Polini 110 c.c.

[Mexicano]

Again me....my friend's BWs 100 has this set-up now:

KOSO 28 m.m.
K&N Air Filter
BGM Reeds
BGM Manifold
Leo Vince ZX (not too much to choose)
Stock Cylinder, just a wider and polished exhaust port
TP Variable CDI
Malossi Multivar, 8.0 Grs. Rollers
Polini Kevlar Belt
Nology Hot Wire
Denso Iridium Spark Plug
BGM Racing Clutch
Malossi Yellow Clutch Spring

He got a new Polini 57.5 m.m. bore (110 c.c.) cylinder, we will install it next week and I'm wondering if we will need a 32 or 34 m.m. carb for best performance, what do you think???

Actually he told me today that at 100 kms./hr. he can go with 1/2 throttle and the engine feels very nice, if he go to WOT the engine hear more deep but top speed doesn't go anywhere far....what could this be?, needs a bigger carb?, bigger main jet?, heavier rollers?, different clutch spring?, needs gearing?

he will install a tacho also next week, so at this time I don't have a clue on r.p.m's.

Thanks,

 

[StepVino]

...
Actually he told me today that at 100 kms./hr. he can go with 1/2 throttle and the engine feels very nice, if he go to WOT the engine hear more deep but top speed doesn't go anywhere far....what could this be?, needs a bigger carb?, bigger main jet?, heavier rollers?, different clutch spring?, needs gearing?...

Thanks,

This reminds me of when I bored out the stock carb,
it was doing this exactly (except for the speeds).

One morning I was taking pictures of the carb, and
forgot to put the stock rubber elbow back, between
carb and air box. When I went for a ride, it ran great.

So, simplest conclusion might me that main jet is too
rich, or stock conection to air box too restrictive.
Changing one or the other might fix it.

 

[Joël]

Actually he told me today that at 100 kms./hr. he can go with 1/2 throttle and the engine feels very nice, if he go to WOT the engine hear more deep but top speed doesn't go anywhere far....what could this be?, needs a bigger carb?, bigger main jet?, heavier rollers?, different clutch spring?, needs gearing?

Thanks,

The problem is simple. The 28mm is too big for the 100cc engine.
That's why the cylinder filling is already at its maximum level at half throttle.

So switching to even a larger carb is really not done.

You should choose a carb size according to horsepowers, not displacement!
A Bw's 100 puts out 10 to 12 HP, a 19/21mm carb is fine for such performance.

Use >28mm carbs when power exceeds 20 HP...

 

[StepVino]

That makes sense too. I punched in numbers into a
displacement-rpm equation, and came up with these
numbers:

Carb size, max power rpm
21mm 8500-9000
24mm ~10k
28mm 11.5k-12k
34mm 14k+

 

[trueOverrev]

do you consider getting a stroker crank??? RUIMA 51.5mm Stroker Crank that gives you a 133cc Minarelli Stroker Set up!

that 28mm carb, will be perfect for that set up!

 

[Mexicano]

Thanks Guys!!!!

 

[DRXRACING]

do you consider getting a stroker crank??? RUIMA 51.5mm Stroker Crank that gives you a 133cc Minarelli Stroker Set up!

that 28mm carb, will be perfect for that set up!

Is there a RUIMA distributer in the United states?
With 51.5mm stroke what would the port timing be with the Polini Cylinder?

 

[Big B NRG]

And mounting longer gears is also a good upgrade

 

[tiba_karotsu]

Is there a RUIMA distributer in the United states?
With 51.5mm stroke what would the port timing be with the Polini Cylinder?

it should be somewhere around 134 to 136 for the transfers & 190 for the exhaust, if somebody here can give me the port height for the Polini cilinder i can run it on my port software to get the real values.

 

[Mexicano]

it should be somewhere around 134 to 136 for the transfers & 190 for the exhaust, if somebody here can give me the port height for the Polini cilinder i can run it on my port software to get the real values.

Tiba:

The stock Bw's 100c.c. is 52 m.m. bore x 47 m.m. stroke,conn rod is 85 m.m.

I got this when I took numbers:

Exhaust Port STARTS opening at 88° (going form TDC)

Transfer Ports STARTS opening at 124°

Transfer Ports FINISH opening at 180°

Exhaust Port FINISH opening at 175°

Exhaust Port STARTS closing at 180°

Transfer Ports START closing at 170°

Transfer Ports FINISH closing at 115°

Exhaust Port FINISH closing at 88°

125° transfers and 175° exhaust, how is that?...not sure if my numbers are o.k., can you confirm them?

