China girl 66... Maximum RPM?

[butre]

are you really serious that they are built from beer cans? If so i'm building my own from Australian beer cans. LOL

it's not really beer cans, that's just an old joke. beer cans are actually a very high quality aluminum. china girls are made of whatever scrap aluminum is available, including beer cans, old broken car parts, etc. if a transmission is grenaded they'll break it up and throw the aluminum housing in the furnace, if the foreman just finished a six pack, into the furnace it goes. the problem is that they don't bother to clean the grime off the scrap.

 

[skyash]

no riding just on the spot my rev gauge says 11000 revs on the go i can get 67kph at just over 9000 with a 36t sprocket but how good is the gauge .and i have herd the stock cdi is made to go from 500 rpm to 8000 rpm .i to sit at top speed all day .

 

[Steve Best]

That's 41 mph!!! What have you done to your engine. 41 is winding out though I know that, I think I was hitting 7500ish around 37 with a 44tooth

Stock bottom end, stock piston, Grubee $20 chrome exhaust chosen for speed, scratched up cylinder with in/ex both ported wider, exhaust port and pipe matched, intake left mismatched stock sizes, factory head with hand sanded extra squish area set to 0.038", NT carb (stock jet, lowered float level and needle), soda bottle intake (no filter for this run), NGK BPR6HS plug, tires at 40psi, chain lubed and brakes attended to.

See! It's easy!

The other night I noticed I was hitting a "wall" just over 60kph even on a downhill but I didn't have a GPS. I switched back to the modified factory head because it delivers more speed than the aftermarket head (less low and mid punch though). At 62-66 kph I would have audible detonation that would cascade worse with a noticeable loss of power whether going up or down a slight hill. It might go away if I try a colder plug, so I will do that. The bike will not exceed 66kph kph under power even down a steep hill. To go faster I have to pull the clutch.

Steve

 

[Steve Best]

So, the math is:
tire-dia x pi x 25.4mm/inch / 1000 = distance of wheel rotation in meters
speed in kph / 60min/hr x 1000m/km / distance of wheel rotation = wheel RPM
(wheel sprocket / shaft sprocket) = 44t/10t = 4.4
(clutchgear teeth / drivegear teeth) = 82t/20t = 4.1
Wheel RPM x (wheel sprocket / shaft sprocket) x (clutchgear teeth / drivegear teeth) = Engine RPM

So my 66kph is 9565 rpm, sound right?

Tire sprocket speed rpm speed rpm speed rpm speed rpm
26" 44t 40=5800 50=7250 60=8700 70=10144
26" 40t 40=5270 50=6587 60=7905 70=9222
26" 36t 40=4743 50=5929 60=7114 70=8300 80=9486

Steve

 

[skyash]

Stock bottom end, stock piston, Grubee $20 chrome exhaust chosen for speed, scratched up cylinder with in/ex both ported wider, exhaust port and pipe matched, intake left mismatched stock sizes, factory head with hand sanded extra squish area set to 0.038", NT carb (stock jet, lowered float level and needle), soda bottle intake (no filter for this run), NGK BPR6HS plug, tires at 40psi, chain lubed and brakes attended to.

See! It's easy!

The other night I noticed I was hitting a "wall" just over 60kph even on a downhill but I didn't have a GPS. I switched back to the modified factory head because it delivers more speed than the aftermarket head (less low and mid punch though). At 62-66 kph I would have audible detonation that would cascade worse with a noticeable loss of power whether going up or down a slight hill. It might go away if I try a colder plug, so I will do that. The bike will not exceed 66kph kph under power even down a steep hill. To go faster I have to pull the clutch.

Steve

i seem to get the wall thing a lot one day i went down hill hit the wall so i kept going for maybe 5min then down one more hill still flat out stuck on the wall at 65kph then the wall just went away the motor went faster and faster revs where so hi ended up getting 77.1 kph and speed wobbles for the hole rode maybe 2km long till i let go of the accelerator . the truck behind me was doing 70kmh. after that when i get to 65kph now it hits the wall .i can still feel it wants to go more but just wont

 

[skyash]

me and my friend have called it the wall forever pretty funny you called it that lol. i tired every thing to move the wall but no luck .

