top end mods to stock part for more power !!!

[rogergendron1]

well we all know that you can deck your head way down on a piece of glass and sand paper till you get the comp you want. we all know about cleanning up your ports with a dremal. but after you have your desired comp and the port you want there are a few more mods you can do to your stock parts to gain way more torque and power !

1 grind ramps in your piston at the exhaust and tranfer ports.
2 cut 1/4-5/16 off the entire piston skirt on the intake side.
3 drill holes in your piston to lighten
4 drill your wrist pin out from 5mm to 7.5mm to lighten

thease 4 mods will give you a noticable increace in power and torque and will help out with vibrations at higher speeds.

also a link to a wrist pin for the 66cc gt5 that is 58% lighter than our stock one !!! http://juicemotoparts.com/products/light-wieght-titanium-10mm-wrist-pin-for-49-66-80cc-engines.html

 

[rogergendron1]

now my queston here is has anyone experimented with doing away with the shady needle bearing by ether drilling out the piston for a larger diamiter wrist pin that fits the crank arm or useing a brass bushing or something instead ? i would like to know how it worked out ?

i would much rather have a brass bushing with oil holes in it than a shady needle bearing !!! actually i would rather have a larger but lighter titainium wrist pin and no needle bearings at all !!!

let me know if you have done this mod and how it worked out for you .

 

[BarelyAWake]

Do you have any before/after pics of your work? Longevity examples - pics of the cylinder walls etc? It's appreciated, but some drawings & this obviously 'shopped pic of a random piston, one that isn't even for our engines is not exactly informative or reassuring for such a comparatively major mod...

 

[maniac57]

Seems to me we had a member who did some hardcore drilling and experimentation with a ht piston...
Ended quite badly if I remember correctly.

 

[mew905]

Seems to me we had a member who did some hardcore drilling and experimentation with a ht piston...
Ended quite badly if I remember correctly.

I did it with (so far) no bad consequences, and my vibrations are nearly non-existant. The image IS ACTUALLY the piston I'm running now, it weighs about 96.5g IIRC (about 14g lighter than stock)



As for cutting the piston skirt, 1/4" is wayyyyyy too much. I was only able to cut off 2mm before my exhaust port got uncovered at TDC. The exhaust port isnt even 100% uncovered at BDC (which is why we cant cut the piston skirt much), even the transfers arent 100% open at BDC, even though the timing is right for a 5000ish powerband, which means that we cant just raise the cylinder or cut ramps in the transfer (it changes the timing, but also allows smoother flow, but stock transfers are actually already timed well), raising them slightly to 120 degrees gives you a bit more of a racey, peaky powerband, as well as raising the exhaust (mine is 178 degrees) to match.

 

[rogergendron1]

I did it with (so far) no bad consequences, and my vibrations are nearly non-existant. The image IS ACTUALLY the piston I'm running now, it weighs about 96.5g IIRC (about 14g lighter than stock)



As for cutting the piston skirt, 1/4" is wayyyyyy too much. I was only able to cut off 2mm before my exhaust port got uncovered at TDC. The exhaust port isnt even 100% uncovered at BDC (which is why we cant cut the piston skirt much), even the transfers arent 100% open at BDC, even though the timing is right for a 5000ish powerband, which means that we cant just raise the cylinder or cut ramps in the transfer (it changes the timing, but also allows smoother flow, but stock transfers are actually already timed well), raising them slightly to 120 degrees gives you a bit more of a racey, peaky powerband, as well as raising the exhaust (mine is 178 degrees) to match.

no no no man you missunder stood ! i left the exhaust side allone and cut 1/4 off the intake side, one side is longer than the other by 1/4 .... the piston has 6 holes drilled on each side not a lot but enough... and ramps as stated above...plus the stock wrist pin mod, 7.5mm drilled....been running that same piston since break in and no vibes till at 6000 plus you start to feel it at anything over 7000, well i just do not go there on a 44 tooth rear lol. i have been running it for over 1500 miles now and the only issue i have is that there is too much compression and my rear tire drags under my FULL wieght when i pop the clutch !! it has to be it just the right position to get some momentum before it reaches TDC, also no store in my aria has an NKG b7sh so i am running a champion equivilant that is too high of a heat range same a a b5hs NKG !!! so after about 10 miles or so i shut the bike off and give her a cool down to make shure i am not over heating , have not overheated yet but i am shure its running hotter than it should be because of the plug. with close to 11:1 copm i should be using a #7 or better plug but can only find a #5 equivilant.

ohh and the vibes i get at 6500 are not like bad shaky vibes they are smooth vibes but strong and it makes me uncomfortable, i would hate to feel a stock top end vibe at 6500 !!! i could not imagine !!!

right about the transfers just a small ramp for them well cut to flow to the center will give you a more poerfull band albeit it will raise that band slightly... the exhaust port ramp made this motor feel like a whole differant beast, all thease mods together will raise the band but not by much and when you do get into it there is plenty of power all around !!

