high compression pistons?

[gs500fromnb]

I'm looking to modify my bike in the coming season. I figured the main mods kind of require you to do all the others... as in if you try to get a cam with more lift, you get more fuel and air, so you would need bigger carbs or jets to allow for this, after market air filter... then all the air and fuel coming in you would need it to be able to flow easily, so an exhaust would be almost required.

I'm wondering how bout high compression pistons? do they make em? are they ridiculously expensive to buy and put on? would there be a decent difference?

i'm trying to figure out what I can do to it to get the most power while not blowing up the engine or cutting its life in half  :lol:

[Blueknyt]

You can overbore for more lungroom, but when you start bumping compression up your taking life from the crank, im sure there is a plateu that the stock crank is perfectly happy with before you have to start worring about it but i dont know what that is.   How hot are you looking to make it? consider a fresh rebuild of the engine and haveing the crankshaft reballenced and the Counter ballence shaft removed (block oil ports if you do this) the CB shaft is almost as heavy as the crank and soaks up a fair amount of power to be turned. by getting rid of it, your freeing up some of that HP to get to the rear wheel. I have been told even stock, a reballence crank and chucking the CB shaft the 500 acts like a whole differnt engine.  i called Falicon down here in Florida and they quoted me 210$ +shipping x2  for reballence(this was alittle while ago) and they reballence for 9krpm,. which is about peak on hp.  prev owner of my GS claimed when he did it, the Vibration wasnt bad, kinda 2 stroke buzzy but liveable.  i havent found anyone else here who has done this to tell me how Buzzy and if its comfortable enough for street use.

[gs500fromnb]

If I can find a way to fit an oil cooler on it then I might be able to get it modified more without killing the lifespan on it...

so would I need to overbore it to get higher compression pistons? or can I just slap some in there (get my mechanic to slap some in in there I mean lol)? or would the cost difference even matter?

Not being overly mechanicly inclined... would removing the CB shaft do anything at all reliability wise? I know removing weight in the engine does wonders to add power. If I need a rebuild to have bumping the compression worth it I might just do the CB removal and cramk shaft reblalance for now and keep playing with a few things and then hope that when the engine eventually goes (hopefully a long time from now ) that its just in a way that  doing a rebuild to an overbore and new piston would fix it.

[Blueknyt]

well believe dgyver is playing with different bore sizes right now. he could probly be a better source of info, however im sure to keep everything reliable, Ballencing, bump bore size but attempt to keep the compression not much above stock, increasing bore alone will bump compression alittle (unless using dished pistons). now also keep in mind, what ever pistons you use, you will have to send them and the rings along with the crank and rods for ballencing as they are ballenced as a package. genrealy going from 74mm-75mm isnt OVER critical on the ballencing, but would also depend on howmuch weight difference btween 2 pistons.

figure the GS maks an average of what, 47 hp at chain? think someone said 52 at the crank? i would imagine that fresh honeing and rings, jetting and exhaust coupled with shedding CB shaft would put most of that at rearwheel. as soon as i can afford it, thats what im going to do with crank and CBshaft, i have a set of 75mm pistons with new rings, i have a head from Kevin C in a box that had some minor port messaging for little better flow, i have a set of 36mm gsxr carbs already mounted on a GS500 rack just need to figure out basline jetting for starting point.
figure it should make for nice runner.

[cernunos]

I believe avg wheel HP on the Baby is 38, around 42 crank. From what I can tell, the jetting, exhaust and advancer mods bump it around 3-5 HP. If we could go from 9.0-1 to about 10.0-1 compression ratio we would probably be able to get somewhere in the mid to high 40's at the wheel with reliability IMHO. Still wondering if the 78mm pistons Dgyver was referring to have the same compression height as the stock GS piston. Not compression ratio but compression height...distance from wrist pin c-l to crown deck of piston. Love the Baby G and this forum.

C.......

[94suzuki500]

dont take out the couterbalancer it might make you bike lose power actually.  In most race bikes they have counterbalancers to help make power and reduce vibration.  Its in there for a reason I wouldnt remove it if I were you.

