Cylinder Mapping Primer





 Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 6

Start The Process
It is not uncommon for two stroke engine builders to never tell what they will do, or have done to the two stroke engine you just had modified. I don't know how this all started but somewhere along the way it was decided that two stroke engine builders didn't need to disclose that information. I think that's a joke. I would never have my work done or recommend anyone get their work done by someone who would not disclose their design plan or their results. If they won't tell EXACTLY what they are going to do to the engine before they do it - or refuse to give out the information, GO SOMEWHERE ELSE!!!
 
This cylinder mapping section is for anyone who wants to understand these engines and the porting/systems surrounding them. It will provide specific answers and an easy and universal way to discern the information. There is a definitive explanation as to what a "Stage 3 or Stage 4" kit is and anyone can reverse engineer one to determine its parameters. If someone performs the cylinder mapping procedure before and after the work has been done, it will be easy to find the changes. This may also be used to see that the changes have been performed as they were outlined (or ordered). Following these simple instructions you can make a port map or take it to a little higher level and design higher output engine parameters. The time it takes to make an engine fast vs really fast is HUGE! The last 20% of the power takes 80% of the time to find.
 
Two stroke cylinder mapping is easy to do - though it can be time consuming. When done properly it will reveal the engines port timing and the area of the port windows. This data can be used to determine the engines state of tune and it is useful to establish a baseline before any ports are cut. A little time and effort will produce very accurate results. A general understanding of mechanics, mathematics and common sense is required to follow this series though. For those who are just starting with this two stroke stuff I'll define a couple of things right now to remove confusion as much as possible.
 
Bore

The width of the hole in the cylinder - usually expressed in mm

Stroke

The distance between TDC and BDC usually expressed in mm

TDC

Top Dead Center, the piston at the top of the stroke

BDC

Bottom Dead Center, the piston at the bottom of the stroke

ATDC

After Top Dead Center, usually used with a measure of degrees of crankshaft rotation or distance in millimeters

BTDC

Before Top Dead Center, usually used with a measure of degrees of crankshaft rotation or distance in millimeters

Deck height

The distance between the top edge of the piston crown (with the piston at TDC) to the edge of the cylinder liner.

cm^2

square centimeters

cm^3

cubic centimeters

cm

centimeters

mm

millimeters

The mean

the average, in this case it is the average in degrees of crankshaft rotation

Front transfer ports

the main transfer ports - they're the closest to the exhaust port(s)

Rear transfer Ports

a secondary set of ports - placed rearward of the mains. Also called 5th ports - This comes from a 2 stroke engine design with a single exhaust port and a pair of transfer ports - that's all. Add a pair or ports behind the mains and you have 5 ports.

Boost port

a steeply angled (usually 50 to 65 degrees upward) port directly opposite the exhaust port(s) - sometimes called the bust port.

Auxiliary intake ports

Passages leading to the transfer port tunnels which are extended from the intake area without entering the crankcase. Also called Boyesen ports.


It is good to measure the deck height of the barrel for future reference (see Part 4). It can be measured before or after the mapping is done though it is probably best to do it when the head has been removed and the barrel is still attached to the lower end of the motor. Instructions on how to find this height and instructions on how to degree the engine to reveal its port timing is also in Part 4. If the engine uses a base plate spacer it is a good idea to measure its thickness and the thickness of the additional base gasket(s) as well - while you're at it (if your engine uses one) measure the thickness of the head gasket.
 
The days of talking/thinking about an engines state of tune as being a "Stage 4" kit or something along that line will be replaced by more universal language - the language everyone can understand.

Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 6






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Date Last Modified: 11/29/2012
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