Can you make a sport cylinder into a race cylinder?

[repherence2]

i just got back on to the forum and seen your thread.

what is your goal?

do you have to keep it "sport". im just asking because you got the Polini Sport.

here on Oahu, as well as the other island, the Polini Corsa has been touted as "Bombproof". the most common combination here on Oahu is the Polini Corsa mated to a Scorpion pipe. in my opinion, you can port a Sport to Corsa durations, but i think the Sport has a different piston than the Corsa. i have read of people taking the Corsa beyond 400 degrees, hence the accolade of it being "Bombproof".

try check out my DD50 engine build thread. i explored a lot of combinations during that build process. the initial build was going to be a Malossi MHR replica, mated to a Taiwan crank, and an Arrow pipe, as recommended by the owner of qwik fix garage of honolulu. later, i bought a Taida 50mm bore kit for cheap. i installed it on the block, put a 360 degree protractor on the cooling fan and checked the durations. i later decided to port it to Polini Corsa exhaust duration 188*. at that point, 190mech recommended that i run it with a Yasuni C16 (for vertical Jog).

lots of random stoney ideas and thoughts in that build thread. go check it out.

[repherence2]

not trying to detract from this forum, but you can also check out hondaspree.net. check out the stuff posted by Arnadanoob, Bakaracer, Tru72, and Wheelman. lots of "dio" information there.

you can also check out Pitobread's work on this forum. i think he put a Stage6 70cc RT for pugeot on a "dio" block.


there's many options

[broyager]

Polini head on the Malossi is a great idea - Zino has done this with his minarelli Malossi Sport to get the squish down.

You can round these edges for better / less disrupted flow into the transfers, not sure how much difference it will make, but it's fun to do. Just make sure to wash and clean the cylinder after, thoroughly.



Polini head may need an extended plug? the Thread looks quite deep on it in the pictures

Also you might benefit from using an oil with a higher flashpoint, which one are you using currently? and at what ratio?

[245luigi]

Hey guys, thanks for answering.

My goal is to see how much more I can squeeze out of the kymco to do better in the races. I know I will never be able to reach Jordan on his elite. Great rider, great bike (more appropriate for the track too), lots of higher end tuning options available etc. I just like two strokes but have never dove into cylinder tuning/pipe length stuff. The races give me an excuse, even if its a losing battle.

I am not trying to keep it sport. I purchased the Polini because it existed and to my knowledge no one has ever run one (at least on my model and discussed it on any forum) so I had no idea what it could do. I basically got it to see its port configuration, compare it to mine, and see if it was worth running as is or as another platform to experiment with.

I will check out all the info you have provided, repherence, thanks! I saw the corsa port map for the elite? dio? on hondaspree.net. But I have learned that port map also only tells half the story. There was no info regarding piston position in the cylinder so I could not calculate port duration. Thank you for providing the actual duration of 188 deg. I am most inspired by the elite/dio stuff because my kymco shares the same stroke as those bikes, but not stud spacing or exhaust flange position. As such, my only drop in options are sport cyls which I am learning to modify.

I am also limited by off the shelf exhausts. Even if I did raise my ex port to 188 deg, the most "race" pipe I have found my bike is the tecnigas triops (I'm running that now) and the gianelli rekord (or reverse?). I'm not sure they could support such revs. Even then, I still have my aformentioned crank problem lol

And yes polini plug does need long thread. Im leaving for Europe today for 3 weeks and as soon as im back, I'll be picking those plugs up. They seem to be available at O'Reillys.

I currently use Motul 710 in this bike. I'm still using the stock autolube, although it is zip tied open. I'm curious if that is partially why the bottom of the previous piston was covered in oil. Maybe I am introducing too much oil?

I keep thinking on that polini head. I'm betting the curvature better matches the polini piston so I'm not sure if it is best to run with the malossi piston. Idk.

I did some calculation regarding compression ratio. Looks like if I deck the cyl .34 mm, I'll be back to Malossi's stock ratio. That would give me a squish of ~1.1 mm on the malossi head.

[broyager]

Triops seems like a really decent exhaust. I'm looking at exhausts at the moment, so have the tab open.

www.pedparts.co.uk/blog/tecnigas-exhaust

Peaks 10.5k on a Sport Pro MkII and 9k on a Polini Sport, so should respond to any timing / porting changes you are making there

RE oil, it does look pretty thick, so might be getting a bit much, I don't know for sure though. The more oil in the mix the less fuel, so will be running leaner / hotter with more oil

[245luigi]

Yea I'm going to stick with it for now since I am pushing the rpm's up. I'm doing everything slowly, 1 step at a time (still want to actually make it to the race!). I'm taking data too kind of like Brent's Project 49. He made it to about 7-8s for 0 - 35mph on a 68cc chinese scoot. I'm at about 11 s. That's why I'm convinced I can do better.

I wish I could actually find out the ratio of the autolube. Oh well, for now I'll keep an eye on it.

[repherence2]

as far as understanding cylinder porting, Big B NRG, might give you some insight. just remember, that blog pertains to Minarelli and Piaggio. but there is some good info there.

--  you can check out this too, sport cylinder basic tuning.  just remember, that web page is for Piaggio, but it can give you an idea on how porting can affect power out put.

[broyager]

Also a nice summary about porting here too, I've read through quite a few times

blasterforum.com/threads/porting-101.58962/

And

www.youtube.com/2strokestuffing /search?query=porting

All that said, something else is going wrong re your times. I'm 6 secs, roughly - I think under that, to 35mph with a malossi sport and tecnigas silent pro, short case minarelli. Have done some porting, and minor crankcase flowing, but those did not equal 5 seconds etc.. Was around 6 secs with a Naraku 70 and largely stock transmission parts too.