 

[rogergendron1]

raising the band by a little is not that bad as long as you have a balanced motor like the dax bottom end or you have a decent bottom stock case and you have lightened up the top end, this means that you can rev higher than stock without worry of shaking your motor appart and reap the benifits of the slightly higher power band at higher rpms for more power. just adjust your sprocket size to compensate if your not looking to gain speed and you want to maintain low end ... for instance your comfy at 30 mph but you do this mod and now your worried that to be in your power band you must cruise at 34mph and you may loos some low end . well go up 2-4 teeth on your sproket and you will be back down to 30mph and GAIN low end from what you had before because you will be taking off from a larger rear and you new cruise rpm will be higher and in a stronger powerband. this will make that same 30 mile an hour cruise seem much more powerfull than it was before you will just be at a slightly higher rpm wile cruising.

if you want to go faster though this mod will get you there at the cost of a tiny bit of low end (wich can be had back with the right tunned expantion chamber) and a racyer power band, with less vibes = more rpms achivable

 

[rogergendron1]

i run a stock 44 t rear because the 36 has me going way to fast for a bicycle... i am not comfortable going over 30 on a bike !!!

with the mods i mentioned and a 44t rear i cruise at 25- 30 no prob and that cruise speed is where ALLLLLLL MY POWER IS !!! i can take off without touching my pedals and verry quickly get up to speed and when i am there there is TONS of power !!!

with the 36t, it took a lil bit to get to 25 and yeh it could take off from a dead stop but with some cluttch feathering but once i hit 25 it wanted to just frigging pull away and keep going up to 40mph lol i dont like going over 30 so i was wasting 10mph of speed that could be turned into torque where i want it at 30... so i swapped back to 44 problem solved ...now i am going as fast as a stock motor with a 36... but with more power than a stock motor with a 44 !!! that is right where i want to be

 

[mew905]

Yep, smaller tires will haul you alot harder too, My friend's Scwinn Stingray chopper bike has a 20" rear tire (Standard size) and can do burnouts, and launches pretty hard. His problem was four-stroking preventing him from going faster than 20mph, that is until his motor finished his break-in. Then he could do a solid 30, but my bike with the 36 launches only slightly slower and with the drilled stock exhaust will do a solid 40mph+, though my first build could do 40mph with a 44T sprocket, so I'm looking for that extra speed with the 36

 

[Wickedest1]

I cannot provide a port map...but this should be enough fer the good tuners...

 

[rogergendron1]

I cannot provide a port map...but this should be enough fer the good tuners...

holy ports batman ? what jug is that from ??? puch???

 

[Wickedest1]

shhhhhh....i cannot and will not disclose this info...lets put it this way, that bike is solely track...i got a 97 dollar ticket on my own street showing it off after ports...

but gentlemen these jugs are like 20 bucks...id bet u could get em cheaper...and whats crazy is piston sizes...my flying horse piston makes my puch piston look like a shot glass...

open transfers
open intake
open exhaust
case match
lap head/cyl/bottom end

14mm carb...

top recorded speed on that engine was 77 mph with a 210 lb rider...
single speeded engine too...
gotta put ur feet on rear passenger pegs and lay on tank for take off or youll eat dirt everytime

 

[Venice Motor Bikes]

One thing to keep in mind when ramping the top of a piston or shaving the skirt, is that these things change the port timing of the engine!

I understand that the port timing was designed for moderate performance & to be good on gas; & changing it can increase performance (if you know exactly what you're doing).
I've tried doing a few of these mods & ended up with a few engines that seriously lacked low end power, (or totally ran like cr*p)...

So please be careful & read all you can before trying any of these mods!!

 

[maniac57]

One thing to keep in mind when ramping the top of a piston or shaving the skirt, is that these things change the port timing of the engine!

I understand that the port timing was designed for moderate performance & to be good on gas; & changing it can increase performance (if you know exactly what you're doing).
I've tried doing a few of these mods & ended up with a few engines that seriously lacked low end power, (or totally ran like cr*p)...

So please be careful & read all you can before trying any of these mods!!

Very good advice!
Changing port timing is not something that you should do without knowing what you are doing.
As Norm said, you can easily HURT performance rather than improving it.
I have extensive experience porting and tuning and even I would study carefully before removing much from a china girl. Normal two stroke tuning may not work on these gems, since there is so much variance in quality from the factory.
Plus the cylinder plating is sketchy at best, so radical mods are a crapshoot.
It's very easy to snag a ring or flake the plating if you open the ports too much.

