Polini 50cc 316B w/c performance tips?

I am new to these engines and I would like some info on what to do to these engines to make them run to the fullest potential. I have a great pipe, carb, and manifold setup. I need to know what mods to the engine itself can be done? I have heard case matching cylinder greatly improves performance. Any other input? Thanks a bunch in advance!

I'm no polini expert but, you should be able to up the compression with a head insert, i would bet you can move to a stuffed stroker crank, maybe switch the reeds to better suit your need for rpms or low end power.

matching the cylinder to the case might not make a noticable difference but it wont hurt any...

raise boost port 3mm, port exhaust port to match pipes flange, knife edge transfer bridges, port match case and cylinder, bend reed limiters to the max, set port timing where the piston top is level with the bottom of the exhaust port and add an ada headkit to raise the compression or a polini 40cc 5 port head cuz the domes smaller.

i've done all the port work to my banshee cylinder and its uncontrollable power!! im gonna have to change gearing now and i just got it running! to bad i lost my pinion which needs to be reverse threaded!
and i got these polini 50cc 5 port race specs from dominantmonkey.com or something of the sort back in the day they had a site up and now its gone.

sr20, the 316b is alot different to the banshee cylinder in design so you dont need to tinker with 90% of the ports. all i had to do was match the crankcase to the cylinder itself.

definitely use the polini blue crank with it, youll find the crown to be about 1mm or so below the exhaust port and that gives you some pretty epic top end power.

squish ~ .5 .6mm

ive been told you can widen out the exhaust to 28mm which would give you arm fulls of free power throughout the rev range but i havent been game to try it on my cylinder yet!

id say a good 14hp could be had with a well setup polini, they are a serious motor

as for head inserts thats a no go, the head of a polini is one peice unlike the BZMs.

There is very little that can be done by the average person. A 50 should have more than enough power for you, but assuming you have it properly set up, a race crank will change the behavior of your engine.
Do not attack the cylinder with anything abrasive. I can guarantee you that doing anything to the ports will do more harm than good.

[quote=hyzer;366438]
ive been told you can widen out the exhaust to 28mm which would give you arm fulls of free power throughout the rev range but i havent been game to try it on my cylinder yet!quote]


yes hyzer!!!! thats what i meant by port match the cylinder to the pipes flange and since the banshee's header port is 28mm i ported my cylinder port that big and the power is insane!!! along with raising the boost port its almost unridable with a .8mm squish. i suggest porting your cylinder it wont hurt as long as you dont take too much off the inner most part. the outside of the port is what you wanna open and port the auxilary ports for a better flow.

problem is sr20 if you start boring out the inside of the exhaust port itself you risk having the piston ring snag on it and your gunna have a bad day then. i just dont have the tools to do the port 100% and round it off so its not worth touching it for now.

boring out the outside of the exhaust port wont do much for the polini you have to get into the cylinder itself for the gains. ill probably send mine off to have this done proffesionally next year

lol listen to sr20 man he knows what hes doing ......i must worn u even though this is a massive inscrese in power!!!!!!! do it at ur own risk and listen to some 1 who has done it already!!!!

just went and measured the bzm header to be 22mm. i think ill leave it

did you get your banshee going yet mate?

ohh i forgot to mention yah you'll want to use some small files and chamfer the ports by hand. it'll take a little while cuz the nickasil is hard but it works good and aslong as you keep the roof of the exhaust port at an eye shape the ring should be fine. just dont remove any from the bottom and i wouldnt take anymore then 1mm from the roof if you decide to do that.

i did all my porting at once so i cant tell if the gain is mostly from the exhaust port or raising the boost port and the rest of the port matching etc.. and i also forgot to mention i windowed my piston with a 1/2" drill bit! all i know is i can barely ride my bike now its in serious need of a gear change. and i went back and had my neighbor help me look for my pinion and i found it! lol

[quote=sr20hardbody;366471]If its unridable at .8mm then its because your using the stock gearing 6/74 which is way too low. i am running a 6/66 and its pretty fun still has gobs of power down low and killer top end . as a matter a fact I am using a C1 clutch on it and completly spun the center out of the clutch
I hit the gas and it grabbed and took off let off the gas hit it again coming outta the corner and WWWHHHZZZZZZZ!!!!! clutch center spinning and the clutch shoes sitting still .. LOL thats with my hybrid motor I built. Way way more power output than the standard banshee motor . I think the polini crank and flywheel made a huge difference . Of course a little longer stoke on the crank always helps .68 difference between the banshee crank and the polini crank and the huge timing difference on the 2 different flywheels . went from .48mm to pushing the head completely off the cylinder with the same base gaskets so I had to add a few to get me set back up to where I needed to be . I put on a PHBG 19 race carb polini greens , BZM reed stuffer , polini flywheel, polini crank, rep cylinder ,piston and cases, removed the case gaskets, and a polini 40cc head = killer combo
I wish someone had a small dyno around here so I could see the difference between the stock motor I took out and the hybrid I put in

and I would touch the ports on a polini cylinder . other than knife eding the port dividers and polishing the crap outta the exh port . Its already going to be more than you will want to handle outta the box set you squish around .50-.60 and be happy with that . . A friend of mine sent me a email he did some porting on a BZM 6t it didnt do much for him and he claims he may have lost some lowend out of the deal . Now would you wanna spend $400 on a new topend and mess around with it and end up losing power ?? Not me !!!! I did knife edge my port dividers on the BZM cylinder and polish the exh port and its really more power than one one person needs to have between there legs on one of these little bikes .

This thread is stupid. The question was, "what can you do to a Polini cylinder to get more power?," NOT "what does a Banshee cylinder need?" Let's stick to an apples-to-apples comparison. We all know that a Banshee jug has a lot wrong with it.

Fake moderator rant over...

did you read my post? those race specs i gave wasnt for a banshee cylinder!!!! it was for a polini 50cc 5 port engine! and since the banshee is a copy of the polini i just applied those same race specs to my banshee cylinder and got awesome results! before i ported my banshee i could ride it easily now i cant after all the porting.


im surprised you guys didnt know about that site that site had the factory race prepared secrets for all these watercooled engine makes. someone i guess compared all the engines factory race prepared and stock and gave all the secrets out but thats prolly why that site shut down. its called dominantmonkey or something like that if you think im lieing search it yourself you wont find the site but you'll find other sites that gave links to that site. and all i remember is raising the boost port and porting the exhaust port is the most important part.

Open up the channel from the reed cage to the transfer ports. Way to much metal to handle anything above a 18mm carb. Throw a 21 on there get it set and you will see more power than most porting.

Thanks Alot everyone! I really appreciate all the feedback... I will post pics and a video of this project after I get it finished.

i ported the blocked matched the cases to the block sharpened the port edges bzm red crank 19mm dellorto blata clutch and bzm reeds i ride my bike with front 6 tooth rear 62 tooth and d boke still wants to get up.

So the BZM Red crank will fit into the Polini bottom end with no mods?

i dont see why it wouldnt fit since back in the day guys were putting it in their banshee engines which is a copy of the polini 50cc. the only thing you'll need to figure out is which crank seals to use. i'd definitly give the bzm racing crank seals a try cuz they're made by bzm yet fit my banshee crank with a pretty tight fit. im guessing on the bzm crank they'll fit better.

you'll also prolly need to add some base gaskets to correct the port timing and with the longer stroke your squish will be tighter. the longer the stroke the higher the powerband engagement point is though which is why you might wanna stick with stock stroke just with a stuffed crank.

I was told that you need to use BZM crnak seals with the BZM crank in a polini?? Not sure if thats true or not . I would jsut stick with the polini blue race crank .