Power valves are they worth it!

Started by Zaqster , Jun 04 2012 08:34 PM

71 replies to this topic

  • thestuz

Posted 02 July 2012 - 02:33 PM

#61

the trouble is the market place.
people wont buy a bike unless its the latest and greatest. thats why we get technology forced upon us.
personally, i think a 300cc 2stroke without a pv would haul just as fast as a 250 2stroke with a pv in all areas.
so, if you had the choice, what would you buy?
i would prefer the 300 without pv, wouldnt you?

i used to ride 2 strokes before power valves were introduced. they were still very entertaining engines with good hp.

Edited by thestuz, 02 July 2012 - 02:35 PM.

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  • MrBlahh

Posted 02 July 2012 - 02:41 PM

#62

thestuz, on 02 July 2012 - 02:33 PM, said:

the trouble is the market place.
people wont buy a bike unless its the latest and greatest. thats why we get technology forced upon us.
personally, i think a 300cc 2stroke without a pv would haul just as fast as a 250 2stroke with a pv in all areas.
so, if you had the choice, what would you buy?
i would prefer the 300 without pv, wouldnt you?

i used to ride 2 strokes before power valves were introduced. they were still very entertaining engines with good hp.

ask anyone that's rode bikes with and without,  with powervalve is a much better bike, there's a reason ALL of the two strokes went to powervalves back in the 80's,  the only bikes that dont use them are crap like pw80's

if I had to choose I would choose the 250 with the powervalve,  just bought a gasgas 250 in fact,  powervalve maintenance is something I worry about when I do a top end, and that's not very often and it's easier than doing the piston,  clean and put back in

not sure why anyone in their right mind would intentionally put back 2 stroke motorcycle development 30 years

  • 75mx125

Posted 02 July 2012 - 03:18 PM

#63

MrBlahh, on 02 July 2012 - 02:41 PM, said:

ask anyone that's rode bikes with and without,  with powervalve is a much better bike, there's a reason ALL of the two strokes went to powervalves back in the 80's,  the only bikes that dont use them are crap like pw80's

if I had to choose I would choose the 250 with the powervalve,  just bought a gasgas 250 in fact,  powervalve maintenance is something I worry about when I do a top end, and that's not very often and it's easier than doing the piston,  clean and put back in

not sure why anyone in their right mind would intentionally put back 2 stroke motorcycle development 30 years

I hear the reason they usually don't use PV on mini's is because the power gained is lost and more on the engine that small to drive the PV. You can feel it on the KX 85, but not the RM.

  • MrBlahh

Posted 02 July 2012 - 03:25 PM

#64

75mx125, on 02 July 2012 - 03:18 PM, said:

I hear the reason they usually don't use PV on mini's is because the power gained is lost and more on the engine that small to drive the PV. You can feel it on the KX 85, but not the RM.

more like the oem's are cheap and those are mass produced at slim margins

Edited by MrBlahh, 02 July 2012 - 03:25 PM.

  • highmarker

Posted 02 July 2012 - 05:44 PM

#65

many guys here (on ktms) are tuning the vavles to pop early to smooth out the bottom end in the woods,  In some example they could have the same result with fix port timing and no valve at all.  Think any thing 300cc + and would be fine that way. My old 490 and 400 maicos had wonderful wide powerbands with no PV's.  Thier lack of reed valves wasn't the best thing though. 500 husky I had had no PV and ripped bottom to top.   I really do think there was tecnology just for the sake of technology in the open class bikes anyway.  The smaller bores needed it more.

Edited by highmarker, 02 July 2012 - 05:47 PM.

  • RhinofromWA

Posted 02 July 2012 - 08:24 PM

#66

highmarker, on 02 July 2012 - 05:44 PM, said:

many guys here (on ktms) are tuning the vavles to pop early to smooth out the bottom end in the woods,  In some example they could have the same result with fix port timing and no valve at all.  Think any thing 300cc + and would be fine that way. My old 490 and 400 maicos had wonderful wide powerbands with no PV's.  Thier lack of reed valves wasn't the best thing though. 500 husky I had had no PV and ripped bottom to top.   I really do think there was tecnology just for the sake of technology in the open class bikes anyway.  The smaller bores needed it more.
My fathers 86 (M-star)Maico 500 was super powerful but also seemed like a looooong stroke engine.  It was the Enduro so it was a torque monster.  not much of a screamer but almost stupid power throughout. :devil:  Fun bike.  Slow reving but idled down the trail at like 10mph. Piiing Piiiing  Piiiing lol  it was geared so tall.... Everyone should be lucky enough to ride one of those machines.