 

[HeadSmess]

one small error in the maths...

bicycle tyres are measured funny, so you get quite a large difference depending on if you run 1.25 compared to 2.25 etc.

i vaguely recall 2124mm being the circumference of whatever tyres i ran when i tried using a speedo.

you cant just use the figure "26x3.14" and get it accurate enough. gotta do the old "chalk marks on the ground and get a tape measure"...

iunno, i always seemed to be around the 8000 rpm for 60km/h. never bothered making pipes designed for much different speeds either. 7500 rpm to 8000 rpm, the one time i tried a 9000 rpm pipe, it never got up there...

8000rpm sounds approximately like "C". tad on the sharp side. standard 440 tuning, C is 7849 RPM or so.


mmmm, overtones...

 

[FurryOnTheInside]

one small error in the maths...

bicycle tyres are measured funny, so you get quite a large difference depending on if you run 1.25 compared to 2.25 etc.

i vaguely recall 2124mm being the circumference of whatever tyres i ran when i tried using a speedo.

you cant just use the figure "26x3.14" and get it accurate enough. gotta do the old "chalk marks on the ground and get a tape measure"...

iunno, i always seemed to be around the 8000 rpm for 60km/h. never bothered making pipes designed for much different speeds either. 7500 rpm to 8000 rpm, the one time i tried a 9000 rpm pipe, it never got up there...

8000rpm sounds approximately like "C". tad on the sharp side. standard 440 tuning, C is 7849 RPM or so.


mmmm, overtones...

Indeed, actually measuring the rollout on the ground in millimetres is the only truly accurate way to program a speedometer and odometer.
For a quick (and approximate) calculation of mph or kph per 100rpm of the drive sprocket I just use Sheldon's gear calculator set to " 26" nominal". It only gives a value to one decimal place so it is a lot more accurate with bicycle gearing (shift kits) because the mph/kph value is higher.

 

[Steve Best]

Another beautiful day so out for some testing I go.
Today's subject is sparkplugs and top speed detonation. Is it ignition or plug related?
I rounded up these contenders:

Chinese Z4, three pronged Z4CJ, NGK BR7HS, NGK BRP6HS, and a B6HS. Included is my comprehensive road tool kit.

I have been running the BRP6HS pretty much since the 3 pronged Z4CJ fouled while running the original 16:1 oil recommendation.
A "projector" plug just seems like a good ideal doesn't it?
Well, it was the worst plug in the bunch. Weak at low speeds and rattley at top speeds.
The worst prone to detonation.

Three pronged Z4CJ gave excellent low speed ignition, better starts and low speed operation which is not this cylinder head's forte. It too however was prone to detonation at top speeds.

B6HS, same heat range I am used to running but non-projected and non-resistor plug. It was new so that might account for the better starts than its projected counterpart. It doesn't account for the less detonation. Overall the non-projected plug seemed to work better.

BR7HS one heat range cooler. Much less detonation at top speeds. Still happens and still cascades worse, but this was the best plug for detonation resistance.

Chinese Z4 seemed to be the best plug overall. Didn't start as well as the Z4CJ and not quite as top speed detonation resistant as the BR7HS but worked very well overall.

Note the Chinese plugs seem to be similar in size to the Champion CJ8 and both seem to work well in this engine.
Also note the heat range system for Champion is opposite NGK. Higher is hotter.
The Chinese heat range numbers work like NGK but may not be the same values.

Not a very comprehensive test, but I learned something.
1) Colder plugs are needed for extended high speed operation.
2) This cylinder head does not like a projected plug;

Your mileage may vary. I forgot the GPS so was unable to make any top speed comparisons.

Speaking of mileage, I used 600ml (zeros are usually an indication of an approximate value!) of fuel to go 36kms at pretty much WOT all the way, which figures to 1.6 L/100kms or 147mpg(us) or about 62kms/L.
I am impressed

Steve

 

[Frankfort MB's]

Could try the b8hs. Very cold plug I don't get any detonation...