Tips from TJ on Porting and Polishing 2 Strokes
by CC Specialty Tools . Purchase the Porting Tools you need at our Online Store.
Determine the level of porting you wish to achieve before you start
cutting or grinding. You need to know what your are aiming for before
you start shooting. Determining this goal up front will also help
immensely in choosing the proper
the job at hand. Is your goal a basic level of porting
Consider chamfering (bevel)
your port openings, radius the corners of port windows and intake
bridges (this is discussed in greater detail below), take time to
smooth out any casting flaws or rough areas (to a degree), and look
closely at the transition from the aluminum of
the port to the cylinder
often there are mismatches here that disrupt air/gas flow into the
combustion chamber. This is the minimum amount of modification I
could recommend. As for achieving a full
race level of porting,
hate to break it to you, but you will need to go a little further
than just what you will find on this article. I suggest at a
minimum you invest in a nice porting
and polishing kit
a few carbide burrs (www.ccspecialtytool.com/catalog/carbide-cutters)
also there are several accessories that you may want to look into
Take your time and pay attention when chamfering
(bevel) port openings (windows).
Often I see this step treated like a minor detail, rushed through
with little regard to method or consistency. The key reason to
chamfer a port window is to allow a smoother transition of
in particular the piston
the port opening. This not only extends the life of this particular
part, but also reduces wear and tear on the entire combustion
reducing overall mechanical
Below are some methods to consider:
1. Your approach should
be to give every edge of the port window a consistent recess and
angle. Putting a sharper angle on one side of a port and a more
shallow angle on the other end, can cause a the piston ring to
actually “walk” or move in position (not a desired
2.Use abrasives or other method to further smooth
the corner of the chamfered (bevel)
port opening. Use of a carbide
burr or abrasive stone,
by itself, can leave a “burr” to the metal (similar to the burr
you would have on the blade of a knife after sharpening) that can
actually damage the side of your piston, or in any case it does not
help your objective. Remember cylinder liners are generally a much
harder metal (Cast iron, Nikasil, and so on) than the surrounding,
usually aluminum, cylinder. Use a felt buff and buffing compound to
further smooth and deburr the chamfered edge. By taking your time an
going through these steps you can insure a perfect and smooth
transition of the piston ring into and out of the port windows.
Don’t go overboard with chamfering. You're not putting a ramp on
the edge of your port window. Dimensions I like to advise are 1mm to
1.5mm, with or parallel to the cylinder wall, and a 0.4mm to 0.5mm
depth into the port.
Here are some online videos that can help you with chamfering
(bevel) youtu.be/WDKiv-nQtwA ,youtu.be/UK1kzEjw1Sg , youtu.be/xY1ThQIr-J8
- Radius or
round the corners (picture a rectangle, then round the edges) of
A rounded corner offers a much less abrupt angle to the piston and to
air flow. Increasing the radius at the corner of a port opening
can optimize flow
even if an increase in overall port size is not desired, or possible.
It is also a great practice to add at least a slight radius to the
upper roof and floor of certain ports, this slight curvature will
also offer a less abrupt transition for the piston ring.
- Recess and radius (only
slightly) the bridge of bridged
This usually applies to intake
and sometimes exhaust ports, which are often bridged to reduce piston
The reason for this is the thinner metal of the bridge will heat
faster and expand (due to thermodynamics)
at a faster rate. This expansion can cause the bridge to bulge out
into the combustion chamber and rub the bottom of the piston
skirt. Very little recess is needed, about 0.05mm to 0.08mm at
the apex of
The radius should begin and end approximately 1 to 2mm above and
below the port.
Keep in mind port
the gas into the combustion chamber plays a large role in the
of power production.
A air/fuel flow that is directed at the center of the piston area
will tend to produce better
top end performance,
while gas flow aimed at the back wall or upward into the combustion
chamber will tend to yield
more torque and
therefore better bottom end performance.
