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Engine/motor geeks.. Question..

#21
FREAKYSTLYEY said:
Rememguys I was really speaking if theoretically not actual motors.

But this far I learned..

Longer stroke same displacement = torque LOW REV
Shorter stroke same displacement HP HIGH REV
Click to expand...

Torque is what you feel when you step on the gas pedal, Horsepower is simply a measure of torque over time. High revs are great for a given application, in most cases it's not the hot setup for a street car.

An engine like a v6 that has 6 combinations per revolution will have more power than a 4 cyl with same displacements.
Click to expand...

In theory yes, in reality maybe not. Compression ratio, cam profile, head design can change an engines power output. To put it simply, there are many 4 cylinder engines out there that could spank V6's.
 
#22
hbarcat said:
Tru dat.

The most naturally balanced engine configuration is an inline six (also a horizonatally opposed, or flat, six).

Among the worst is a 90 degree V-6.
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A 90 degree V6 is a funny animal, you're trying to fire a hole every 60 degrees of rotation. Think back to the odd and even fire 231 Buick V6 and the early Chevy V6's that shook like a dog crapping a razor blade. It wasn't until they added a balance shaft that those things ran somewhat smooth.
 
#23
FREAKYSTLYEY said:
I'm pretty knowledgeable a out engines and the such but I cant for the life of me figure this out.

Why does an inline 4 on a sport bike rev higher and make has it's power higher up than a v or parallel twin. BUT a inline rev revs higher than a v6 and that revs higher than a v8.

Please help me
Understand.
Click to expand...
+
FREAKYSTLYEY said:
Rememguys I was really speaking if theoretically not actual motors.

But this far I learned..

Longer stroke same displacement = torque LOW REV
Shorter stroke same displacement HP HIGH REV

An engine like a v6 that has 6 combinations per revolution will have more power than a 4 cyl with same displacements.
Click to expand...
No, a V6 does not have 6 combinations per revolution.

There are four strokes going on at the same time in a 4-stroke engine for each revolution of the crank.
One piston starts at top dead center and when the crank is performing its first stroke, that piston is drawing in air and fuel into the cylinder. In the cylinder head, the intake valves are open and the exhaust valves are closed.
At the same time, another piston starts at the bottom of its stroke and already has fuel and air in the cylinder. When the crank is rotating, this piston is going up and compressing the fuel/air mixture. Both the intake and exhaust valves are closed.
At the same time, another piston starting from the top of the cylinder has completed compressing the fuel/air mixture and the spark plug fires off. The intake and exhaust valves are closed in this cylinder. The expanding explosion pushes the piston down.
At the same time, another piston starting from the bottom of its stroke is full of mostly burnt gas. The exhaust valves open and the intake valves stay closed. When the piston moves up, it pushes out the exhaust gases.

In a V8 or flat 8, two pistons are performing one of the above actions simultaneously. Opposing actions keep the engine relatively balanced.
In an inline 5, two of the five pistons work at the same time. In an inline 6 or V6, two of the six pistons work at the same time, In a V12, four of the 12 pistons work simultaneously while the other 8 of the 12 pistons work in 2 piston pairs. To offset vibrations in engines that do not have 4, 8, or 16 pistons, the crank is counter balanced with weights molded into the crank.
On top of all this, the exhaust valves actually start opening before the piston his bottom dead center in the power stroke. and the intake valves actually start opening before the piston hits top dead center in the exhaust stroke. So during those strokes, the intake and exhaust valve are both open. But, the flow of gases keeps exhaust gases going in the exhaust direction instead of back out the intake manifold. So, very high revving engines, actually push out exhaust gases with unburnt fuel. This is why you may see fire coming out of the exhaust pipe of a race car or drag racing car ;) ... The fuel ignites on its way out. There is nothing eco-friendly about drag racing.

Don't ask about Wankel rotary engines. :rolleyes: Very high revs are attainable.
 
