Horsepower, Our Vintage 250s and the new KTM 250 @ 50 HP

[1982 XC 430]

So the newest KTM 250 SX is rated at 50 HP. This is about the same as our open class Vintage bikes. I have a 2000 KTM 250 and yes it is faster than my 82 250 XC. Mostly the low end and mid range I assume due to the powervalve. One would think that 30 years later a 250 would indeed make more HP, but how? Water Cooling may help a couple of laps into a race but not on the first pull on a Dyno. The Power Valve should broaden the powerband but we are only talking about peak HP here. A flat side Carb may be worth a few. The latest Reed Valves a few more. Maybe the latest Ignition another couple. But I still don't see what makes a new 2 stroke Engine have a least 1/3 rd more HP. Ok so maybe we shouldn't compare new vrs old HP ratings, but yes the new Engines do make more.
Ok, So lets use all the engineering that has been done in the last 30 years on our bikes. I think the Bore and Stroke are basicly the same, so lets just steal the Porting specs, Pipe Specs and bolt on the rest. Some how I don't think its going to work out that easy. What have they done ?

 

[ruwfo]

I'm assuming your referring to the MX Action test
http://motocrossactionmag.com/Main/News/2012-MOTOCROSS-RACING-IMPRESSION-WHAT-ITS-LIKE-THE-7956.aspx
1st the stock Husky's 250 were HP slugs compared to there Japanese counter parts (76-80's), they made
a broader power, even the CR versions. Husky designed there big bore bikes 1st, then what ever parts could be used on lower models were.

High HP means compromises else were (ride ablity,reliability), Huskys were know for there superb handling & tuned their HP for tractability. Basically everything you mentioned is true (powervalves,H2O,flat slides,better electronics), But still 50HP is very impressive , see what technology can bring, better materials & machining tools, coatings, etc.

Look at the newer 426 Hemi vs old, same HP(425), better MPG (8 vs 20+), & more reliability.

And of course Racing improves the breed, thank "The Man" for that.
Husky John

 

[1982 XC 430]

The biggest advantage the New Hemi ( which is not a a Hemi) has over the old one is Fuel Injection, Varible Valve Timing, Cylinder Design and a Computor to run the show. The new KTM 250 has none of these, Ok so the PowerValve and Varible Valve Timing have the same effects. With Direct FI and a ECU in the near future ( if they can sell enough to make it worth wile) the 2 Stroke will become a modern engine. But it hasn't yet, and yet its making 50 HP.

 

[fran...k.]

No the bore and stroke are not the same. The last 250 of this section moved in the direction that modern stuff is now. stroke 72 mm (same as 420 auto) and bore of whatever it takes perhaps 66.4mm witout looking it up. Ktm, husky, yamaha all the same now. Correct me if wrong.

You forgot filled crank.

You are right about new vs old horsepower. There is sae and two others. Not sure why but kw is prefered over hp in the chainsaw world.

You have the lack of cylinder studs in the modern designs allowing passages in those areas. There is some room in the 250 of this section and again the last designs can be seen moving towards what is modern now.

That ktm sx 250 you mention is a case reed, Though I havn't seen the inside of one I suspect it is like that 125 in my current avatar in that it has little square transfer ports most of the way around the cylinder. The powervalve in that ktm is more like the modern 250 husky with one flapper and two side exhaust ports that open up at higher revs that are above the transfers towards the front. Those thru case to head rods with threads comprimise the ability to do this. Even that ktm sx 250 has a 36 mm carb doesn't it? So if max hp was the main objective as opposed to going around the track fastest there is still some easy gains, possibly.

 

[Motosportz]

the new bikes are WAY more refined. Everything. Airbox to muffler everything is far better designed and makes a lot more power because of it. better flowing airboxes feed way better carbs, into way better reed blocks, into way better bottom end configurations, into way better transfer ports, into way better cylinder and head designs into power producing powervelves, then into way better expansion chambers and out better mufflers. Then there is water cooling which allows far better tolerances and BAM, you have way more power. Don't over look far better metallurgy and machining tolerances too.

you think thats crazy look how far 4 strokes have come. Same thing, want more efficient everywhere offing way more compression and BAM more power.

 

[Norman Foley]

the new bikes are WAY more refined. Everything. Airbox to muffler everything is far better designed and makes a lot more power because of it. better flowing airboxes feed way better carbs, into way better reed blocks, into way better bottom end configurations, into way better transfer ports, into way better cylinder and head designs into power producing powervelves, then into way better expansion chambers and out better mufflers. Then there is water cooling which allows far better tolerances and BAM, you have way more power. Don't over look far better metallurgy and machining tolerances too.

you think thats crazy look how far 4 strokes have come. Same thing, want more efficient everywhere offing way more compression and BAM more power.

