82 cr250 cylinder

[Kartwheel68]

Power valves give more bottom end but they take away more from the top end to put it on the bottom.

What? That is absolutely not true at all.

 

[fran...k.]

What? That is absolutely not true at all.

I was able to resist replying to that one.

My take is with the power valves in Husqvarna motorcycles one gets better low rpm power and a lot less noise while down there. My 2004 WR250 says 42 sae hp on the certificate of origin, what do you think was on the certificate of origin for what this thread title is?

I believe Bill's statement is true if one is to take the balls out of the power valve governor.

 

[justintendo]

I was able to resist replying to that one.

My take is with the power valves in Husqvarna motorcycles one gets better low rpm power and a lot less noise while down there. My 2004 WR250 says 42 sae hp on the certificate of origin, what do you think was on the certificate of origin for what this thread title is?

I believe Bill's statement is true if one is to take the balls out of the power valve governor.

the sound levels you speak of are very noticeable..power valve bikes are very quiet until the valve opens!

 

[justintendo]

Power valves give more bottom end but they take away more from the top end to put it on the bottom.

more nonsense..

 

[Kartwheel68]

I was able to resist replying to that one.

I changed my original reply before I posted, it was less diplomatic.

To bill, by having an "adjustable" exhaust port height, you get both more bottom end power AND more top end power than a non power valve engine. A power valve WILL do what you said if it is not functioning correctly and is stuck in the down position, it will then add power down low and rob power from the top. If it is functioning correctly you get the best of both, which is why all modern two strokes from the mid-80s on have had them.

 

[Bigbill]

Then how come the power valve bikes aren’t as fast top end wise as the non power valve bikes?

 

[silverstreakNZ]

I was going to reply to that . Deleted everything I wrote .
Face palm bill

 

[fran...k.]

Then how come the power valve bikes aren’t as fast top end wise as the non power valve bikes?

Example please. Non power valve engine on KTM two cycle freeride as compared to any current 2cycle Husqvarna. Is not as you imply.

 

[Kartwheel68]

Then how come the power valve bikes aren’t as fast top end wise as the non power valve bikes?

Fast, as in miles per hour or power on the top end of the rpm range? If you are talking about top MPH that has to do with transmission and secondary drive ratios. If you are talking about top end RPM range power, power valve engines make more top RPM power. They are not the same thing.

 

[justintendo]

Fast, as in miles per hour or power on the top end of the rpm range? If you are talking about top MPH that has to do with transmission and secondary drive ratios. If you are talking about top end RPM range power, power valve engines make more top RPM power. They are not the same thing.

yeah but not like a 390..on those the tire never stops spinning.

 

[Bigbill]

The fastest dirtbikes,,,,,,,think about the 500cc husky that was posted here at 123mph a while back.

View: https://m.youtube.com/watch?v=LMbSn7Ijo7k

My drag race car ran the 1/4 mile in 12 seconds. I know my 99 husky wr 250 turned in the same times.

 

[Bigbill]

yeah but not like a 390..on those the tire never stops spinning.

Trust me the only time the rear wheel on the 390cr stopped churning was when I shifted it. I was on the throttle all the time she was wicked.

 

[87husky500xc]

The difference is in the transmission.... all the factories didn’t just go to a system that sucks. There is a reason that every modern two stroke has one.

 

[oldbikedude]

Fake news......lol

 

[Bigbill]

Fast, as in miles per hour or power on the top end of the rpm range? If you are talking about top MPH that has to do with transmission and secondary drive ratios. If you are talking about top end RPM range power, power valve engines make more top RPM power. They are not the same thing.

It was told to me that the power valve takes the rpm/speed from the top end and puts more power on the bottom end.

The air cooled bikes have more topend with no power valve. Maybe I was told wrong.

 

[87husky500xc]

The air cooled bikes from seventies and early eighties will never have the top end that the new p/v bikes do. A power valve just reduces the size of the exhaust port at low rpm to create a wider power band and opens as the rpms increase to let the exhaust flow at necessary rate for maximum performance on top. This makes for a more rideable bottom end while also being able rev out from mid to top quite quickly. Ever ridden a bike with a stuck power valve? It sucks(this experience comes from other people’s machines, not my own haha)

 

[Kartwheel68]

It was told to me that the power valve takes the rpm/speed from the top end and puts more power on the bottom end.

The air cooled bikes have more topend with no power valve. Maybe I was told wrong.

You were told wrong.

 

[fran...k.]

For comparison I found some pictures of the insides of the 250 ktm freeride two cycle cylinder. It is a case reed unlike the bikes in this section. I think it is kind of a price point bike for example no counter balancer no damping clutch, no power valve. There may be other 250 non powervalve engines out there but this is the only one from the current parent company of Husky. Trials bikes may well also be non power valve. Not sure what is out there in other parts of the globe.

 

[Bigbill]

Doesn’t the power valve change the exhaust port timing? When it opens the exhaust port it exhausts hot gasses sooner? When it’s closed it lowers the exhaust port and gives more bottomend.

 

[SteveJ]

Doesn’t the power valve change the exhaust port timing? When it opens the exhaust port it exhausts hot gasses sooner? When it’s closed it lowers the exhaust port and gives more bottomend.

Yes, but a power valve engine can have exhaust port timing that is more aggressive to begin with, since the power valve can tame it down for bottom end.