Porting

[elroyjetsn]

The ports on these pushrod engines seem extremely restrictive. Has anyone been able to rework them any? I wonder if the head has been fitted with bigger valves to go with the move from 125cc to 200cc displacement. The ports seem very small for a 200.

[winwun]

Polishing oftentimes works almost as well as enlarging.

[TeamCheap]

I think it could help wake up the engines a lot but then you'd burn up the clutch and trash the tranny and maybe even break an engine mount.

OK so a better clutch can be had but the trans is what it is unless you find some better gears that fit it and can the case handle anymore ?
But in the end by the time your all said and done you could just go buy a JAP engine that produces better, more reliable power for the cost you'd have it modding a china engine.

If I had the knowledge and shop to do the modds I would do it just to see how far it could go but sadly I do not.

The thing about the china engines that appeals to me is they are so cheap and can be messed with without fear of blowing up a WAD of cash.

[DDG1976]

There's a company in Nashville, Tn. that extrude hones. You gasket match the ports with your favorite dremel, then ship the head to them, they extrude hone it and ship it back to you. The insides will look like glass, and you will get a flow chart back from them. I'll do a search and post the comp. name. It was neat to see how pushing gritty putty through the head did what it did, there's no humanly way to get it that smooth with a dremel inside.

[Frog]

Quite a lot of evidence that glass smooth is unnecessary and may be even counter productive in terms of gas flow - certainly polishing by hand is not worth the effort - theoretically at the gas / wall interface gas speed is zero in any event. Dull smooth is probably just as good if not better (some small scale turbulence above the interface may be helpful).

Porting that takes out bends and avoids or removes sudden changes in profile / cross sectional area are good.

And yes I guess there would be an easy 20% more power to find in the head if you looked - its just that 20% of what we have is not much 8O and may not be worth the time and effort. Having said that if I had the head off for another reason ................

Although I am no expert the above reflects my understanding (and practice) gleaned when tuning two strokes some years back.

Frog

[Willys]

I have a Baja fat tired mini bike that I bought for my daughter to learn on before the China Hybird......I wasn't happy with it...ported and polished and made a better header pipe, removed the govener.....better plug....NOW!! It goes twice as fast and is quick off the mark too! I bet for what I did...it is twice the bike it was. Now..is it worth doing on a China bike????? Yes..it depends upon what you use it for though. How much $$$ you have to spend and are you willing to loose fuel mileage?

Personally I don't plan on doing it on her bike as it is strickly a learning tool for use in the fields behind our home untill she is old enough to legally ride the streets and then I will buy her a Jap bike.....just a more sensible approach to the problem...sorry.

[suprf1y]

I do a fair bit porting as part of my business.
If anybody could post some pics of these ports, I could probably tell you if its worth it, and maybe even what to do.

[Frog]

Originally Posted by suprf1y

I do a fair bit porting as part of my business.
If anybody could post some pics of these ports, I could probably tell you if its worth it, and maybe even what to do.

Be good to know what you think - unfortunately I do not have a picture :(

Frog

[elroyjetsn]

Originally Posted by suprf1y

I do a fair bit porting as part of my business.
If anybody could post some pics of these ports, I could probably tell you if its worth it, and maybe even what to do.

That would be great! On the exhaust side, the valve guide boss appears to block 1/2 of the port maybe more!! Haven't looked at the intake.

Wouldn't want to overdo it, though. The little 125 gearbox is pretty maxed out already at 15hp. :roll:

Polishing the ports is bound to increase airflow, but at the cost of some fuel effiency.

[Frog]

If you have to polish then exhaust port only I think.......... but I doubt polishing will make any appreciable difference in our engines (couple of horsepower on a 350hp v8 does not translate to much on 200cc!) . Polishing the combustion chamber is done for other reasons. Slimming down and smoothing the valve guide boss Wayne mentions would be good though - sounds very restrictive.

On a related note is the bulge in the down pipe a catalytic convertor? - seems improbable but I can not see another reason for there being a bulge :?

If it is getting rid of that has got to be a first step............

Frog

[elroyjetsn]

Originally Posted by Frog

On a related note is the bulge in the down pipe a catalytic convertor? - seems improbable but I can not see another reason for there being a bulge :?

If it is getting rid of that has got to be a first step............

Frog

Frog,

Good question?? Maybe there's a honeycomb in there

[elroyjetsn]

Originally Posted by DDG1976

There's a company in Nashville, Tn. that extrude hones. You gasket match the ports with your favorite dremel, then ship the head to them, they extrude hone it and ship it back to you. The insides will look like glass, and you will get a flow chart back from them. I'll do a search and post the comp. name. It was neat to see how pushing gritty putty through the head did what it did, there's no humanly way to get it that smooth with a dremel inside.

Hmm, sounds expensive though?