rpm tunning question

[guen84]

my 51mm set up was flying around 8500-9000k, ive tryed lower weights and it reved in the 10500 area but did not seem to get any faster... r's shot up faster and peaked but i was going slower.. was doing some research on my set up says pg long produces peak at 9800-10200 rpms and the 51mm ruima bore w/expansion pipe produces peak power at 10k... my set up is in signature, 2k grabbers & 1500 center on zx clutch with 669 belt.. whats the deal with this something in the tranny area? or could i have raised my ports so much to keep compression down that i lowered my powerband???

my compression is 150, with 50mm head 1.85mm base gaskets 1.5mm head gaskets, exhaust duration 180 intake 132. if that helps any..

[Bear45-70]

If rollers are changing your max RPM, your rollers are way to light. The variator should be in the go fast position long before you reach max RPM.

[guen84]

i was running great at 48g went to 45g and the revs went up that much.. i know 3 grams is kinda a big jump for fine tunning, but how do i get my r's in the peak power area with out lowering weights??? with 48g i never seen rpm's over 9500. just trying to make sure its tunned to the best of my abilities

[Bear45-70]

i was running great at 48g went to 45g and the revs went up that much.. i know 3 grams is kinda a big jump for fine tunning, but how do i get my r's in the peak power area with out lowering weights??? with 48g i never seen rpm's over 9500. just trying to make sure its tunned to the best of my abilities

You need to change rear gears, not run the transmission in second gear.

[guen84]

i was running great at 48g went to 45g and the revs went up that much.. i know 3 grams is kinda a big jump for fine tunning, but how do i get my r's in the peak power area with out lowering weights??? with 48g i never seen rpm's over 9500. just trying to make sure its tunned to the best of my abilities

You need to change rear gears, not run the transmission in second gear.

ok, i was kinda wanting to do that, but i really liked the take off i was getting.. with the info i provided can u help on wich gears would be best?? the 7.97's or 7.58? my main concern is take off, but there is not that much difference between 8.44's and 7.97.

[guen84]

any comment on raising the cylinder up so much that it changes peak power?? im not even sure if thats how it works. thats why im asking.. been reaserching all day kinda gave me a headache so i figured id just ask..

[Wheelman-111]

Greetings:

First off, beware if you've raised up the cylinder and still seeing 150PSI BEWARE! That 51mm kit has thin walls, and isn't very forgiving of overheat conditions. My first one grenaded with 135 PSI in fact. Look for more like 125 for a decent chance at durability. Add a head gasket or hog out the head itself if you've maxed out the base gasket option. Use a #9 plug unless it's very cold - maybe an 8 if so. Jet rich and downjet very cautiously or it's over in a heartbeat. If you downjet and it suddenly gets cold out, the mixture shift toward lean can be enough to overheat. Some people have been known to swap filters trackside to make sure the engine has enough fuel in the mix to stay cool.

Next, 8.44 is just tall enough for a Contessa. The 72cc Corsa doesn't have nearly the torque of your 90cc, but it's happy with 7.58s as well as 7.97s. I've gone 68-69 with both ratios, and the take-off is marginally affected with the taller gears if I keep my variator load around 32grams. It spins up to 9800 or more immediately upon application of full throttle. I am using a +1000-ish spring - 1200 nominal, but it's softer than the blue 1000 I had before. If you're using a true +2K spring, that may be your problem. In addition to needing a much heavier variator load, the force of that spring has been known to pop the rim off fome brands of rear pulleys. On the plus side, it might decrease belt slip a tad, but is it worth the risk of a roadside breakdown? Anyway, its not needed with the rangier belt ratio the ZX pulley provides - assuming you're also using an oversized front pulley as well. Polini for ruckus at 94mm is pretty good.

For better top speed, consider a 654mm ZX belt instead of the 669. Theoretical top speed should improve considerably, assuming your engine is producing good power here. With your 90, I'd guess you could use Primaries at 6.9:1 or the Giant secondaries I posted in Aftermarket Tooth Tally that yield 6.3:1. If the power's good, the acceleration should still be decent and the top speed - once again if you have the power - should exceed 70.

[bakaracer]

Raising the jug up to increase the port duration narrows the power band. Its does raise peak power some and also raises topspeed due to higher max rpm but you do narrow the power band up which makes for a more difficult fine tunning.the higher the exhaust duration you run ,the higher the cylinder compression needs to be so using pump gas your going to run into issues. For your bore and stroke I wouldn't go lower than 7.58to1 gears any thing smaller then that your making the motor work to hard to try and turn the gears and push your weight and the bikes weight.if you like the lowend takeoff, leave the gears you got now. As for your trans setup,you can use 1k centers springs too for street use. And please get other roller weights other than straight gram weight increaments. Either buy or make some in between ones. Now you see how much 3grams can change how the motor runs. Even 1.5g makes a big difference.

[guen84]

Greetings:

First off, beware if you've raised up the cylinder and still seeing 150PSI BEWARE! That 51mm kit has thin walls, and isn't very forgiving of overheat conditions. My first one grenaded with 135 PSI in fact. Look for more like 125 for a decent chance at durability. Add a head gasket or hog out the head itself if you've maxed out the base gasket option. Use a #9 plug unless it's very cold - maybe an 8 if so. Jet rich and downjet very cautiously or it's over in a heartbeat. If you downjet and it suddenly gets cold out, the mixture shift toward lean can be enough to overheat. Some people have been known to swap filters trackside to make sure the engine has enough fuel in the mix to stay cool.

