Crf450 common issues????

Don K said:
Short stroke large bore long rod motors create a long dwell period that provides a more efficient combustion cycle. Hence more power but at higher rpm.

Just a thought, but I think I'm in the ballpark with it.

DK
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Hmmm well a 250 2 stroke has a 72mm stroke, a 125.40mm long rod and revs to 10,000 rpm it's raced in its upper rpm band, a 450 4 stroke has a 62mm stroke a 105.50 mm long rod revs to 13,000 and is raced in its lower rpm band

Interesting in how the rolls have reversed in these 2 engine designs with regard to stroke and rpm yet they still are raced in their traditional rpm bands. High rpm for the 2 stroke low rpm for the 4 stroke.

If torque is the only real calculation then these factors don't make any sense.
 
Taft Racing said:
Hmmm well a 250 2 stroke has a 72mm stroke, a 125.40mm long rod and revs to 10,000 rpm it's raced in its upper rpm band, a 450 4 stroke has a 62mm stroke a 105.50 mm long rod revs to 13,000 and is raced in its lower rpm band

Interesting in how the rolls have reversed in these 2 engine designs with regard to stroke and rpm yet they still are raced in their traditional rpm bands. High rpm for the 2 stroke low rpm for the 4 stroke.

If torque is the only real calculation then these factors don't make any sense.
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The 250 two stroke is a 10G rev engine?? The 450 four stroke is a 13,000 rpm engine? Those two figures seem kind of backwards to me.
 
TS Motorsports said:
mike grady said it best, "horsepower is nothing more than a mathematical figure, torque is the only measurable thing in the equation"
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Torque is a measure of work. Horsepower is a calculation of how much work. For instance;
20ft.-lb. of torque x 6000 RPM = 22.85 HP.
10 ft.-lb. of torque ×12,000 RPM = 22.85 HP.
 
PD Power said:
The 250 two stroke is a 10G rev engine?? The 450 four stroke is a 13,000 rpm engine? Those two figures seem kind of backwards to me.
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Makes you wonder why anyone would chose to run a 250 doesnt it? Come off the corner with more torque and rev higher with a 4 stroke. I will take it! But 13K rpm is a very high figure because the factory rev limiter is set much lower. The 4 stroke will still run more rpm in stock configurations and the kart guys are all trying to tune the two strokes to lower the band some and the 4 stroke guys are having trouble with to much wheel spin off the corners. To each their own.
 
Taft Racing said:
Hmmm well a 250 2 stroke has a 72mm stroke, a 125.40mm long rod and revs to 10,000 rpm it's raced in its upper rpm band, a 450 4 stroke has a 62mm stroke a 105.50 mm long rod revs to 13,000 and is raced in its lower rpm band

Interesting in how the rolls have reversed in these 2 engine designs with regard to stroke and rpm yet they still are raced in their traditional rpm bands. High rpm for the 2 stroke low rpm for the 4 stroke.

If torque is the only real calculation then these factors don't make any sense.
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Thats apples to oranges. Two stroke vs Four stroke.....
Theoretically DK is correct and I agree with him. All of the NHRA and NASCAR engines have gone bigger bore shorter stroke for years. I honestly dont think the rod lenght has much if any effect on the actual RPM capabilities (but I assume he was talking about 4 strokes only and so am I).
Look up the F1 engines bore and stroke. Also look at what the rev their engines to.
 
Jimbo925 said:
I don't care what math says. Its what my butt cheeks tell me on the track that matters. I ran a straight pipe and a full exhaust. While the straight pipe rattled your ear drums, it didn't seem to pull real hard outta the turn. Half way down the straight, it would kinda hit like a 2 stroke and rev very quickly but only for about 1500 rpm or so. So it made very narrow power at a peaky rpm then would just go flat. On the other hand, with a full exhaust, the motor seemed to pull harder off the turn for longer. It seemed like a much more linear power curve and it pulled all the way to the rev limiter. This was on my crf250r. I couldn't tell you actual numbers from a Dyno but I know how it felt and what was faster on the track.
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I think you were feeling the total length of the pipe being off and it had nothing to do with straight pipe vs running a muffler. If you had the correct length pipe and had everything else in the motor tuned to work with it and no muffler you would make more power. Changing the length of the exhaust is tuning for the most scavanging possible from the cylinder while the exhaust valve is open and the more effective you are at doing so the more hp you will make. You can make it more effective at lower or higher points in the rpm band by changing the length, and you can widen or narrow the band some but back pressure is not going to help.
 
