Hp vs. Torque

[paul]

could you explain what factors effect torque/hp in an internal c engine / am i right in saying that the larger the cylinders and the longer the stroke the more torque your going to get but short quick strokes in a smaller cylinder engine would give you more hp? im i on the right track?

[Matra et Alpine]

could you explain what factors effect torque/hp in an internal c engine / am i right in saying that the larger the cylinders and the longer the stroke the more torque your going to get but short quick strokes in a smaller cylinder engine would give you more hp? im i on the right track?

nearly, a stroker longer than the bore will give more torque than power and lower revs.
a stroke shorter than bore will give less torque, more power and higher revs.

[KnifeEdge_2K1]

nearly, a stroker longer than the bore will give more torque than power and lower revs.
a stroke shorter than bore will give less torque, more power and higher revs.

just to continue onto matra's idea

the reasoning behind this is becuase with a short stroke you have higher max rpm since the pistons will be moving slower then a long stroke engine of equal displacement at the same rpm. since hp = torque * rpm/5252 the higher the rpm the higher the horsepower

explaining why a long stroke engine gives more torque at a low rpm is a bit more difficult, work = force times distance, to simplify it will be the force of the combustion cycle * the stroke, but thats work and not torque, but since the piston is only pushing down but its the con rods and the crankshaft thats creating torque this would be how i can word it in the simplest terms, its not an accurate representation or model of what's actually going on but it is good enuff

[PerfAdv]

A high torque engine is essential in accelerating a heavy load, whether it be a large SUV or tractor-trailer or bus. A large bus needs more torque than horsepower to get going. You cannot use a low torque/high Hp engine to move heavy vehicles. Ever raced a 4X4 in low range, they accelrate like crazy to about 40 mph then they run out of breath. That's all torque low Hp.

So torque is useful in launching a vehicle. Hp comes into play in propeling it faster, once the torque has done its job. Of course the lighter the vehicle the less torque is needed initially but a healthy torque curve is essential in tackling a variety of corners. Imagine coming upto a hairpin slamming on the brakes and having to accelerate out, you need torque. In a corner in which speed can be carried through torque is not essential and Hp can pull you through.

Too much torque? On a curvy mountain road or track, even with moderate acceleration if you're experiencing wheelspin. If you spend all the time limiting the wheelspin, you have too much torque. Only a car modded for the 1/4 mile would exhibit this on the road. Too much power for anything but straight-line acceleration.

Conversely having to rev to 5,000 RPM to get a decent launch means too little torque.

Verdict: A truck/work vehicle cannot do without torque a sportscar can.

[fpv_gtho]

explaining why a long stroke engine gives more torque at a low rpm is a bit more difficult, work = force times distance, to simplify it will be the force of the combustion cycle * the stroke, but thats work and not torque, but since the piston is only pushing down but its the con rods and the crankshaft thats creating torque this would be how i can word it in the simplest terms, its not an accurate representation or model of what's actually going on but it is good enuff

i explain it to people quite simply....the longer the stroke, the bigger the radius on the crankshaft, so the more leverage the piston has over its movement

[Matra et Alpine]

i explain it to people quite simply....the longer the stroke, the bigger the radius on the crankshaft, so the more leverage the piston has over its movement

I was about to reach for a drawing package to equal some of Egg-Nogs explanations, but those words are even better Simple, concise, 100% accurate. I love UCP
Good post fpv

[fpv_gtho]

And while your at it, youve just proven life goes on without the rep system

But thanks anyway, you could even go on from that to explain piston velocity to explain why shorter stroke engines rev higher, easier

[Matra et Alpine]

And while your at it, youve just proven life goes on without the rep system

hah. you know when I was reading your reply my FIRST desire was to give you rep and I think this is the kind of case it WAS good for and originally meant for -- and may be some day - - - - .
Not sure I like the idea that every second post might become a "good post fpv' type of reply

But thanks anyway, you could even go on from that to explain piston velocity to explain why shorter stroke engines rev higher, easier

I think you hust have given 80% of it

but for those listening ...
shorter stroke means that for a given partial revolution of the crank that the piston covers less distance. if it covers less ditance in the same time then it is clearlly travelling slower than a piston on a crank with a long stroke. As piston speed ( well momentum ) is the limiting factor in an engine's ability to rev then clearly the shorter stroke engine has the piston travelling slower for the same rotational speed of the crank (engine rpm).

So with piston speed being the limit, then a short stroker is doing MORE RPM than a long stroker for the same piston speed/momentum. So short strokers can rev higher ( to where the valves become the limiting factor )

[fpv_gtho]

You could infer thats why F1 engines look so low..combination of dry sump lubrication as well as a very small stroke, they rev to 19000rpm afterall (and then of course theres some designs that have a vee angle of over 100 degrees)

[Matra et Alpine]

You could infer thats why F1 engines look so low..combination of dry sump lubrication as well as a very small stroke, they rev to 19000rpm afterall (and then of course theres some designs that have a vee angle of over 100 degrees)

Can't find the reference but IIRC F1 engines are currently about 40-45mm STROKE. So to help visualise that .... make a thumbs-up sign and then BEND your thumbe, The length of the tip of your thumb is about the total movement of a piston in an F1 car. CRAZILY short.

The ITV-F1 tv show credits used to have an animatino of the Toyota F1 eninge in X-ray and it was amazing to get the tiny up-down movement in context with the size aof the bore and the engine and the car. It really is tiny.

Even with such a short stroke the piston speed is huge. At the change in direction of a piston, it and the crank and conrods are subjected to about 8000G of force !!!

[fpv_gtho]

Its some crazy stuff to think about....You would think that they'd be getting pretty close to the limit where the strokes only just long enough where there IS a stroke, and any smaller, the way the crankshaft might have to be constructed would jeopodise its strength. I havent seen an F1 crank yet so im only speculating here of course....

[paul]

ok cheers guys! i just love engines cheers for sharing your knowlage!

[kko]

ok cheers guys! i just love engines cheers for sharing your knowlage!

ditto

[paul]

Its some crazy stuff to think about....You would think that they'd be getting pretty close to the limit where the strokes only just long enough where there IS a stroke, and any smaller, the way the crankshaft might have to be constructed would jeopodise its strength. I havent seen an F1 crank yet so im only speculating here of course....

yes f1 cars are facinating things the other day i was doing the maths trying to find out how many times a f1 piston goes up and down in the cilynder in 1 second

in 1 secon the piston does 125 odd strokes at 1900 rpm

and is traveling over 700mph thats nearly the speed of sound!!!

was going to go on to work out the weight the piston would have had to carry at the end of each storke but did not know how much a piston weighed!

ps:im pretty sure this imformation is correct please correct me if i have done that maths wrong!

[KnifeEdge_2K1]

torque ratings are the ammount of torque put down per stroke, hp is a measure of power which is ammount of work done in a specific unit of time

work is force * displacement

there really isnt a simpler way to say this

you really cant differentiate hp from torque since power is a function of torque(force) and time