Planet Minis

chump

I was reading on the mototuneusa.com page that you actually don't do an engine any favors by porting and polishing instead you should add to the intak with epoxy and constrict the size for more rapid flow through the valve port. he didn't list little minis in the engines that benefit but it's intriging. Could this work for 125cc mini? of no why not?

heres the link

http://mototuneusa.com/homework.htm

Z50King

No, it wouldnt help because you are making it harder for that little bore to suck the mixture in.

cyclerider57

It's all in the motor combination. Yes increased velocity is a good thing but if a motor can take a bigger port then that is the way to go. Porting is about finding the balance to work with each motor application.

EDIT: Not being a jerk but the bore doesn't suck anything in. When piston goes down it creates a low pressure area. Air wants the pressure to be the same so it flows into the filter, carb, ports, combustion chamber.

__________________
The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

chump

EDIT: Not being a jerk but the bore doesn't suck anything in. When piston goes down it creates a low pressure area. Air wants the pressure to be the same so it flows into the filter, carb, ports, combustion chamber.[/quote]

Question? did you read the article? if no. read it. if yes, why does it work with a yz400f and not a 125sx?

Z50King

Im talking about how small the bore fo the engine is. the piston is inside the bore, and the bore would determine the sucking power. small bore, like a 125, small suck, big bore, like a 400, big suck

Not trying to be a jerkypoo.

Piston creates a low pressure area in the what? Cylinder, also called by me the bore, for size reference, AKA big bore, no one calls it a big cylinder.

Z50King on the Defense.

50mAfIa

well my first porting was on my 50 with a stock head and 88 kit, opened the intake the size of the "ported" intake manifold and opened the exhaust port up a good amount, well this thing flat out smokes my other stock head un ported 88 kitted bike, so its all in the right port job, big tho is not always good tho, as some people think bigger is better

cyclerider57

I didn't say it wouldn't work. I was just pointing out that it will not work in all cases. That guy can spend the time and money to test every application to see if it works. Nobody can tell you for sure if it will work or not until they TRY it with your application. He is talking about engines coming with ports that are to large from the factory. In the fifty market with my experience I haven't came across an application that fits that spec. That is ME and the engines I have worked with. Just try it. That's the only way to be sure. I'm not saying it won't work but with your application I would be surprised if it did.


Z... It's funny when you try to defend yourself. I wasn't attacking you though. I don't care about how big the piston, cylinder, etc is. I was just saying that the piston going down doesn't SUCK the air in. The air flows in under its own power because it wants equal pressure. That is why port flow is so important. To make the air more likely to flow in. It's not like a hose with a pump pumping water. Just wanted the "lesser" knowledged people to know that before they go messing with their motors. Don't take stuff so personal mang.

__________________
The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

five0addict

this does not apply to minis because the ports are all close to the same size as the valves, the problem from overporting is taking in too much feul to the intake, but not fitting it all through the valve. porting is useless without large valves or a high lift cam.

also dont worry about overporting on the 50 style heads. i dont think theres even enough material to remove to start working backwards.
that article sucks tho, no real comparisons on a dyno or flowbench.

2wheeltyson

WARNING there is a lot of bad info in this post. porting doesn't always have to be about enlarging anything most of the benifits on these minis comes from removing imperfections and restrictions. this could be flashings of the cast or a intake manifold that isn't following the same lines as the carb outlet or head intake, (matching these sizes will make the most differance). but the original poster was onto something there is such a thing as overporting which actually decreases velocity and doesnt let the fuel atomize properly. the same thing can happen with too large of carb which is also becoming more common. with these little engines the porting is more criticle than big bikes because one horse on this engine means alot more than one horse on my 450, its all so much more finesse.


this of coarse is only my oppinion.

birddogg

Suck-squeeze-bang-blow are the 4 cycles of a 4 stroke, or a GOOD night. Sure the air wants to equalize, but only because it has to. It has to fill the void that the piston creates on it's downward stroke. All matter occupies space. Gas, liquid, solid, it doesn't matter. An engine IS a pump, it's a high-tech air pump.

chump

[QUOTE=Z50King]Im talking about how small the bore fo the engine is. the piston is inside the bore, and the bore would determine the sucking power. small bore, like a 125, small suck, big bore, like a 400, big suck

Piston creates a low pressure area in the what? Cylinder, also called by me the bore, for size reference, AKA big bore, no one calls it a big cylinder.

[QUOTE]

small suck is to big suck as big high velocity is to small high velocity.

just because it doesn't have as much sucking power doesn't mean it wouldn't do the same on a smaller scale. right?