Formulas, Math and Calculations

[Paul Wright]

This thread is for math formulas only.
Put the purpose or name in the post heading so it can be searched for easily.
Example: "Mean Piston Speed" or "Air Velocity".
All math should so original source or references (where it came from) and/or proof; meaning, please explain how it was derived and how it works.

[Paul Wright]

There are two verticle (1 up & 1 down) piston strokes per crank revolution.
So for example, with a 3" stroke the piston travels 6" per revolution.
Multiply by the number of revolutions per minute and you get the total inches of linear travel per minute:

RPM * stroke * 2

The stroke is in inches so we divide by 12 to get feet:

RPM * stroke * 2/12

Fraction is reduced to
2/12 = .167

RPM * Stroke * .167 = MPS in Ft/Min

dividing the result by 60 will give it to you in feet per second.
Air Velocity is often in Ft/Sec so keep the MPS in Ft/sec if using both in an equation.
It's important to keep track of the units or it can get away from you.

This equation is for Mean Piston Speed. It's the average speed. Instantaneous speeds can be much higher or lower all the way to zero at TDC and BDC.
The instantaneous speed at any crank position can be calculated with a much more complicated formula that utilizes trigonometry and the rod length variable.

[Paul Wright]

Here's the amount of flat milling for 1 cc reduction in chamber volume:

SBC 64cc head 0.0055" per cc;
SBC 76cc head 0.0059" per cc;

Must mill SBC manifold surface 0.0123" for every .010" the heads or deck are cut to restore proper alignment and fit. The distributor collar to manifold dimension will be affected if changing deck/manifold height. They make distributors with an adjustable collar to solve this problem.

BBC manifold is 0.0193" per 0.010" cut

Amount to mill off bottom of intake or block China Wall per .010" cut of the deck;

SBC 0.0173"

BBC 0.0193"

[rhamm1320]

Here is one for calculations

http://www.virtualengine2000.com/ProgramDownload.htm

http://www.virtualengine2000.com/images/Calcul2.jpg

[Paul Wright]

Artie is correct about my rookie mistake in converting RWHP to FWHP. I was multiplying RWHP by 100 + the percentage loss which is incorrect. The correct way is to divide the wheel HP by 100 - the loss percentage. They look like the same thing but the answer is different.

For example:
450 x 1.15 = 517.50 (incorrect)
450 / .85 = 529.41 (correct)

To get wheel HP from flywheel HP you multiply by 100 - percentage loss.

Example:
529.41 x .85 = 450 (correct)
529.41 / 1.15 = 460.36 (incorrect)

I got dyslexic and multiplied when I should have divided and added when I should have subtracted.

I apologize for the confusion. At least the peer review system is working perfectly. This helps keeps the info accurate and this site better than some others.

Pass me the crow crumpets.

[Paul Wright]

Amount to mill off bottom of intake or block China Wall per .010" cut of the deck;

SBC 0.0173"

BBC 0.0193"