Honda PCX150

[sendler]

In the search for more power from a motorcycle, the first move is usually to change to a louder pipe. Modern fuel injected engines make this easy as the closed loop adaptation from the O2 sensor often has enough range to adapt to the free flowing exhaust to get the mixture right back on the map without any electronic "rejetting". A cutaway of the muffler of the PCX, and other photos I have seen where people have actually disassembled the can to remove it's guts, shows that the gasses come in the front through the catalyst, travel to the rear in a large pipe where they exit into the volume of the can, come back to the front of the can through a few large baffle openings where they enter another smaller pipe that runs all the way to the back again where they run into one more flat "wall" baffle before rushing around it to get out. An excellent, large volume design and almost as silent as any car. I like cheap homebrew mods so I decided to try some Black and Decker tuning and save my $300 from buying a nice Leo Vince. If I didn't like it I can always find a take off exhaust to buy that someone else has just laying around after replacing theirs.
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The cutaway image wasn't completely accurate in showing all the supports inside the can so I ended up with a few extra exploratory holes but eventually found a sweet spot to open up the can which eliminates the trip through the long skinny pipe and the dead wall baffle at the outlet but I get to keep my cat and my $300. That muffler is built to last! The steel is very strong and is 1-2mm thick. It could very well be a structural part of the swing arm.
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The original small pilot holes surprisingly let out very little additional flow or sound so once I found some open room I went to larger holes in two steps. I had two 10mm holes and it still didn't sound very loud while revving on the stand so I drilled one more. Now that I have ridden the bike I would probably recommend a little less as it is getting pretty loud at full throttle but does still settle down to a tollerable level while cruising being just audible above the music in my in ear monitors.
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The dynos of the CBR250R usually show big gains at the lower rpms, dying away to 0% gain through the first induction tuning suck out from 4,500 to 6,000, and gaining again to 9% up through the upper midrange with a big peak at 8,700 and then falling back to stock above that to redline. The drilled PCX feels about the same. A CVT bike will never run at low rpms so there is no performance to gain there and the final pull to top speed at 9,600 rpm feels about the same although cruising at 9,000 rpm is using less throttle than before. Not a big gain at full throttle on top.
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Fuel economy is up slightly by 2-3% as is the weighted hill climb speed, from 48 mph to 49.5 at 7,000 rpm. 0-50 mph test runs were very windy again and are quite difficult to do accurately but averaging all of the two way runs, the improvement was less than I would have thought. Down only .3 seconds from 13 to 12.7.
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Next up will be some DR Pulley sliders at 12gm and then a "1500 rpm" (whatever that is referring to) torque spring to increase the pulling rpm from the stock 6,600 up closer to 8,000.
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[sendler]

