Porting a china girl

King krab

New Member
Joined
Jul 6, 2016
Messages
1
I had a completely standard 80cc motor straight out of the box on a Mountian bike with 26" wheels put one tank of fuel (98 octane) on second tank had mate beside me in his 4x4 got up to 83kms no sweat
 


Steve Best

Well-Known Member
Joined
Sep 22, 2012
Messages
1,235
downhill doesn't count.
Mine won't do 83kph (52mph) downhill unless you pull the clutch and hang onto a passing truck!
Seriously. It will not exceed 66kph unless the clutch is pulled. Engine acts as a limiter.
Also tried for max speed on the bike downhill, in a tuck and drafting, 79kph. Clutch pulled of course.

As for the time to modify a stock head, bare minutes.
Well worth doing for the learning and comparison value alone.

There are 3 main modification goals, 1) squish band width, 2) squish band gap, 3) compression.
Squish band width is helpful in reducing both detonation AND reduces timing advance need.
More area helps low end torque but exceeding 50% of head area is generally not helpful.
Squishband gap is essential to be in the 0.010" to 0.040" range for effectiveness. 0.020" to 0.030" preferred.
Compression helps low and mid-speed performance and torque but increases heat, especially in the piston.
I'd believe Jag's advice on compression. With Yamaha Blaster's we set a higher limit but it is a stronger engine.
For well piped 2 strokes I've generally dropped compression and timing to let the pipe do its work.

Of course cylinder height can be adjusted with base gaskets and will adjust compression, but you still have to keep squish gap in mind. A higher cylinder typically produces a higher powerband, all other things being equal.

As for head cooling, I've had no problems with any head overheating that I could tell, but then again, our temps here seldom exceed 30c with 15c to 20c being the norm.

Steve
 

Bufu racing#1

Member
Joined
Feb 23, 2016
Messages
42
that's because you guys have to buy a degree wheel a learn how to use one. I'm at 70+ mph on gasoline!
same none balanced 38mm zea50 crank. =)

i build and own the fastest china motors in the world and ill take the pepsi callange with anybody.
I'm a god


1....these cylinder you all have are chrome plated all of them
2... all of your cylinders tranfers are to low and sometimes not even even on both side .. yes even with a 38mm crank .. x cylinders, even worse..
3...all of the china cylinder are made from factory to have (blow by) we correct this.


britt vanegas on facebook
 

jaguar

Well-Known Member
Joined
Nov 25, 2010
Messages
3,453
the transfers are only too low if you are targeting a high RPM output. For normal street use they are OK after being made equal.
I didn't think the out of round cylinders could be fixed because of the thin plating. Can you describe your fix?
 

butre

Well-Known Member
Joined
Dec 2, 2013
Messages
2,502
the transfers are only too low if you are targeting a high RPM output. For normal street use they are OK after being made equal.
I didn't think the out of round cylinders could be fixed because of the thin plating. Can you describe your fix?
sleeved cylinders. it's easy enough to do if you have access to a lathe. supposedly you can get up to a 52mm bore out of a sleeved china girl cylinder but I imagine wall flex becomes an issue at that point
 
Top