2Go-Fast

The Serval cylinder uses the banshee head layout, and that bolt pattern has a head bolt directly in front of each bore, so there is no way to use a power valve with that head bolt pattern....so, no, would be the answer to whether the Servals will ever have a power valve......sorry

I check a few of these sites out from time to time, and when I saw the questions asked in this post, (and where you were from), I recognized a question that I had worked quite a while on with one of my dealers very recently, (actually I think it was Friday). The side view that I am attaching should show the use of a 4mill Serval cylinder with a 7mill crank, the port durations are shown at the top of the page when using a .012 gasket, and when using no gasket and sealing the cylinder down. Actually, the port timings are very close to where they will be when the 7mill Serval is finished. Hope this helps, Calvin Pollet Sideview of CPI-S6861P_Special_Serval_Cub .pdf I guess this site does not allow opening of "pdf" files on the screen, so you will need to download the file....sorry

I don't post in here much, but this is one of those threads that could "lead people" the wrong way if some "extra info" is not made available.....so here goes. The Serval Cub is NOT a modified current Cub casting that was machined differently.........it is a COMPLETELY different casting, made with completely different internal tooling....made SPECIFICALLY as a 4mill stroke Serval Cub. I will try to explain why it had to be done the way we did it. "Larry's Shee" was right on target when he suggested making a "map", what he was referring to is a "portmap" of where the ports are located, or a portmap of where you want them to be....(or in this case....BOTH) If you were to do the layout, you would see that you would be going the wrong way if you used the 7mill Cub casting to build your "Super Serval Cub"....... (OMG....not ANOTHER cylinder.....lol)....here is why. When machining a cylinder, I first "set" the tops of the transfer ports in relation to TDC, this allows me to get the transfer port timing that I want. I have chosen to open the "main transfer" ports first because IMO, our test results using OUR PORT LAYOUT has shown better results using that port configuration. Many....many factors come into play when setting up a port layout, but for the sake of this thread, we will "skip ahead" to the setting of the exhaust height and it's relationship to TDC. If we look at a 4mill Cub portmap as shown on the CPI website, you can see the transfers are set at 130 degrees, which puts the highest port at 1.754 from the top of the cylinder, and with the top of the main exhaust port set at 197*, it would be located 1.123 from the top of the cylinder. The reason this is relevant is because this is the "blowdown" number....(BLOWDOWN - the difference between when the exhaust port first opens allowing the spent fuel to escape through the exhaust port, and the transfers first open.....OR the time that the pressure inside the cylinder "blows down" to a pressure which allows us to open the transfer ports)......in this case the measurement is given in thousandths of an inch instead of degrees of crank rotation). In the case of the 4mill Cub, the blowdown is 0.631.....whether you deck the top or the bottom of the cylinder, the "blowdown number" remains the same......it is SET during the casting process, and even if we machine it differently it remains whatever it was set at when the casting was made. Blowdown numbers for some of the Cubs and SuperCub castings: CPI-6854........ 0.550 CPI-6858........ 0.631 CPI-6861........ 0.650 CPI-6864........ 0.679 We have not put the Serval Cub cylinders on our website yet, so the portmaps for the 4mill Serval Cub is a little harder to come by, I believe Andy from M&M ATV may have posted the portmap, but it may be easier to post it here rather than search for it, so I will attach it to the bottom of this reply. What it will show is the blowdown on a 4mill Serval Cub is exactly the same as on a stock stroke Cub...... 0.550, the problem is the stock stroke Cub would need about 0.162 more metal on the top of the cylinder to make it have the same numbers as a Serval......believe me, if I could have built a Serval port timing Cub without the expense of new tooling, I would have. Sorry to get so long winded, but sometimes these things are hare to explain.....hope this helps, Calvin Pollet Port layout for CPI-S6858P_Serval_Cub.pdf

Not intending to sound like I know a lot about too many things, but I am VERY familiar with what the Cubs were designed for...I am also very familiar with many ways they can be setup.........That being said, you are totally missing my point.......he already HAS a Cub cylinder, he doesn't need to buy cylinders to have an engine that can make good power if he needs it "later on down the road", it sounds like what he needs now is a dune engine, and a Cub is VERY capable of being setup as a duner. Would I recommend someone go out and buy a Cub for a dune engine......NO, he wouldn't need to, but if he already has a Cub, why not use it, and have the ability to go faster if it is needed. I have always said that the very first thing ANY two-stroke needs for performance is a pipe, had always said a pipe is the best "bang for the buck" as far as a two stroke goes........BUT......when the Cubs first came out a Cub was put on a bone stock Banshee, with the only changes being the cylinder and pistons, (stock pipe, stock head, carb, ignition......STOCK EVERYTHING), and the Cub made more improvement then a set of pipes......and made more improvement in "horsepower per dollar spent" then pipes did........The reason I brought this up is because it DID increase the "pumping pressure" with the exact same domes......it DID have a better torque curve "down low", and it DID make more power as well. As more and more people built pipes for the Cubs, more and more pipes were made to make MORE power and rev better..........that is not what he needs. He doesn't need a "restrictive pipe"........he needs a pipe the WORKS WELL at lower rpm.

Talk to a builder that has tested different pipes with a Cub cylinder.....you would be AMAZED at the difference in the amount of bottom end power that can be gotten out of the Cubs with the correct pipe for the type of riding that YOU do. Most people want "the most power I can get", and that is what most of the engines are setup for, but with different choices of pipes, the powerband can be changed drastically. This is somewhat of a simplification, but a Cub will put more pressure, (compression), into the domes even at as low as kicking rpm, so it is capable of building good power at lower rpm if the setup is correct for your type of riding.