Math Equations...?

[c00t3r]

Hi Everyone, I'm looking for an equation(or series of equations) for a circle that, given a distance traveled around a circumference(distance in mm the center of the lower crankpin travels), and referenced to a start angle(port open angle) and an end angle(mean port duration) will give me a vertial distance travelled. I've been searching for a while now, and haven't found anything of use. I was hoping that someone here might be able to point me in the right direction. I'm working on a spreadsheet that does some of the more tedious math for me when determining the state of tune on a given 2 stroke engine. This calculation would help me determine the distance from the top of a given port the mean area line is located at. I can then calculate mean port area, and so on and so forth, without making a physial drawing and calculating with a t-square and protractor. Any help is appreciated, thanks.

Tom

[3WW Star-Yamahondaman]

WOW !!!!......... HECK all's i do is use my finger to check thing's when Porting ...
the common thing is 1.5-2 mm's up on the Exhaust and 2-2.5 Wider at the TOP
TROLL has the Macdizy thingy for that mess ............

[c00t3r]

I found it on MacDizzy.. figures.. look for two hours and finally ask a question... ten minutes later you stumble on it.. thanks anyway guys.

Tom

[ATC-Eric]

Dang, first post and you've been here for 3 years!

What do you ride?

[c00t3r]

I have 1 and a half ATC250R's. I'm workin on a new dirtbike for next summer. I don't post much, but I read a lot.

Tom

[rally4x4racer]

theres a cooter lurkin out there... yikes!

you never posted the formula..

[c00t3r]

In spreadsheet form HT=(r+c)-(rcos(a))-sqrt(c^2-(rsin(a))^2), where
HT= piston height
r=stroke divided by 2
c=con rod legnth
a=crank angle, in radians
d=crank angle, in degrees
dtor=degrees to radians = PI/180
a=d*dtor

And if we know this, we can then extrapolate, from the change in piston height, where, measured from the top of the port down, the line that represents the mean area of the port lies. Assuming you have measured port duration, and a few dozen other things correctly.

[rally4x4racer]

you using this instead of a flowbench to test how a port will flow?
thanks for sharing..

rcos is a little confusing .... I started breaking it down like r*c*o*s

so is rcin...

[c00t3r]

Yes, in the end I want to be able to input several easily measureable parameters, port width, shape, port duration and calculate sizes of ports to determine the state of tune. I'm trying to learn to port the right way without several hundred dollars worth of software. So far i'm on the right track. My neighbor has a yz250 that I did that'll come right over if you crack it at 45mph. I've done a couple others with overall good results.

[rally4x4racer]

i hear ya bro, its all about making the big money spendin fools look bad

when you get your measurements down just right you should make metal templates that slide into the ported head and sell them to us dummies- that way we can port ours to perfection and not have to do all the work!

[thefox]

What is involved in the flowbench testing? I have heard about it but how does it actually work?

[daputz]

you found your hook up

Macdizzy is where you need to be if plan on using the different porting sofftwares and proven timing and durations. Nothing there is free but they will always point you in the right direction.

[rally4x4racer]

I like cooters method for porting better - I will even port blind - i dont really care. i can not answer your question very good but basically strap a head to the bench with the equipment attached to it and put some air over it. the equipment will put everything on a PC screen for you to analyze - in differ colors so you can tell when you improving or not.
grind, test - grind, test.... send owner large bill to make payment on your equip.

this is an injector, but it is similar to the readout

[daputz]

What is involved in the flowbench testing? I have heard about it but how does it actually work?

flow bench testing is great......................but you need to know what you are looking for to begin with. Do you want volume or velocity? at what range? what duration?

Here is a ques..........................when someone adds material to port/head to get a desired result (making the port smaller instead of hogging it out changing angles...) is it still considered to be porting?

[c00t3r]

Of course its still porting, it takes the same amount of calculating to come to the conclusion that more material is needed in a certain area. Whether its for the purposes of streamlining airflow, say transfer tunnels, or the floor of a port on a four stroke, or optimizing air velocity for a desired RPM. Adding material is often MORE time consuming because of the need to weld in layers, or epoxy layers to reach a rough shape, and then start cutting/sanding to create the final port shape.