Any port timing gurus ?

[Astrolopitec]

Hi
I took the time to map my cylinder. It's oviously made for a 47 crank but it works great with my 42.
Can anyone spot any major timing deffects or areas of improvement ?

 

[Egebo]

You need 2 more things, before i can say anything about your portning.
First i need to know your "mean area" of each port.

http://www.macdizzy.com/cylinder_map3.htm <-- INFO about mean area

And then i need to know what your target RPM is.

 

[melf #50]

it's not only the cilinder that does it all , everything around it must be perfect to to gain power , if your exhaust isn't build for more RPM you will not gain but loose power...

 

[Egebo]

it's not only the cilinder that does it all , everything around it must be perfect to to gain power , if your exhaust isn't build for more RPM you will not gain but loose power...

Thats right.
Many sees porting as something witch just gives power.

But in fact i cant rouin the powerband completely.
Porting actually makes the engins torque fall, by releasing the working gasses earlier or more rapidly.
But it alsow allows the engine to flow effecieltly at higher rpm.
And you need higher rpm to compensate for the lost torque.


And as melf #50 says it not only the port shapes and timing that counts.
The differens in pressure, inside the cylinder and ind the exhaust is just as importent.

 

[Eoin70]

i worked out the timings for you
170exh / 112/transfer
it should make some great torque but it doesnt appear to be make many rpm's

 

[Egebo]

Just translatet an excel doc, i made some time ago, into english.
It calculates time areas and put them into an angel area diagram.

http://www.megaupload.com/dk/?d=R9D6BFVR


All info about right portmapping and measuring "mean port area's" can be found on www.macdizzy.com

 

[Astrolopitec]

Thanks a ton guys !
Time to get me self some metric graph paper.
I'm doing this for my personal enlightment. I'm actually quite happy with the current performance. If you keep in mind that I'm not aiming for a racer but for a reliable long distance cruiser. My hope being that a high geared, low RPM motor will operate under less stress. So far it seams that that's exactly what I'm getting. Porting for high RPM would tend to defeat my original purpose.
Boy ! That spread sheet is super! It'll save hours.
Now. If my blody byke computer were to arrive. I could compare actual with theoretical RPMs. ( six weeks waiting ! )

 

[melf #50]

there a tools wich you can buy to measure in degrees , it's much easyer , I only use degrees , for me it's the only way...

 

[Egebo]

My hope being that a high geared, low RPM motor will operate under less stress. So far it seams that that's exactly what I'm getting. Porting for high RPM would tend to defeat my original purpose.

Keep in mind then, that you want your exhaust angle area in the lower part of the exhaust interval, and the transfer angle area in the mid-upper part of the transfer interval.

That should provide a god low rpm effeciency

 

[Astrolopitec]

Got you ! (after a while...)
And thanks again for the spread sheet.

 

[Egebo]

Got you ! (after a while...)
And thanks again for the spread sheet.

No problem.
Made some months ago for a danish forum, but noone really seemd to use it.
Så im glad someone finaly got to use it