72cc BBK

[mono]

Its funny how the Chinese don't know the same math the rest of the world does. I know mine quite well.

The math is obvious and simple, even for the Chinese, but the reason nobody cares about exact numbers in lots of cases is because they don't matter that much most of the time. There's no use, for example, bothering with a 4..5% difference in displacement if other variables in the same system make much larger differences in both actual and perceived performance...

Manufacturers just choose the actual sizes of their products for convenient design and production instead of aiming for round numbers. They round up the marketed numbers to the nearest common sounding number, because using numbers like 81.248cc in the name of a vehicle or aftermarket part would sound rather ridiculous to most people...

This is not something that's limited to Chinese manufacturers or motorcycle business, it's standard industry practice - and I'm happy with it, because it increases the signal to noise ratio of this already far too chaotic world 

[MotoRandy123]

What ever happened to the old truth in advertising law? My 200 is only
a 175, I could use the extra 25cc's. Some 163's are called 200! When
your talking 80 cc's 8 is 10 percent! That's a lot in my book....

[mono]

I agree, there's a difference between rounding up for convenience and shameless inflation, and while 10% is not really dramatic in my book, selling a 163 for a 200 is over the edge indeed...

[LoveMyKymco]

Same reason a chevy 350 was only 346 CI, it just sounds better and if you dont know any better you go for it.
A 4-5% increase in cylinder bore can increase CR by .2-.4 ratio so it does in fact make a huge difference. If the piston were to be say dished instead of domed it wouldnt matter as much but if its the design for same design it will in fact make a difference.

[mono]

A 4-5% increase in cylinder bore can increase CR by .2-.4 ratio

This could only be important for kits that come without a matching cylinder head - and even then, the shape of the piston crown is the most determining factor, not the bore size....

Heck, I own a 72cc kit with a hollow shaped piston, which, when measured, proved to have almost the standard compression ratio with the standard head, although the displacement was increased by a factor of 1.4 ...

Apart from that, more compression doesn't always mean a significant increase of power. The compression vs. power curve is almost flat near the knock limit, which means that if the compression for your setup is already quite high, the only thing you'll gain is an increased chance of detonation...

_{(Interesting read for example : http://rescomp.stanford.edu/~efroeh/papers/RDH_Engine_Performance.pdf )}

[LoveMyKymco]

The size of the bore directly effects the degree of slope towards the crown. Like I said it matters more on domed pistons more than dished.
Most 72cc kits have dished pistons and usually have same if not lower compression than stock.

[mono]

Still, when it comes to choosing a kit to buy, the only sensible prediction you can make from the size of the bore is the exact displacement in cc, which still says very little about the performance it will achieve compared to other kits with only a few cc more or less, especially when the kit comes with its own cylinder head...

From my experience, I prefer better build quality, a head with larger valves and a slightly lower compression ratio over a few cc more... Especially since a few percents of difference in performance isn't noticeable by any sane person without a dyno, but reliability sure as hell is....

[Vivo]

What ever happened to the old truth in advertising law? My 200 is only
a 175, I could use the extra 25cc's. Some 163's are called 200! When
your talking 80 cc's 8 is 10 percent! That's a lot in my book....

Manufacturers will claim that the badge on your vehicle is the model of your vehicle and does not really reflect the actual engine displacement or even a part of advertisement. The spec sheet says the actual engine displacement, right? However, when it comes to specific engine parts...it's a different story...

[MotoRandy123]

Well if you call it 280Z that's ok but if you call it Yager 200i it should be close to 200.
It's like computer monitor's, used to be a 17" was 17" now it's 15.8" viewable. Their
always trying to pull one over on you. I'm surprised the Chinese 50's don't all have
big numbers on the side. "Squiggly 1000, Super Power 350, Mega Max 900!"

 Kymco missed it with Super 8 and Super 9. I think those numbers are lucky in the Chinese
culture. Here it sounds weak. "Mine goes to 11!"

[mono]

"Mine goes to 11!"

 

[LoveMyKymco]

Id ride the squiggly 1000

[Vivo]

Well if you call it 280Z that's ok but if you call it Yager 200i it should be close to 200.
It's like computer monitor's, used to be a 17" was 17" now it's 15.8" viewable.


Yeah....just like seedless water melons that contain seeds......

[JC]

The oil pump isnt really necessary. I didn't change it on mine i left the stock one in it. I dint want to split the case to install it so i just left that part alone. BTW it isnt any more chinese than kymco is! I am not talking bad about kymco either i prefer my kymco over beamers and zumas and other scooters. My agility 50 will beat theirs all day even before a BBK.

While I love my a50 as well, there is no way in hell the agility would touch a Zuma on any day of the week for many reasons even with it derestricted. The Zuma is a 2 stroke and if both are stock the 4 stroke doesn't have the torque to hold a candle to the Zuma.
On the bbk, I've found that many sites have kits for short money. I'm researching one that is Taiwanese instead of Chinese because of quality. So far I've looked on monsterscooterparts.com, scootertronics.com, enviromoto.com, and racingplanetusa.com. Anyone that wants to comment on experiences or thoughts on quality, please let me know

[MotoRandy123]

Well I was reading a 2 stroke tuning book and it turns out the displacement doesn't really tell the story.
It's really displacement above where the exhaust ports close that counts. I don't think you can get
enough info to tell how good a cylinder is before you buy it. The pipe makes a huge difference too.
I'd buy a kit that had pipe, cylinder and head all matched for best performance.

[wordslinger]

...big difference in 2 stroke cylinders....ports are in the cylinder wall....4 t ports are in the head ..