Crf450 common issues????

ABR #69 said:
Ok girls, you're all pretty in your own way.

The reason the torque was lost at the bottom end, is based on the pipe design. The engine didn't magically lose torque. The pipe wasn't designed to accentuate the torque, so it fell off on the bottom. When it got into the higher rpm range, it picked up because that's where the pipe was designed to work.

Four strokes are also pipe dependant, not as much as a two stroke. But, they rely on pipe design to make the power usable in a designated rpm band. That is why a four stroke can have lots of torque on the bottom, yet still pull way up on top and run really good. The pipes can be designed for more all around power, easier than a two stroke pipe. Depending on if you know what you're doing or not. I admit, I don't know that much about either engine's specific needs, but I know they are dependant on the pipe to make it usable.
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This is pretty much all I was trying to say. Al, what a guy feels on the track and what translates to a dyno DON'T necessarily match up. I was simply stating FACTS of my own experience. I tried a couple different things and that's what I found. SORRY I didn't use scientific language or mathematics to explain my point. I'm not a mathematician nor a scientist. I'm a RACER and what translates to my language is ACTUAL RACE RESULTS. Not sitting behind a keyboard playing hero in text.

Let me say this, then Tim and Al can have more fodder to argue their points. EVERYTHING is based on math and science. EVERYTHING we know as racers was developed by SCIENTIST and they used MATHEMATICS to come up with the solutions. Years ago. WAAAYYYY before even Alvin J Nunley.

Final thoughts. Yamaha, Honda, Suzuki, Kawasaki, KTM, and what ever other manufacturer, have spent MILLIONS of dollars doing scientific and mathematical studies to make their exhausts work with their engines to work better than the other guys. $$MILLIONS AND MILLIONS$$$. In both 2 stroke and 4 stroke configurations. Now, aftermarket companies have spent COUNTLESS more dollars to develop their pipes to make the engine performance even better. So when I say DON'T straight pipe it from my own experience, I mean that is what I had found. When my straight pipe didn't have the "power" (TORQUE) off the corner but hit good "power" (HORSE) on the top but it was very "narrow" (came in hard and signed off quickly, about 1500 rpm), I decided to go back to the FMF power bomb pipe. When I did, the motor was MUCH happier all around. It pulled harder and smoother (TORQUE) coming off the corner and pulled hard all the way to the 13,500 rev limit (HORSE). There was no noticeable bottom end lag (giving up TORQUE) nor was there a violent, narrow top end (HORSE) spike. The FMF made the kart very predictable and easier to drive. I believe all you SUPER SMART engine guys and mathematicians, like Taft and Nunley, call that a LINEAR POWER CURVE.
 
ABR #69 said:
33,000lbs being the weight moved 1' per minute to get 1 hp. Since 1' in a circle is the 6.2832 dividing the two gives 5,252. Since a dyno has to go in a circle, you need that constant of 5,252. So, the constant has to be used to measure them all. Regardless if it never actually reaches 5,252 rpm. Only significance it has with RPM is that HP and Torque will cross at that rpm because that is the constant. The constant is not the RPM, just the measure of a 1' circle it has to travel to make the hp standard. Did that help, or only muddy the waters?
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I got it. So regardless ofengine. The formula is the same and the constant never changes. Thanks
 
Yup, because that constant is just part of the 1ft equation for hp. Just used to translate the 1ft part to a circular motion for the dyno.
 
If you lift 550 pounds 1 foot in 1 second you are said to be working at the rate of one horsepower. If you continue lifting that 550 pound weight at the rate of 1 foot in 1 second for 60 seconds you will have done 33,000 lbs. Ft. of work. (Not to be confused with Foot Pounds) If you divide that 33,000 lbs. Ft. number by 2 pi radians, (6.283, the number of radians in a circle) you get the number 5252.3.
10 x 5252.3/5252.3=10 HP. This means 10 pounds of torque equals 10 HP at 5252.3 revolutions. The two 5252.3's cancel each other out and that's where the two curves cross.

