How can an engine LOSE torque as its RPM goes UP???

>>17526211
if the valves are closing to quickly for the engine to breathe an optimal amount, for example

>>17526211
lots of different reasons, its more common in older carborated engines though

>>17526211
Because the valves open as a fraction of each revolution. As RPM increases, the valves are still open x% of the time, but now that same airflow has to feed more and more combustion cycles. Effectively, it's running out of air.

Also, internal friction increases drastically at higher RPM. It's mainly piston/cilinder contact that causes this, because those need to have a good seal (=more friction) in order to prevent blowby.

Friction, oil pressure, valve overlap, rotating assembly balancing, etc

>>17526211
for pic related the horse power and torque numbers are not equivilant, if they were hp will always exscide torque at 5252 rpms cause math. might be why graph looks so weird

>>17526211
Volumetric efficacy drops off as air has to flow faster through the same space (valve skirt).

>>17526273
Only is stupid units.
In proper SI units
Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488

>>17526259
Pretty much this. You can also get valve float where the valves can no longer effectively open and close at those a speeds so they stay open.
Also with force inducted cars, you need to set a fuel cut at a certain point so the engine does tear itself apart and on a dyno graph it would look like a shelf.

would/does the charge velocity ever reach supersonic in an internal combustion engine

They've done their best to flatten out that torque curve over the years but they can't make it truly flat. Variable electronic ignition. Variable valve timing and cam phasers that get stuck when people don't change their oil. V-tech kicked in yo. An extreme example would be to get rid of the throttle altogether and do something like BMWs VANOS, where the valves do it all, all the time. VANOS is always kicking in yo. I guess you could throw direct injection on the pile, but I think that's more for emissions and efficiency than it is flattening the torque curve.

And that's why people love V8s over I4s - they already have a naturally flatter torque curve. You might have heard people talking about low end and midrange? They're referring to that torque curve. That's what people perceive and feel in daily driving. No replacement fer displacement.

>>17526845
Nothing good. It would create turbulence in the intake and that would lead to unwanted lean conditions and misfires.

>>17526892
i can imagine how it would be if it did.
i was thinking can something rev so fast that would be trying to induce the charge to supersonic
it seems like it would be a brick wall against the rpm if you could rev it that fast
shit i should have taken science in school

>>17526211
HP is a literal function of torque, it includes RPM and torque.

Not to mention gearing multiplies TQ,

This subject gets brought up a lot, people saying shit like HP wins races or TQ wins races.

Don't get me wrong, I have 2 v8s, one with 4.10s, the other with a blower at about 20 psi. I love torque more than anybody. But once you factor in gearing, HP is what really matters. Sure, being flatter and less peaky helps too.

So, to directly answer you. How does HP climb after torque drops? Well, think of it this way. Since HP comes directly from TQ and RPM, your torque can SLIGHTLY drop and continue to increase or hold HP? How? obviously, by increasing RPM.

At the same time, TQ has to decrease DRASTICALLY as you increase through RPM, for HP to drop. Thats basically when you're way past peak HP, and the engine isn't flowing. Whether its in the heads, cams, intake manifold or exhaust.

>inb4 muh electric motor has a completely flat torque curve, so everyone should switch to electric nao

>>17526845
Lets do the maths shall we.

Let's take an idealised engine with 500cc with a 90% VE across the entire rev range. It there for needs to fill the cylinder with 450cc of air every 4 revolutions of the engine, and to make life easy lets say the valve throat and skirt are identical in area and there are no velocity changes as the charge changes direction (this is deliberately simplified), and finally we will say the engine revs to 8000 rpm giving 2000 intake strokes per min or 0.03 seconds to fill the cylinder.

So we know the volume flow through the valve is going to be .45L/0.03s or 15L/s (or 0.015m^3/s)

The speed of sound is 340.3m/s ish giving us a flow cross sectional area of 4.41e^-5 m^2 or a valve diameter of 7.5mm.

Now piston speed therefor airflow is not constant over the stroke of an engine so the figures are all oversimplifications but I doubt you will find a 2 valve head for a 500cc cylinder anything like that small as most are ~40mm for a normal engine with a 7mm stem.

>>17526926
Flat, yes.
What you want, less so.

File: gmaxonts[1].gif (2KB, 364x234px) Image search: [Google]

2KB, 364x234px

>>17527092

>>17527086
a 4 stroke engine completes a cycle every 2 revolutions

>>17526297
>Measuring Cars in watts
Absolutely homosexual, as expected of Welcomers.
t. Eastern europoor

>>17527164
Yes, sorry, that increases the valve diameter to 10.6mm

>>17526211
As RPM increases, the time available for combustion to occur completely decreases, and as a result the sweep of crank angle which the piston is able to effectively apply torque to the crankshaft decreases.

>>17527208
so basically the pistons are moving too fast for combustion to take place properly?

b

>>17526273
Because horsepower is an imaginary number.
Torque is measurable.
Horsepower is calculated based on torque and rpm's

>>17526889
so a car with more low end torque would feel faster in typical urban/suburban traffic?

>>17531563
Yes.

>>17527946
No, it's like going fast as fuck on your bicycle in a high gear, to the point where pedaling won't make you go any faster since the pedals are rotating too fast to put force down on them with your legs.

File: C__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_1498971182739.jpg (92KB, 1920x1040px) Image search: [Google]

92KB, 1920x1040px

>>17531563
This is the quality of questions from nu/o/.

What does torque do? I'm going to have to leave this place before I loose my mind. I realize now why having a conversation here is so mind bottlingly impossible.

What does torque do. Magical times we live in. Pure enchantment.

>>17531563
No, gears exist.

>>17533903
Really bottles the mind

>>17533903
>another windows phone user

based negro

>>17527086
Cool but speed of sound is just 343 not 340.3

>>17526297
How did you derive that factor? I've always wondered about the power torque rpm relationship in si units

>>17534554
It depends on temperature at 15c (stp) it is 340.29m/s at 20c it has increased to 343.21m/s