Whats up with it, im a amateur and will be porting my mhr rep and dont really fancy buggering it up.
There are a lot of mistakes in it..
Let's see it step by step.
The "General" sheet is ok, quite accurate no mistakes.
The "Timingen" sheet is also works fine
In the "Compression" sheet we can find a silly thing
The compression ratio as it's name shows is a
ratio so it hasn't got unit. The author wrote bar, as a pressure, but it's not true!
"Time-Area"
Small mistake: For me and for others too the "opening time" at cell C12 means when the port starts to open, that one is a "port duration" in seconds, so this can mislead the amateurs.
And the main problem is the whole Time-Area calculation. That one is not Time-Area!
Matematically it is correct, but what it contains is "useless".
This calculation shows, if the bike revs 8000 1/min=133,3 1/s, than 1 rotation is 0,0075 sec. And that 0,0075 sec is for 360 degree turn, it's still ok, but than the author think 0,0075/360*182 is correct but not. We all know that 182 is duration between 89 degree (opening) and 271 degree (closing) but the calculator see only one number "182" not two.
That 182 "degree" can be anywhere between 0-360, for example between 5 and 184 LOL. So this can give us false numbers, because all this depends from where it is that's a problem. Degree to mm depends from stroke and conrod length, varies every degree. This calculation can be true for any stroke and bore motors with 295cc displacement. Noway!
1 degree rotation is equal to a constant change in distance (mm) in this calculation. This formula is linear, but the crank movement isn't so the result is too far from the real, we can't say this is Time-Area. Another problem we can give only a port area (with constant width) not complex shape because of the linear calculation. So the port must be square or rectangular, because of the things above, it's important in which position the port wider or narrower. So if two port has a same duration and area but different shape they have got different Time-Area.
I enclosed a document (it's not a real existing port, I just made it for a demostration) how the port area changes when the crank rotates. It's also demostrate what happens if we mirror a port (the port has got the same duration, area and shape, however at a different position). Because the port is mirrored, the total port area changed!! ->
Time-Area (Pdf)
Too much thing is indeterminate , this calculation it too universal!
Comment: it's a pitty we can find quite similar calculations at G. Jennings book. Sure it's a quite old book with obsolete formulas, datas... And also conatins the same mistake what I write down to next rows.
So another problem with this calculation is the units again. The calculator divide
degree with 1/sec and the result will be seconds. We can't take away the units with a high hand. So the D12 cell is not sec but sec * ° (secondom * degree).
Thus the end of the calculation the final unit is not sec-cm^2/cm^3 but sec
°-cm^2/cm^3.
If we convert the port duration to radian instead of the "°" we will get the
MEAN Timea-Area and the right unit!
But as I said it's not very accurate for the precise calculations.
"Angle-Area"
I try to use a moderate word, but it's bullshit, it's a fantasy.
The calculator divide the Area
mm^2 (in the sheet it's typos because we can see mm^3) with the cylinder volume
cm^3 and the result is
second. What the hell?? And how?
To cap it all just multiply with
degree
Not only the calculation is ludicrous, but the unit is wrong too, the unit is
° x mm^2/cm^3 So the unit at the end of the calculation is a cheat.
And now something about these areas.
In real we can calculate the time-area from the angle-area.
So it's even a good joke the author don't know the relationship between this two things as we can see.
The Angle-Area show us how big is the opened port area at concrete degree.
Then we can just sum all these and we've got a total port area. That summarized port area is a very big value!
We calculate A (mm^2) d(Phi) we should integrate the areas between Phi1 and Phi2 where Phi1 is the opening angle and phi2 is the closing angle.
d=delta
If we did the integration and multiply the result with the 1/ (2* Pi* n) we have got the Time-area it's unit is sec-mm^2.
n=RPM
If we divide the result with the cylinder volume we have got the common form -> sec-mm^2/cm^3 or sec-cm^2/cm^3 etc..