13 gram dr pulleys installed with filing mod, results.

[wingz]

Is that how it works? I always figured that if you had trouble getting up to the red line in the first place, then making the gearing longer wouldn't help with that. I wasn't sure if power would actually drop if you went above the peak power range of 8500 rpms.

Like if I'm running at 69 mph at 8900 rpms on a flat road because my PCX can't push past wind resistance, wouldn't the PCX run slower if I extended the gearing? If your torque remains unchanged, then it wouldn't make sense for the speed to go up unless you have more torque at 8500 rpms than you do at 8900 rpms.

Just wondering since I was debating whether or not to have the KN Planning torque driver installed when I put in the 31mm throttle body and manifold and finally balance out the rich AFR from my BBK install. I expect to get a bump up in power, in addition to putting in 8g rollers to increase the pulling rpm, so I figured I could afford to take the hit on that.

Yes. Power drops above 8500rpm. Longer gearing in the final drive won't decrease realisable torque on the wheel because you can compensate in the CVT.
I am a minimalist when it comes to mods... I only installed sliders and the gear set. Didn't see the need for changing the torque driver.

If you are modifying your engine, keep in mind that a more powerful engine requires heavier sliders/rollers to counter the increased torque on the torque driver.
Also, obviously, changing the power curve of the engine should influence your gearing requirements. There is a longer gearing option than the 45/15.

[Valiant]

Yes. Power drops above 8500rpm. Longer gearing in the final drive won't decrease realisable torque on the wheel because you can compensate in the CVT.

Hmm, interesting revelation. I wonder if it would be safe to assume that the power drop might be caused by the high rpms not allowing a full volume of fuel mixture into the cylinder? Since the time between each cycle is shorter, there's less and less time for the fuel mix to flow into the chamber. I figure that might explain why with my current BBK setup, there's more power in the mid to low range, but at the high range my top speed only went up about 4-5 mph.

I am a minimalist when it comes to mods... I only installed sliders and the gear set. Didn't see the need for changing the torque driver.

Would be an interesting experiment. The torque driver by far provides the most dramatic change in gearing(I recall one member got 89 mph on the stand with it). Might mean the belt won't fully lock out until you get at some ridiculous speed like 75 mph. Of course, if your engine doesn't make enough power, it might just mean your belt will never be fully locked out. I could also see the gearing getting so long that even the lightest weights(8g IIRC) would put pulling rpms well below the peak power range of 8000-8500.

If you are modifying your engine, keep in mind that a more powerful engine requires heavier sliders/rollers to counter the increased torque on the torque driver.

Why's that? Sounds like doing so would put pulling rpms down below the peak power of 8500. If nothing else, it seems like the longer gearing I've got is causing a lag before the clutch engages, whereas before there was no lag. Previously I was using 13g weights, but now I have 10g weights.

[Pcxdemon]

After 8500rpm power drops because valves start floating..to lift your rpm ceiling you have to install harder valve springs. Then your engine could safely run up to 10500rpm. A guy in japan that races a Pcx was experimenting of how high he can push the rpms and found that even at 11500rpm was still ok but at 12k it blew apart. So recommended safe rpm ceiling with upgraded valve springs is 10500 -11k.
Yuminashi sells progressive double valve springs as an upgrade. I got my installed and power is right there till it bounces of the stock limiter at 9400.

[Valiant]

After 8500rpm power drops because valves start floating..to lift your rpm ceiling you have to install harder valve springs. Then your engine could safely run up to 10500rpm. A guy in japan that races a Pcx was experimenting of how high he can push the rpms and found that even at 11500rpm was still ok but at 12k it blew apart. So recommended safe rpm ceiling with upgraded valve springs is 10500 -11k.
Yuminashi sells progressive double valve springs as an upgrade. I got my installed and power is right there till it bounces of the stock limiter at 9400.

Yikes . I'm feeling a wee bit weary about my scoot shop trying to set the limiter at 11500 rpms. Granted, I doubt the PCX would ever rev that high while my 200 lbs fat ass is on the thing.

From the sound of it though, if I already have the stiffer valve springs installed, then it doesn't sound like I'd need to fuss over extending the gearing anymore. It also doesn't sound like it would be too bad to have pulling rpms a bit higher(maybe 9000 or so).

