Porting,shavin,polishing??

[fasterblaster09]

Exactly what do you do when you shave,port,and polish.I know I soudn stupid,but ill neevr know unless I ask.Thanks.

[eganracing]

porting is opening up the intake and exhaust holes to allow better flow. Ive never heard of shavin before but its probaly the same concept. polishing i think is just smoothing out the intake a exhaust ports.

[Cody_300ex]

On the intake side of the the head you just take out material. You don't take to much out or you will lose all your bottom end. Some people use air-powered dremals, some use electical powered dremals, all perfrence. You leave it rough to help out on fuel atomisation(sp). On the exhaust side you take material out and polish it so the exhaust gases move out of the head easier, without restriction. When I polished mine it looked like a mirror in there, I polished for 2 days on it till it pleased me. When a head gets shaved the machince shop cuts a tiny amount of the bottom of the head where it seals against the jug/cylinder. You shave a head to get more compression or to even the mounting surface up, over time they can get warped.

[cals400ex]

shaving the head also changes the timing so some will not recommend it unless you can degree a cam

[wilkin250r]

Good explanations, but let's get a little more into the thoery behind it all.

Power and engine design is often a trade-off. Smaller air passageways means higher air velocity, which is good for low-rpm power. However, they present a restriction when you want to start pushing large amounts of air through, like during high RPMS.

Engine design, in stock form, usually favors low-end power for ATVs, because of they are much heavier then dirtbikes. However, if you are a racer, you want more top-end power, so you want to remove all those restrictions inside the engine.

It's a bit more complex then just grinding them out an making them bigger. There is a lot of design, testing, and calculations involved in removing areas of turbulence for the best compromise between flow and velocity.

The intake ports are widened and remove corners, edges, and areas of turbulence, but the walls are left rough to allow small turbulences to atomize the fuel mixture better.

Exhaust ports are widened, and then polished to a mirror-like shine for two reasons. One, to minimize restrictions, but also to minimize carbon build-up. It's much more difficult for the carbon deposits to stick to a polished surface.

[fasterblaster09]

Alrite thanx eevryone,I kinda get the picture now.

[Cody_300ex]

Originally posted by wilkin250r
Good explanations, but let's get a little more into the thoery behind it all.

Power and engine design is often a trade-off. Smaller air passageways means higher air velocity, which is good for low-rpm power. However, they present a restriction when you want to start pushing large amounts of air through, like during high RPMS.

Engine design, in stock form, usually favors low-end power for ATVs, because of they are much heavier then dirtbikes. However, if you are a racer, you want more top-end power, so you want to remove all those restrictions inside the engine.

It's a bit more complex then just grinding them out an making them bigger. There is a lot of design, testing, and calculations involved in removing areas of turbulence for the best compromise between flow and velocity.

The intake ports are widened and remove corners, edges, and areas of turbulence, but the walls are left rough to allow small turbulences to atomize the fuel mixture better.

Exhaust ports are widened, and then polished to a mirror-like shine for two reasons. One, to minimize restrictions, but also to minimize carbon build-up. It's much more difficult for the carbon deposits to stick to a polished surface.

Wilkin, you need to be the exriders offical genius. lol

[Metzroth]

by shaving maybe you mean milling the head? All the does is make your head sit lower on the top of your jug making a smaller "squish?" area. Basically it ups your compression a little bit. not sure if Squish is the right terminology but it is something like that.

[wilkin250r]

Originally posted by Metzroth
by shaving maybe you mean milling the head? All the does is make your head sit lower on the top of your jug making a smaller "squish?" area. Basically it ups your compression a little bit. not sure if Squish is the right terminology but it is something like that.

Yes, squish is the correct term.

It does bring the head and valves closer to the piston, increasing compression.

However, for ATV engines, shaving the cylinder is generally more effective, especially the 400EX, but it's typically not necessary, a properly design high-comp piston should give you everything you need without shaving the head or cylinder.

[cals400ex]

the only reason i would like a shaved cylinder/head over a higher compression piston is because you can then run a flat top piston which will give a better flame travel across the top of the piston. however, you should clay the motor and degree the cam then too.

[wilkin250r]

Well, yeah, there is that. But unfortunately, it's extremely difficult, there's only so much you can do with the valves in place. It's not like a 2-stroke with a clean slate on combustion chamber design.