It was like a modern day donkey engine.... haha

Edited by RhinofromWA, 02 July 2012 - 08:24 PM.

  • jqueen

Posted 03 July 2012 - 08:30 AM

#67

Zaqster, on 22 June 2012 - 04:39 AM, said:

So u enjoy usable power , 4 strokes have much more just get urself a nice tractor like 200 buddy wont spin too hard for you

So u dont like usable power , go get an electric bike and rig an on/off throttle, should be perfect for you.

  • 75mx125

Posted 03 July 2012 - 02:20 PM

#68

highmarker, on 02 July 2012 - 05:44 PM, said:

many guys here (on ktms) are tuning the vavles to pop early to smooth out the bottom end in the woods,  In some example they could have the same result with fix port timing and no valve at all.  Think any thing 300cc + and would be fine that way. My old 490 and 400 maicos had wonderful wide powerbands with no PV's.  Thier lack of reed valves wasn't the best thing though. 500 husky I had had no PV and ripped bottom to top.   I really do think there was tecnology just for the sake of technology in the open class bikes anyway.  The smaller bores needed it more.

I read an article a while ago that the big bore Maicos had some odd design that allowed them to make power instantly off the bottom, yet kept going into a really good top end. Other manufacturers tried to copy it, but none could figure it out. Maybe they should try to get that figured out again.

  • highmarker

Posted 03 July 2012 - 05:43 PM

#69

ktm had it figured out with their 495, then threw it all away with the watercooled 500.  


think I posted this before we lined all those old big bores up, aircooled and water cooled and there was no winner in a 1/4 mile dirt race despite brochure hp bragging rights,. Traction was always the problem, why it was stupid for them to try to pump more power out them instead of focusing on wide powerbands you could use.

Edited by highmarker, 03 July 2012 - 05:45 PM.

  • Zaqster

Posted 03 July 2012 - 07:56 PM

#70

Corus, on 25 June 2012 - 08:37 AM, said:

Impulse is Force multiplied by Time. So basically the area under a dyno curve, the more area, the greater the impulse.

I'm just going to ignore your exaggeration about it being worth half of what your bike is worth, unless it is, well then I guess I would be trying to cheap out on maintenance too and start cutting corners.

Is there really more top end power in your bike? You said you put "lugs" to replace the power valve, so I'm assume that it would cover the same amount of the opening that the power valve did when it was wide open. So perhaps it only seems like it's more of a "snap" because you're lacking a considerable amount of power in the low rpms, and still keeping the same amount of power at high rpms, which would allow for a great change in power output from low to high rpms. Of course that would result in you thinking there's more "snap" when there's actually less power overall.

By your own self admittance, you don't ride in the power band all the time, so it seems logical that it would benefit you to have a power valve to give you more power in the sub-power-band range.

highmarker, on 29 June 2012 - 03:54 PM, said:

fwiw, if you rig the pv wide open,.  then rig the valve closed  then overlay the dyno curves. This is pretty much what it'll look like:   The grey shaded area at the bottom of the curve is what is gained by the valve being closed, the grey are at the top is what is gained by the valve being open.   The transistion should take place between  p1 and p2  and be fully open by 7.on this motor,

Posted Image
so by having the valve out will create a steeper curve resulting in more snap, not thinking it has more ? but less torque in the low rpm delaying power a few rpm, my bike does seem to rev out more than it used to with pv , might be cause mine were worn a fair bit but it reved close still and more consistant and smooth, now its ping ping ping snap !

Edited by Zaqster, 03 July 2012 - 08:03 PM.

  • Markopolo400

Posted 02 August 2012 - 03:50 AM

#71

This thread was very entertaining, thanks. :)

  • AS64

Posted 02 August 2012 - 11:51 AM

#72

The motor is made a certain way for a reason. Don't screw with it.
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