Truls221

Andre, I don't know what you mean by leaving the ports unaltered with a 60mm crank. Thought this was impossible............. I have done a few calculations; With a 1,5mm head gasket the transfer port timings have an angle of 123,1 degrees. If you raise the exhaust port 2mm you will have a duration of 186,3 degrees. And a blowdown of 31,6. The advantage with a 1,5mm head gasket is that you only have to lower the exhaust port to be level with the piston crown. I am not unfamiliar with grinding and machining and regard this as an easy task. But I'm not an engineer and do not have a diploma for the theory stuff........ If using the 0,8 head and base you'll increase the transfer port duration to 126,6 and by raising the exhaust port 2,2mm, it will have a duration of 189,8 degrees. Blowdown is still 31,6. Now all the timings are close to proportional with the increase in capacity. The tuned rpm should therefore be similar to a stock mal210 with 57mm crank. But this is only the cylinder. The the two examples above could in combination with a properly tuned reed inlet and exhaust, affect the maximum power ouput with maybe 5-10% Anyone who are running with the 0,8 head and base gasket?? Regards truls

Many good opinions here! The engine I'm working on now is based on a reed casing welded by worbel. going to koblenz in two weeks. On this engine I have consequently chosen the reed housing over the crankshaft. The reason is because I believe that the boostports take a lot of the gasflow which should have gone in to the main transfer ports. I don't know what port-angles I will use, i'm working with the timings right now. First of all, i do not want maximum power at more than 7000 revs. This is becasue the ideal engine lands on max power rpm when changing gears, or were the power curve are steepest. We have only four gears, you know!! Another issue as I'm using a 60mm stroke crank is, which blowndown angle do you need to get the same tuned rpm?? As far as I know you can use the angle area formula, which I don't remember by head. (i have it somewere). When increasing the capacity of an engine, the increase in blowdown angle has to be proportional. Compared to a standard mal210, which have a 30 degree blowdown, a long stroke should have 31,6 degrees to achieve the same angle-area value. I'm far from an expert on this issue, but believe that I have a small overview. What has to be done to achieve the 31,6 degree blowdown? The 0.8 base and head gasket is not a stupid idea? But i believe the tranfer port timing gets a little too high. For example a 0,6 and a 0,9? I haven't got the time to calculate out this now, but later......... regards Truls

I would use a bitubo COSA. The scooter gets a good ride height and the sidepanel on the motorside gets less rubbing from the engine............

AND just to add; if some of you have been to sweden and seen a scooter race, you know which engine I'm talking about!!

Andre, I don't mean to overprove or neglect yours or anybody's experience. I 'm not an expert nor do I have any monster engine, yet. But I do know, that by listening to other peoples knowledge and by reading theoretical stuff, you get a small overview. I'm building an engine for my racer right know, going to koblenz in two weeks to pick up a casing welded by worbel. A good example of how a perfect compromised engine can be built i have seen a couple of times. the engine have a stock malossi barrel, with only the piston modified a little, welded on reed housing with a husquarna 125 reed placed 1mm (!!) above the crankshaft halves. A custom expansion chamber is also fabricated and fitted. The engine have max power at some 6000 rpm and even pulls the original 4. gear with 23/65 primary. The amazing thing about this engine is that it puts out 28hp at the rear wheel, with a standard stroke crankshaft and mal210 with untouched port timings. With this engine everything is as close to perfect as possible. I doubt that there are any other reason for the big power achievement than the inlet and the exhaust. With standard stroke and untouched mal210, mrb and sip performance I believe 22hp at the rear wheel is the limit. And with all respect, Andre, I know that your engine is a lot more than just this............... Interesting picture by the way, anyone who can explain a little more about it?? Regards truls PS! I know that some of you probably hate english, but i know you'll hate my german a lot more...........