Wes Snow said:
Thats apples to oranges. Two stroke vs Four stroke.....
Theoretically DK is correct and I agree with him. All of the NHRA and NASCAR engines have gone bigger bore shorter stroke for years. I honestly dont think the rod lenght has much if any effect on the actual RPM capabilities (but I assume he was talking about 4 strokes only and so am I).
Look up the F1 engines bore and stroke. Also look at what the rev their engines to.
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I wasn't looking to disagree with him just point out the differences in what these companys have done to each of the engine choices. obviously the market and performance needs for those markets are different than what we need in dirt oval karting,
 
The Harley/Buell pro-stock bikes....are a better comparison that NASCAR, etc.
Harley's/Buell have been top dogs in NHRA pro-stock bikes for years and years. An exception happened about 4 years ago, when a Suzuki won the points championship.
The Harleys have a 5" stroke, and run a max RPM of around 6000.
Their best competition, the Suzuki's run short stroke very high rpm engines.

One must be very careful about deciding which design is ultimately the best. A change in bore/stroke relationship, for example, could create a really fast motor, only to have someone figure out a carb/timing/cam combination with an entirely different bore/stroke combination, which outruns the previously unbeatable engine cited as the ultimate.
 
Out of the Blue Karen put a sewing machine in the winner circle at the Gators running out of their own wallet.
 
Why would you say that Pro Stock bikes are are better comparison? The only Harley Buell engines in pro stock bike are the ones that Hines build and they are just slapping that name on a purpose built race engine and are not selling any to any competitors. The "Harley motors" may have a 5 inch stroke (I dont know) but I know for a fact that they turn more than 6,000 RPM's. More like 10,000 would be accurate.
 
Taft Racing said:
I wasn't looking to disagree with him just point out the differences in what these companys have done to each of the engine choices. obviously the market and performance needs for those markets are different than what we need in dirt oval karting,
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It is interesting Tim and I like discussions like these. I was not trying to disagree with you I was just stating a few things to add to the discussion.
 
Very true, lol, still have to get the bugs worked out, for sure got the power though. The 250 is more like a rubber band when it pulls, more controllable, but the 450 sure is fun to ride! Maybe I'll dust off the 250 and get a win since no other 250 around here seems to be able to get the job done. Lol In all, it still doesn't matter what engine it is as long as the whole package is right, anything can win.
 
Trackchampion said:
Very true, lol, still have to get the bugs worked out, for sure got the power though. The 250 is more like a rubber band when it pulls, more controllable, but the 450 sure is fun to ride! Maybe I'll dust off the 250 and get a win since no other 250 around here seems to be able to get the job done. Lol In all, it still doesn't matter what engine it is as long as the whole package is right, anything can win.
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No other 250 except for Peters YZ , Schreifels Bama, Anderson's Honda. Other than that your right lol
 
When did victors win, not against mine, I recall winning with him second, when did Ron's win, not against mine,, Ed won at Jasper, give you that one, I wasn't there. lol. Don't forget it's all fun, without the ribbing racing would be boring! Lol
 
Doubt it, lol. We played there Saturday and it ain't right, plus my tire selection is low. The motor is perfect just have to get it to handle the turns better, plu Fruitland is small, don't need much horsepower. Good Sudam can win all day long.
 
Wes Snow said:
Why would you say that Pro Stock bikes are are better comparison? The only Harley Buell engines in pro stock bike are the ones that Hines build and they are just slapping that name on a purpose built race engine and are not selling any to any competitors. The "Harley motors" may have a 5 inch stroke (I dont know) but I know for a fact that they turn more than 6,000 RPM's. More like 10,000 would be accurate.
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It's not Buell it's VH VRod HD logo'd V-twin . Can you buy it no. Can built your own no. Buell get your check book and buy one go racing.
 
Trackchampion said:
Doubt it, lol. We played there Saturday and it ain't right, plus my tire selection is low. The motor is perfect just have to get it to handle the turns better, plu Fruitland is small, don't need much horsepower. Good Sudam can win all day long.
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Remember its a state race 200+ karts will be on that surface. It'll get black and all the grip you can stand. Bring your helmet strap lol
 
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