Tuesday, December 22, 2009

Super Stock Ciao

The lowly Vespa Ciao is one of the most elegantly designed motor vehicles ever produced. Truly the 'volkswagen beetle' of mopeds, its simple, rugged, compact, and designed for cheap mass production. Its no wonder the tuning scene in Europe has gone completely bonkers for these bikes. The parts, knowledge, and resources available for these dwarfs even the mighty puch. Being knocked-off in India doesn't hurt either, making this the most produced, cheapest, and simplest moped powerplant ever.

Ever since I picked up this low-mile rigid Ciao, I knew it was a vehicle with massive potential. TreatsHQ declared 2008 the year of the Ciao with a flood of vespa parts, and I was itching, but other projects took center stage, and it got shipped all over Wisconsin as my beat-around loaner bike. Two years came and went until about a month ago when I decided to set it up for my girlfriend, because what's better than pretty girls on Ciaos? Pretty girls on ridiculously fast Ciaos! (especially when they are stock and embarassing kitted bikes)

The Ciao's massive potential lies in its unique induction system. Rotary-valve induction is different from piston-port and reed-valve induction, in that the opening and closing of the intake valve is controlled by a mechanical valve, usually a disc on the end of the crankshaft, that opens and closes with the rotation of the engine. The rotary valve offers the low flow-resistance of a piston port, with the asymmetrical timing of the reed valve, for a 'best of both worlds' situation. The main drawback to rotary valve induction is the extra cost of the mechanical hardware which forms a tight seal, and extra complexity. Vespa engineers, however, solved this problem by incorporating a recessed area into the crankshaft web, and placing the port on the back of the crankcase where it would be covered and uncovered by the rotating crank web. Genius!

Seeing as this is the only moped made with this style of induction (aside from a few rare Kriedler models) I wanted to see what could be done in the way of unleashing the potential of the rotary valve. Rather than piston ports which just offer two dimensions of tuning (duration and area- time/area) and reed valves which are pretty boring (bigger=faster, yawn!) the rotary valve allows for tuning of duration, advance, area, and in the specific case of the vespa there is a lot of room for improvement. I started the tuning process by researching and studying the rotary valve system itself, and based the entire performance build around the idea that tuning for certain intake characteristics could yield high torque across a wide powerband, with maximum power in the mid-upper mid range. Two years gave me a lot of time to study and think about the improvements I wanted to make, and my research had already yielded a pretty conclusive game plan before I removed the first screw.

Valve Modifications:
Starting with the rotary valve, the geometries of the parts themselves can be improved for flow, specific opening and closing characterisitcs, etc. Looking at the assembly in 3-d, the passage of air from the carb inlet to the cylinder is hampered at any number of places, most likely due to manufacturing considerations. Right away the inlet 'manifold' nipple that the carb clamps onto is much too small to flow enough air. The rotary valve is very efficient, and capable of extremely high intake velocities, so the carbureation can remain relatively conservative, but there is no reason not to maximize the size of the intake tract. The largest I could bore the front half of the Dellorto SHA 12:10 carb out to was close to 14 mm. To maintain the integrity of the nipple inlet, i went to a more conservative 13-something for the nipple, and to match, the back-half of the carb. This was reamed far enough in, that the rest of the porting in the intake port could be smoothed for minimal flow disturbance.

The 'pencil grinder' which is a tiny little pneumatic 1/8" shaft grinder I bought at harbor freight, is invaluable for this stuff. I could actually stick the whole grinder right in the intake hole for the finish work. I left things a little rough because I really dont care that much about making it look good. A slight bit of surface roughness can actually improve flow characteristics if you are dealing with a convoluted shape, but to be honest, I'm just too lazy for all that tiny grinder bit junk. As you can see, I've opened the port up just about as big as i can safely go. The edges are round, because anytime you flow through a square tube, you basically have no flow in the corners anyhow, and this will make the transition easier and prevent any weird eddy-current crap. The primary concern is not breaking the seal made by the crankshaft web on the ground smooth surface around the port. Opening it up 'all the way' like this is only going to change your intake timing by a matter of a couple degrees and this engine is already absurdly conservative in porting.

Because the crankshaft serves as the rotary valve, opening and closing this port, the modifications made to it, directly translate into the modifications made to the port timing in the cycle. To calculate this, in degrees, just measure the diameter, dummy. I used a paper strip wrapped around the crank web, then i double-checked using the diameter, because the paper couldn't be tight or it would shortcut the recessed area of the crank web. Simple geometry will get you into radians of port timing, then degrees if you prefer. I'm not going to share all this, because I think this might be a competitive bike in stock cylinder racing, and I want a leg up on y'all, but if you really want to copy me you can probably figure it out from the picture. I also added some 'flow improvements' to the open area, sortof like knife-edging but in multiple dimensions.

Man grinding on that hardened steel is a real pain-in-the-butt. I still have slivers all up in my fingers. Brutal. The results are well worth it however, the modifications to the intake tract like this can easily out-flow a smallish 4-petal reed. Just think about how much flow area there is while this port is open! Compare that to four little slits 1/8 by 1/2 inches. Not to mention the fact that no energy of the incoming air is being lost opening the valve. We're talking about serious flow here, from a 13mm carb. Exciting!