Here's mine stock to ported, again I'm not sure if I've made huge differences to stock, performance wise.




What belt are you using, roller weights, and which contra / rear torque pully spring?

[245luigi]

Great info from both you guys!! Great reading. I have been following Alex for years. Such a mad scientist. Its given me some inspo for sure.

So if I remember right, I have a malossi belt (tried a gates, stock, and bando, Malossi was best). Funny thing, I knew my belt was an issue because of my very first race. I had the bike setup for top speed not the tiny track so upgeared etc. My bando belt blew at the end of the first day and i had no spares of nothing, didnt even know if I was into racing. A guy with an agility 125 had a belt. It was huge but worth a try. My bike got so much faster!

When I got back home, I opened the cvt and the starter bendix had worn a groove into that belt. It was floppin all over the place. Anyways I tried a bunch of belts and the malossi fit best. I need something a little longer but I dont think it exists. The belt currently sits slightly low in the torque driver and almost reaches the edge of the variator. I just picked up a polini belt, 2mm longer than the malossi. Havent tested it yet. Heres a pic of the mark on my variator with the malossi belt:



Rollers I think im at 6g. I need to lower these due to the raised exhaust port. Contra I wanna say +1500 rpm. I can get more solid deets as soon as I'm back.

Im also running a malossi var, polini speed clutch, just grabbed a polini bell, and a malossi straight groove torque driver. You can see in the recent races my starts are junk, so I'm sure i need to adjust the clutch which should bring the times down. I'm glad to hear there certainly should be more I can pull out of the bike.

Thanks for those port maps! Do those ports are higher than mine but im guessing its an engine design thing.

[broyager]

Yes, the extra length is going to get the belt more out to the edge of the torque driver at low speed, but also afaik (my disclaimer) it's a fine line with belt lengths, mm will make a difference. I've found a tight belt is better than one that might max out the travel of both variator and torque driver, better for acceleration, which is what I care about.

Contra; the Malossi Yellow that I use (297042.y0) is supposedly 6.1k. I don't know if this is, engages at, or plus from stock, but this changed my whole bike, got everything into the powerband at wot, and at any other point when required. I live around alot of hills, so the engine gets into the rev's whenever I need to accelerate, and at whatever speed. White did not work for me.

Malossi actually make a bunch of springs, not just red yellow white etc, at least for my bike and similar

29 7042.Y0 57.8 90 4.1 6.1k yellow
29 7043.R0 57.8 90 4.2 6.8k red
29 8323.G0 57.8 91 3.9 4.9k green
29 8324.V0 57.8 91 4 5.5k violet
29 8325.A0 57.8 91 4.1 5.5k a?
2916111.B0 57.8 103 4 6.0k black
29 8360.W0 57.8 118 4 3.3k white

It's very hard when giving specific advise, but I would get a much stiffer contra, 5G rollers or 5.5G sliders, up a couple of jet sizes on your main, maybe more even. Also make sure you don't have an air leak.

Not sure about engine design, your stroke is longer than minarelli 41.4 vs 39.2, so yeah I'm not sure how that affects the read on non minarelli port maps....

[broyager]

Sorry my link earlier is bung, below is good

www.pedparts.co.uk/blog/tecnigas-exhaust

[245luigi]

Thanks broyager! I will be rediving into CVT tuning now in general because of the starting line issues and raised exhaust port. I will keep your recommendations in mind! I have a couple torque springs to play with too. I know 2strokestuffing's advice is "use the lightest contra that prevents belt slipping and all tuning should be done with the rollers" but its always a case by case basis as you say. I'll make one swap at a time and see what each modification gets me.

I know on the track we race, generally acceleration is more important than top speed. There are loads of turns that kill your speed and a single "straight". So its all about getting out of the turn quick and speeding up fast to the next one. I think between each turn I can hit about 30 mph before the next one. Straight I'm hitting 40 mph right before the hairpin. So I'll def keep in mind the belt stuff.

Check out this calculator: lambretta-images.com/tuningh/port-timing-calculators/

Port timing is a function of stroke, con rod length, exhaust port height, and where the piston is below cyl deck at tdc. So a port map really tells 1/4 of the story. Cyl position relative to the piston tells 3/4! So port maps help, but actual durations are king! At least thats what I am learning

[245luigi]

Back from Europe and back to working on the bike.

I acquired solder that was exactly 1.5 mm thick to check squish. Before I was twisting thin solder to get enough thickness. With solid solder I hoped to get better numbers.

Opening the cylinder I saw this burn pattern:



I learned my Malossi kit's squish from factory was actually 1.28 mm.

I then put the Polini head on the Malossi Cyl and Piston. Due to the differences in curvature between the Malossi piston and Polini head, squish varied radially outward probably not in a good way. Starting from the center of the piston going radially outward, when the squish band began it was at .7 mm then grew to .99 mm at the circumference of the bore. Here is a pic of what that solder looked like:




Probably not good as during compression phase, mixture would be pushed towards the plug and the outer ring of the bore.

As such I decided to deck the Malossi head.

Here is the before:



During:



And after:




I achieved a squish of 1 - 1.1 mm removing the wall from the sides of the squish band. So I dropped squish ~ .2 - .3 mm. I think I'll stick with that for now. Any more lowering will require taking meat of the top of the cylinder. It started but ran out of light for a proper test. Thats next.

[broyager]

Nice one, let me know if the o-ring still fits and seals ok after taking that lip off, I need to do exactly the same thing.

[mopedmofun]

I am very interested in this. There is very little Kymco 2t upgrade info online, I just got one. Thanks for your research!