an elementary tech question guys

[Flatbutt1]

I follow the tech threads closely and have picked up a bunch of information. I've searched for info on torque but it doesn't appear to have been dicussed much though mentioned plenty ,yes.
I think I understand how torque and RPMs combine to develop horsepower, but what design elements of the engine develop the torque? Stroke? Bore? Combo?

thanks!

[850dunstall]

bore and stroke relationship does have an impact on development of torque, by no means a expert at this, but given a fixed volume ie cc, common ratios of bore to stroke are now in the range of 1.4-1.5 to 1, which is known as an oversquare engine,

I believe as you reduce the bore and increase the stroke you produce more torque...

stand back while i raise my umbrella and let the experts have a go at it..

[Rapid Dog]

dumbkoff! No Torque for YOU!

[shannonnunley]

Originally posted by Rapid Dog
dumbkoff! No Torque for YOU!

Rapid... are you on meds? You've been full of it the last couple of days..

buttplug

[Rapid Dog]

mmmm...shannon, we're not even going to talk about the "Show your Mistress" thread...even I wouldn't attempt interveening there...

[shannonnunley]

a little ?

[Rapid Dog]

uh...I'm not sure what you are speaking about...
that said, very little I am sure!

[Flatbutt1]

Uh, torque as a source of controversy?
Hmmm, welcome to the Prozac nation.

[Flatbutt1]

So if we increase the stroke with a longer con rod that would increase torque by increasing the distance between the wrist pin and the crank shaft? Could it be that simple in theory?

[twobmws2003]

longer stroke more torque shorter stroke less torque (higher revs). formula one engines have very short strokes small displacement rev at 18 thousand rpm make 800 hp and somewhere around 250 ft/lbs of torque and of course can run at 200 + mph. diesels (like the one on the 2 1/2 ton I drove in the army) on the other hand redline at 3000 but can pull a tree out of the ground.

basically.

[roger albert]

This is largely a mythy. In any event, it has VERY little (but not nothing) to do with Rod Length, which shouldn't be confused with Stroke. Large displacement older motors generally had long strokes. In an effort to get more power, strokes have been decreased to get decreases in piston speed. Displacement is maintained with larger bores, which further allow larger valving. The stroke=torquer / big-bore=revver is mostly an historical progression, but has much less to do with any fundemental truism, than what the materials of any given era have allowed.

Now, so as to be clear, I"m not saying there is no such correlation, but that it is by design, rather than some fundemental principal. The long stroke motors tend to have long piston cycles where most every bit of burning gas is used to push the piston down (not much overlap or advance) which certainly helps torque production, but as for long-stroke and torque, they are not synonymous.

[Len]

It's very much as roger says. You can design a short stroke high torque engine but it is easier to get high torque with a long stroke. The breathing of the engine is as important as the lenght of the lever. Just think of the de-tuned naked roadsters that the Japs turn out. These are all based on the supersports bikes engines. They have torque but have not had any change in stroke.

[brad black]

another thing is that big bores give more room for big valves and room around them. if you want lots of valve area you need a big bore to put them in. and if you're running big valves you likely want to make lots of power, so you want to rev it too. short stroke lowers piston speed at high revs, letting it rev higher before it pulls the rods apart.

so big bore engines generally have historically been high rpm/high power engines. whereas low power engines haven't needed the bore size for valve area or the short stroke for rpm, so they make good power at lower revs. and tend to be longer stroke, probably because of the myth believed by the designers.

which gives rise to the long stroke/more torque thing. essentially it's crap.

an engine of a given capacity should be able to make a given amount of torque dependant on that capacity and comp ratio at some point in the rpm range, irrelevant of bore or stroke. usually around 100 nm per litre. a 2v ducati will make it lower, as it has less valve area. a 4v one makes it higher. the watercooled 996 has more comp, so in reality it out torques the 992 cc 2v everywhere. where that maximum torque is produced depends mainly on air flow potential and cam timing. which comes back to design and intended use.

the discussion should be about maximising power production at certain rpm. and how typical designs go about that.

of course, there;s always exceptions. the original gsxr1000 was really just a stroked 750, but that didn't worry it too much.

[Nitro]

HP cannot be measured directly.

All we should care is torque, the flatter curve the better. HP should be banned, outlawed, it's evil stuff.

Anyhow,

HP = (Torque * RPM)/5252

Try it with your dyno chart.

