Picture of Beginner's Port and Polishing
Please keep in mind that performing anything suggested in this instructable is at your own risk. If you have no experience with a dremel, practice, this project is potentially dangerous if not approached properly.

Now that the disclaimer is out of the way, let's get started.

This instructable is for anyone looking to get a bit more performance out of their car and learn a bit more about their car in the process. The basic principle behind modifying a car is to have more air/fuel enter the combustion chamber. The port and polish basically makes it easier for air/fuel to flow into the combustion chamber and gasket matching permits a greater volume. (more gas and air equals bigger/more powerful explosion equals more torque and horsepower)

Keep in mind that this is a very large project. I have put over 20 working hours into my sunfire's head.
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Step 1: Gather Materials and Tools

For this you will need:

1 or 2 heads (car dependent)
Various sanding bits for the dremel
Face mask (inhaling metal shavings is no fun)
Permanent Marker
High Accuracy measuring device (optional and preferable for those who intend to get really serious with this project)

Step 2: Examine the head(s)

Picture of Examine the head(s)
Every car will be different, the head pictured came from a 98 Sunfire (Engine LN2). Make note of any manufacturing defects. Usually the better-defined bumps are intentional for fuel atomization. On the sunfire's head, there was a mold ring (left over from the casting process). We will start by removing any defects.

Step 3: Begin Grinding

Picture of Begin Grinding
DO NOT grind away the topmost lip, this is the seat for the valve and damage will cause leakage. Use a lower grit sander to start on moderate speed. Slowly shave the excess metal off until the port is smooth. Do not rush this, it's greatly preferable to spend weeks on this than destroy the head and have to buy another.

Step 4: Gasket Matching

Align the exhaust and intake gaskets one at a time and mark how much of each port is to be removed. Leave 1 to 2mm of metal between the gasket and the holes. Once finished with this it's time for polishing.
amr90003 years ago
Yes porting and polishing increases the flow of air to the engine but this only makes it easier for the engine to run faster it doesn't allow it to get there faster.
if the air has more room to move then at low rpms it will move into the cylinder slower. Similar to a rocket with a pole or without one.
this equals more horse power and less torque, not both..
sorry I had to explain that before someone did this unknowingly..
RickO5 amr90002 years ago
Not quite. You can definitely get more horsepower and more torque at all RPMs. The gain is more at high RPM because of higher air speeds, but its not a gain at the cost of low RPM torque.

As long as you're only smoothing the intake, and not making the intake appreciably bigger, you will speed up the air flow, causing more air to enter the cylinder, and making more power across your entire RPM range, with the most benefit at high RPM.

If you are increasing the diameter of the ports my a large amount, then your airspeed lowers, and you have the kind of effect you describe. This isn't what he's doing here though.
amr9000 RickO52 years ago
Touche. But of course there is no way to maintain the same size of the intake. So it isn't a big enough change to hurt the bottom end, but I can't see how it's possible to help the whole range either.. especially not if it gets worse as the hole gets bigger.

Also, I'd like to see a way to further close the intake, increase pressure. Would be Awesome!
Pressure is adiabatic according to Psig@ sea level 14.7psi. an engine is just an air pump. Restricting the flow into the engine will not change the pressure (remember atmospheric pressure) we are not talking boost like a turbo. It's normally aspirated. Increasing the flow into the cylinder without drastically reducing the velocity of the airflow is what you want. If the velocity is reduced so much the fuel will puddle in the ports and not remain optimally atomized for burning and the result will be a dog that runs bad and wastes fuel. It's an old book now, but I recommend "Maximum boost" by Corky Bell. A turbo system done right will provide performance and some drive-ability. 1.5 liter will run like a 3 liter, and for you UK guys you won't pay the penalty for the big engine to the taxman
RickO5 amr90002 years ago
Some engine builders will add metal by welding, or by pressing in a tube with a smaller inside diameter, and then blending the ports appropriately.

What a basic port and polish does is just smooth out big casting marks, rough edges, and potentially gasket material or metal at a gasket surface. These obstructions to the port don't appreciably decrease the size of the intake, they just cause lots of turbulence and resistance to air flow. You also don't want the diameter to change from large to small and back to large really quick (which is what might happen if a gasket is sticking out into the airflow). You get no benefit from higher velocity for a split second, and all the downsides of trying to pull air through a smaller hole.

