Random questions about engines.

[freakazoid]

So I've been trying to figure out a few things. How do you figure out how much an engine can theoretically put out for torque, horse power and RPM. What is it that gives it those numbers? Stroke? Displacement? Through my reading I did discover that the Octane you should use is regulated by the compression ratio, that's pretty neat.
I've been trying to look it up but all I can really find is HP=RPMxTorque/5252. Ok, so how do you find torque?
Well torque=HPx5252/RPM.

[Fitz]

So I've been trying to figure out a few things. How do you figure out how much an engine can theoretically put out for torque, horse power and RPM. What is it that gives it those numbers? Stroke? Displacement? Through my reading I did discover that the Octane you should use is regulated by the compression ratio, that's pretty neat.
I've been trying to look it up but all I can really find is HP=RPMxTorque/5252. Ok, so how do you find torque?
Well torque=HPx5252/RPM.

I'm no engineer, but HP/Torque has a lot more behind it than just the displacement and stuff. Like, you get more HP by getting more fuel and air in there through mods, etc.

Paging birdman!

[BobR]

When I needed to figure out the HP and torque on my bike after a few mods, I took it and put it on a dyno. Sorry, that's probably not much help.

bob

[230RN]

Boy, that brings me back to the Power Lab in High School many years ago.  Like 1953.

Here's a start for you. 

TORQUE AND THE PRONY BRAKE

Part 1
https://www.youtube.com/watch?v=9Wi51Kf8bzA

Part 2
https://www.youtube.com/watch?v=weJhTdnlUAo

These are both kind of folksy presentations and not "slick" or "professional" but give you a sort of  hands-on look at the theory.  The actual formula for horsepower, showing the two terms for torque (force on and length of the lever arm) appear 3 minutes into Part 1.   Actual testing of the engine starts at 2:20 Part 2.

The theoretical instantaneous torque depends on the instantaneous pressure in the cylinder, the area of the piston, the angle of the connecting rod to the crank at that instant of time, and the diameter of the crank's motion among other things... and for only one cylinder in the engine. 

But all of this varies throughout the power stroke and neglects the torque "losses" required for the compression stroke, friction, runnng of the valve gear, etc., etc.  That's why it's usually an empirically-derived average value under actual running conditions using a modern dynamometer or in the past, Prony brakes (sometimes called the de Prony brake.)

Terry, 230RN

MORE ( Big ole honkin' Prony brakes attached by looong belts to old farm engines):
https://www.youtube.com/watch?v=g82Exz-CVjw

Note the big scale to measure pounds of force on the Prony torque arm and the fumes (probably steam) coming off the brake drum when they load this engine down:
https://www.youtube.com/watch?v=58E00wOzr_c

[French G.]

You don't, it's all theory until you dyno it.

[230RN]

DOUBLE POST

[birdman]

Well, its really complex, but effectively, you can start with volumetric efficiency, go from there to brake mean effective pressure, and then to torque, and get torque as a function of RPM and thus power.
But its damn complex.  I did it once before the E46 M3 was released based on what I thought the motor was built like, and hit the dyno curve to within 3-4% across the whole range over 6 months before any details were released. (Got some props on bimmer.org for that)
But that took me a day or two.

[230RN]

So did you write an app for it? 

[brimic]

Volumetric efficiency is at least as important as bore + stroke- basicly how much fuel+air mix can you stuff in a cylinder during the intake stroke- A naturally aspirated engine that has near perfect exhaust scavenging, an intake manifold with runners of the correct dimensions for the desired rpm range, and heads that are carefully matched and polished can approach or sometimes exceed 100% volumetric efficiency- a turbo can nearly double that number. That's why a 2L 4 cyl turbo can put up numbers that are close to a 5L V8.

Fuel to air mix- There are a lot of interactions going on with this- the fuel is sprayed into an air stream, some is atomized, some condenses on the inside of the intake runner/heads, while some is evaporating off the surface of the intake runners/ heads. The better you can control the exact fuel mixture by the geometry of the combustion chamber/piston face as well as through the control of the fuel injection system, the more power you will create.

You don't, it's all theory until you dyno it.

That right there.

[birdman]

Volumetric efficiency is at least as important as bore + stroke- basicly how much fuel+air mix can you stuff in a cylinder during the intake stroke- A naturally aspirated engine that has near perfect exhaust scavenging, an intake manifold with runners of the correct dimensions for the desired rpm range, and heads that are carefully matched and polished can approach or sometimes exceed 100% volumetric efficiency- a turbo can nearly double that number. That's why a 2L 4 cyl turbo can put up numbers that are close to a 5L V8.