There is software out
there that will help you immensely with your calculations
on timing, port
and so on.
(not a bad place to start www.macdizzy.com/19891hopup.htm )
(Also a guy named Tom Turner, on our user's list
at www.ccspecialtytool.com/about-cc-specialty-tool ,
made TSR ) There are free and low cost options out there now(BiMotion
and www.porting-programs.com/ comes
to mind). Some have limitations but they can start to show you the
ideas and principles behind port modification and design. Another
option is purchasing templates that have proven design, and making
slight tweaks or modifications to them.
Port timing can
be critical to your results. The exhaust port timing, and the pipe,
will determine a great deal about your cylinders performance. In
general the higher the roof, or top edge of the exhaust port window
higher the powerband will be in the rpm range.
Typically a pressure wave return time is.003
If the exhaust port begins to open at 80
degrees of rotation,
the wave would return exactly when needed at 10,000
at that point, the time it takes for the piston to move from 80
degrees to 260
If the exhaust port is modified to open at 100
rotation, then the peak of the powerband would lower to around 9,000
based on the same timing principle. Keep in mind that raising the
roof or upper edge of the exhaust port will decrease the trapping
volume of the cylinder. The earlier in the cycle that the exhaust
port opens during the descent of the piston, also means the later in
the rotation cycle that it closes on the up stroke. This also
explains why Power
great options for 2 strokes. Power valve setups can allow the exhaust
port height, area, and potential volume to be varied. This
will yield a much broader
useful rpm range.
an essential part of porting
but you need to select the right ones for what you are doing.
Long shank cutters may be able to reach farther, but the shortest
shank burr you
can get away with will offer a greater
level of control and precision.
The differing patterns and cut options(diamond cut, spiral cut, and
an aggressive Alumni-cut) will yeild different results, and for that
matter, varying the rpm of the tool rotation will have
optimal results with different cut patterns. We have
several customers that find it necessary to invest in custom carbide
for a particular application.
Don't buy into the "CNC
you gotta take your stuff to a shop with a million dollar CNC machine
to get your cylinder
CC Specialty has several CNC machines and related
equipment, and we still use the tools we sell for any
porting and polishing, and even the detail work we do on tools
and equipment around the shop. We have clients all over
the world that use their multi-million dollar CNC's to do some of the
major cutting, but 100% of
our customers still use our tools to do the detail work (hint: that's
why they are our customers).
We have several customers that do porting work, by hand, that has out
performed cylinders modified by the latest and greatest CNC and CAD
design machines and software.
There are some other performance enhancers you may wish to look into
for certain build projects. Among these are Boost
Bottles / Boost tubes,
these help maintain and regulate or utilize pressure pulses in the
carbs. The addition of boost ports may be another
consideration. Turbo and
even supercharger setups
of various configurations can be very useful, however, they are
often more complicated with 2 stroke tuning than with 4 stroke
applications (on a tangent, I did witness a 50cc
turbo 2 stroke bike that
would do over 150mph, but I digress).
Consider the altitude and
average weather and humidity of
the track or race you are building for, these factors can
have a considerable influence on performance due to changes in Air
Density. When evaluating
altitude, remember there is approximately a 3%
air density for every 1000 ft of elevation increase above sea level,
in relation to standard atmospheric (you can find much more info
about this on the web, more than you could ever hope to use). Weather
and humidity also play a big role because they can change air density
as well. Temperature will change air density by causing an
increase when the air is colder and a decrease when it
warms up. As a general rule you should enrich the air/fuel
mixture as air density increases, and lean it out when there is a
decrease in density. (Fun little side note, our race
group at CC Specialty got
reminded of this the hard way in jetski racing. We
had a monster of a 550cc ported and race ready out
in Texas, where this little red and yellow bullet
would scream and fly faster than just about any parallel twin
known, but when we brought it to Alabama for a sponsored race, it
stalled every time, went back out to Texas for repairs, and BAM!
it was back to being a monster, all because of the air density
- MacDizzy is
a long time customer and a great source of information on 2 strokes.