The guys at Scooterworks.com had an NCY drivetrain upgrade kit for the PCX which allowed them to determine that the contra spring has the same dimensions as all of the standard GY6 125cc springs. They stock the "1000 rpm", 1500, and 2000 rpm springs. I tried the 1500 for $18 shipped and installed it with the stock weights which will take about 20 minutes next time. It is really stiff! I'm glad I made a rough measurement of the comparative spring rates before putting it in. You can measure it with a digital scale. Choose a socket with an extension in it that is about 70% of the free length of the spring and place it inside the spring on a scale. Tare the scale to zero and then press down with your hand until it is just skimming the top of the extension which is being used as a travel gauge. I found 6.5kg for the stock spring vs 10 kg for the new one. The aftermarket spring is a whopping 35% stiffer. Takegawa lists their spring at 11%. I wonder what it really measures. I put the NCY in anyway to see what it would do. My PCX is now much more responsive. It now immediately down shifts, or revs up, whichever way you want to look at it, when increasing the throttle. All of the rpm ranges were shifted upwards. Even mild coast down. Light cruise at 30 mph is running 5,000 rpm now and it immediately jumps to 6,400 on accel. Maybe this is the 1,500 rpm the rating is referring to. Once past 30, the pulling rpm continues to rise up to 7,400 whereas it used to be 6,600. I may get a chance to do some timed runs later today but it feels much quicker. There is still some action at 50 mph. The stock drive train has the weights locked all the way out by 50 mph with almost no kick down available. The new spring still allows some down shift from 7,000 to 7,400 at that speed. Pulling speeds of 8,000 are said to be at the power peak so I can still go with slightly lower mass in the weights but the 12gm sliders I have are probably too low now with this spring. There is a big loss of top speed though so I am going to try the next lighter spring and then play with the weights and may even spend some more money to see if there is any difference with a kevlar belt. I'm not sure if the loss comes from the rear torque pulley being still too active over 60 and pulling the weights off of the stops, or if the added spring force is squashing and stretching the belt slightly causing it to ride lower in the front pulley even though the weights are all the way out. Top speed now varies from 62-65 mph at the rev limiter depending on the wind. I used to get 67 every day easily. The good news is that there is quite a bit of untouched metal on the face of both pulleys. Once I settle on how much spring and mass to use, it occurs to me that there may be another big advantage to the sliders. It might be possible to tune a set for any given combination of parts on a bike by looking at the remaining virgin metal. We might be able to remove some of the material on the part of the slider that is in contact with the variator at the outer stop little by little until full belt travel is achieved.
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The last image shows the famous torque grooves. Honda is using a progressive profile. Kick down should become less active at high speeds.
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[sendler]

The changes made by the super stiff contra spring are a wash and choosing to change it will depend on your intended use of the scooter. The big advantage is increased 5-40 acceleration. I haven't done any timed runs in this range but the spring makes the trans instantly down shift over 1,500 rpm when cruising at 20 mph and gunning it. With the initial increase in speed that is also occurring, the rpms jump right from 5,000 to 6,800 and continue to wind up to 7,400 by 40 mph. The 0-50 times are down some to between 12.5 and 11.8. call it 12.2 which is .5 seconds lower than before the spring but this maybe too broad a test to really show what is happening between any rolling speed and 40 mph. The problem with 0-50 as a test is that the launch is very slow. There is a programmed delay in the engines output on take off. I haven't timed it but it is at least half a second. Maybe more. No changes will ever effect this unless you get into a replacement fuel ECU or something. So this is always dead data right in the front of the timed run. The next issue with using 0-50 as a yard stick for playing with the trans is that by 50 you are close to max gearing and will be near the power peak so changes in 40-50 times will be very much less affected by the small amount of gearing change that is left at the top of the gearing. 50 mph used to run about 7,000 under load and now with the spring it runs at 7,400 as it is still getting 400 rpm of kick down under high load. It used to be much less active with only about 150 rpm of change between light cruise and gunning it. The change in gearing (as indicated by the change in rpm for any given speed) is much less between 40-50 than it is between 5-40 mph. But by far the longest portion of the run is from 40-50 which isn't going to change much regardless of what you do to the trans operating points. What I am trying to say is that most of the .5 second improvement from the stiff spring is between 5-40 mph at which it becomes pretty significant. This is more beneficial to shooting through city traffic than climbing a hill on the highway. For blasting around in the city, having a stiff spring to spool up quickly and launch you out of corners is really fun.
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But in just a day of riding I can see several down sides to a super stiff contra spring. There is an obvious increase in the running losses in the belt. I think the increased compression on the sides of the belt, and the increased tension, are creating added friction and heat losses. The loaded hill climb speeds are down a percent to 49 mph. Top speed is often way down to the 63 mph range. Some of this my be due to the tighter belt riding down lower in the front pulley but I am also sometimes not making it to redline, indicating some loss somewhere. Fuel economy is also down 6% to 90 mpgUS. Partly due to higher rpms everywhere but I think also due to increased friction losses in the belt. Maybe a stiffer Kevlar belt could give some of this back but for highway commuters it looks like the light factory spring with lighter sliders might be the better option. An after market torque pulley with more aggressive slots could give a similar amount of kickdown using the stock spring as what the stiff spring gives now, without increasing the losses in the belt, but I haven't seen one for less than $160 and I am not ready to go there.

[sendler]

Here are some screen shots of what the DR Pulley sliders do differently from rollers. This is actually a very nifty invention and has been patented. Good for them.
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The only draw back seems to be the possibility of the low ratio going below the design threshold and allowing the belt to go slack on some bikes which causes a shudder on take off until the weights swing out to take up the slack. Some people have had to add a shim to stop the travel of the variator.
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I think it would be pretty easy to make the sliders heavier with my triple beam scale which could easily tune them all back into balance within a couple 1/100 of a gram after adding some epoxy putty to the center of each one. The 30 mph cruise rpms are up to about 6,000? The sliders are much more responsive than the rollers. Less friction? The revs jump right to 7,800 when cracking the throttle and it is pulling at 8,000 by 40mph but the revs drop straight back down 2,000 rpm when reaching a cruise.
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Top speed is back up to 68 mph so there is a slight gain in the gearing there from using the sliders. I had been stuck at 66 for the last few weeks with .5mm wear on the belt already at 2,000 miles. I am hopeful that I can still see more top speed gains by tuning with a file the control edge of the slider that is responsible for the high stop as I still have 2 mm of unused pulley with the stock rollers. And I may take them up to 13 gm, the stock rollers were 18 gm, to see what that does. The epoxy will be very easy to drill back down if I want to lower the mass again. Surprisingly, my weighted hill climb trial was unchanged in top speed even though the rpms were running 8,000 at 45 mph instead of 7,000 which is right at the power peak of 8,000 and is using a gearing advantage to increase the revs. Fuel economy was unchanged so far so I don't see any need to add mass to the 12 grams that I have in there now.

[Bruce]

Very interesting. Thanks for taking the time to post your experiences.

[euromodder]

Interesting.
Scooters like this could half many people's fuel use, at rather low cost compared to a car.

[renault_megane_dci]

you documented this very well, thank you.

I wonder what the slider loaded up to factory settings will do (you said you'll do that, right ?) same as short shifting ?

[sendler]

The sliders seem to have a little less stiction(high tech lube impregnated plastic) than the rollers so they have a more dynamic response. The are much less prone to developing flat spots and ridges than the round rollers also so they maintain their maximum dimension better to retain all of there original pulley deflection for top speed. And the top speed is increased slightly with them as they are shaped to slide out slightly father than the rollers. I was disappointed to find that my weighted hill climb speed (270 pounds of rider and ballast vs a steep steady 7% two mile hill) stayed the same even though the rpm was higher. I could add 1 gram of mass to each one to bring the pulling rpm back down a bit but it pulls at 7,800 rpm now which is not outrageous. And the weights are still fully deflected by the time I reach 50 mph so my economy above that speed will be unchanged. Over all fuel economy is actually up a couple percent this year for some reason so I have no real reason to open the drive train up again at this point. I will spend some time on it eventually to try to trim out the last few mph of top speed out of the front pulley travel but have to focus my spare time on aero mods to the CBR250R right now. If not for the fact that I bought the PCX for my son to commute on, I would definitely be building a tail for it as well which could add another 15%? of fuel economy versus running the Givi trunk that I have on it now.

[renault_megane_dci]

In France, PCX do have a stop and start function.
Do you get it in the US ?

Could be an awesome EOC system if one could trick the ECU in thinking the bike has stopped on the push of a button !

[sendler]

Originally Posted by renault_megane_dci

In France, PCX do have a stop and start function.

For some reason the US regulations did not allow the eco start/ stop function??!
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You can't coast on it though as there is always too much engine braking down to about 5 mph when the centrifugal clutch finally lets go. It has a nice AC Generator type starter motor which fires the engine up silently so I do manually shut it off when decelerating up towards a stop. I can actually see installing higher stall clutch springs just so it will coast a bit sooner.