At nowhere on the track can you measure the HP. You measure the torque, you check the rpm, and you calculate the horsepower.

All of this information is in Wikipedia. Look for James Watt. He needed some sort of comparison so that farmers could see how much work his steam engine could do compared to a horse.
 
Jimbo925 said:
Let me say this, then Tim and Al can have more fodder to argue their points. EVERYTHING is based on math and science. EVERYTHING we know as racers was developed by SCIENTIST and they used MATHEMATICS to come up with the solutions. Years ago. WAAAYYYY before even Alvin J Nunley.
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I will quickly point out that I didn't come up with any of this stuff, I'm just passing it along. And if you're going to insult me, at least spell my name right.
 
My apologies Al. Fat fingered my phone. Wasn't meant as an insult. Not at all. Just saying that you've been around a long time. You have a lot of experience. No doubt. But the accepted numbers and formulas you cite have been around long since before anyone probably alive today.
 
Jimbo925 said:
My apologies Al. Fat fingered my phone. Wasn't meant as an insult. Not at all. Just saying that you've been around a long time. You have a lot of experience. No doubt. But the accepted numbers and formulas you cite have been around long since before anyone probably alive today.
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yes, back in the 1800's, James Watt. It just seems that they need to be brought up now and again because there's a lot of people that have misinformation on these formulas.
 
iam new here and maybe this isn't the correct forum to ask this question.......But which one will come of the corner better??? My 10/60 ratio or my 12/72?? :)

(Just kiddin' guys...PLEASEEEE don't try and answer that question PPPLLLLEEEAASSEE) :)
 
Jimbo925 said:
This is pretty much all I was trying to say. Al, what a guy feels on the track and what translates to a dyno DON'T necessarily match up. I was simply stating FACTS of my own experience. I tried a couple different things and that's what I found. SORRY I didn't use scientific language or mathematics to explain my point. I'm not a mathematician nor a scientist. I'm a RACER and what translates to my language is ACTUAL RACE RESULTS. Not sitting behind a keyboard playing hero in text.

Let me say this, then Tim and Al can have more fodder to argue their points. EVERYTHING is based on math and science. EVERYTHING we know as racers was developed by SCIENTIST and they used MATHEMATICS to come up with the solutions. Years ago. WAAAYYYY before even Alvin J Nunley.

Final thoughts. Yamaha, Honda, Suzuki, Kawasaki, KTM, and what ever other manufacturer, have spent MILLIONS of dollars doing scientific and mathematical studies to make their exhausts work with their engines to work better than the other guys. $$MILLIONS AND MILLIONS$$$. In both 2 stroke and 4 stroke configurations. Now, aftermarket companies have spent COUNTLESS more dollars to develop their pipes to make the engine performance even better. So when I say DON'T straight pipe it from my own experience, I mean that is what I had found. When my straight pipe didn't have the "power" (TORQUE) off the corner but hit good "power" (HORSE) on the top but it was very "narrow" (came in hard and signed off quickly, about 1500 rpm), I decided to go back to the FMF power bomb pipe. When I did, the motor was MUCH happier all around. It pulled harder and smoother (TORQUE) coming off the corner and pulled hard all the way to the 13,500 rev limit (HORSE). There was no noticeable bottom end lag (giving up TORQUE) nor was there a violent, narrow top end (HORSE) spike. The FMF made the kart very predictable and easier to drive. I believe all you SUPER SMART engine guys and mathematicians, like Taft and Nunley, call that a LINEAR POWER CURVE.
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What 450 do you have that has a 13,500 factory rev limiter?
 
iam new here and maybe this isn't the correct forum to ask this question.......But which one will come of the corner better??? My 10/60 ratio or my 12/72??
Click to expand...

The 10/60 of course! The "Moment of Inertia" is less.

DK

PS, Another question for those inclined. What accelerates better, a two stroke or four stroke of equal size, stroke and bore?
 
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