a new project. Don't ban me please!!
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FaliconKen
- Posts: 0
- Joined: Wed Mar 10, 2021 10:41 pm
>>there is cheaper to way to make this yfz get near 500c.c.
True, but the object isn't just to get a bigger engine - it's to get the proper power characteristics for best acceleration.
We have experimented with different cylinder bore and crank stroke combinations and have learned much about these engines. When our testers put a 98mm bore (468cc) or 100 mm bore (487cc) on a stock stroke Honda CRF-450, we didn't get much in the way of improvement. When we stroked the crank to 66mm on a stock bore (480cc), it made a huge difference at the track. I'm not talking the dyno, where traction is a non-issue, I'm talking about knobbies-on-dirt real world acceleration, where peak power means a lot less and the traction-control advantages of a longer stroke become evident. There was little difference between the stock CRF and the big-bore 487. But the stroker 480 killed our big-bore 487 on dirt, even though they were close on a dyno. How could this be?
One key (among many) to good power characteristics is the bore stroke ratio. On the CRF-450R, the bore/stroke ratio is 1.55 for a stock 96mm bore and 62mm stroke. That is, the bore is 1.55 times the stroke. With the stock stroke, a 98mm bore would be 1.58, and a 100mm bore would be 1.61. The stroker 480 has a ratio of 1.45.
Now, if we stroke the crank to 69.5mm in a stock bore, you have a ratio of 1.38. This configuration pulls like a mule and is the easiest to control. The downside is this long stroke requires spacer plates, longer cam chain, new engine mounts, etc.
We also tried a 98mm bore and 66mm stroke, which gives a ratio of 1.48. It doesn't perform quite as good as the longer stroke, but is almost as fast and doesn't use a spacer plate. Most of our AMA 500cc pro customers are using this configuration, but many are starting to change to the longer stroke/ smaller bore.
If you keep increasing the bore, you get to a point of diminishing returns. The wider bore increases the length of the burn (distance from the spark plug). On the Honda MotoGP bike, they are said to have a bore/stroke ratio of about 1.50 - for a bike that runs on pavement. The Ducati MotoGP bike has a much higner ratio and you can see it light up the tire coming out of the turns. On pavement, the lower ratio engine seems to be a clear winner.
A rule of thumb is short stroke engines rev easier, and long stroke engines make more torque. Once your tire loses traction, a short stroke engine will quickly rev, and it becomes difficult to regain traction. Longer stroke engines have a less abrupt "hit", which makes it easier to maintain traction. It appears that bore/stroke ratios higher than 1.50-1.55 might be going in the wrong direction, and lower ratios seem to be much more effective.
Keep in mind that all this is GREATLY simplified, and there are many other factors to consider.
As far as the YFZ is concerned, here's the bore/stroke ratios:
Stock YFZ 95x62 = 1.53
480cc Big bore 99x62 = 1.60
508 cc dogriders 99x66 = 1.50
488cc Falicon kit 97x66 = 1.47
I'd suggest watching the dogrider's video, look at these ratios and draw your own conclusions.
Disclaimer: I'm just Falicon's web guy. I'm NOT in Falicon's engineering dept. And I'm the dumbest guy here. So take everything I say as opinion, and make your decisions based on your own engineering analysis, or consult with a professional engine builder. Yada Yada Yada...
True, but the object isn't just to get a bigger engine - it's to get the proper power characteristics for best acceleration.
We have experimented with different cylinder bore and crank stroke combinations and have learned much about these engines. When our testers put a 98mm bore (468cc) or 100 mm bore (487cc) on a stock stroke Honda CRF-450, we didn't get much in the way of improvement. When we stroked the crank to 66mm on a stock bore (480cc), it made a huge difference at the track. I'm not talking the dyno, where traction is a non-issue, I'm talking about knobbies-on-dirt real world acceleration, where peak power means a lot less and the traction-control advantages of a longer stroke become evident. There was little difference between the stock CRF and the big-bore 487. But the stroker 480 killed our big-bore 487 on dirt, even though they were close on a dyno. How could this be?
One key (among many) to good power characteristics is the bore stroke ratio. On the CRF-450R, the bore/stroke ratio is 1.55 for a stock 96mm bore and 62mm stroke. That is, the bore is 1.55 times the stroke. With the stock stroke, a 98mm bore would be 1.58, and a 100mm bore would be 1.61. The stroker 480 has a ratio of 1.45.
Now, if we stroke the crank to 69.5mm in a stock bore, you have a ratio of 1.38. This configuration pulls like a mule and is the easiest to control. The downside is this long stroke requires spacer plates, longer cam chain, new engine mounts, etc.
We also tried a 98mm bore and 66mm stroke, which gives a ratio of 1.48. It doesn't perform quite as good as the longer stroke, but is almost as fast and doesn't use a spacer plate. Most of our AMA 500cc pro customers are using this configuration, but many are starting to change to the longer stroke/ smaller bore.
If you keep increasing the bore, you get to a point of diminishing returns. The wider bore increases the length of the burn (distance from the spark plug). On the Honda MotoGP bike, they are said to have a bore/stroke ratio of about 1.50 - for a bike that runs on pavement. The Ducati MotoGP bike has a much higner ratio and you can see it light up the tire coming out of the turns. On pavement, the lower ratio engine seems to be a clear winner.
A rule of thumb is short stroke engines rev easier, and long stroke engines make more torque. Once your tire loses traction, a short stroke engine will quickly rev, and it becomes difficult to regain traction. Longer stroke engines have a less abrupt "hit", which makes it easier to maintain traction. It appears that bore/stroke ratios higher than 1.50-1.55 might be going in the wrong direction, and lower ratios seem to be much more effective.
Keep in mind that all this is GREATLY simplified, and there are many other factors to consider.
As far as the YFZ is concerned, here's the bore/stroke ratios:
Stock YFZ 95x62 = 1.53
480cc Big bore 99x62 = 1.60
508 cc dogriders 99x66 = 1.50
488cc Falicon kit 97x66 = 1.47
I'd suggest watching the dogrider's video, look at these ratios and draw your own conclusions.
Disclaimer: I'm just Falicon's web guy. I'm NOT in Falicon's engineering dept. And I'm the dumbest guy here. So take everything I say as opinion, and make your decisions based on your own engineering analysis, or consult with a professional engine builder. Yada Yada Yada...
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FaliconKen
- Posts: 0
- Joined: Wed Mar 10, 2021 10:41 pm
Yeah, I was referring to the YFZ 450 quad. I am getting the Falicon parts this week or next. I'm now trying to find a polisher to polish the cases. I've watched the dogriders video. They seem to know their stuff, and they bikes seem to run good.
I'll keep everyone posted on this project.
Ken, thanks for the info, and welcome to the site!!
I'll keep everyone posted on this project.
Ken, thanks for the info, and welcome to the site!!
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cannibalq8
- Posts: 0
- Joined: Wed Mar 10, 2021 10:41 pm