#24
A lot has been covered, but yes, RPM is mainly about size and weight of components and the natural design of the engine. Another thing to take into account is the intended purpose of the engine. Yes, a 600cc 4 cylinder bike motor can rev to 15k+ RPM and put out 150+ hp, but it is only expected to last maybe 50,000 miles. If your car engine needed rebuilding at 50k, I don't think you'd be very happy about it. Hence why in order to get the same power out of a street car you need at least 1.4 liters and likely a turbo.

This is also how Formula 1 can get 750+ hp out of a 2.4 liter V8 that spins 18,000 RPM, or NASCAR gets 900 hp out of a 5.8 liter V8 that spins 10,000 RPM. They're designed to last only a few thousand kilometers at the most. (good read on the subject of those engines here if interested: http://www.epi-eng.com/piston_engine_technology/comparison_of_cup_to_f1.htm )

Theres also a lot more that goes into the theory behind the engines, but I'd have to sort through the thread a lot more to try to figure out what has been said and what hasn't.

(and as a quick aside on the post directly above mine while I'm posting this... The fire coming out of Top Fuel drag cars when they run isn't really due to the RPM, its the fuel. Where gasoline burns at a stoichiometric ratio of roughly 14.7 grams of air to 1 gram of fuel, Nitromethane burns at roughly 1.7:1. This means that the best way to run an engine on Nitro is to simply throw as much fuel at the engine as possible with as much spark as possible, and whatever the engine doesn't burn it spits out the exhaust. If you ran a normal engine like this it would just die. Nitro fuel systems don't have injectors or carburetors at all, simply ports where fuel flows at high pressure from the end of the hose.)
 
#28
I have a 2006 VW GTI with a 2.0 liter inline 4 Turbocharged engine that after tweaking the software and doing some mods put out 289 Hp and 321 ft lbs of torque to the wheels at 5800 rpm.

I think what influences displacement/power ratio the most is components used and combustion chamber design, plus being able to manipulate timing,fueling and boost can dramatically increase power output.
 
#29
Mike N said:
I'm old, I have no idea what a 4G63 is. Sounds like something Verizon offers on a cell phone.
Click to expand...
Mitsubishi engine code for the inline-4 engine used in Mitstubishi Eclipses and Eagle Talons. Those in the import sport compact car/tuner scene like to throw around engine code and body code names rather making references to the car model name.
 
#30
Ripper said:
...(and as a quick aside on the post directly above mine while I'm posting this... The fire coming out of Top Fuel drag cars when they run isn't really due to the RPM, its the fuel. Where gasoline burns at a stoichiometric ratio of roughly 14.7 grams of air to 1 gram of fuel, Nitromethane burns at roughly 1.7:1. This means that the best way to run an engine on Nitro is to simply throw as much fuel at the engine as possible with as much spark as possible, and whatever the engine doesn't burn it spits out the exhaust. If you ran a normal engine like this it would just die. Nitro fuel systems don't have injectors or carburetors at all, simply ports where fuel flows at high pressure from the end of the hose.)
Click to expand...
Fire coming out of the exhaust is related to what RPMs the engine is running at. At lower RPMs, the engine will take in less fuel/air into the cylinders and will not likely have unspent fuel getting put in the exhaust gases such as to ignite. Le Mans and Formula 1 among some race cars won't get flames coming out the exhaust unless they are running near redline.
Various drag cars will put on a fire show at mid to high RPMs but will not at idle.
 
#31
Mike N said:
4 cylinders or V8's tend to be well balanced naturally, a 90 degree V6 is not.
Click to expand...

That isn't really true- 4 cylinders are not that well balanced in second order vibrations (hence 2x-freq balance shaft or two), and the usual 90-degree crossplane V8s have significant end-to-end vibration (hence why the crank throws have to be so big), and 90-deg flatplane V8s have the same second order issue as inline 4s. I would not say that they are well balanced naturally at all- that would be inline-6 and V12 territory.

All of this depends on the actual bank angle, of course, but that's way more info than the OP is interested. Mike and a bunch of others have answered that well, though in reality the answer really is "....depends."
 
#32
Ripper said:
(and as a quick aside on the post directly above mine while I'm posting this... The fire coming out of Top Fuel drag cars when they run isn't really due to the RPM, its the fuel. Where gasoline burns at a stoichiometric ratio of roughly 14.7 grams of air to 1 gram of fuel, Nitromethane burns at roughly 1.7:1. This means that the best way to run an engine on Nitro is to simply throw as much fuel at the engine as possible with as much spark as possible, and whatever the engine doesn't burn it spits out the exhaust. If you ran a normal engine like this it would just die. Nitro fuel systems don't have injectors or carburetors at all, simply ports where fuel flows at high pressure from the end of the hose.)
Click to expand...


yeah, that is a common misconception about the flames.
the blower on a top fuel takes more horsepower to turn than most street driven cars have. That is because the pressure is so great the fuel mixture is on the verge of compressing into a solid. the heat in the combustion chamber is so great that the electrodes are completely burned off the spark plugs by 1/3 of the way through the pass. The engines run like a diesel, on heat and pressure until the fuel is shut off. The flames you see do have a small amount of unburned fuel, but most of what you see is very hot compressed gasses igniting the hydrogen in the atmosphere, as they expand and lose pressure and heat.
 
#34
placedesjardins said:
Mitsubishi engine code for the inline-4 engine used in Mitstubishi Eclipses and Eagle Talons. Those in the import sport compact car/tuner scene like to throw around engine code and body code names rather making references to the car model name.
Click to expand...

we like to throw around engine versions rather than car models due to the fact that we tend to not use the engines in the same cars they came from.... just like a small block isn't really used in the same cars they came out of. :P
 
#35
Angus said:
I'd like to see tech on this, because I do not believe this is accurate. The pressures are not getting anywhere near high enough to compress the nitro into a solid at those temperatures.
Click to expand...

I'll work on that tomorrow if I have time. I have the equations, but not the time right now. They're ~6.5:1 compression with up to 75 psi boost. With the amount of fuel being put in it isn't out of the question. Really just shows how volatile Nitro is.

Also, the wiki page on top fuel engines is surprisingly in depth. http://en.wikipedia.org/wiki/Top_Fuel#Top_fuel_engines
 
#36
Ripper said:
I'll work on that tomorrow if I have time. I have the equations, but not the time right now. They're ~6.5:1 compression with up to 75 psi boost. With the amount of fuel being put in it isn't out of the question. Really just shows how volatile Nitro is.

Also, the wiki page on top fuel engines is surprisingly in depth. http://en.wikipedia.org/wiki/Top_Fuel#Top_fuel_engines
Click to expand...

What equations are you referring to?

75 psi is a fair bit, but nothing insane, pressure-wise. Not sure what you mean when you say "volatile", as being especially volatile is going to make it more difficult to revert to solid phase.

I did a quick lookup of a PT phase diagram for nitro, and at 298k (which is a much lower temp than intake temp even with fuel cooling), the freezing point is at ~0.4GPa, or ~58000psi (and nitro is a stable superpressed liquid up to about 2GPa). At higher temps it would have to be even higher. Even in a slow-burning combustion scenario, the chamber pressures are not going to peak that high. I'm happy to be wrong, though, since I've never worked with nitro engines in an engineering context.

I'm curious what Lee H has to say. Nitro engines are really cool, though. :)
 
#37
Slightly off topic - but relevant in a way; did you know that all mammals, on average, have the same number of heartbeats in their lifetime? The little mouse fluttering rapidly and the whale thudding steadily will have about one and a half billion beats each if they live to their old age.
 
#38
Sneakypete said:
Slightly off topic - but relevant in a way; did you know that all mammals, on average, have the same number of heartbeats in their lifetime? The little mouse fluttering rapidly and the whale thudding steadily will have about one and a half billion beats each if they live to their old age.
Click to expand...

Not true. It was a theory proposed to explain different life expectancies among mammals (and others, actually), but there are so many exceptions and such a wide variance that's it's really nothing more than a theory.
 
#39
Well yes, but it's all in the word "about". There is undeniably a link between body size, metabolic rate and life expectancy. Anyway, I'm lucky to have low blood pressure (fainted a lot when younger) but always had a raised pulse rate - even when completely relaxed it will be at least 80bpm. If that 1.5 billion is correct I should have died 20 years ago!
 

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