boost port?

[needforspeed]

does anyone know what a boost port on a 47cc is and how to make one
any comments appreciated
thanks,
ed

[zameil]

I think what you're referrring to is the exhaust extention port.
They bolt on to your barrel and make like an extension between your pipe and barrel.
They will give you more bottom end but you will need to re bend your pipe to fit properly.

https://www.pbr.8k.com

[tblumer]

wrong, a boost port is another transfer port generally added opposite the exhaust port.

[blah]

That's right tblumer, If your motor has a reed valve then you can boost port the hell out of it, some feed from the crankcase, some feed though the piston and others can go direct from the inlet port. On Piston port motors it can be tricky, i wouldn't feed from the inlet port without a reed valve. Watch where your ring ends are, you don't wan't them falling into a port, either you can move the pin or make sure you don't port too close to them, all depends on what engine you're doing. If you don't have enough room for boost on the outside of the clinder then more room can be made with devcon or a good epoxy filler, don't use araldite it gets soft when it gets hot. Before doing anything make sure you read how it's done, books like a used first edition of "Two-Stroke Performance Tuning" by Alexander Graham Bell can be had for less than the price of making some YEIS clone and would reward you many many times over.
Obviously, you have to know what you're are doing and have some practice, i started many years ago on a Victa, we had the hottest lawnmower on the street

wow, for a first post i crapped on a bit

[needforspeed]

thanks for the feedback.
does anyone know how one of these can be installed on a reed induction motor?
thanks,
Ed

[Freddie]

Blah - thanks for the feedback... now off to do some mad reading to find out how to do it!!!

[mega]

thanks for the feedback.
does anyone know how one of these can be installed on a reed induction motor?
thanks,
Ed

boost port: here is the synopsis. I thought of adding one, but the issue that i had was that my BB Cylinder was too thin (plus i didn't want to deal with patching it up with additional welding or JB goop.)

anyway, if you have the 40cc cylinder, its a better canidate for this mod.

to add a boost port you would need some grinding tools. bacically, you will be adding a small channel from the end of the cylinder (opposite side of the exhaust port) just shy of the end of the stock intake port.

very important thing to understand, bigger is NOT always better in this case. as the piston goes down to BDC, this closes the reed valve, compresses the A/F mixture in the case, and when the piston passes intake ports (@ BDC the intake ports are around 3mm exposed open), A/F is injected into the combustion chamber (note 'injected' since the case was pressurized as the piston goes to BDC). this forces the A/F to enter rapidly. (the pulses from the exhaust stroke keep the AF mix inside the cylinder, btw, thats a whole diff story :-) )

anyway, with the added boost port, this adds an additional port to the induction of A/F mix, giving it a 'boost'. (by having a boost port you are likely gonna have an increase in RPMs ~ 600+)

BUT!!! doing this operation is very critical (adding a boost port that is). so be very careful when doing this procedure.

here is a picture that will speak a thousand words.

thanks to 'Rexracer' from PBP and Jeff @ PBP for the pics :-)

[mega]

more explanation :-)

[tblumer]

I was looking all over PBP for those first 2 pics to post, they're the best explaination. Good work!

[needforspeed]

does anyone know how deep/long to port it out?

[blah]

does anyone know how deep/long to port it out?

How long is a piece of string?
It all depends, some people open the boost port up earlier than the transfers to help spent gas out the exhaust, others open it later to help push transfer gas up. Some of my rules of thumb are, Keep the angle steep like 55-60 degrees that way when the reverse pulse from the pipe is pushing back into the cylinder it's less likely to go down the boost port, at 30 some is lost, i got this information from William D. Glenn who wrote his thesis on it. You can easily raise the boost port later if you make it a few degrees lower, obviously don't start out with the boost ports higher than the transfers. The depth is up to the cylinder wall thickness, if you plan on getting it deep then put some good epoxy behind it first, trust me it's esier to do it before, not 15 stuff either, Devcon f Aluminium is not that expensive, use Devcon titanium if you're made of ca$h. Basicly, because of the steep angle, you want to go as deep as you can. Width depends on where your ring ends are, you should really know where they are before you start cutting into your cylinder. An even safer rule of thumb would be experiment when you have a spare cylinder handy.
Does this help:

[mega]

How long is a piece of string?
It all depends, some people open the boost port up earlier than the transfers to help spent gas out the exhaust, others open it later to help push transfer gas up. Some of my rules of thumb are, Keep the angle steep like 55-60 degrees that way when the reverse pulse from the pipe is pushing back into the cylinder it's less likely to go down the boost port, at 30 some is lost, i got this information from William D. Glenn who wrote his thesis on it. You can easily raise the boost port later if you make it a few degrees lower, obviously don't start out with the boost ports higher than the transfers. The depth is up to the cylinder wall thickness, if you plan on getting it deep then put some good epoxy behind it first, trust me it's esier to do it before, not 15 stuff either, Devcon f Aluminium is not that expensive, use Devcon titanium if you're made of ca$h. Basicly, because of the steep angle, you want to go as deep as you can. Width depends on where your ring ends are, you should really know where they are before you start cutting into your cylinder. An even safer rule of thumb would be experiment when you have a spare cylinder handy.
Does this help:

excellent pic

[zameil]

How are you guys getting around the Nikelsil coating on the barrel?
Or are you just not worrying about that?

[blah]

Nikasil is less than .004" thick, I use a diamond cut tungsten burr to break through, rough out with a course cut then shape the ports with whatever burr hasn't fallen off the bench

Btw, i'm guessing some of these chinease engines don't use Nikasil, i'm sure they are using some cheap alternative? I know the RC guys have problems with Nickel based coating peeling off of brass but i think it sticks pretty well to Aluminium, either way it's a good idea to leave a little chamfer all the way around your ports, It's kinder on the piston and rings as well.

[zameil]

I'd say it's a cheaper alternative of the coating on the chinese bikes.
I guess I'll just bite the bullet and do it and hope the coating doesn't flake.

I've got a spare barrel here I was toying with the idea of doing,By the way the "Boost port" down here (Australia) is called a transfer port or extended induction port.
When I saw the word boost port I assumed the exhaust side.
I hate living here sometimes. Our terminology is so different.

Also toying with the idea of drilling the piston, Anyone done it and if so what gains did you get?