Ueberarbeiteter 210er Malo von SIP

[Andre]

Ich kenn welches....aber das leih ich nicht her...

[manni]

Ne , kenn ich auch nicht, deswegen wirds beim nächsten Polossi nicht mehr eingebaut.

[moonraker]

zwischenfrage, der worbel schreibt ja aus symmetriegründen, den kolben auf beidenseiten um ein paar milimeter zu fräsen (ÜS freigeben).

ich habs nur auf der seite gemacht, wo der kolben den ÜS zumacht.

wird ers überstehen?

mfg, roland

[Andre]

Eigentlich ist es ja auch nur auf der einen Seite nötig...hast du schon richtig gemacht...

natürlich wird er das überstehen!

[Truls221]

The diagram graham has made on p.41 in his book is not a reference guide to port timings and duration. In fact it doesn't take into consideration the width of the port, which, as you probably know, can change the time-area and the character of the motor totally. How do you know how to calculate this, if not using time-area. The angle-area formula shows just this:

(total port area/cylinder displacement)*port duration

and the timearea formula:

(60/rpm)*(port duration/360)*(mean port area/displacement)

See how the angle-area and time area can vary if only the area of the port changes.

Port open period only is way too average.

Thats my opinion.

[volker]

@Truls

That's also my opinion. It would be really interesting to test a smallframe with a Polini HP75 and to compare it with any other good 75ccm cylinder.

Have you seen this exhaustport design? It is only great! In the Scootercenter Köln catalogue they have a good picture of this cylinder. Polini built in two "teeth" on the top edge and one on the bottom edge, which are "handing over" the piston rings. The port has something about 170° duration and is unbelievable wide. Something like this I would like to have in my primavera. This should make it possible to have the original gearing and no problems with the 4th gear.

Another question. Where did you find the formula for the time area? Is it really so simple?

Hälsningar,

Volker

Bearbeitet 2. April 2003 von volker

[Truls221]

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

[Lucifer]

@ Truls, Volker...:

Guys, that thing isn't quite that simple, due to the more complex relationonship between linear motion of the piston and the rotary motion of the crank (the same formula you have to use for the relation "mm before OT vs. °KW v. OT", the timings!)...!

In prinziple you have to multiply the free area of a port at given Piston-position (in relation to stroke) to the time at certain rpm, which this ara is open! Therefore you have to make a perfekt blue-print of your port-layout, lay it over a graph paper, and measure out (just count the square-mm) the areas at certain points of stroke (or °KW before OT)! This problem becomes even more complicated by ports not entering the bore rectangular, so you have to correct your measured areas by the sinus of the entering-angle,.....! Keep in mind: channels enter usually not rectanguar into the cylinder, but angled to the bore in both horizontal as vertical plane too!

If you keep an eye on Bönsch's famous book (page 97ff), you will find mor detailed explanations....

When you have done all that stuff, you will find out, that the timearea will be reduced with increasing rpm, because less time is available for stuffing the mixture into the combustionchamber as well as scavenging all that burned stuff out again after ignition!

As a matter of fact, this limits the rev-range of your twostroke engine, far before modern (note: our scooter is far away to be "modern"!) mechanical restrictions....

[volker]

@Lucifer

Your are right, - this calculation has to be quite complicated, at least, if it's done precisly. Here the page you were talking about:

!!!No, this picture was too big for imaging here!!! Check the link below instead!

This is here to find.

For my Malossi 136 I calculated some time areas with the Blairs DOS-software: Blairs Progs 61 and 63..., but I missed the angle in the exhaust port downwards! Thanks for the hint! The exhaust was allways the most restricting time area, even when I calculated the ports (without the downward angle!) This must be even worse in reality, with this angle!

No way to come even close to 8bar bmep or something around 20hp, if I keep the port durations as they are determined by Malossi (175°/120°).

We will see how the motor is, when I soon have it all together for assembly. Even my home-made-aluminium-casted floating chamber is dense! :love:

Regards,

Volker

[gravedigger]

Ich fahre allerdings auch so ein adaptierets CVF und mein Kolbenbild war absolut symetrisch. Hätte ich eigentlich nicht erwartet. Scheint also gar nicht so schlimm zu sein.

vielleicht geht ja auch gar nicht soviel durchs cvf durch? Kennst du ein Gemisch das Bock hat bei 6000 Umdrehungen innerhalb der ihm verbleibenden Zeit einen 180° Bogen zu machen um dann erst gesmashed und dann verbrannt zu werden?

warum funzt dann das originaltuning?

da ist es ja noch schlimmer mit den ecken als beim malossi

ist auch eine art CVF.

[polinist]

warum funzt dann das originaltuning?

da ist es ja noch schlimmer mit den ecken als beim malossi

ist auch eine art CVF.

Weil der original halt noch mehr zugeschnürt ist. Von den Massenfertigungstoleranzen nicht zu sprechen...

[gertax]

Ich fahre allerdings auch so ein adaptierets CVF und mein Kolbenbild war absolut symetrisch. Hätte ich eigentlich nicht erwartet. Scheint also gar nicht so schlimm zu sein.

vielleicht geht ja auch gar nicht soviel durchs cvf durch? Kennst du ein Gemisch das Bock hat bei 6000 Umdrehungen innerhalb der ihm verbleibenden Zeit einen 180° Bogen zu machen um dann erst gesmashed und dann verbrannt zu werden?

warum funzt dann das originaltuning?

da ist es ja noch schlimmer mit den ecken als beim malossi

ist auch eine art CVF.

beim originaltuning gibts auch keinen (und der beim malle is auch noch schnell) gasstrom der hinter den Löchern im Kolben vorbei saust...

[gravedigger]

ich würde mal von venturi beim malossi system sprechen oder so ähnlich