Foekema Symmetric Two-stroke

Nederlands
FST prototype
Foekema-Kreidler/50cc-Racing
FST date of announcement January 19th 2008

FST a new twostroke scavenging system
About 2 years ago I got the idea to change the way of scavenging of the twostroke engine. The current way of scavenging exist almost from the beginnng of the 2-stroke history and never changed, unless the many other systems which had been founded. But thinking to get more power you automaticly come to new ideas. So to me it came about two years ago, and that is the Foekema Symmetric Twostroke (FST).

It was not my intention to announce this new idea before making and testing it, but I was supprised when reading the magazine of Kickstart of january this year. Frits Overmars also got a new idea, which he called the FOS system. When reading, I thought: "I'm not sure, but it could be the same". Lucky for me he didn't explain the system, otherwise he would be the first. May be it is different, than we will have 2 new systems at almost the same time. The idea is not very difficult, but realising ideas like this is not that easy, because it has to be made very precisely. Many things in two-stroke tuning has been made since the beginning of the two stroke. That is why I thought that someone else already did the same in the past. Till sofare I didn't want to spend time for this because there are many more important things to do when you wanted to be the fastest 50cc sprinter in the world on the 150 meter and the 1/4 mile.

The only thing I did was an announcement on the Kreidler.nl site, but without an explenation. Also I did tell it to some friends. But because in the current circumstances, I can't wait to explain my new system. That's why I like to introduce you the "Foekema Symmetric Two-stroke" (FST)
Who would be the first realising the idea in a working prototype is another question. Althought this system should produce more power than the current way, it still is the question, if in practice this will be prooven

FST scavenging
Symmetric is one part to explain the system, but most important is the 100% Time Area. The whole scavenging will proceed in a symmetric way. After burning the gasses, when the piston goes down, the 4 exhaustducts opens first at the same time and the burned gasses leaves the cylinder. These ducts are fully symmetric around in the cylinder, so the gasses can flow into the 4 exhaustpipes very fast. After that, all symmetric transfers opens also at the same time and fresh gasses flows from all directions right over the piston to the center of the cylinder. This result in a flow of the gasses in the direction of the chamber, while pressing the last burned gasses to the edge of the cylinder. In the chamber the fresh gasses will turn around in the direction of the four exhaust ducts, behind the burned gasses.
So two rows of fully symmetric and 100% Time Area ports. The upper 4 ports are exhausts, the lower row are transfers. Which results in much maximum Time Area capacity, which is 100%. There is no more room left for ducts.

Advantage of FST scavenging
The big advantage is that the whole scavenging will proceed much faster than in the current two-stroke way, because of the maximum TA capacity. That is why a much higher rpm is reacheable with the same or even a lower duration of exhausts and transfers.
Beside this there is another great advantage the symmetric scavenging keeps the temperature in the cylinder completely the same all arround. In the current way there are always risks that one side of the cylinder is more hot than the other side.

Realising an operating FST engine
Realising a FST engine is not that easy, because it has to be made very precisely, because otherwise the scavenging does not proceed symmetric. Each small deviation in transfers or exhausts has a negative influance in the process.
There are still some details of which some very imporatant to keep in mind. But that I will keep for me, till the system has been ready for operating later this year.

A pitty !!!
Yes a pitty for me, because I did prefer to appear one day on an event with an engine operating with this FST system. Altought the news has gone, a well operating system will be the next challence to realise.

Several forums
These subject is to find on next forums:
1. www.kreidler.nl
2. www.scootertuning.net
3. www.2stroke-tuning.nl
4. www.RD350.nl
5. http://zundapp.messageboard.nl
6. www.apriliaforum.nl

On some of them there is also written about the FOS systeem, in which is clear that nothing of the system has been explained, before 19th of january 2008.

Letter of the announcement January 19th, 2008
This letter has been send on January 19th 2008 at 20.00 hr, to many 2 stroke enthusiast over the world and the respons was more than anyone could imagine, which does stimulate to make FST to a succes.


Hello 2 stroke enthusiast,

Hereby I will inform you about my new 2 stroke system. About 2 years ago, I got the idea to change the way of scavenge of the cilinder. This idea is not very difficult, but realising ideas like this is not that easy, because it has to be made very precisely.

Till so fare I didn't want to spend time for it, because there are many more important things to do when you want to be the fastest 50cc sprinter in the world on the 150 meter and the 1/4 mile.

But I was very supprised when reading the magazine of Kickstart of january this year, that someone else also got a new idee about that, he called it the FOS system. When reading, I thought: "I'm not sure but it could be the same".

Lucky for me he didn't explain the system, otherwise he would be the first. May be it is different, than we will have 2 new system at almost the same time. May be there will come more new 2T sytems at this moment, because I heard from good friends, that there are more young people in action with new systems!

That's why I don't want to wait any longer and introduce you the "Foekema Symmetric Two-stroke system" (FST system)

Read all about it on my website.
http://geocities.com/lucfoekema/FSTsystem.html

Kind regards,
Luc Foekema

More chapters about tuning
Tuning
Expansion Exhaust
Chamber
Inlet system
Ignition
Simulation
Rotary valve
Gearbox
Kreidler 6V racing engine




FSTsystem Central or symmetric scavenge


FSTsystem Central or symmetric scavenge


FST Portmap, 2 rows of ducts on another



May be the first cylinder with two extra transfers in 1968



Drachten 2002 on the 1967 sprinter

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