Next, 8.44 is just tall enough for a Contessa. The 72cc Corsa doesn't have nearly the torque of your 90cc, but it's happy with 7.58s as well as 7.97s. I've gone 68-69 with both ratios, and the take-off is marginally affected with the taller gears if I keep my variator load around 32grams. It spins up to 9800 or more immediately upon application of full throttle. I am using a +1000-ish spring - 1200 nominal, but it's softer than the blue 1000 I had before. If you're using a true +2K spring, that may be your problem. In addition to needing a much heavier variator load, the force of that spring has been known to pop the rim off fome brands of rear pulleys. On the plus side, it might decrease belt slip a tad, but is it worth the risk of a roadside breakdown? Anyway, its not needed with the rangier belt ratio the ZX pulley provides - assuming you're also using an oversized front pulley as well. Polini for ruckus at 94mm is pretty good.

For better top speed, consider a 654mm ZX belt instead of the 669. Theoretical top speed should improve considerably, assuming your engine is producing good power here. With your 90, I'd guess you could use Primaries at 6.9:1 or the Giant secondaries I posted in Aftermarket Tooth Tally that yield 6.3:1. If the power's good, the acceleration should still be decent and the top speed - once again if you have the power - should exceed 70.

Its a ruima spring pretty stiff, do have a westgerman 1k (blue) from vt to try. I am running the polini for ruckus vari. R u saying the 669 belt is better for low end and the 654 is better for top end? From my reading kinda thought the 669 was the belt to use with both oversized pully and oversized vari. Just trying to get this zx trans figured out. N for what good it is, its a true kymco clutch

[guen84]

Raising the jug up to increase the port duration narrows the power band. Its does raise peak power some and also raises topspeed due to higher max rpm but you do narrow the power band up which makes for a more difficult fine tunning.the higher the exhaust duration you run ,the higher the cylinder compression needs to be so using pump gas your going to run into issues. For your bore and stroke I wouldn't go lower than 7.58to1 gears any thing smaller then that your making the motor work to hard to try and turn the gears and push your weight and the bikes weight.if you like the lowend takeoff, leave the gears you got now. As for your trans setup,you can use 1k centers springs too for street use. And please get other roller weights other than straight gram weight increaments. Either buy or make some in between ones. Now you see how much 3grams can change how the motor runs. Even 1.5g makes a big difference.

I'd like to keep the 8.44 and gett into the 10500 rpm range for the top speed runs (not very often) are there any good sources for a tunning weight kit other than the straight grams kit I have... I hope its not like the dumb minerellis with there .3 gram crap. My buddy's aprilia spent 2 days tunning n only went thru 3 different grams of rollers (it was a 9 roller vari)

[bakaracer]

Minarellies are not the only motors that have those .3 gram or .7gram or odd weights. The 16x13 rollers which these motors use have them in those odd weights too. Malossi,polini,stage6 doppler all have them or you can make your own with a step drill bit and pocket scale. Don't expect to get your bike dialed in all in 1 day if you don't have all these odd weights on hand. As for your 10500rpm limit . You seen the tach go that high so you know the motor will rev up there. For it to sit at that rpm you need to set the bore so its past that rpm limit so around 11k. So if you need to lift the exhaust port to match the intake transfer timing then that's what you have to do.

[guen84]

Minarellies are not the only motors that have those .3 gram or .7gram or odd weights. The 16x13 rollers which these motors use have them in those odd weights too. Malossi,polini,stage6 doppler all have them or you can make your own with a step drill bit and pocket scale. Don't expect to get your bike dialed in all in 1 day if you don't have all these odd weights on hand. As for your 10500rpm limit . You seen the tach go that high so you know the motor will rev up there. For it to sit at that rpm you need to set the bore so its past that rpm limit so around 11k. So if you need to lift the exhaust port to match the intake transfer timing then that's what you have to do.

Thanks I'll start looking for these odd size weights don't won't to mess up the kit I have so I'll buy some new ones since I'm in the ball park. Only question is if I change center spring back to 1k will my weights be way different. I justvdont want to start buying weights in the wrong direction.. as far as raising exhaust port I'll leave that be for know, that's getting over my head...

[Wheelman-111]

Greetings:

Weights will need to be lighter using a softer Contra spring. I'm using 30-35 grams with my +1200, for example, to run 10K RPM on the tach. Yours will be different.

Bakaracer no doubt is correct in saying that port timing dictates the best power RPM.
RE-read my earlier caution about the delicacy of the 51mm kit however.
High piston speeds magnify tuning issues.

On a different note, I'm still waiting for a close-up of your avatar for uhh, Scientific Reasons.
If it's not too much trouble, could I also borrow that Elite saddle for a while?

[guen84]

Greetings:

Weights will need to be lighter using a softer Contra spring. I'm using 30-35 grams with my +1200, for example, to run 10K RPM on the tach. Yours will be different.

Bakaracer no doubt is correct in saying that port timing dictates the best power RPM.
RE-read my earlier caution about the delicacy of the 51mm kit however.
High piston speeds magnify tuning issues.

On a different note, I'm still waiting for a close-up of your avatar for uhh, Scientific Reasons.
If it's not too much trouble, could I also borrow that Elite saddle for a while?

thanks on the weights.. im well aware of the thin walls on these cylinders will be my 4th one 2 have already became paper weights.. will be running 100 octane race fuel and castor 927.. that combo made this terrible instalation job last all season with temps as high as 450.. i know i got lucky... ill try n get a larger pic up of avatar its only a cell phone pic.. as far as my seat goes i knew some would notice my fine sewing job of re doing the seat my self... but some thing tells me thats not why you want it...

[guen84]

i have a old 50mm cylinder that i polished the ports on was thinking of having that honed out to a 51mm piston.. i was thinking to have it done to the actual piston im gonna use... what piston gap should i have?? will the porting be ok?? 50 and 51 both look exactly the same.. besides the big hole in the middle.. any words of wisdom?