amr9000 RickO52 years ago
Right but by smoothing out said marks etc. The only way it can go is bigger. I just don't see how it would help the bottom end. It honestly doesn't matter though, this modifications will hardly help anyways without some other more serious mods.
The physics are arguable in my opinion, but I don't know enough about them to say much more :P
I ported a few heads back in the day. (And ruined one or two.) The principles are the same. For those unaware be very careful when modifying the ports on your head(s). Minute changes can drastically change the air flow in the port. Bigger is not always better. considerations to the lift and duration of your camshaft as well as the RPM range and intended use (Street/ Race) Lots of cylinder heads have been ruined and most will (shockingly) flow less than before you attacked it with the grinder. Professional porters use a flow-bench to verify that changes are actually doing more harm than good. Once you have achieved a port mod that actually works you need to have templates for the intake and exhaust so you can repeat the ports in the rest of the head. Read a bit. Most successes are to start small with a little work under the valves in the pockets paying close attention to the last 20mm or so to the approach area underside of the valve. A five angle valve job will bring marginal increases in flow, but will also shorten the life of the valve because of the narrower margin on the valve seat. There is a bit of a compromise in a street engine because you are trying to increase airflow(and fuel) into the engine for more power without dramatically altering the torque curve. You want a curve that's flatter not peaky unless you are building an F1 engine for high rpm. Matching your ports to the gasket and your manifolds would do more than you would believe in respect to the power. On a fuel injected engine a throttle body 2mm larger would compliment your 'street' porting in conjunction with a cold air intake that gets the air from outside the engine compartment. (Not some powder coated aluminum tube that looks cool) Aluminum attracts heat. Composites like plastics and phenolic s do not. A high flow catalytic converter with a good muffler ( not a fart can) Will help. The engine works as a system so, changes to the airflow affect fuel requirements, ignition timing and spark demands.You might even want to purchase a book or two on modifying engines and porting before you plug in the dremel and start grinding. There is some solid science behind this beyond just grinding ports bigger. Not to mention the potential for cutting a little too much and discovering where the water jackets are on your DOHC Honda head. There is a reason why people keep some stuff secret and make people pay for a quality port job that (increases) power. Learning curve is steep.
  Nice instructable! I think I'm going to do this to my new cb550 four. I just have a few questions.
1) Is there really a lot of gain to be had just by cleaning up the ports and then polishing them? It seems like you could get even more power by opening the passages to be able to move a larger volume in the same amount of time, but then you would be fighting the valve size. Honestly though, I have no idea what I'm talking about, because I haven't worked on four strokes much.
2) Isn't it more effective to have a rough surface if you want better gas flow? With a little gas stuck in the grooves, there will be a layer of gas that forms which will be much smoother than you can polish. You don't want any ripples in the surface, but wouldn't it be better to have a slightly rough (think sandblasted) surface? I know polishing will stop carbon buildup, but there shouldn't be much carbon buildup in a 4 stroke unless you're burning oil.

I'm hoping to make a instructable on porting, polishing, and port matching 2 stroke engines soon. I mostly work on small displacement 2 strokes which are way different from a 4 stroke.

Keep up the good work!
Whether or not you get a lot of gain depends on how bad your intake and exhaust are to begin with, and how rev happy your engine is. The lower the revs, the less it matters. I've seen heads where there isnt much to be done, and I've seen others that are really awful.

Glass smooth finish does create problems on the intake, but not just for the reason you mention. On the intake, if you have a carburetor, or an engine with single point injection (IE an older engine), the problem is worse. The droplets are bigger to start with, and they're traveling a longer distance.
Wiki does a nice job explaining:
I like the wiki's mention of "Less than 1% difference" between smooth and slightly rough.

Also a cool article:
hellinabox (author)  xfirexstarzx5 years ago
Port and polishing is worth the effort if you plan on doing significant modification to the engine. A stock engine with stock exhaust and intake won't see much of a gain but an engine with full bolt ons or a turbocharger will. The gasoline won't form a film on the sides of the cylinder, if it did it would significantly reduce your gas mileage (that's fuel that isn't getting to the pistons). The only reason you would want the intake port to be rough would be for atomization of the fuel. In the case of the LN2, the small bump on every intake port is for that purpose. The exhaust should be glass-smooth all the way through.

For the CB550, I'd suggest looking around a bit more as the instructable was written on a fuel injected engine. I can't say myself whether or not there are any differences on carburetted engines as I don't have much experience with them (other than driving).
wrksnfx3 years ago
Here is a link to some information that can help all most anybody regarding head porting and matching it applies to most of all engines except rotary engines it's shown being done on a Mustang cylinder head but it still the same principle.

*Hellinabox this also works for carbureted cars it's was done by the teenagers in the 50's up to current date for high performance (hipo).
lpeters23 years ago
do yo do this to inlet and exhaust
hellinabox (author)  lpeters23 years ago
Yes, polishing both sides allows for maximum airflow.
whitsey5 years ago
 nice guide :), as for the finish on a port the exhaust ports can be polished up to a mirror finish but not the intake ports
this is becuase the air will "cling" to a polished surface, like water will stick to glass

harley_rly5 years ago
nice instructable. certainly a lot cheaper than buying performance heads, or having them professionally port and polished
admin5 years ago
Hey, this is a great instructable and is very informative. Just one thing is missing... pictures! It really helps a lot when trying to follow directions so you should consider taking some photographs. Once you do that and leave me a message when you have so that we can publish your work. Thanks! Thanks for the cool instructable and we hope to publish this soon!