boost porting 66 er 68 cc motor has anyone done this? pics please

[Nitropeewee]

found this on another forum

--------------------------------------------------------------------------------

Here is the mod that i did to my motor. I attempted to balance the crank while it was apart and stupid me didnt look up any info on it... So it now vibrates like all **** at 25mph. I didnt half the weight of the reciprocating assy. But not all was lost... Before the crankshaft and boost port mod i could at most do 34mph according to my speedometer. Now the same speedometer read 43mph! Now im not going to tell everyone that it is dead accurate since i do not have a gps to test it but i know im going approx 40 mph since i was keeping up with traffic... The crankshaft can only be holding the engine back and the sound of the motor at that rpm is very smooth. Current mods to my engine include porting intake and exhaust, expansion chamber, homemade glass pack and steel pack muffler, 44 tooth sprocket, NGK b5hs, polish the head and piston top, and 2 boost ports. The two ports were about 1/4" wide and are as long as the ceiling of the transfer ports. They are about 3/64" deep and are centered between the intake and transfer ports. The end of each port is angled towards the intake port and utilizes a steep angle to aim at the sparkplug and help scavenge the exhaust charge out of the cylinder. Im satisfied with this mod and would do it again but will be tearing the motor down again to install a new balanced crankshaft... Please excuse the poor grinding on the one port, they ran out of grinding stones at the store and i will clean it up on the next tear down
Attached Thumbnails

 

[Just_Gasit]

I can't see any pictures but I'm very interested in you port work. I also look forward to hearing about how the balancing works out.

 

[kiwirider]

I would like to see the photos if you have any. I am interested in the boost ports you have made, sounds interesting. have you fixed the vibration??

 

[machiasmort]

Pics didn't post! Your leavin us hangin!

 

[Nitropeewee]

sorry think i may have miss lead u guys a bit. thats a post ive found on another forum. the guy had some pics posted but i couldnt really tell what he did. i wanted to know if anyone here has dun this? again sorry if i misslead u!

 

[ratty]

What Nitropeewee is referring to is a thread from the 'other' site. I read that post over there not too long ago. This seems like a good idea. The guy that did it said it added a little power and made the engine run smoother, albeit the work looks pretty crude (not that I could really do much better!). Do a title search for "Boost porting the 67cc china engine" , there you will see the article pictures and all. The is another guy that made a post in that thread that says instead of adding boost ports, he opened the transfer ports all the way up. I will have to try one of these methods as cheap as these parts are! Looks and sounds very interesting!

 

[ENO]

Porting

Hey Nitro..ENO (Down Under)..Go to a member "runnamuc" who has just done it..You might even Private Message him to get a quicker response..Good luck Eno (Oz)