Kelly hit it right on the head.....

 

[rajobigguy]

Kelly hit it right on the head.....

Yes he did but probably the biggest reason for todays power over 1982 is the addition of the power valve which allowed for far more radical port configuration without having the ill effects of a hair trigger power band. You can take one of the older engines and get trememdous HP #'s but they will be practically unrideable by the time you're done.

 

[Motosportz]

Yes he did but probably the biggest reason for todays power over 1982 is the addition of the power valve which allowed for far more radical port configuration without having the ill effects of a hair trigger power band. You can take one of the older engines and get trememdous HP #'s but they will be practically unrideable by the time you're done.

Some of the big old non PV motors made some pretty nice power like my YZ465. Still i think those were just over 42hp so no were near what the new stuff makes.

 

[Norman Foley]

Yes he did but probably the biggest reason for todays power over 1982 is the addition of the power valve which allowed for far more radical port configuration without having the ill effects of a hair trigger power band. You can take one of the older engines and get trememdous HP #'s but they will be practically unrideable by the time you're done.

Friend had a Yamaha RZV500 that YPVS was not working, so he wired the power valves open.... unrideable is one way to describe it!

 

[rajobigguy]

Friend had a Yamaha RZV500 that YPVS was not working, so he wired the power valves open.... unrideable is one way to describe it!

RZV's are pretty wild rides even when the power valves are working, hard to imagine what one would feel like with them wired open. Is it soemthing like crack the throttle, count to three and then hang on for dear life?

 

[Norman Foley]

RZV's are pretty wild rides even when the power valves are working, hard to imagine what one would feel like with them wired open. Is it soemthing like crack the throttle, count to three and then hang on for dear life?

Yes and I did it across a steel deck bridge to boot!

 

[rajobigguy]

Some of the big old non PV motors made some pretty nice power like my YZ465. Still i think those were just over 42hp so no were near what the new stuff makes.

Yep, most of the big open class 2Ts were in the neighborhood of 50 HP and it was possible to get upwards of that out of a 250 if you didn't mind having a power band about as wide as a human hair. Now days it's possible to have a 40+ hp 250 and still be civilized enough that some of us mere mortals can handle them.

 

[rajobigguy]

Yes and I did it across a steel deck bridge to boot!

I can see it now, screw throttle all the way open, have just enough time to think to you're self "Gawd this things a dog" then it comes on the pipe and feels like someone set off a box of TNT behind you.

 

[firecrackerkid]

I can see it now, screw throttle all the way open, have just enough time to think to you're self "Gawd this things a dog" then it comes on the pipe and feels like someone set off a box of TNT behind you.

Things haven't changed so much: 1975 my 15 yr old cousin says "can i ride it?" it being my brand new honda CR125. 2 seconds later bike on ground with broken rear fender, cousin on his a@@!

 

[Motosportz]

Things haven't changed so much: 1975 my 15 yr old cousin says "can i ride it?" it being my brand new honda CR125. 2 seconds later bike on ground with broken rear fender, cousin on his a@@!

I put my wife on a YZ250 once, she got clear to the first bush. I guess throttle response on a YZ250 is not for the uninitiated.

 

[Norman Foley]

I can see it now, screw throttle all the way open, have just enough time to think to you're self "Gawd this things a dog" then it comes on the pipe and feels like someone set off a box of TNT behind you.

A bit more than my RD or RZ350 for sure! Felt like those guys on rocket sleds in the 50's.

 

[Norman Foley]

Some of the big old non PV motors made some pretty nice power like my YZ465. Still i think those were just over 42hp so no were near what the new stuff makes.

Starting old big bores can be a trick... Friend bought his KTM 420 out of the back of a pick up in an urgent care parking lot. Drove past twice in an hour and then finally went in looking for the guy and sure enough, he was having his broken ankle X-rayed! It kicked back one too many times and a deal was done... Sold!

 

[Kartwheel68]

Maico was the first to come use the now standard 66 bore 72 stroke in a 250. The biggest difference is the power valve which allows very radical port timing with the valves open for max HP. My friend has a TZ125 making 40+ HP, but it would be unrideable off road, the power valve allows that kind of port timing and with the valve closed produces good low end too.

 

[rajobigguy]

Maico was the first to come use the now standard 66 bore 72 stroke in a 250. The biggest difference is the power valve which allows very radical port timing with the valves open for max HP. My friend has a TZ125 making 40+ HP, but it would be unrideable off road, the power valve allows that kind of port timing and with the valve closed produces good low end too.

See post #7, Glad you agree with me

 

[fran...k.]

I will disagree with the airbox business. The placement of the modern shock creates problems in getting a straight flow like the dual shock models in this section.