There are several terms
will need to become familiar with when you start
modifying 2 stroke cylinders so
please go over this link and the related
pages: www.macdizzy.com/cyl_primer.htm .
MacDizzy is also kind enough to provide you with some very useful
engine building formulas www.macdizzy.com/formulas.htm .
As far as information and good
porting and polishing, forums can
be a double edged sword. One of the best articles I have found on any
forum is from John “Mixxer” Ziehl of Venom Performance and VooDoo
HVP. Read this article and check out the excellent illustrations.
This guy knows a few things about Porting and Polishing. Follow this
link and be a more informed
I have read some great advice and insight on certain forums. That
being said, I have read a good deal of pure BS and poorly educated
speculation as well. One of my favorite is that porting makes little
difference, and to be honest, if I was worried about beating you in a
race, I would tell you the same thing : ).
- Here are some useful resources with several 2 stroke porting theories and formulas. I don't know that I would consider this information the indisputable truth and it is fairly specific to these particular smaller cc cylinders, but it can be a very enlightening as to observable relations in altering 2 stroke port timing, enjoy: Relation of port timing to peak RPM , and Port timing for a specific 48cc cylinder, (this doesn't apply to all cylinders obviously), and Piston "ramp" modifications because some guy want to do similar mods, A very DIY way to increase compression , and Port time duration as related to a specific cylinder , and exhaust port shape related to this specific cylinder
This is a pretty good discussion from a long time customer, Eric Gore
at Forward Motion. These two links are a great guide, and will help you and
your understanding of porting and polishing. This first link will
discuss terms and the 2 stroke cycle .
The next link will go over some basic principles
behind the goal of porting and polishing,
. I might have a slightly different approach for some of the
subjects, but his explanation for porting and polishing is great!
This is a great free
Some advice on making a port
map www.macdizzy.com/cylinder_map.htm .
I recommend knowing what you got before you start changing it too
Typically I don't endorse too many products, but if you are starting
out in porting these
little Sport Port templates can take a whole lot of the guess work
out of the equation www.racelogic.com/sportport/index.shtml .
If you are unable to find a template for your project at this site,
there are ways to cut out templates on CNC machines. A template can
help tremendously, since what may appear to be a simple enlargement
of the port, might actually involve several complex radius changes.
At any rate be sure to measure twice and cut once, the aluminum is
easy to take out of the cylinder, but tricky to put back in.
you are doing major
level of tuning,
remember to take an "overall" approach to the project.
Increasing horsepower by
increasing the amount of fuel and air that your motor can move in and
out is only one piece of the puzzle (a very big piece,
but still just part of the goal). Modifications to reed
valves / reed blocks,
or sometime disc
often required. Take into consideration the pulses that
occur (in particular on the intake side) during normal engine
operation, often these pulses will change based on rpm. Expansion
the exhaust are a big consideration! Lubrication and cooling need
to be taken into account, some of our customers use our tools too
also increase the openings for the oil flow and modify the cooling
systems (water jackets on liquid cooled) in various ways. Even
the transmission will
need to be considered, since the power production
characteristics will be altered at this level of tune.
few videos that
can tell you a little more about using the correct
what you can do with the right equipment, and you get to see some of
porting tools in
action youtu.be/T_BXeXoGzD8 ,youtu.be/U_2JkElSAis , youtu.be/agXWUoCkGVU , youtu.be/MNJy59ZIdGY , youtu.be/s4iLffvAjbQ ,youtu.be/UJbtzxtPpSs , youtu.be/rvX-BFqt2lw , youtu.be/4RLLbL4pAQ4 ,youtu.be/kMvvdc8R9oU , youtu.be/GwtquXIAOrk , youtu.be/WDKiv-nQtwA ,youtu.be/UK1kzEjw1Sg , youtu.be/xY1ThQIr-J8, youtu.be/T_BXeXoGzD8
Here is a handy link
with some very good information on
porting and polishing. I am not saying it is perfect but it is very
handy for the DIY guy out there looking to do some 2 stroke
it yourself DIY porting and polishing for the beginner and
is a quick video about some of the basic tools I will use for porting
and polishing youtu.be/N7xmKQ0_H7A
Anonymous on Sun, 09/04/2011 - 21:52.