[wingz]

The limit seems to be different depending on the slope.
I don't know if it is a fuel restriction or floating valves, but it is definitely a "hard" limit.
On level or gentle downhill roads, my limit was about 110km/h but on steep downhills it was about 125km/h.
Anyone know what causes this?

I say "was" because I haven't checked since installing the gear set.
It could have been a slight difference in gearing in the CVT... now that I have a tach, I'll be able to get more info.

[wingz]

If you are modifying your engine, keep in mind that a more powerful engine requires heavier sliders/rollers to counter the increased torque on the torque driver.

Why's that? Sounds like doing so would put pulling rpms down below the peak power of 8500. If nothing else, it seems like the longer gearing I've got is causing a lag before the clutch engages, whereas before there was no lag. Previously I was using 13g weights, but now I have 10g weights.

This was discussed in another thread... MG was wrong. In trying to understand his point, I confused myself to the extent that wrote some dubious stuff to support his incorrect conclusions.
(I wish I could put a subsequent note in that post to point out that it is incorrect)

But here is how it works...
A more powerful engine applies more torque to the rear pulley.
More torque on the rear pulley brings the rear pulley halves closer together. As the belt moves outwards on the rear pulley, the front pulley halves are pushed apart.
The combination of front pulley halves moving apart and rear pulley halves moving together lowers the gear ratio and increases rpm.
To counteract this, one installs heavier rollers/sliders which push the front pulley halves closer together forcing the rear pulley halves further apart.
This increases the gear ratio and decreases rpm back to where you want it.

[Pcxdemon]

The limit seems to be different depending on the slope.
I don't know if it is a fuel restriction or floating valves, but it is definitely a "hard" limit.
On level or gentle downhill roads, my limit was about 110km/h but on steep downhills it was about 125km/h.
Anyone know what causes this?

I say "was" because I haven't checked since installing the gear set.
It could have been a slight difference in gearing in the CVT... now that I have a tach, I'll be able to get more info.

After 8500rpm or so your power drops of sharply due to valve float and camshaft profile,preventing you at times (without ideal conditions like wind in the back or drafting or going down hills) reaching the limiter and top speed. Thats why you only hit the top speed and feel the limiter kick in is because the gravity aids you going down the steep hill..
If you upgrade the valve springs and install higher lift camshaft you would pull speed up to 12000rpm...where eventually the bottom end would self destruct.

[wingz]

http://www.hondapcx.org/viewtopic.php?f=9&t=1061#p15223
Valiant, check the 3rd curve in the 1st post (PCX150) power vs km/h.
Not this is not an engine dyno so it includes the effects of the CVT.
But above 90km/h, the CVT has maxed out. It is clear that the power drops dramatically at higher speeds.

[Valiant]

But here is how it works...
A more powerful engine applies more torque to the rear pulley.
More torque on the rear pulley brings the rear pulley halves closer together. As the belt moves outwards on the rear pulley, the front pulley halves are pushed apart.

Little confusing, but shouldn't there be an opposite effect? I would think more torque would actually force the pulley apart, given that the belt is sitting in between the pulley. But I suppose one could say the same about the front pulley. Again, it's still confusing given that changing the weights wouldn't lessen the torque on the rear pulley in the least.

Has this actually been tested? I do recall reading about a recommendation to use heavier weights with a BBK, but I never heard an explanation on why. And if anything, that actually sounds a bit backwards given that the torque curve has a higher peak at lower rpms compared to the peak rpms of the power curve.

The combination of front pulley halves moving apart and rear pulley halves moving together lowers the gear ratio and increases rpm.
To counteract this, one installs heavier rollers/sliders which push the front pulley halves closer together forcing the rear pulley halves further apart.
This increases the gear ratio and decreases rpm back to where you want it.

But again, that seems to be going against the point IMO. If peak power is at 8500, and engine mods only move the peak further rather than back, it still seems like target pulling rpms should be 8500 and up.