It's torque baby we love

[Moybin]

I've seen at least one electric drag bike which uses a "10 HP" electric motor out of a fork lift. It will usually outrun any bike it's up against for several reasons. Though it weighs more due to the batteries, the electric motor produces constant torque at all RPMs, and the thing never shifts, so there is no period of time when the bike is coasting.

It's a real eye opener to most gas guzzling drag racers to have a whisper quiet, tank heavy, electric homebuilt blow their doors off.

So to support Nitro, HP is meaningless, a holdover to the 18th Century way of measuring things. It all about Torque, BABY!!!

[levert]

Hardly an elementary question.
I would think as Roger has already noted torque production is from the amount of pressure on the piston over time(stroke).
Complex issue, not being an engine designer it always appears that where you gain in one area you loose in another,much of these shortcomings have been partially solved by variable timing, exhaust system valves,modern ignitions etc.
I think some of the next big advances has to be in metallurgy, higher piston speeds, better valve springs etc.I remember when the first chrome bores came out, WOW.

What about alternatives to piston engines?

I thought at first this thread was on toques, a great Canadian invention that keeps your head warm, also a much easier topic to discuss.

[Nitro]

We need the Vulcan 2000 engine in the S! Just stratch it out to 180

[roger albert]

I got to work on an electric car (actually, a Hybrid) for a year back in college. Putting the "10HP" in quotes was writing well. That's a big advantage of Hybrids. An electric motor is rated at some constant value, but they're much better than combustion motors at making, briefly, MUCH MUCH more than rated power. Makes them great for intermittent duty such as in Hybrids, and other short duration events, such as drag races. The reason is that the e-motors have their rated outputs based on thermal limits (and some margin/safety/derating factor), rather than peak current limits. The motor has some thermal mass, and even if ran > 10X the constant current rate, will take a while (seconds or minutes) to reach the melting point of any given component (Be that conductors, or their insulation) In fact, many motors will briefly handle >100X rated current (of course, only very briefly)

An upshot of this is that electrics and hybrids show performance 'fade' over multiple back-to-back peak power runs, just as brakes fade, due to thermal/heat buildup during heavy cyling.

As for the constant torque, it's a gift, but one that requires judicious use and some added complexity. In our work, the electric motors required some relatively complex (for the time, 12 years ago) extra controls (requiring very expensive electronic motor drives, which are today commercially available and much more economical) to limit torque at low rpm. The peak torque from 0-rpm's up e-motor characteristic made it very easy to break traction. Picture taking you bike to the right rpm and throttle position to make it's torque peak, and then alternately chop/fully-open/chop/fully-open the throttle, only faster than you as a human can move, and on wet pavement. Basically, e-motors absolutely require traction control - it's not just a nicety as on combustion engines.
As with motor control in general, there are both open loop and closed loop versions. The open loop basically just factor in a slow rise rate in current no matter what the throttle has done to it (analogous to a dashpot on old carb'd vehicles) or closed loop, which look at wheelspin, normally via differential wheel acceleration rate, and then reduce drive current as needed. It was fun stuff. A lot of good SAE papers are written on this stuff.

[Moybin]

levert: your quoted question "What about alternatives to piston engines?" brings up memories of Mazda RX-4s when I was younger, and in the Pacific NW.

Those things ran huge rpms for the day, nearly 10K, maybe more. Guys would street race them against anything, and if they got the throttle/clutch combination just right, they could really skoot off the line. If they got it wrong then those rotors would slap to a stop, carbon up the plugs and be the devil to get started again. More than once all I had to do was rev my engine in neutral, nod at the stop light, pop into gear and motor away like grandma and the guy next to me would stall that rotary and be two blocks behind still trying to get running.

My point is there are a lot of alternatives to pistons, but most of them, like turbines, are more efficient on a much larger scale than is practical in a 2 or 4 wheeled vehicle. There must be several million man-years of R&D in piston engines by now, far more than anything else out there except turbines, and Chrysler proved those don't work well in cars. Too many tip and windage losses on those tiny blades, and too demanding a work load for anything like conventional materials.

So I guess we get to burn some form of fuel for a while longer.

Long live the piston revolution!

[levert]

www.ericksonmotors.com

Check this thing out.Saw one of these operate, hardly any noise and the exhaust is cool enough that the pipe is rubber.

Why something like this is not yet in cars is beyond me.I still look at the operating diagram and have a tough time figuring it out, how someone even thought of this is wild.
I'd bet there are tons of unique engine designs on the board, I just hope I live long enough to see some of them.