Dune, trail, drag, and agressive ports

[NN2]

Obviously a drag port is for drag, dune for dune, etc. but what makes them different from one another? Are there differences between shapes of ports, sizes, etc?

I plan on having my cylinders ported for trail with a 4mil crank but didn't know if I want something more agressive than that.

[csrmel]

porting does very basically 2 things. i changes the rpm's at which the engine starts pulling hard, and it tries to improve overall flow.

 

when someone gets a trail port or a mx port basically the rpm's are changed little to none, but the ports casting flaws are cleaned up. some parts are shank edged, etc. basically a trail port or mx port doesnt add much power.

 

something more aggressive like a midrange port raises the exhaust and transfer durations which means the exhaust pipe wont twattled until a later rpm. building torque at a higher rpm means more horsepower. also the casting flaws are taken care of and such. this is what most people get.

 

a dune port is basically a real agressive midrange port. generally speaking its designed to give ya lots of top end without completely killing the bottom end and midrange. casting flaws and such....

 

so we come to the drag port. this is for all out power. the higher rpm's at which you make torque, the more horsepower you have. a drag port is designed to make loads of torque at high rpm's. it does this at the expense of bottom end power, and even midrange. drag ported motors can have fancy triple exhaust ports that cost a lot of $$$.

 

keep in mind that you can get any porting you want. want something in between an mx and a dune? or an agressive dune port? how about a mild drag port. you can do almost anything you can think of. the words mx dune, agressive and drag are only words.

 

 

 

also note that just as important as the porting, youre type of exhaust pipe basically dictates what porting you can go with. you HAVE to match youre porting to youre pipe. you would lose a lot of power by using a drag port with a pro circuit pipe, or a shearer pipe with an mx port. if you dont match the pipes and port work you power suffers and funny things happen to the powerband. maybe the bike is super peaky within a narrow rpm, or maybe it never really gets on the pipe.

 

 

you need to have the porting matched to whatever pipe you run. and the pipe must be matched to whatever type of riding you run. sounds funny but you almost have to build a 2 stroke backwards from the pipe on up.