Effects of porting

[NCyz250racer]

Ok I'm not really sure what the overall effects of 2 stroke porting are. Does it increase top speed or just acceleration or does it just shift power around to make the bike faster in certain situations. I understand that Eric has a mo better porting that increases both bottom end and top end so would that mean that the bike pulls better from lower rpm and has a higher top speed in a given gear? Thanks for all the help.
Rob

 

[DOTdirtbiker]

porting

ok, ncyz250 guy, I would have to say you are on the right track when you say motor pulls from low end into high better/farther, that is if such porting exists by forward motion. If it exists, I would get it-give it a try. Porting would increase top speed and acceleration, I believe, but top speed can be most noticably affected I would say.

but I am under the impression that you really can not have the best of both worlds.. Like timing, if you advance it you gain lowend but lose topend, if you retard it you gaintopend but lose lowend...if you increase one you will be ultaimately sacraficing the other. If you had a 125 I would say increase the cc's. If you had a 500 (2cycle), I would say port and polish it for low end and use an exhaust system to match (lowend). Well a 250 is the happy medium, so I dont know for sure. Um, I guess I would personally go for as much low end as possible, within reason, there as well in order to make the bike more ridable, tractable and controllable since I am not very skilled of a rider (or not a racer) even though I have been riding (ATC250r350x/ Banshee/ enduros xl/r350, dt125, f9 350, CM400T, xp800, Vmax600, srx700, sxr700, tx340 440/ etc.. ) various bikes for nearly 20 years. Make the bike more like the trend...trench digging 4-strokes! I ride a cr500 with 600cc kit and I am finding the need for more low end power, but there is a key reason most likely exclusive to me and that is I ride on road. When I ride on the road I do not want to over rev my engine (I dont want to wear it out too fast). 5000rpm is plenty for a cr600 to move you down the road and you dont have to redo the topend every 2yrs. If it doest blow more like should last 6 years at least. I have/had a '85ytz250 still on the original topend. When the topend wears (and it will wear out faster when used high reving) it won't run well in hotter weather (or slower riding) because the piston superheats I think. But for offroad (and/or racing)its a whole different ball game. When I did ride a 79rm125 offroad and the throttle stuk wide open I had a very hard time controlling the rear end. I dont like that high reving power too much, but a little is great and that is why I ride a 2cycle on road besides the fact that I do my own engine work and I dont like to work on four stroke engines. Just my personal opnion.

 

[john stu]

humm cr600? i was really sure there was no big bore kits for the cr500 who makes this kit?

 

[oldfrt613]

Yes, you can have the best of both worlds. What you have to realize is that we buy production motorcycles. This means that compromises are made in the mass production process. The engine will not be manufactured exactly as it was designed. The manufactures have to accept variations in castings and machining in order to make bikes affordable. What a good porting job is going to do is bring these variations closer to the intended design. Manufactures also have to design bikes to make most of us happy. A good tuner will adjust the engine characteristics to suit YOU, much like suspension tuning. You will find that porting/head mods are the best bang for your buck, just make sure you find a reputable tuner. Don't be discouraged by Eric's low prices - he is an excellent tuner without the big name overhead !

 

[Eric Gorr]

It really depends on the make and model bike. Porting is a process of robbing Peter to pay Paul but in some cases if the manufacturer made such a design boggle that they leave the door open for massive improvement you can get more power across the board. Some bikes are so good stock that they can't be improved.

 

[X men]

Eric, have you ever had the opportunity to work on a Gas Gas 300 engine ? Over here in europe that bike is generally rated as the best enduro (by the readers of Moto Verte) and they call it the 3stroke. Because it has lots of torque at low and medium rpm and high output at high rpm. I wonder if there is still room for improvement to be found in this engine without changing its fundamental strenghts. What do you think ?

 

[X men]

No opinion on the possible gain by porting a GG 300 ? :(