[sendler2112]

All engines have a power curve. Due to cam timing and intake tuning. Cams are a trade off between power and efficiency and a choice must be made regarding what rpm the cam makes horsepower peak at. The PCX is designed to peak at 8,500 rpm. Below this it makes less power. Above this it makes less power. This is normal for any engine.
.
The rev limiter is set to 9,200 rpm for early 125's and at 9,600 for later, non Euro 1 ESP engines. This feeling of lagging in and out at rev limit was erroneously identified as valve float by the Thai kids when the bike first came out. There is no valve float anywhere in the running of the stock engine.
.
If you change to a cam with more lift and more overlap for a higher rpm power peak, then you may need stiffer valve springs.

[wingz]

Has this actually been tested? I do recall reading about a recommendation to use heavier weights with a BBK, but I never heard an explanation on why. And if anything, that actually sounds a bit backwards given that the torque curve has a higher peak at lower rpms compared to the peak rpms of the power curve.

But again, that seems to be going against the point IMO. If peak power is at 8500, and engine mods only move the peak further rather than back, it still seems like target pulling rpms should be 8500 and up.

Yes it has been tested by those who have modded their engines (such as pcxdemon) and it is perfectly logical.

In practice, as you suggest, it depends on how you modify your engine.
For the sake of understanding the concept, it is best to assume the simple case of the mod increasing torque over the entire RPM range.
The way the torque driver works is that increased torque pushes the rear pulley halves together to lower the gearing.
That is it's fundamental purpose... if you don't understand how, then look it up for yourself.
If increased torque (from engine upgrade) increases rpm above target, you would increase the weights to compensate. It is that simple.

[sendler2112]

Fastest acceleration and highest rear wheel torque of any geared powertrain occurs when the engine is operated at the power peak. Not the torque peak.

[you you]

Fastest acceleration and highest rear wheel torque of any geared powertrain occurs when the engine is operated at the power peak. Not the torque peak.

So it has maximum torque when not at maximum torque?

[sendler2112]

The maximum torque at the rear wheel is highest at the power peak because of the gearing multiplication in the trans.

[Valiant]

Yes it has been tested by those who have modded their engines (such as pcxdemon) and it is perfectly logical.

In practice, as you suggest, it depends on how you modify your engine.
For the sake of understanding the concept, it is best to assume the simple case of the mod increasing torque over the entire RPM range.
The way the torque driver works is that increased torque pushes the rear pulley halves together to lower the gearing.
That is it's fundamental purpose... if you don't understand how, then look it up for yourself.
If increased torque (from engine upgrade) increases rpm above target, you would increase the weights to compensate. It is that simple.

Again, kind of confusing since I would expect heavier weights to come with the downside of premature upshifting. It also doesn't sound that bad if it works as you described, as I would think the intention of lighter weights is to delay the upshift in order to allow higher rpms. So it sounds like it's working as intended.

Besides which, I would think the symptoms would be really obvious when riding, as the engine would rev up, but your speed won't go up, or you overshoot your target pulling rpms, and that would prompt the user to add more weights anyway.

The maximum torque at the rear wheel is highest at the power peak because of the gearing multiplication in the trans.

Gearing doesn't multiply torque IIRC. Quite the opposite IMO. The maximum amount of torque you can have is the torque the engine produces. So in the lowest gear you have access to the full power of the engine. Useful for going uphill, but not very useful in getting you to move fast. With longer gearing, you trade torque for more work done, or more revolutions of the wheel for each revolution of the engine.

I don't think the trans plays any role in the power peak, given that people have modified their trans, but peak power will still be at 8500 engine rpms. The trans is just there to take advantage of that power peak.

[Mel46]

I came across this kit and wondered if it made any more difference than just the variator and rollers, which is what I hear about the most

[Valiant]

What kit would that be?

[Mel46]

http://www.amazon.com/NCY-Super-Transmi ... cy+for+pcx
Sorry, the link didn't copy before.

[Valiant]

The clutch would give you a stronger takeoff, but would probably cut your fuel economy by about 8-10 mpg. The rear pulley however makes your PCX acceleration more linear and responsive to throttle control, assuming you use the straight slots. The center spring is typically stiffer than stock, which raises your pulling rpms and basically acts like using lighter rollers.

This is a video showcasing how an aftermarket torque driver works:


I believe ScooterMan tried the kit with much the same results. Outside of the variator and drive face, the only other item that might improve your riding experience is that rear pulley.