MOPED ARMY

Thinking about it the angle postion of the exhaust opening is directly related to the open angle period... i.e. the larger the number ATDC the smaller the exhaust open period and viseversa

the beginning... its the the same horse different stick

I want to be sure about this before I produce this pipe. I was planing on making one for my polini before I blew it up and I think when I measured the point at which the exhaust begun to open after TDC it was like 55 degrees(if I remember correctly), and the program says thats too small of a value, it wants between 70 and 105

true true but then where does the ATDC come in?, I'm just wondering if anyone has actually herd of this:

("Exhaust Port Opening Angle (deg ATDC) ___") business and can for sure tell me that they know what it means, just so I can answer this mystery.

you said your polini measurement was "if you remember correctly" maybe go back and check before you get in a muddle...55 would give it an exhaust port timing of 250 degrees which is massively too much, so i reckon you've remembered wrong.

i've always read ATDC as after top dead centre so yeh i assume, as i think crackstar is saying, that "Exhaust Port Opening Angle (deg ATDC) ___" means the point at which the exhaust port opens after top dead centre

I can help you out here. At top dead center the degrees equal 0. All the ports are symmetrical (they open at the same degrees before and after TDC) So if it asks for the degrees ATDC then they mean at what degree of the crank does the exhaust port just start to open. Should be a number about the size they said. Thing is that number is a bit misleading because it does not tell you the exhaust port duration. That is given by 2(180-x) where x is the degrees ATDC. so if you measure 55 degrees ATDC then 2(180-55)=250 degrees symmetrical around BDC. Now that number is not right because if that where the case the cylinder would only be closed for 110 degrees every cycle. The exhaust would be huge if that were the case. Numbers closer to 180 degree total opening are big, and 250 just wouldn't work. I don't remember if they ask for transfers too or not in that program.

How are you measuring the degrees btw?

awesome, I think I finally get it...

-noogie, you're proboly correct, I'm proboly remembering wrong

-Crankstr, I understand now why it doesn't matter that I know the duration because it is directly related to the difference of the full rotation and the point at witch it opens, or 2*(180-x) like Mr jesse stated so eloquently, thanks! I can't wait to get to Richmond this weekend and Measure this dood so I can build my three stage monster rad pipeie jam!

Thanks for all your helps 'n stuff

Oh God, and we wonder why the rest of the world is producing more engineers than the US! lol!

i'm gonna put up a video when I'm done, hopefully by next week

event timing attached

even more event timing attached

Thanks Wari, I already peeped that on yer Myspace. I was more wondering how the Mota program worked out compared to doing Jennings calculations with paper and stubby pencils. I have to cut a new degree wheel for my Moby tomorrow, the last one I made only fits Bosch magnetos, doing CNC work at a sign shop has its advantages...