Limiting factor for RPMs?

[dieselgeek]

A longer stroke requires more power to complete a rotation in the same amount of time as a smaller stroke needs......

Absolutely incorrect. You can't state that. The longer stroke requires MORE DISTANCE TRAVELLED but you can't say it requires more force. FOr the ninth time, it's getting old telling you how this all works. THe issue with you and the rest of us here is MOST DEFINITELY NOT that your "theories" are advanced or out of the box - the issue is that you base these ideas on incorrect understanding of physics. Of course your ideas sound awesome - because you never bothered to learn the Basics first... newsflash, that does NOT make you smarter than everyone else here. In fact quite the opposite is true.

The rod journals spin in a circle, it takes time and energy to get around that circle if you increase that circle you increase the distance that needs to be traveled around that circle and the only way to not increase the time it takes to get around the circle is to increase the speed at which the circle is traveled, and to increase speed you need to increase the energy spent.......

No mention that the longer stroke has more leverage on the crankshaft, thus makes more torque per energy spent pushing on the piston? LAME.

Basically saying that a 350 can rpm faster than a 454.........

You can't state that in general either. And WHO GIVES A SHIT which engine can "free rev" faster? meanwhile, what about the hundred other factors you are leaving out? rotating assembly mass? You keep talking about "rpm faster" but you have yet to state where and when this would benefit anyone. You aren't even making any kind of claim that can be discussed or debated...

Or at least that is how I see it.........

And you see it wrong, period. No ifs ands or buts, no "we don't understand" - you do drugs and it screws up your brain, and these lame ideas are the result. It's not us - it's you. Period.

[dieselgeek]

And for the love of God:


Warning!!!!!! This Member is 75% of the time thinking of theories that do not coincide with yours and are generally outside the box, 25% of what he says is along the main stream of what other people think, it is not that he disagrees with you, it's that he thinks differently than you........


Let me add this.

WARNING! That member doesn't know the meaning of the word "theory" either.

[squirrel]

It's all about the acceleration of the crankshaft, how quickly it turns to reach a certain rpm and since a short stroke has less of a distance to travel it will spin faster than a longer stroke when equal forces are applied to the pistons....... Basically the shorter stroke will peak rpm's faster because it has a shorter distance to travel.

I guess if you're trying to get a crankshaft spinning as quickly as you can, then this might be worth discussing.

Longer stroke = more intertia in the crankshaft that you have to get moving
Longer stroke = more distance the pistons and connecting rods have to move
Longer stroke = more torque available on the crankshaft (due to the longer "arm") to get it moving

How about if you put some numbers on it? Do you know how to calculate the moment of inertia of a crankshaft?

[Bob Holmes]

Well, I guess I'm weird. I want the lowest "revving" engine that will get me to my goals.

I don't make enough money to want to rev the wee out of an engine.

[The Outsider]

reads how I recall it:

http://www.thecartech.com/subjects/a...e_formulas.htm

meq = equivalent mass of rotating parts [kg]

= [ Iw (1/rw)2 + Ip hf (if /rw)2 + Ie ht (if ig / rw)2]

where:

Iw = polar moment of inertia of wheels and axles ≈ 2.7 [kg m2]

Ip = polar moment of inertia of propeller shaft ≈ 0.05 [kg m2]

Ie = polar moment of inertia of engine ≈ 0.2 [kg/m2] + polar moment of inertia of flywheel and clutch ≈ 0.5 [kg m2]

hf = mechanical efficiency of final drive

ht = mechanical efficiency of transmission system (hg x hf)

ig = gearbox reduction ratio [ig1 or ig2 or

[squirrel]

We're just trying to figure out the moment of inertia of the crankshaft, first....

[TC]

Well, I guess I'm weird. I want the lowest "revving" engine that will get me to my goals.

I don't make enough money to want to rev the wee out of an engine.

Reher-Morrison has a different view.......

http://www.rehermorrison.com/blog/?p=220

[The Outsider]

Well, I guess I'm weird. I want the lowest "revving" engine that will get me to my goals.

I don't make enough money to want to rev the wee out of an engine.

That makes sense.

On the other hand, the trend toward higher-reving engines (and "EcoBoost"-style turbo mills) is driven by necessary increases in "power density." In other words, a smaller, higher-reving engine can be lighter for a given torque rating and can burn less fuel at part-throttle during times of "off-peak" loading (which is the overwhelming majority of the driving cycle). On the other hand, larger engines are easier to spec (and often cheaper) for increased low-rpm torque (at the penalty of higher fuel consumption in Otto-cycle designs).

An unintentional benefit is that engines that turn over 6,000 r.p.m. tend to sound "racy" whether they are or not. Now you can buy'em for almost no down and reasonable monthly payments.

In the early days of the car, huge 500+ cubic inch engines were not uncommon in competition. For example, Ford's 1902-1903 "999" and "Arrow" racing cars had 1,155.3 cid inline-4 engines (bore of 7.25 inches and a stroke of 7.0 inches) which didn't rev much over 1,000 r.p.m. and made between 70 to 100 horsepower at the crank. The general trend over the past 120 years has been toward increased efficency, as measured by torque per cube (h.p. merely being a measure of torque output over time) and reductions in fuel consumption.

[The Outsider]

Reher-Morrison has a different view.......

http://www.rehermorrison.com/blog/?p=220

Of course they've probably got different goals, too.

[squirrel]

Reher-Morrison has a different view.......

http://www.rehermorrison.com/blog/?p=220

"My subject is racing engines, not street motors"

I guess if you're racing, then you have to do what it takes to win that class.

I'm with Bob, I can't afford high RPM