To finish everything up, I ground out the transfer ports to match the modifications to the cylinder (which we'll talk about later) and to ensure smooth flow between the back of the crank-case and the transfer ports. Its hard to imagine how this all works in three-dimentional space, but I think I was able to clean everything up for a small improvement. I ported the case about as big as I felt comfortable, so if this engine ever does end up with a kit, it wont have to be rebuilt.

Disassembling and reassembling these cases is the nicest piece of cake in the entire moped tuning world. We're talking easier-than-legos easy. Heated bearings, dropped them on, heated cases, plopped it all together with a nice brown-paper-bag gasket and a few dabs of sealant. I splurged for the nicer bearings and seals from my friends at Allied Bearing(still cheaper than the moped shops) because I have a feeling this engine will have the ever-loving piss revved out of it, and I want it to be reliable for many years of blasting.

Cylinder Porting

To say the stock porting is restrictive is an understatement. I took a port tracing to start with, and was very confused by the results. The port map i traced showed the bottom of the exhaust port was 46 mm from the deck. A lot of very slow stock bikes (cough, Batavus, cough) have a ridiculously high deck height, making the piston come a few mm short of the deck at TDC. This drops the compression dramatically and gives you that nice speed restriction Iowa tuners and 'Scared Mommy' magazine are always raving about without having to make pesky tooling changes. I figured this is what was going on, and the wear pattern from the rings seemed to agree, coming well short of the top, so I proceeded to calculate my new port map assuming the bottom of the exhaust was BDC. Once I got everything together, however, I realized the real reason for the discrepancy was due to the piston coming up and covering 3 mm of the exhaust port at BDC.

This is huge

For 3 mm of the already tiny exhaust port to be covered at BDC is shocking to say the least. Correcting this massive error alone could account for an additional 5-10 mph on a stock bike. Its the same thing as raising a stock exhaust port 3 mm, not to mention the transfer ports, which are level with the exhaust on the bottom. To correct this error, I machined a whole 3.25mm off the top of the stock piston, along the edges, leaving more material in the top of the crown to effectively create a 'squish band' between the stock head and the modified piston.
This will drop the edge of the piston to the proper placement for the exhaust port timing, but will cause the piston to rest a full 4 mm below the deck height. I solved this problem with an iron fist. More accurately, the facing mill, which I have now nicknamed the 'iron fist' as it has proven itself to be an invaluable and dangerously aggressive tool for dealing with these sorts of things.
As you can see, the casting wasn't machined on center, but the milling was done true to the cylinder base face, so it should be accurate, not that it really matters all that much for this. Four millimeters is quite a bit, and what you see left of the top fin, is thin enough to slice tomatoes... which reminds me of an infomercial.

Once the cylinder and piston agreed with my theoretical port map, I did a little math and came up with a port map to highlight the strengths of this little machine. Since this is all for my girlfriend to have a nice, cute, reliable bike she can ride with the gang, I didn't want to make it too crazy, but it would have to keep up with the rest of the Cranks at 35-40 mph. The Ciao is so light, and geared so low, that torque isn't as critical as mid to top end power, plus the Tecno Circuit is a pretty torquey pipe. I also have a lot of faith in the stock single-speed dry clutch. Its simple and easy to get/make parts for, so I figure I can sacrifice some low end if I lighten/tighten up that clutch. The rotary valve was designed, along with the pipe, and the cylinder, to start pulling hard around 2-3k rpm, and hang on up to 8-9k. I went pretty huge with the exhaust and transfers, because I know that pipe will keep the low end manageable, and I wanted to have a little bit of power on the top end when the pipe is starting to poop out. I'll probably keep stock gearing for daily riding, but the plain ol' pulley makes it really easy for me to alter the 'gearing' with a short trip to the machine shop, so I might play with that a bit depending on what the GF likes.

The transfers on this engine leave a lot to be desired, and present a serious challenge for the tuner, because there just isn't any room around them to open them up conventionally. Everything has to stay symmetrical for proper scavenging, and that means getting into the two interfering studs next to the exhaust and the one transfer. To lay things out, the studs were drawn into the port map, and I started measuring. The exhaust port is off-center in relation to the transfers. For a moderate build, it could be widened 4 mm on one side (away from the stud, thank god) and probably make 90% of the performance gain my build is going to see. To push it a bit farther, I went even bigger with the exhaust, and bigger with the transfers, shifting them all away from the offending stud near the exhaust. The Transfers couldn't go out much, but they had a few mm to go in, by removing the absurdly thick cylinder skirt and making them 'finger' or fully open ports. I like to be precise about these things, so I took the cylinder into the machine shop and roughed out the ports. I also added a 3rd transfer 'boost' port in between the two gudgeon pins opposite the exhaust. This is directly adjacent to the third stud, so it couldn't be very deep away from the piston, but the boost port doesn't need to be very large to have a huge impact directing and energizing the air out the exhaust port. This should really liven up the 5k-7k rpm range where the pipe is starting to come off its powerband, and give a lot better torque on the bottom before the pipe is hitting. This is the cylinder back from the machine shop, rough, but the important stuff is all there.

