Truls221

here it is, http://home.no/trulsherland/duration_calc.xls

For example I could guess with a little help from the formula that carsten fichtls expansion chamber is between 1047-1051 mm long from piston to stinger..............

To let people better understand this formula, I´ll be posting an Excel-sheet as soon as I get a webspacing.

ultimately, my point off view would be to fit this engine in a ´56 frame with light on fender. undoubtfully much better looking than a px or cosa frame will ever be! anyone have any pictures of a cosa casing compared to a PX old?

Been reading some chapters from blair's book which I found on the net. Discovered some nice formulas, which can be used together to calculate the exhaust duration. What you need to know is expansionchamber tuned length in mm (measured from piston to stinger), max power (kW) and rpm, and swept volume in cc. The formula for calculating the length of your expansionchamber; Lt = (83,3 * v * d)/rpm where d is exhaust duration and v is speed of sound in the expansion chamber. v is calculated using a constant k = 401,8 times exhaust temperature Tex in Kelvin. v = (401,8*Tex)^0,5 Tex is calculated using the formula for BMEP = (6,0 *10^5*kW)/(cc*rpm) Tex is = 534,67e^0,0485*BMEP Put all these confusing formulas together, and you can find the exhaust duration. Useful if you see a dynograph from an engine which you know the expansionchamber tuned length of. d = (Lt*rpm)/(83,3*(401,8*(534,67e^(0,0485*((6,0 *10^5*kW)/(cc*rpm)))))) Don't know if the the formula is very useful, but it's interesting to see how the exhaust duration differs from engines otherwise quite similar.

Semi off-topic question: Is it possible to weld the cylinderbase gasket face, when reboring and re-nicasiling the cylinder afterwards??

But why enlarge the cross-section by modifications done to the CVF system? I'm sure that the basic design of the cylinder has it's limitations concerning what is too time-consuming and gives a minimal power increase. But I doubt that it is so close to perfect that it is impossible to improve. I have not studied modern two-stroke cylinders too much, but those I've seen, both motocross and hairdryer cylinders have one thing in common. short spigot and cylinder closer to the crankcase compared to a malossi 210. i assume this in addition of large transfers gives a larger cross-section. What are the advantages/disadvantages of a malossi 210 compared to the advantages/disadvantages of for example a motocross cylinder?

As a comparison here is the diagram from andre, completely different. Main differences is enlarged spigotwindows, massive welded crankcase, and as a result is that the gasflow has an easier way to travel. The next evolution to my cylinder is to weld around the gasket face and enlarge the transfer as to the dotted line on my drawing.

Very interesting topic :) I find it rather strange that what I been planning to discuss on this forum is already taken out of my mouth. But we can start with what Volker mentioned in some earlier post. A friend of him had done some tests in a flowbench and discovered that gases going through and S-formation is considerably slower than a flow going trough and U. And logically a flow going through an I is the best. In short we can say that double the bends, half the speed of the flow. The question is then how to make the transferports like this. As we know, the way the gasflow has to travel through the crankcase transfers is truly an S-formation with a standard malossi. lengthening the spigot windows improves this somewhat because the crankcase transfer port angles can be made slacker. But the best would be to use a packingplate, welded on crankcase as johannes said, and welded on cylinder. I have an illustration a'la Andre`to show this. Allthough i do not know how easy it is to weld on a nicasil linered cylinder. anyone have experience? The goal is to make the gas flow faster, and to allow more gasses in the transferports, and as gerhard said it is preferrable that the transfers is long, and straight, to gain speed. But most important is that the gasflow have as much mass as possible. this is what improves the power most considerably. better cylinder filling and more pumping capacity. some would probably say that bigger transferports would make a lower crankcase compression so it gains nothing, but then again as the flow is more effective, this compensates. As you have probably read in the graham bell book is that modern motors have a lower crankcase compression, than engines earlier in the two-stroke evolution. And more power. I guess we can all agree that it is much potential in optimizing the gasflow. PS! I kindly ask someone to post some pictures for me, as I do not have the ability to do this myself?

I think the piston modifications and the boost port modifications are those which raise the output most significant. Such minor modifications as spigot grinding and opening up the crankcase transfers would not offer any better flow when not welded up and perfectly matched, and even though still not very effective. I think increasing the duration and the area of the exhaust port can be very effective, but only if it is within the working area of the exhaust. I think briefly that the exhausts offered around are too average for a specificly ported engine, and the result could be that the powerband is narrower and the engine gives 2 more horsepower at peak, but what is then the point? The compression ratio also defines the effectiviness of the exhaust modification, as you raise the exhaust you lower the compression, so this should be altered as well. The SIP statement is not completely bullshit, and I think the cylinder could be a nice "beef-up" to the average tuned engine, but without doubt, you cannot build a 30 horsepower machine just by adding parts from their catalog.

