Beginner's Port and Polishing





Introduction: 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.

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)

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

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.

Step 5: Polishing

Now it's time to swap out that low grit dremel bit for a high grit one. Go over the entirety of the ports until they near a mirror shine. Once finished you can have the head decked and pressure-checked by a professional.

Step 6: Conclusion

And that's it, install the head on the car and enjoy the power boost. Of course like all car modifications the increase will be dependent on the rest of the car (what other performance parts are installed). The LN2 specifically has a lot to gain from a gasket match and port/polish because of lower manufacturing standards.

This is my first instructable and constructive criticism is more than welcome. I look forward to prototyping some of my ideas and posting them.



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    Hii where i can buy Right angle porting tools for porting 2 stroke cylinders in India can anyone help me plz?


    Nice instructable. you can actually make a flow bench using a vacuum cleaner and a manometer. It would certainly not be of the same quality as one in a race shop but it will suffice.

    Leaving the inside of the port a little bit rough does theoretically help create turbulence that causes the fuel and air to mix a little better. Grinding away the irregularities as was stated is a good start but, I am also concerned about making the port larger as you have stated as it really can change a lot of things in your acceleration and power curves. Be very careful making the port larger by much.


    Interesting, but as someone who spent years with a Superflow Flow bench modifying cylinder heads for the GTU and Camel Light Prototype Classes of the old IMSA racing organization and doing cylinder head quality control on heads coming into the race shop good cleanup is all that should be attempted without the use and hours upon hours of practice in front of a flow bench and test heads. A port shape should not really be changed unless you have some empirical data from actually testing a 'cut' port shape that tells you that you actually have improved the airflow at some particular point in the valve lift/acceleration curve. A good clean up of all casting flash and irregularities with a fairly textured finish (60-100 grit seems optimal). Larry Meaux has been rough texturing port surfaces with a rough carbide burr and seeing HP gains! All in all, a nice the $$ and buy a'll love it.

    The only thing i can suggest is to add pictures for step 4. I understand how to do this step but some May not. Other then that great diy

    It all depends on what you're building. Porting is one thing polishing is another.

    Flow characteristics are yet another and both port or polish can change the dynamics of the head. Velocity is something to take into consideration when working on a head.and you can increase velocity easily if you know what areas to work. A sbc motor and many other lose performance when someone ports the bottom of the exhaust port on the slow side which is the bottom. By enlarging it, it actually decreases the velocity of the exhaust leaving the head and hurts performance.

    If you want to port and or polish look into the head you are working on. 9 out of 10 times you will find professional advice on the internet about that head being ported. Don't jump into doing this without looking into the perimeters first.

    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..

    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.

    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

    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.