The exhaust nipple was also reamed out as large as I felt I could go before compromising the integrity of the metal. I'm kindof touchy about exhausts, because of bad experiences with my Sachs, and dont like to take chances. At this point I still didnt have the pipe so I couldn't match them, but it turned out to be very close.

Once things were roughed out in the machine shop, it was grinder time. A lot of it. Probably about 5 hours total behind the grinder cleaning up the transfers, booster, and cases to make sure everything matches.

Still pretty rough

Getting a lot better

Finished.. with a custom-made base gasket, felt rubber for maximum sealage.

Whew, thank god for photo montage, that would have taken all day

After finishing up the cylinder, and cleaning everything up really thoroughly, the head was bolted back on and i did a quick compression test. I didn't take any photos of the embarassment, but I think my face mill left things a bit too rough, because I had to use a modified puch aluminum gasket and a tiny bit of goop to hold it in place. Ugh, i hate gasket goop, oh well, things seal great now. Torquing those 3 7mm nuts is very touchy, if they are just the slightest bit off they are real prone to leaky nonsense. Who uses three studs? Whatever.

Frame and other such necessary junk.
As much as I hate to admit it, moped engines actually have to go into frames at some point to realize their true potential. I guess that part just doesn't interest me much. Once the engine was back together, and the electronics were re-installed, I slapped it back in the bike. The wiring was a mess from a previous owner, but I had to redo most of it anyways because full-rigid wasn't going to cut it for a daily driver. As much as I love the ciao's aesthetics, either springer front or rigid, they are both almost un-rideable on Milwaukee's war-torn roads. After doubling the speed, I didn't feel very good about putting my girlfriend on something even I had trouble controlling, so I started trying to find different forks. I had a pair of maxi, garelli, and hobbit forks laying around, all of which I tried. The Hobbit forks seemed to be the best fit for size, looks, etc, and they have the same threads as the top nut from the garelli forks which uses the same 'outside' bearing as the vespa forks. Bingo. The tube was the perfect length for the ciao, but not big enough to fit the post style handlebars. Blah blah, boring stuff. Wiring, handlebars, brackets for the headlight. Not done here, but you can see it coming together.

Running with the pipe on.

First start went perfectly. Fired on the first kick, jetting was correct for my basement. No funny business. I adjusted the timing a bit, initially I retarded it a bit from stock because of the porting, but after running it a bit, it seems like stock timing works best. The cold streak we've been having has prevented me from getting out and test-running it, but it pulls really hard on the stand... cant wait until I finish my brake dyno. More results and pictures of finished bike to come!


First ride on the bike was kinda lousy actually. It was on a very cold day at the beginning of January, and the jetting was way too lean, no power whatsoever, and super boggy. I brought it back in and adjusted the timing, which for some reason was way off, possibly didn't press the foot down enough when gapping. I made a quick hi-flow air filter to richen it up.

The finished bike came out pretty clean, I had to make some headlight brackets.

Here it is all done.

I'm really serious about clean engine bays, wire routing, cables, etc.

So, fast forward a couple weeks, the nice weather yesterday was just too much, I finally got out again on the bike and got a chance to wind her out a bit on lincoln memorial drive. The results are sortof dissapointing. Only 43 mph top speed on the flat, but it picks up to 46 on the down hill (a bit too fast for a rigid if you ask me). I think the compression is too low. I never did actually turn down the head, so i might still have to do that. Also the questionable rings I re-used might be weak. Also the warm weather threw my jetting off again, and now its too rich.

I'm really not happy with the low end either, before the pipe hits, it has no power whatsoever. I know I need to tune up the clutch quite a bit, but there should still be more torque than there is. Correct jetting, finer timing adjustments, and some serious clutch tuning will all be conducted as soon as i have some time. Stay posted for more awesome.


  1. put that piston in a lathe and get a nice sharp cutter; give it a sweet finish at high speed for your last thousandth. I'd love to see how it turns out!

  2. At least you have your ove glove, right?

  3. ove glove for the win.

    its going together as we speak, hopefully my TREATS get here in time for the X-Mas unveil.

  4. wow graham, this is amazing. i really like what you've done. really makes me want to play around with the stock cylinder. although i broke my dremel months ago...but eventually i'll need to get a new one to work on other things. so maybe i'll find my way back to this post to get some ideas. i'm really interested to see how this performs

  5. AHHH my treats came to the wrong house... DAMN YOU UPS! I'm going to go pick them up in a little bit. Results after christmas.

    plus amazing things about deck heights and stuff. surprising results, astonishing conclusions...

  6. I just got some serious science dropped on me. Thanks. This makes me wish I hadn't just shelled out for a DR kit!

  7. How do you fit the engine in the frame? I have a 78 ciao and I can't get the engine in the frame because of the crank shaft

  8. did you drill a hole in your piston to accomidate for the boost port? i'd really like to see how you'd do that

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