Saw the movie, awesome!!!!! Which scooter was it that raced against worbel in the final? It was blisteringly fast!!

none new projects this winter, just some perfection of the old. i have to shorten the benelli front fork on my sprint racer. and fit a 10 inch rim instead of the 12. maybe get a real brake disc because the old one is not very good. regarding the engine, first of all i´m going to get the snapping reed petals sorted out. then to get a new conrod/bearing set for my crankshaft and weld this damn thing tight. then make a new cylinder head with more compression. about 12,5:1 geometric. next is to spindle down the flywheel a little more to shave some weight and lastly get the scoot on the dyno to adjust the carburetion properly. to finish of everything there is a little welding on the rear frame to make it flex less. but that´s about it. the goal is to make the scoot a little faster, and a lot more reliable. will be posting some pictures on the forum if people are interested. so long, truls

Thanks for the replies. The fact that the petals hit the crankcase could be the problem, allthough I can´t see any signs of it, carefully looked over with the petals bent manually fully open. I think therefore the reeds may expand a little more with the flex of the reedstop, this is the only thing I can think of. The other petals showed no signs of wear and is in perfect condition. The petal that broke was the one at the back, on the lima-side of the engine. I know of course that the crankshaft don´t twist by this reason, but it seemed strange that this happend with a brand new crankshaft after so short driving distance, seems like I have to do some welding there. BTW, does anyone know which year honda used the six-petal membrane, or were I can get new ones for replacement? cheers truls

I've spent the last six months fondling with the jetting for my scoot, got it quite good and then I changed to a new exhaust and the sympthoms showed up. Thought it was the new exhaust all along (could still be a factor), but then it showed that one of the six petals had snapped in half lenght. Not good for fuel pump underpressure, not good when riding wide open throttle. :uargh: But I didn't spoil the whole engine, just a twisted scamcrank as the victim of two races and some street driving. total running distance of 150km. Do anyone have experience with their petals breaking after very short time? (it's a cr125 membrane) Anyone have an idea why this happened? thanks for any replies truls

With 48mm stroke there is more duration of the ports letting it rev higher. the area of the ports are still the same and the time area is less for the shorter stroke, there is less time for the gasses to flow and they flow faster making more power. Off course the 221 would make most power of the two at 10000rpm. But with a 221 this would mean a lot of working with the porting layout, changing areas and durations, I don't think the basic design of the cylinder and piston would let this happen. At 12000 with a 221 the piston speed would get too high and the rings will start to flatter when maximum power is achieved at more the app. 9000 rpm. the stroke is the only determinating factor for this to happen. For me it seems that when combining 48mm stroke with a malossi 210 the proportions become what is more similar to a modern motocross cylinder. Can somebody else do some calculations around this and see if we get the same results. In the logic theory it's not that far off the line??

This is a bit off topic, but as this topic was a little widespread from the start, please forgive me. First of all I don't think that a big and involving cylinder transplantation is the most reliable you can do to your motor, but when it first is to be done, I would use the PX80 engine case as a starting point. The crankcase is small, with a welded on reed housing you can get a high compression. I think fitting a mal210 would be easy compared to many of the other transplantations done. Capacity 177ccm. Off course weld on and spindle out to the cylinder spigot, fit M8 studs. Not sure about the connecting rod length, but the cylinder can be shortened 10mm from top, set 1mm higher at bottom, increasing the durations of the ports to some very nice numbers. Raising the exhaust port 0,5mm widen it 4mm provide a time-area often only achieved by motocross engines. Exhaust duration 200,1 degrees, main transfer duration 132,4 and blowdown of 33,8. The engine would probably be able to rev to 13000 and with max power at 10000, 30 hp would be no problem. Maybe the gearing would come to short, but then again, a tuned t5 engine reach almost the same revs. Off course this transplantation would be involving in making a purposeful exhaust, and expensive to the cost of decent components like crankshaft, carburetor etc but not much more expensive than normal high level tuning. I think the most favourable issue is that the cylinder kit is cheap and quite easy to replace compared to f,ex an aprilia cylinder and other foreign cylinders. Then fit this engine in a smallframe and you have probably the ultimate thrill!!

