Cylinder porting

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May 3, 2006
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#1
Cylinder porting is an exiting theme for many, but the truth is that on todays stock racing bikes, there is very little to do. Many hear about the wonders of time areas, but when we open those already optimized cylinders, we see very little room to do anything. Some think that raising or lowering the top edge of the exhaust provide detectable gains, some others think that cleaning up the internal passages may be the answer.
I just want to share experiences on this area with some of the readers and learn what have done the best on what.

Thanks for the feedback :ride:
 
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#2
While it's true that big power gains aren't likely while sticking with pump fuel, porting is and will always be an excellent way to tailor your bike's power curve to suit your needs and desires, and for less than the price of a two-stroke pipe. And some bikes are a little better developed than others from the factory...
 

splatt

Resident mental case
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#3
The idea of porting a 2 stroke is to change the power characteristics of a given engine similar to changing cams in a 4 stroke.

Steve
 
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#4
Well if you think porting is a waste of time and that nothing can be gained, then you obviously have not spoken with any of Eric Gorr's customers! Contrary to this thread I will still be sending my stuff to Eric so he can work his magic!
 

mtk

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#5
griffbones said:
Well if you think porting is a waste of time and that nothing can be gained, then you obviously have not spoken with any of Eric Gorr's customers! Contrary to this thread I will still be sending my stuff to Eric so he can work his magic!
What he said.

I've NEVER heard of a CR250 owner being dissatisfied with a port job from Eric Gorr, let alone anyone who had a ported CR265 done by Mr. Gorr.
 
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#6
Griffbones, I think you missinterpreted my post. I respect the experience and knowledge of Eric, and very sure he always can find corners to gain some competitive advantage. What I said is that "on cylinder porting itself" there is not too much room to play on modern racing bikes contrary to enduro bikes where there is plenty of room..! Manufacturer's have all kind of equipment and they know exactly where to find the power, and that is one of their selling points. Why to underpower??? The answer is that sometimes they sacrifice some power for reliability, cost and emmisions. :yikes:

I have worked on racing bikes such as KTM's, KX's, YZ's and see that the circunsferential wall left out is barely to hold the piston ring. Then the choices are going up or down depending on where do you want the power band. Or perhaps playing with the blowdown period. With some sense on how a two-cycle engine works we suspect the final effect, but sometimes a threshold is reached and no more gains are possible. That was basically my question: what modifications are worthwhile????And here we are talking of motocross racing not mountain rides. :blah: