Math Project

[Ralph]

i have a math project due soon on math and engines. I was doing some research and figured this would be the best place to go. Basically we have to show that math is realy important for engines to function

im just looking for some formulas, I think i can find the CC size formula somwhere on the site. IM gonna bring in things like timming, shapes of the cam lobes, fuel racios. If u guys have anything else u think i could put on it let me know, also if u know anything about what i just listed that would help alot also...

[KrazyKid300ex]

bore and stroke? that has some formula for it i think

A tip: So you do not look like a fool on your presentation, its ratio.:confused:

[ZSK]

The equation for displacement is:

1/2 the bore X 1/2 the bore X 3.14159(pi) X the stroke=displacement

Make sure your units are correct here's an example for a 300ex bore is 74mm and stroke is 65.5mm

Convert to centimeters to get cubic centimeters in the end

3.7cm X 3.7cm X 3.14159 X 6.55cm= 281.7cc

[Ralph]

k thanks, i just thought of something else, jets, and needles. the differant sizes, also is there any ratios with air to gas? i guess i could also bring up gas/oil ratios.

[KrazyKid300ex]

idk, there might be something for the gas/air but i dont think so

[hondafox440]

Air to gas is the ratio changed by your jetting. Only so much fuel/air can enter your engine at once. For example, a larger main jet allows more fuel (thus less air) in, so the fuel to air ratio is greater. The opposite is true, smaller jets let less fuel in so the fuel to air ratio is less.

[VIC]

Originally posted by hondafox440
Air to gas is the ratio changed by your jetting. Only so much fuel/air can enter your engine at once. For example, a larger main jet allows more fuel (thus less air) in, so the fuel to air ratio is greater. The opposite is true, smaller jets let less fuel in so the fuel to air ratio is less.
I think then the same goes for a free flowing filter, no lid , ect
then it would be more air to to gas thus needing larger main.

[hondafox440]

Right, thats why you need to change your jetting, because you altered the volume of 'stuff' (air and fuel) that can enter the cylinder, so you must increase the amount of fuel (enlarge the jets) to compensate.

[remlapr]

Isnt' there a formula for estimating max HP output of a motor? Yes - I KNOW there are many factors that result in the final actual HP output of a motor, but I think I remember some of the gearheads I went to highschool talking about it... If so that would be a good one...

[VIC]

http://www.maximumsled.com/mountain/garage/2strokeprinciples/two-stroke_animation.gif

this would be cool if you did a power point presentation

[wilkin250r]

How complex do you want to get? Thermodynamic energy created by burning fuel, you can write the equations for Boyle's law for tempurature and pressure. That pressure pushes against the piston and rod, which creates a torque on the crank.

You can write equations for the reverberation of pressure waves in a two-stroke pipe.

"optimum" air/fuel ratio is 14.7 parts air to 1 part fuel, by weight.

[Ralph]

im gonna get as much info as we can get, its a 15 minute presentation. a speech, powerpoint and poster, im puttign all those mooving images from how **** works.com and were take old pistons and **** to take up sometime teaching key terms so people know what the hell were talking about.

Right now im gonna Go into the formula for finding C.C. size and how without a system of math engines could not function. Im gonna go into timing, compression. How do u go about finding compression lets say u have 13:1 compression, what 13 are there to what 1. Pound per cubic centermeter? just a guess.

[VIC]

This place also has a bunch of info on 2 strokes. I think it has formulas as well you'll just have to find them.

Macdizzy (http://www.macdizzy.com/2stroke.htm)

[wilkin250r]

Originally posted by Ralph
How do u go about finding compression lets say u have 13:1 compression, what 13 are there to what 1. Pound per cubic centermeter? just a guess.

It's a ratio of before and after.

There is a difference between internal volume and displacement.

For a stock 400EX, the bore and stroke is 85mm x 70mm. Do the math, and you get 397cc (cubic centimeters) The compression ratio is 9.1:1

When the piston is at the very bottom of the stroke, the internal volume of the cylinder is not 397cc, it is actually about 440.6cc. When the piston is at the top, the volume is about 43.6cc (this is called the "combustion chamber")

The compression ratio is calculated by dividing your displacement by your combustion chamber volume.

397cc / 43.6cc = 9.1

A high-compression piston has a dome on top of it that will decrease the volume of the combustion chamber. If your piston has a dome on it of 7.5cc, then your combustion chamber is now 36.1cc instead of 43.6cc. For the same displacement of 397cc, your compression ratio is

397cc / 36.1cc = 11

[Ralph]

that makes sense, thanx for clearing that up for me, this could actualy turn out to be a very imformative thread