have pretty much zero real estate under the rear of my bike for the hardware.

I know someone here has converted his bike to fuel injection for a high pressure turbo setup, but then of course I run into the problem of nobody offering different pistons to accommodate it.

Maybe I should just try cutting up a gsxr head and see how many times I f%$k it up before it works right lol.

Quote from: NighthawkNFLD on February 26, 2017, 02:36:27 PM
This is my first bike and like I said. It's getting just about everything over time regardless of the money to gains ratio. I'm probably going to end up with a 2018 gsxr 1000 in the somewhat near future so I'm well aware faster bikes are out there.

As far as I know the Broussard (sp?) guy is the only guy to hit 70+hp and obviously he went balls deep with his mods. I was just wondering if anyone here was familiar with any such similar setups.

Pod filters, Full exhaust, CR carbs, port/polish, aggressive cams with necessary valve springs and proper jetting/timing mods should get me past 60hp I'm thinking.

I've considered turbocharging but I'm pretty sure carbed turbo setups are only good for up to 8ish psi... and I have pretty much zero real estate under the rear of my bike for the hardware.

I know someone here has converted his bike to fuel injection for a high pressure turbo setup, but then of course I run into the problem of nobody offering different pistons to accommodate it.

the limit of the carbs are actually just the floats! if you could re-make the floats in maybe carbon fiber, or aluminum. everything else would work fine.

and yeah I believe someone has made a GS port injected.. its been awhile since ive seen that thread.

Unless you are going to class race it cams is money that won't do much.
The motor breathes very well cleaned up. Bigger air filter and lighter better flowing exhaust will help a little.
But what ever you do you have a flexi swingarm, overweight linkages, flexi forks, poor front damping, medium speed braking at best, and a ton of out of date weight all over the bike. Address the handling first and you will enjoy pushing the bike much more.
Having said that the best bang for buck engine mod ( apart from the exhaust  and getting it jetted right) would be higher comp pistons. The stock compression is on the low side. But then that allows you to run lower rated fuel.

Quote from: RichDesmond on February 25, 2017, 02:19:02 PM
There isn't any way to balance a vertical twin so that it won't vibrate badly, short of using a balance shaft.

Actually there is. You can re position the crank to a 90 or some other weird number like 45 etc etc - but a GS crank wont come apart like a XS650 crank would.
An XS650 vibrates more than a GS but its not oppressively bad, and the pistons rise and fall together.
That counterbalance has ruined many a GS motor, but well, that isn't the only issue IMHO with the motor. Not even the worst.
The clutch push rod running left to right, and the rear cam chain guide IMHO are the absolute worst.
Cool.
Buddha.