So, what is it that makes an engine accelerate?

Think acceleration rate...
Since acceleration itself is a rate , specifically the rate at which velocity changes versus time, I assume by this you are referring to the rate at which acceleration changes versus time.
Well I started thinking about this the other day when posting on the other thread ... ..........
.......................
......My fingers are now tired.
For years I've had a lot of similar stuff rattling around in my poor brain. I've always assumed that the engineers somewhere must have written the necessary formulas to relate the expansion rate of the burning gas to piston position and speed, to cylinder pressure, to crank angle, etc, etc. Got to be a big Kray somewhere capable of running simulations, right? :D

Impossible for the rod to be the hypo. if the rod and throw are @ 90*.
Correct. At this point the hypotenuse would be the line from crank centerline to piston pin centerline.

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. :D
Steel;
Engine don't accelerate, vehicles do. But some do increase RPM faster than others..... :) :)

Since acceleration itself is a rate , specifically the rate at which velocity changes versus time, I assume by this you are referring to the rate at which acceleration changes versus time.
For years I've had a lot of similar stuff rattling around in my poor brain. I've always assumed that the engineers somewhere must have written the necessary formulas to relate the expansion rate of the burning gas to piston position and speed, to cylinder pressure, to crank angle, etc, etc. Got to be a big Kray somewhere capable of running simulations, right? :D
Old...yes, this is all about acceleration over time, since we're trying to get from point A to point B in the least amount of time as possible. Increasing velocity is increasing acceleration, etc, but that's symantics AFA my question.
What makes an engine accelerate? Your second paragraph touches on where I think this will eventually go.
Busby, in his not-so-eloquent terms says it's the short rod that helps. (I'll get back to you and your short jokes later, pal.) There's too many other things to consider to say that the rod ratio by itself is going to "make" an engine accelerate or not. But where's the motivation coming from? I'm thinking more in terms with what's going on in the combustion chamber. Good burn vs. better burn, vs. best burn. In this sense, Daryl Morgan may have a point.

Hey now ... I don't have any fantasy about your short rod! We're talkin' engines here ... not what your deficiencies are.
If you want a more rapid RPM ramp, you'll need a short stroke/short rod/big bore motor, period. It's been proven. You'll never change the facts ... including how short you might be.
I'll say this.
OK...No I won't.
However, in regards to your "short" comment, think about it this way, BIG guy. Put you in your boat, run it. Now put ME in your boat.
Advantage who? :yuk: :D

For an engine to accerate: Correct sequence of events....

Busby, in his not-so-eloquent terms says it's the short rod that helps. (I'll get back to you and your short jokes later, pal.) There's too many other things to consider to say that the rod ratio by itself is going to "make" an engine accelerate or not. But where's the motivation coming from? I'm thinking more in terms with what's going on in the combustion chamber. Good burn vs. better burn, vs. best burn.
Well ... I agree 100% ... but when we're speaking about an internal combustion engine, we're speaking about volumetric effiency, right? And how does the stuff get into the chamber in the first place? By the pistons downward motion creating a vacuum. If the rate of the downward motion directly effects the VE, then the rod ratio it very important in equating what your goals are when building an engine. In a not so eloquent term ... I will explain to you Scott that this is the first stroke ... the intake stroke ... the beginning of how we make an engine run.
Once you grasp this idea ... we'll work on the next stroke ... compressing what we've filled the cylinder with ... it's called the "compression stroke", let me know when you're ready Scott ... in your post you were moving onto things way too quick, kinda prematurely, but you might be used to that ...

For an engine to accerate: Correct sequence of events....
hey ... I didn't get to page two yet ... I see you have already started speaking about what I am getting to ...

When a swimmer finds his stroke and kick rythum he or she is fast.....
When a cyclist finds his pedeling rythum he or she is fast. . .
When a runner finds his stride he or she is fast. . .
When an engine has a tuned induction and exhaust path, it is fast. . .

When a swimmer finds his stroke and kick rythum he or she is fast.....
When a cyclist finds his pedeling rythum he or she is fast. . .
When a runner finds his stride he or she is fast. . .
When an engine has a tuned induction and exhaust path, it is fast. . .
well put ... timing is everything ...