[Blueknyt]

C i think your right, wasnt there an article claiming 52 at crank?

parallel twins have alot of mass being thrown in the same direction, and its not latteraly with the rest of the frame. to help Kill this vibration Counter weights are added 180 degree's out of phaze of crank effectively killing most the vibration, keep in mind it takes power to move weight and the crank is effectively moveing another crank minus the compression resistance of another set of pistons.  By reballencing the crank, you equalize the masses being tossed around to a closer degree of cancellation.  you will still feel vibration but not bad from my understanding, the extra hp tp rw makes it more fun and is said to be worth the price.


But perhaps im just confrontive with 94, will another engine builder/racer/mechanic step up and explain how the CB shaft works and pros cons of ballencing cranks?

[sprint_9]

But perhaps im just confrontive with 94, will another engine builder/racer/mechanic step up and explain how the CB shaft works and pros cons of ballencing cranks?

Yes someone who has done this please speak up, I would too like to know.  

gs500fromnb some of the info in this thread might interest you.

http://www.gstwins.com/forum/viewtopic.php?t=15515&highlight=

[Blueknyt]

while i admit i read the posting too quickly i got the jist of it the first time around, but something made me come back to read it again

In most race bikes they have counterbalancers to help make power and reduce vibration. Its in there for a reason I wouldnt remove it if I were you.

:guns:  toe's are getting sore arnt they

granted, they are there for a reason and in the above quote, only ONE of those is ligit. depending on application, a COUNTER BALLENCE shaft can be used as a drive sorce for pumps,distibuters or as a refernce indicator. I cant honnestly remember any race built engine Bike or otherwise that Has a counterballence shaft to MAKE power,but i could be wrong. Anyone?

[sprint_9]

Yea I dont really know on that, I dont know how extra rotating mass would gain you power.  The less rotating weight you have the more power you will have.  Im sure a nicely balanced engine will perform better but theres many machine shops in the country that can perform a good balancing job on our bottom ends that the absence of the balancer shouldnt matter vibration wise.  Those are my thoughts.  Also thought of this, snowmobile engines dont have a balancer and they make loads of horsepower without problems.

[coll0412]

Do be complelty honest I really dont see it a that much of a power leech.
Although having to accelerate more mass takes away from available power, I think rasing the comperresion ratio, and better flowing heads and carbs would do wonders for this bike

Just my two cents

[Blueknyt]

yeah, flowing more would produce more power, you can punch out the stock cyl and push in the GSXR 1027cc(i believe) cyl and machine the cases so bottom of the cyl fit in. then you have lots of meat you can Bore out for larger pistons. You can really open the ports up but due to the angle of the valves, and the closeness of the valves you can only go so big, same with the cams, you can go High lift but there is a cap as the valves must have time to close before next one opens or they will hit , duration cant be too long for same reasons. just adding high compresion pistons puts the risk of eating valves well within reach should you missshift or hit a false neutral and bounce the redline. this is something iw ould not do for a daily driver

[Mat]

i remember reading that sometimes heavier cranks are used on lower power bikes to keep up momentum

even falicon desings cranks to be heavier than stock


from the falicon webiste

"Contrary to popular belief, it isn't always wise to get your crankshaft lightened! With 25 years of crank modifying experience behind us we know what your crankshaft needs for it's particular application. Companies that make blank statements saying that a lightened crank will make your bike go faster and decrease crank gyro effects should be avoided. All crankshafts and their applications cannot be lumped together with one generalized statement. The physics of flywheel effect and dampening ability come into play when a crank is being modified. When we manufacture crankshafts WE SOMETIMES DESIGN THEM TO BE EVEN HEAVIER THN AN OEM CRANK, so it stands to reason that one should use a crankshaft company that knows when, where, and how much to cut on your crankshaft."

[Blueknyt]

lightening isnt the same as balancing.  drag racers often opt to lighten things with mass, specialy rotating mass.  swing a wooden bat, then swing an aluminum bat, which one is easier and swings faster? problem is when talking the stresses of a crank/flywheel, it can compromise the strength if taken too far, or wont be able to cancel out the vibration harmonics well enough to keep a crank from snapping.  this doesnt happen in cars as well as bikes.

[dgyver]

The largest Megacycle Cam that can be installed in a unmodified GS head are the 384-20 with a .417" lift. Any larger and you will need to make room for the lobe.

Wiseco makes 78mm GPZ piston and are a stock item for them. The 79mm pistons are not made any more but may be found, if you are lucky. Wiseco stopped making the 79's in 1992. Custom pistons can be made but are $$$$$. J&E will custom make pistons as well.