Stroker Motor Question!

[SnellCRP]

I would go with just the bore and increased compression. There are many other things like thin gaskets, increased timing, better carb, headwork, cdi, lighter flywheel that will make power without the major engine modifications required to build a good stroker. You can always add a stroker after all the above mods if your bike is still not powerful enough, but as you probably know the more engine mods the more heat, decreased reliability, increase in maintainance, and higher motor octane rated fuel you will have to run. Just try and decide if you want to trade reliability for power. Don't forget we like to ride the quads more than work on them. Hope I've helped.

[SnellCRP]

To get cc displacement of your stroker use this formula: (bore x bore x 0.7854 x stroke x number of cylinders). For example if you had a 440 piston and a 4mm stroker crank it would calculate like this: 89 x 89 x 0.7854 x 74 x 1 = 460365.3516 so your cc would be 460cc. To test the equation you can replace the #'s with the stock #'s to verify the equation is accurate. 85 x 85 x 0.7854 x 70 x 1 = 397216.05 so you know what the stock cc's of your EX are (397cc's) you have just verified the equation is correct. Good luck with your build and keep us informed with your progress.

[wilkin250r]

Originally posted by SnellCRP
To get cc displacement of your stroker use this formula: (bore x bore x 0.7854 x stroke x number of cylinders). For example if you had a 440 piston and a 4mm stroker crank it would calculate like this: 89 x 89 x 0.7854 x 74 x 1 = 460365.3516 so your cc would be 460cc. To test the equation you can replace the #'s with the stock #'s to verify the equation is accurate. 85 x 85 x 0.7854 x 70 x 1 = 397216.05 so you know what the stock cc's of your EX are (397cc's) you have just verified the equation is correct. Good luck with your build and keep us informed with your progress.

Just to clarify the fine details. Stock bore is 85mm, stock stroke is 70mm. If you convert these two to centimeters, just move the decimal place left one digit, so the bore is 8.5cm and the stroke is 7.0cm.

Plug these numbers into the formula, and you get 8.5 x 8.5 x .7854 x 7.0 = 397.216cc.

If you have a 4mm stroker crank, you increase the stroke from 70mm to 74mm, and you can convert it centimeters it becomes 7.4cm, and you can calculate.

[SnellCRP]

Sorry, I was calculating with mm not cubic centimeters.

[wilkin250r]

Right. I just didn't want somebody calculating, and then figuring they must have done it wrong because they came up with three hundred thousand...

Of course, it may be easier to use mm, but just change the .7854 to .0007854.

bore x bore x .0007854 x stroke

85 x 85 x .0007854 x 70 = 397cc

[Cody_300ex]

What would we all do without wilkin250r or SnellCRP?