doing some basic porting and have been looking at diff forums. Seems
alot of the stuff i read on there, some guy says all i need are some
files and maybe a dremel, another says i need the stuff you sell. you
people sell a lot very expensive stuff, why would i need this stuff
if i can get it done with less?
Anonymous on Mon, 03/10/2014 - 00:33.
tell you this much. I started porting 2-strokes with a dremel and a
file and though you can do it, it's a real waste of time. It'll take
you about 15 different bits, 4 hands, and at least a few days to do
it correctly (good luck). If you really want to do it properly, you
need to use the correct tools.
have two 2007 GP1300R jet
Anonymous on Sun, 10/18/2015 - 02:01.
have two 2007 GP1300R jet skis that did roughly 65 mph. They ran neck
and neck when me and my wife raced each other. I ended up blowing
mine up one day and when it came time to rebuild the engine I took my
time gasket matching every single intake and exhaust piece. I spent
hours upon hours which turned into days removing the casting flaws
and edges where the cylinder liner meets the case. I wondered if I
was wasting my time and if it really made that big of a difference. I
started out enthused but after a couple of days of porting it got
old. But I didn't give up.
When I took the ski out for it's
initial engine break in period I couldn't believe it. It was spooky
fast. My ski's top speed only went up to 70 mph except it hit 70 mph
right now. My wife rode it and it scared the crap out of her ... at
first. After riding mine neither me nor her wanted to ride hers.
used carbide bits with a die grinder, sand paper, rubber fuel hose
different diameters with sand paper wrapped around it, mini diamond
files of different shapes that I purposefully broke to get to the
edges that were near impossible to get to, flapper wheels etc. Oh
yeah and lots of light into the port your working on helps. Thats my
pay off of Porting and Polishing
ccadmin on Tue, 10/20/2015 - 11:22.
to hear you stuck with the Porting and Polishing to the end, so you
could reap the benefits. You are absolutely right, it can be
meticulous work, with a need for precision and patience. However you
summed it up perfectly when you said “ After riding mine neither me
nor her wanted to ride hers” . The power delivery and performance
had changed in such a noticeable way, it was kind of scary. Thanks
@ CC Specialty Tools
tools are the best option
ccadmin on Sun, 09/04/2011 - 22:54.
title kinda says it all, but I will elaborate. A dremel is for wood
working or engraving your favorite paper weight, but not for porting
and polishing on a 2 stroke. Files are great for busting out of
prison or maybe a gal to do her nails, but not for professional
porting of any kind.
Pro's don't look at it as the cost of the
tools, you look at it as the cost of messing up a cylinder head, the
cost of not doing it right and wasting all your time, the cost of
getting your butt kicked in a race because you were at a huge
disadvantage from not having enough horse power, the cost of all
those hours you spent trying to make tools made for something else
work for porting, when the right tools would have got the job done in
no time, and did the job right!
Bottom line, your better off to
get the right tools for the task at hand. You can drive a
nail with a screwdriver if you hit it hard enough, and you can pull
out a screw with a hammer if your willing to tear some stuff up, but
why go through all that if the right tools for the job are available.
At CC Specialty we have taken extensive time and made every effort to
ensure we can provide you with the best tools for porting and
polishing. Take advantage of that. A
mechanically inclined person, that is willing to learn the basics and
fundamentals of porting, and apply those to various builds and
projects from customers, can make a very good living porting and
polishing. Don't impede your progress by using the wrong equipment.
Anyway that's my opinion.