Drag Porting

[DALLUGE909]

i ported my banshee cylinders. these are the specs:
exhaust- open 82deg duration 196deg
transfers- open 116deg duration 128deg

this was for duning and a little hill racing. now i just want a fast hillshooter. if i raised both the transfers and the exhaust 2 deg. would that be too much? could i raise the exhaust even more? any input would be appreciated!

[fast350]

ask eviltwin, or 370, they know these things

[DALLUGE909]

eviltwin or 370, do you have any suggestions? my bike has shearer inframes, 32mm mikuni roundslides, v force 3 reeds, coolhead w/ 18cc domes, and the stock crank and cylinders.

[flotek]

Originally Posted by DALLUGE909

eviltwin or 370, do you have any suggestions? my bike has shearer inframes, 32mm mikuni roundslides, v force 3 reeds, coolhead w/ 18cc domes, and the stock crank and cylinders.

well there comes a point when yo u gotta look at what your doing with the bike ,for hillshooting yo u may be robbing peter to pay paul when yo u start getting up there i n durations ,shearers wil l have no trouble running a 200 +exhaust port but yo uwill lose lowend especially o n a stock stroke 350 . also theres way more to a port than just the transfer and exhaust port timing ,the angles shapes and sizes wil lbe very crucial to the output . id probably go with a 198 and 130 and give your self plenty of exhaust area and get your transfers angled correctly ,like i said yo ucould go higher but it would lose alot of midrange torque for hillshooting if yo u did and yo umight not get fro m point A to point B any faster , advance the igniiton timing 5 degrees to gain some lowend back and might want to try 17cc domes too .

[DALLUGE909]

thanks for the input. the timming is set at +7. as far as angles are concerned, i planned on making the ports flat on top. also want exhaust port to be about 48mm. does this sound correct

[flotek]

sounds like your o n the right track ... but i would pitch angles upward some and how your aiming them is critical . ex. and transfer shapes are critical too , drag porting is a bit different than standard mX or duner port other than obvious higher port timing... alteast way i do them is .my 2 cents

[370banshee]

the way the transfers are angled is a critical part of a useable powerband... you'll want to angle the intake side transfers toward the exhaust...

[DALLUGE909]

ok,
exhaust open:81deg atdc
transfers open:115deg atdc
widen exhaust to 48mm
angle the secondary transfers towards the exhaust
how about the mains. should those just be aimed towards each other(no angle)?
also, for the exhaust shape i have heard that it is shaped like a trapazoid, with the top being longer than the bottom, and the top being curved also. does this sound correct?

[flotek]

flat top exhaust roofs have a peaky powerband that comes on violent due to the sudden drop in pressure from the charge ... by having a roundish exhaust it makes a more linear powerspread ,theres a a ton of ways to set it up for power i would be trying to get al lthe exhaust area i could if it was me .theres a ton of little secrets on doing the full drag ports that are stil l new to me some of which i keep to myself

[370banshee]

i think you guys are tlakign about 2 different things... he's talking about a 197duration exhaust... and denyn your talking about a full drag port.... or maybe i'm missing the boat... seems to me a full drap port shuodl be somewhere in the 202ex duration range... with a big wide exhaust port.. tall transfers and hard transfer angles toward the exhaust port... but i'm a newbie to all this..... i like trail porting... haha