 

[rogergendron1]

Very good advice!
Changing port timing is not something that you should do without knowing what you are doing.
As Norm said, you can easily HURT performance rather than improving it.
I have extensive experience porting and tuning and even I would study carefully before removing much from a china girl. Normal two stroke tuning may not work on these gems, since there is so much variance in quality from the factory.
Plus the cylinder plating is sketchy at best, so radical mods are a crapshoot.
It's very easy to snag a ring or flake the plating if you open the ports too much.

this is verry true !
however thease type of mods are for people who know what they are dong and have the knowalge !!! my bike has all of the above done to it and its a MIDRANGE BEAST !!!!!!

video of it here !

http://www.youtube.com/watch?v=eTq7H9Vl5lw

 

[DavDaddy]

well we all know that you can deck your head way down on a piece of glass and sand paper till you get the comp you want. we all know about cleanning up your ports with a dremal. but after you have your desired comp and the port you want there are a few more mods you can do to your stock parts to gain way more torque and power !

1 grind ramps in your piston at the exhaust and tranfer ports.
2 cut 1/4-5/16 off the entire piston skirt on the intake side.
3 drill holes in your piston to lighten
4 drill your wrist pin out from 5mm to 7.5mm to lighten

thease 4 mods will give you a noticable increace in power and torque and will help out with vibrations at higher speeds.

also a link to a wrist pin for the 66cc gt5 that is 58% lighter than our stock one !!! http://juicemotoparts.com/products/light-wieght-titanium-10mm-wrist-pin-for-49-66-80cc-engines.html

How much horsepower do you think you're getting after your mods?

Also any mods non sprocket/chain related you'd recommend for turning more RPM's?

 

[Rstar23]

One thing to keep in mind when ramping the top of a piston or shaving the skirt, is that these things change the port timing of the engine!

I understand that the port timing was designed for moderate performance & to be good on gas; & changing it can increase performance (if you know exactly what you're doing).
I've tried doing a few of these mods & ended up with a few engines that seriously lacked low end power, (or totally ran like cr*p)...

So please be careful & read all you can before trying any of these mods!!

I have a hyper build that's like 1 week old, have mz65 pipe, have not touched motor,want this as street bike,how can I port based specific for the MZ pipe?like lower/raise intake and/or vise versa exhaust?any tips?

 

[Venice Motor Bikes]

I have a hyper build that's like 1 week old, have mz65 pipe, have not touched motor,want this as street bike,how can I port based specific for the MZ pipe?like lower/raise intake and/or vise versa exhaust?any tips?

My best advice to you is to NOT touch the piston in any way, & not raise or lower the port heights; (only clean up the rough casted edges & maybe widen the ports a little).
Also, matching the intake & exhaust ports to the exact shape of the manifolds is a good way to increase power.

One more thing that's very important... Since your engine is very new, wait until you have run several gallons of gas through it before doing any of these mods!! I've found that if you completely break in the engine first, it will make the engine more likely to last longer after the mods.

 

[Rstar23]

My best advice to you is to NOT touch the piston in any way, & not raise or lower the port heights; (only clean up the rough casted edges & maybe widen the ports a little).
Also, matching the intake & exhaust ports to the exact shape of the manifolds is a good way to increase power.

One more thing that's very important... Since your engine is very new, wait until you have run several gallons of gas through it before doing any of these mods!! I've found that if you completely break in the engine first, it will make the engine more likely to last longer after the mods.

OK cool, def sounds like some sound advice. That's the direction I was going in anyways. Just trying to do as much research as possible before I did anything drastic. I have the small gas tank & I'm on the end of my 2ND tank now. Been running lucas semi synthetic ashless at 16:1 for first tank, second tank added about a cup n 1/2 of reg gas to whole mix seems to be good. 1 drop on floor overnite just rite 4 me. Also on 2nd tank added zeda race cdi, I really could tell the difference in the punch, drilled air holes n filter. Running stock pipe @the moment w out baffle. Mite put back on my MZ65 pipe today. Expecting my 11 tooth n mail soon but won't install until about 2 more tanks maybe 1. Anything I need to do to clutch cover? Maybe have to grind it for chain clearance/prevent binding I've read?? Seems legit, bigger diameter sprocket.

 

[Venice Motor Bikes]

OK cool, def sounds like some sound advice. That's the direction I was going in anyways. Just trying to do as much research as possible before I did anything drastic. I have the small gas tank & I'm on the end of my 2ND tank now. Been running lucas semi synthetic ashless at 16:1 for first tank, second tank added about a cup n 1/2 of reg gas to whole mix seems to be good. 1 drop on floor overnite just rite 4 me. Also on 2nd tank added zeda race cdi, I really could tell the difference in the punch, drilled air holes n filter. Running stock pipe @the moment w out baffle. Mite put back on my MZ65 pipe today. Expecting my 11 tooth n mail soon but won't install until about 2 more tanks maybe 1. Anything I need to do to clutch cover? Maybe have to grind it for chain clearance/prevent binding I've read?? Seems legit, bigger diameter sprocket.

Go ahead & start running it at 32:1 (or 40:1); & it's also OK to start running the MZ pipe.

When you start to install the 11t sprocket, you'll see instantly where you need to grind the case.