This is the port map from the Polini:

Regards,

 

[tiba_karotsu]

ok here are some numbers according to the stock port map of the Polini kit using a Ruima 51.5mm stroker crank;

exhaust port duration 178.9
transfer port duration 129.4
boost port duration 117.6

it seems the Polini kit is a good candidate for a stroker crank like the Ruima 51.5mm, the port timings are still at acceptable values for street use & have a lot of room for improvement. the above values are taken with no deck clearance, from the top of the ports to the deck of the cilinder.

 

[tiba_karotsu]

here are the numbers for the tuned Polini kit with a standard crank (47mm);

exhaust port 174.2
transfer/boost 124.7

looks like you got them right on the money.

 

[Mexicano]

Tiba,
So.....what about if we use the Polini just like it is?......does the numbers I came from: Exhaust: 164°, Transfer 104° & Boost 88° are correct?

Do you think this Polini as it is will improve this engine or we are going to get less power?

Thanks,

 

[Mexicano]

Some Pics

 

[Big B NRG]

Proably it will not be better with stock stroke since it will do less revs.
The 10cc more issn't really gonna compensate for that.

The polini 110cc looks like a stock 50cc mina cylinder. Like tiba said, alot of room for improvement, even with 51,5mm stroke.

Can you me a picture of the cylinderfoot (looking into the transferchannels of the cylinder) ?

 

[Mexicano]

Can you me a picture of the cylinderfoot (looking into the transferchannels of the cylinder) ?

Here you go Big B!

 

[Mexicano]

Suggestions?

Proably it will not be better with stock stroke since it will do less revs.
The 10cc more issn't really gonna compensate for that.

The polini 110cc looks like a stock 50cc mina cylinder. Like tiba said, alot of room for improvement, even with 51,5mm stroke.

What can we do to improve power with this new cylinder?, with the stock cylinder is doing 9,000 r.p.m's, we would like to do at least 10,000 r.p.m's

The stock CR is 7.5:1, Do you think if we raise the CR to 9.0:1 would help?

Thanks for your advise.

Regards,

 

[tiba_karotsu]

Tiba,
So.....what about if we use the Polini just like it is?......does the numbers I came from: Exhaust: 164°, Transfer 104° & Boost 88° are correct?

Do you think this Polini as it is will improve this engine or we are going to get less power?

Thanks,

i punched in teh numbers using the stock crank & port heights of the Polini cilinder & here they are;

exhaust port 164.1
transfer port 104.1
boost port 87.9

those are way too conservative & it's probably timed for a very restrictive pipe & carb, this cilinder holds a lot of promise i would be excited if i can port that to a more aggressive tune like midrace spec, some thing like below;

exhaust 185
main transfer 128
secondary transfer 124
boost 118

i would widen the exhaust port to 68% of bore size & port the outlet to 30mm oval & have roost make the exhaust pipe, this would make for a very torquey engine but if you wish to use a 51.5mm stroker crank with this kit i'll do it like this.

exhaust 185 = 28.65mm
main transfer 130 = 39.9mm
sec transfer 130 = 39.9mm
boost 118 = 41.95

widen the exhaust to 68% & bring down the floor of the transfer & boost ports to level with the piston crown at BDC to get as much area as possible for best results.

 

[Big B NRG]

What can we do to improve power with this new cylinder?, with the stock cylinder is doing 9,000 r.p.m's, we would like to do at least 10,000 r.p.m's

The stock CR is 7.5:1, Do you think if we raise the CR to 9.0:1 would help?

Thanks for your advise.

Regards,

I agree with Tiba, you should raise the timings, so it will produce more power at higher rpm.

With the 51,5mm the transfer timings are good, with a raise of the exhaustport timing to around 185 maybe even up to 190, you should have a quite fast cylinder. Offcourse make the floors the transfers lower (because of bigger stroke) so the transfers are just as big as the length of the stroke.

Also if you have the tools to adjust your transfers, make them wider, there is enough room to make them alot wider. Especially the second transfers can be made alot wider.

I see alot of potential in this cylinder, I even could be made to a full race cylinder.

 

[Mexicano]

Thanks Guys!.....but we are not using the Ruima crank, will use standard crank, this engine is for daily street use, so my friend want a very reliable engine. but as fast as possible, said this, what port timings do you recomend for an engine like this?

Regards,