So, what is it that makes an engine accelerate?

[MikeF]

Impossible for the rod to be the hypo. if the rod and throw are @ 90*.
What I was getting at was,
The piston would be moving at it's fastest speed at this point at a given rpm. :boxed: And by that time the BANG has already done most of it's work.

[BUSBY]

I hate to have to quote myself ...
What happens when the crankshaft is at 90? You'd think that the piston is halfway down the bore, right? Well that's not exactly true. The angularity of the rod at that point brings the piston down a little bit further - the connecting rod length is the hypotenuse of a triangle where the short side is the sideways distance from the center of the cylinder to the center of the crankpin.
Pythagoras was a Greek mathematician who lived about 2500 years ago, and who developed the most famous formula in geometry, possibly in all of mathematics! He proved that, for a right triangle, the sum of the squares of the two sides that join at a right angle equals the square of the third side. The third side--the side opposite the right angle--is called the hypotenuse of the right triangle. The two shorter sides are usually called "legs."
This formula is called the Pythagorean Theorem in honor of Pythagoras. It is usually written as the equation below, where a and b are the measures of the legs of the triangle and c is the measure of the hypotenuse.
http://www.***boat.com/image_center/...358formula.gif
So with my original post of the crank being at 90* (from TDC) ... the hypotenuse would have to be the rod angle :squiggle:
http://www.***boat.com/image_center/...hypotenuse.gif

[Oldsquirt]

So with my original post of the crank being at 90* (from TDC) ... the hypotenuse would have to be the rod angle :squiggle:
http://www.***boat.com/image_center/...hypotenuse.gif
Ummm, don't you mean rod length?

[MikeF]

Picture this,
http://www.***boat.com/image_center/...ypotenuse1.gif
Large black circle is crank journal.
Red circle is rod journal.
Yellow circle is piston pin.
Piston speed should be at it's max in this position. Yes/no. Or is it at 90deg to the bore? :boxed:

[Norseman]

Picture this,
http://www.***boat.com/image_center/...ypotenuse1.gif
Large black circle is crank journal.
Red circle is rod journal.
Yellow circle is piston pin.
Piston speed should be at it's max in this position. Yes/no. Or is it at 90deg to the bore? :boxed:
Mike;
Piston speed is Zero at TDC
Maxium piston speed should be at two points relative to crankshaft rotation about 75 degrees and about 285 degrees of crankshaft rotation
Maximum piston acceleration will be about 10 degrees before and after top dead center.
Bob

[MikeF]

Mike;
Piston speed is Zero at TDC
Of course. :rollside:

[Beer-30]

I've been waiting a LONG time for the opportunity to present itself to open this can of worms. This is the grand daddy of all questions regarding engine performance, and I'm really curious as to who thinks what. What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B? Lets face it...this is what wins races, not dyno numbers. So, is it horsepower? Torque? Both? Neither? :idea:
Let 'er rip.
Throttle position!!
LOL.

[BUSBY]

Ummm, don't you mean rod length?
No ... I meant angle, refering to the diagram the length of the rod was irrelevant ... just trying to make sure that we were all speaking of the same angle/segment of the triangle ...

[BUSBY]

What happened to Scott? I'm ready to talk about the next stroke! Compressing what we brought in ... and what effects heat plays ...

[Oldsquirt]

No ... I meant angle, refering to the diagram the length of the rod was irrelevant ... just trying to make sure that we were all speaking of the same angle/segment of the triangle ...
Yeah, I know what you were getting at, just busting your butt about calling a straight line(the hyp) an angle.
BTW, as interesting as I find this, it's giving me flashbacks to my physics, geometry, trigonometry and, worst of all, calculus courses taken 30-something years ago.