Engine Porting - Gases out, Fuel Air in

[Egor]

Ghost0 - Yes that is the way we did it at first. The reason I like to do the port instead is that the piston is tapered from the top to bottom and if you cut the skirt it starts making noise (rattling in the hole). I cut a moon shape leaving the sides to hold the piston. The port timing is conservative and can be increased a fair amount. It is easier to cut the piston. Have fun, Dave

PS: Round all mods over easy, cracks start on a scratch or a ding.

 

[Ghost0]

I am curious about ignition timing vs porting. If we port to achieve better "breathing" and higher RPM, at what point will we be out-revving the ignition timing?

 

[OldPete]

I am curious about ignition timing vs porting. If we port to achieve better "breathing" and higher RPM, at what point will we be out-revving the ignition timing?

Out-rev ignition advance? No, not hardly.
Increased turbulance at higher rpm kinda takes care of that. In fact, sometimes built engines need to have the advance slightly retarded from stock for best power out-put. Say from 34degrees to 28degrees. There is no hard n' fast rule for jetting or timing once serious modification begins.

Note: Gasoline always burns at the same rate, turbulance just mixes it up.

 

[Egor]

I moved the timing ahead about half a key, but I put it back because I did not like the way it ran slow. It would run fast OK but most of the time you are just pulling away from a stop. the timing on these engines is not very hot, but it is what it needs. you can not spin one of these engines too fast or it will just tear itself up. I have found that if you want to go faster you need to gear it up. It will pull the gears with the porting done. Have fun Dave

PS: Two strokes need good cooling and the fins on these engines are just barely adequate, it would help if they were larger. The Dax stile head helps.

 

[BSA]

Could I just file away about 1/16-in from the bottom of the intake port, and about 1/16-in from the top of the exhaust port. I don't want to overdo things.
Could I just use a normal file to enlarge the ports. Obviously I have to be careful to make sure that there is no shavings or flash on the sleeve after filing. Is it true that it helps the piston rings if the ports are slightly rounded.

Forgive my ignorance, I'm new to mucking about with engines at this level.

BSA

 

[alex]

ok, so I have a very old engine, and I am constantly gunning it for short periods of time, and the farthest I would ever go full throttle is about .5 miles, do you think I would blow my motor up with a porting job like in the pictures? p.s I run a 32/1 mix, would I have to change that?

 

[Egor]

BSA - any moving of the port timing will help, use a felt pen and mark what you want to remove, it will take longer to use a file but it should work. On the intake I would go further don't worry there is a lot of room for carving. We used to carve a notch in the piston also to lengthen the intake time, you can do that also but if you can move the port down its better. Yes it is true a rounded port makes for easier transfer. On racing engines they use straight ports for the affect we don't need that.
Alex - It should not make a difference if your engine is old just in good condition. If you port it I don't think you would be able to hold the throttle open for a half mile you would be going to fast, you would find that just cracking the throttle will give good results. I have noticed a big increase in fuel mileage, as the engine runs more efficient. And "no" your fuel mix is OK. Have fun, Dave

 

[BSA]

BSA - any moving of the port timing will help, use a felt pen and mark what you want to remove, it will take longer to use a file but it should work. On the intake I would go further don't worry there is a lot of room for carving. We used to carve a notch in the piston also to lengthen the intake time, you can do that also but if you can move the port down its better. Yes it is true a rounded port makes for easier transfer. On racing engines they use straight ports for the affect we don't need that.

Thanks very much dave, I will open up the ports on my 80cc when I get it.

BSA

 

[mastermechanic5]

ok so it started raining today so i figered i would take my bike inside and do some porting so i enlarged and port matched my intake manifold, then port matched the exhaust, then removed the casting flash. tomarrow im going to do the cylinder ports and put the motor back together. just a couple questions, the intake and lower head gaskets were kinda soft and degraded so i ripped off the intake gasket and might leave the head gasket because its still intact just wondering if i can use high temp RTV sealent on those surfaces or is there a better solution? the motor internals were nice and oiley and im on my 4th gallon the piston and cylinder wall arnt really showing signs of wear good to see i also looked at my connecting rod and it has a bushing and there arnt any oil holes hope that wont be a prob when i start reving high.

 

[mastermechanic5]

went too far

well looks like i screwed up, i got everything back together and took it for a spin and it lost a lot of low end and doesnt top out as fast:???: maybe if i replace the intake manifold i will get some of that back? i did a lot of porting on the intake manifold. so i gess i need i new head now right?