The best reed is a properly tuned one. Regarding size and placement, as close to the cylinder as possible with the biggest possible area. With a vespamotor this has its limitations. Also important is the frequency of the reed petals. For example, a reed tuned to 8000 rpm have a frequency of 133Hz. There is no use of a big reed if the petals do not have the right frequency. And there are many aspects involved with this, thickness, elasticity etc. A MRB reed is too far from the cylinder and the result is that the backpressure from the exhaust gets too weak resulting in poor communication with the reed. Any of the reeds from a CR125, YZ 250 etc. would be big enough in area. But of course, you'll have to tune them to the right frequency. A CR 125 membrane are tuned much too high to suit a vespa with a targeted max power rpm at 8000.

As I've read many postings regarding the mal210 stuff, it seems that most riders are thinking of all the modifications that can be done to the zylinder and piston alone. These modifications don't do anything else than better the flow a little, if talking about what worbel have done to them. What is called "auslasswinkel erweitern" I do not regard as a good solution. The reason is because this only risen and shorten the power band to a higher rpm. What gains most power is the modification to the inlet and exhaust, as well as optimal carburation. What can be done to a standard stroke mal210 is to widen the exhaust port, to extend the time area further. it is also important that the time-area of the inlet port system and the exhaust have the same values. By chamfering the ports down to the level of the piston crown also help the direction of the flow into the combustion chamber and out of the exhaust port. Another very importan issue is the head and the combustion chamber. I write this point because i don't see the necessity of buying expensive modified cylinders when you can buy them straight stock and modify them yourself. Cheap and easy! Save your money and spend them on a big reed! regards truls

With this engine, you'll loose noticably much midrange power if using any carburetor bigger than 32-33mm. This is the theory, and in 99% of every case it is the practical result. I know mr.worbel has a dyno showing a similar engine of yours, with idenctical power curves but higher top-end, by comparing a 30mm carburetor with a 39mm. Although he says nothing about how many weeks he spent to get the mixture right! If you have the TMX38 in your hands, slip it on, and tell us what the difference is! Grüss and regards Truls

Guten Tag! My german are very poor so i'll write this reply in english. Carburetor and venturi size are directly connected to peak power at a given rpm. For example, an engine with the capacity of 210ccm will with a 38mm carburetor be tuned to the rpm of 9520. To gain any power in connection with this you'll have to tune the reed or inlet, cylinder and exhaust. If not, the increased air flow will be obstructed and therefore flow slower. With a long stroke crank, increased capacity, the tuned rpm will be 9041. A proper tuned engine involves a hell of a lot of time spent calculating, measuring etc,etc. A believe carsten fichtl's engine is a good example of this. For most people it may seem that bigger = better. But to just hang a TMX38 onto an engine, for example an unworked m210 with mrb and expansion chamber will probably loose power. But off course, if done properly you are able to gain big power. The conclusion: The biggest carburetor is far from the best. But if properly tuned, it is possible to achieve big power gains by using the right carburetor.

Entschuldigung für die Verwirrung! Ich bin der Sündenbock. Volker war nett und gab mir ein par Bilder über seine Zylinder, und ich schicken sie zum einen freund von mir. Mein Freund ist ein Kabeljau, weil er die Bilder am die Yahoo seiten geschickt gehabt, aber ich muss wirklich beklagen! Und mein Deutschschreiben ist skrekklich, ich weiss............. :) Grüss Truls Herland

Ich sprecht Deutsch nicht so gut, aber Englisch ein bisschen................. I think the problem with your engine has a simple explanation. The PHB 28 has a very small floater chamber compared to the capacity of the venturi. So when you reach full throttle the floater chamber is becoming empty, the reason maybe that the fuel hose is too long, have the wrong diameter or have a bend or block in it. It could also be the position of the carburetor that is incorrect. I had the same problems with a polini 177 and PHB 28, the floater chamber would empty very fast at full throttle. The reason this may happen just in 4th gear, could be that the motor revs to a lean mixture and when changing gears rapidly the floater chamber gets the chance to refill during gearchanges, but when the 4th is engaged, assuming that the revs are constant the floater chamber become empty............ It is quite hard to tell from your explanation excactly what the problem is, but as I understand this happens only in 4th gear at full throttle. Does it also occour when throttle is constant fully open in 2nd or 3rd gear???