October 22nd, 2007


land-speed-record scooter update

I spent much of this weekend further hot-rodding my Aprilia RS50 scooter. Progress to date:

Back in April of this year, I replaced the cracked stock (iron 49cc) cylinder with an aftermarket aluminum 80cc cylinder, piston, pin, and head assembly. This added immense more power over the stock output; no longer did I need to feather the clutch when starting off - the stock engine died if I let the clutch out too quickly - and it gained torque and horsepower across the RPM spectrum. However, the new engine was limited by the geared-for-acceleration sprockets and teeny-tiny carburetor.

For your reference, here is how a high-performance two-stroke engine works:

Click the image to see the wiki article.

Here's what I did to my scoot this weekend:

  • Replaced the sprockets. Stock is 12 teeth front and 47 teeth rear, resulting in a theoretical top speed of 62 mph at 12,000 RPM. My new sprockets are 15:43, with a theoretical top speed of 85 mph. Also, the rear sprocket is now aluminum, meaning shorter life but a lot less unsprung weight for quicker acceleration. I didn't replace the chain (it only has about 3000 miles, and the sprockets looked nearly new), but I did clean the grime out of it and thoroughly lube it.

  • Replaced the stock carburetor. The stock carb has a tiny 12mm bore, and it also features a water-heated passageway to make it easier to start in cold weather while also reducing the intake air-mass. These features limit power in two ways, reducing flow and reducing the amount of fuel/air mix entering the engine. My new carb is a 24mm Mikuni unit. That's twice the diameter, resulting in something like four times the airflow. And sans heated intake, it moves a lot denser fuel/air charge.

  • Clearly, the stock airbox with its tiny snorkel would have strangled this new carb, so I removed that and simply capped the Mikuni with a free-breathing, washable, pod-type filter.

  • Next in line bringing fuel/air mix into the engine is the reed cage (that's the little rectangular flapper device between carb and engine in the graphic above). In a two-stroke engine, either a rotary valve (as in most Vespas) or a reed cage allows the intake charge into the engine at the right moment. My new cage uses bigger reeds that open further to let in much more intake charge. The reed petals are also made out of carbon fiber, which is far lighter than the stock metal petals, so they open and close much faster for better intake timing.

  • I also did some other needed work, like replacing a cracked blinker lens and cleaning every part of the machine that is normally covered with body panels and the like. I must have spent several hours just cleaning and Armor-All-ing the plastic.

So, how did it work? Here are my top speeds so far:

Stock: In stock trim, this bike will do about 45 mph.
Stage One: Otherwise stock, the 80cc cylinder kit brought top speed to about 60 mph.
Stage Two: With new gearing, new carburetor, new reeds, and new air filter, I hit an indicated 76 mph at just under 11,000 RPM. Top safe RPM on this engine is 12,000 RPM, so the theoretical top speed of 85 mph is probably attainable with this new configuration.

Stage Three will include a new exhaust chamber (exhaust resonance makes a huge difference in two-stroke engine tuning). Stage Four: Back to 49cc cylinder kit (for the land-speed-record run) with nitrous injection! With the addition of a racing exhaust chamber and nitrous injection to the current intake and gearing setup, I hope to boost the little 49cc engine back up to its 80cc performance, meaning the 49cc stock-body/power-adder record should be mine!

However, I have to admit that the biggest barrier to higher speeds right now is me. I'm six feet tall and rather broad across the shoulders. With my helmet tucked behind the windscreen and resting on the gas tank, my elbows pressed against the middle of my thighs. Also, I weigh about 180-185 pounds, about as much as the scooter, itself. When it comes time for the real top-speed run in 49cc configuration, I think I'll ask my friend, Alex, to do the run for me. He is probably several inches and 40 pounds lighter, which means he'll get up to speed quicker and be able to reach a higher top speed. *sigh*

More news as I get it!

galaxy M51

Astro-image of the day: the Milky Way

When's the last time you had a night-sky view like this?

Click the image to see the story.

True, you can't see color like that with your naked eye, and the nebulae are tougher to see without a time exposure, but the naked-eye view of the portion of Milky Way that we can see from Earth is still spectacular.

When I was a boy living in western Minnesota, on Moon-less nights I could see a sky like this by simply walking a half-mile from our house, which stood about a mile from the nearby small town. We lived in a little valley beside the highway, half-way between the golf course about 500 feet vertically uphill (thus the half-mile walk up) and the lake about 1000 feet of walking downhill. I often dragged my Crown Optics 6" telescope up that hill to the wide, dark skies visible from the golf course.

PS: OMG - I did a quick search and found the original 1982 advertisement for my first serious telescope! I bought it with dishwashing money, plus a 35mm camera, an assortment of eyepieces and other accessories, and a big guide-scope just like on the "Research Series" telescopes. Collapse )

Interesting to be reminded that it was a Meade Optics brand, and my next telescope is also a Meade Optics instrument... more on that when it arrives. I plan to start uploading my own Astro-image of the day in the next couple of months after getting used to the free CCD camera included with the purchase. And, because tmseay is now storing his Celestron 8" SCT at my place, I plan to organize some mini-star-parties in the coming months, taking advantage of the dark skies south of town.

That was a fun trip down astronomical memory lane. And if you've never seen the Milky Way in all its glory, get out to some dark skies sometime and just lie back looking up. Bring a binocular and slowly scan through the clouds of gas, dust, and stars that leap out of the eyepieces like fireworks. It's glorious.


childhood memory

normalcyispasse reminded me of this; he's teaching in Korea now, where I lived for about a year during my first-grade year. Thought I'd share the story here:

When I was a little boy living in a boss-owned neighborhood north of Seoul, the boss-man invited my mother and me to his house for frequent dinners. Americans were rare then; it was during the Vietnam War, and soldiers' families weren't supposed to be there. So it pleased him to have as guests these exotic foreigners, especially me and my brother with our blond hair.

I recall eating many things I wouldn't have touched while living in the US. But Boss Man explained to me that since my dad was away serving on the DMZ, I was the man of the house and must eat what's offered to save face for my family. Gourmet items he offered included things like transparent soup - served in glass bowls, of course - with complete fish (and other objects) floating within them; octopi the size of small children; "Thousand-Year Eggs" and their attendant bouquet; and all manner of stinky and spicy foods I couldn't hope to recognize and wouldn't touch today. But I ate them, because Boss Man and his sons had frequently demonstrated how important "face" was to them, and I didn't want to harm my family.

I would love to be able to watch the Koreans' faces while I stoically put such delicacies into my mouth, a little 6-year-old boy eating what I'm sure many of them wouldn't dare try. I do recall hearing some of the Korean party guests laughing as I ate something. Ha ha.