from what i know about the mb cylinder is that the outlook of the ports, are too quadratic, with a small radius in the corners, hmmmm must be good for the piston. Secondly the area of the ports are simply too great compared to the duration, and the angle-area and port time area is then similar to a 13000rpm revving motor. The blowdown angle is about 28 degrees, and this, without explanation says why this motor doesen't make the power it is expected to do. As for the piston, the boost port holes should be enlarged a lot because this port is dominating, caused by the thight transfer port passes. Suggestions to make this cylinder better, shorter conrod, piston with lower compression height, (KX 250 piston?), and spindle off the cylinderbase about 15mm to enlarge the transfer port passes. Then the exhaust should be widened and raised, to make a decent radius and oval shape. The conclusion, is that the work to make a £1000 conversion give more power than a good malossi based motor, is to involving and time consuming. Making exhaust, finding a new 22/22 conrod to use, welding the motor case, carburetion, etc,etc... it is no doubt that with an additional £1000 and the same amount of working hours, this cylinder can make more than 35hp, who is the first one to try??

The malossifork is probably the best you could ever build into a vespa to improve the handling. I have myself built a Paioli/Benelli fork into my sprint frame using a 60mm distance. The handling is improved, in the way that the frame is bending more into the turns, steeping the angle of bank and lowering the center of gravity and therefore increasing the corneringspeed. At brutal acceleration when the front wheel are about to come up, the steering is extremely nervous and impossible to handle. But a steering damper solves this problem easily. The front wheel on the Benelli is a 12 inch, on the gilera runner it is 10 inch, just a bolt on conversion. i run with a 120/70-12 front tire, and a 120/90-10 rear tire, having excactly the same diameter. The malossifork for the runner have the same steering crown as the fork from the bennelli, for my matter beeing simple srew loose the old legs and replace them with the new ones. But the genuine malossifork is expensive, and I can't afford it yet. truls

I've spent the last couple days messing with the jets for my mikuni tmx 35. When I had the RZ right hand exhaust, it went quite ok with 310 HD 20 ND and the needle in the second clip. Now when I changed to the new scorpion exhaust, it is still running to rich, on 1/6 throttle, and on full throttle at aprx. 6000 rpm. This is when using 300 HD, 17,5 ND and needle in same position. Does anyone have the same carb, and what jets are you using? Any tips will be appreciated. regards truls

I think the fun with tuning vespas is to see things break!! To know that you have built your own engine completely. Sure it would be fun with a seven speed, unbreakable engine casing with ten-plate clutch and 60hp. But for how long? You would either kill yourself soon or it would be standing in the dust after a couple of dyno runs and a lot of applause! rgrds truls

Ich glaube dein Motor lauf zu fett. And with the 26mm you get less power. This is because the dellorto have not a 100% cylindrical bore, and when SIP bore it out all angles and conicals get distorted. A friend of mine run with this carb, and his machine is noticably weaker with this carb he says. Another comparison is a GL 150 which have the Si 20/17 carburetor. We tried to bore it out to 20, but afterwards it was revving slower and it had less top end. But back to the issue, you could try a 55/100 pilot and a 120-125 main jet. On my engine with SI 24, mal 210, rz rechts, and a lot of porting. I use BE3, 55/100 and 125 main jet. It runs quite perfect, not too rich at least. Another thing you could try is to change spark plug heat grade. Very small difference but could be all you need. goodluck

Great achievement!!!!! How much have you increased the exhaust port area? I think the difference between the cones are amazing!!! The blowdown period is 29 degrees? Are you using a packing plate under the cylinder? Spindled down? Please tell me more details of the engine.......... I finished my own racer today, can't wait to get it on the dyno!! truls

Does anyone have any dynocurves for an engine with 6-petal welded-on reed housing?? Any replies would be appreciated thanks Truls

Mit 123 kubikk und eine 32 gasser hast du eine abgestimmte drehzahl auf 11500! Ich wollte nicht mit dieser gasser und die traurige originalzylinder gefährt.

Hi Volker! I have seen pictures of the HP75 cylinder, I think it looks amazing. A good example to explain the differences between cylinders with the same duration. I found the time-area formula on an XL-sheet which I downloaded from www.macdizzy.com I believe it is the correct one. Another close aproximation is the formula from a book written by John Robinson. Ta= ((K*A)/N)/cc were K is a proportional to the ports duration. K(180) = 19.65. A is the mean area and N is the engine speed. If you compare the values from the different formulas, they shows a slight difference, but I believe the first one is the most correct. regards Truls