Fuel to air mix- There are a lot of interactions going on with this- the fuel is sprayed into an air stream, some is atomized, some condenses on the inside of the intake runner/heads, while some is evaporating off the surface of the intake runners/ heads. The better you can control the exact fuel mixture by the geometry of the combustion chamber/piston face as well as through the control of the fuel injection system, the more power you will create.

That right there.

Actually, quite a few engines can exceed a VE of 100%, in many cases! by substantial margins.
Fun experiment:
Assume air at STP
Assume maximum power AFR

Look at the highest non-turbocharged peak torque/displacement engines out there (peak torque RPM = peak VE)
Calculate power at that point and determine what overall airflow needed to be.
Bet you will find quite a few that are in the 110-120% range

Hints:
458 Italian speciale makes 120N-m/liter
E46 M3 makes 110 N-m/liter
2L S2000 makes 110 N-m/liter

Also, those engines (plus the ferrari 430 and other ferrari NA V-8s, the porsche Carrera GT v-10, and a couple other choice ones) are also the highest HP/liter commercial cars out there

All the improvements in NA engine "power" (variable intake runners, variable cams, eliminating throttle plates, variable exhausts, are all to maximize VE and broaden the peak.

[birdman]

Volumetric efficiency is at least as important as bore + stroke- basicly how much fuel+air mix can you stuff in a cylinder during the intake stroke- A naturally aspirated engine that has near perfect exhaust scavenging, an intake manifold with runners of the correct dimensions for the desired rpm range, and heads that are carefully matched and polished can approach or sometimes exceed 100% volumetric efficiency- a turbo can nearly double that number. That's why a 2L 4 cyl turbo can put up numbers that are close to a 5L V8.

Fuel to air mix- There are a lot of interactions going on with this- the fuel is sprayed into an air stream, some is atomized, some condenses on the inside of the intake runner/heads, while some is evaporating off the surface of the intake runners/ heads. The better you can control the exact fuel mixture by the geometry of the combustion chamber/piston face as well as through the control of the fuel injection system, the more power you will create.

That right there.

Only double?  LOL.
I've run 21+ psi of boost on the street, even accounting for IC losses, its well in excess of 200% atmospheric VE.  And on race gas, far far more.

Example: Alpha-omega GTR--nearly 2000hp out of 3.8-4L, compared to 400-500 for a NA equivalent, or a VE of >400% (not surprising, given nearly 35-40+psi of boost).

What is really fun is when the turbo is sized right, and the exhaust is just right and you can get intake pressure > exhaust back pressure over a big segment of the exhaust stroke, and end up with a massive increase in VE, as it becomes self scavanging.

[brimic]

Only double?  LOL.
I've run 21+ psi of boost on the street, even accounting for IC losses, its well in excess of 200% atmospheric VE.  And on race gas, far far more.

Example: Alpha-omega GTR--nearly 2000hp out of 3.8-4L, compared to 400-500 for a NA equivalent, or a VE of >400% (not surprising, given nearly 35-40+psi of boost).

What is really fun is when the turbo is sized right, and the exhaust is just right and you can get intake pressure > exhaust back pressure over a big segment of the exhaust stroke, and end up with a massive increase in VE, as it becomes self scavanging.

Neat!

[Brad Johnson]

Back to the OP...

Torque is the amount of force being measured, in this case expressed in units of lb/ft.  One ft-lb of torque would be the twisting force applied to a fastener if a one lb weight were hung on the handle of a one foot wrench.  Horsepower is a calculation, force applied over time.  Thisis why you see a lot of small, low torque engines making a butt-ton of HP.  Move the torque peak higher in the RPM range and the HP will go up even thought the measured torque never changes.

 Torque output per unit of fuel is dependent on so many factors as to be unestimable on a SWAG basis.  Throw in that power increase claims for aftermarket parts or mods are not a one-to-one "add it up" process.  Best thing for the newb is to find a good internet forum dedicated to your brand/model of bike.  Someone there will likely have done the mods you're attempting and can give you an idea of the result.

Engines are magnificently intriguing. That they work at all is amazing.  The fact that they do it so well, and for so long, is astonishing.

Brad

[birdman]

Also, never, never, never, is exhaust back pressure a good thing.
So many people state incorrectly that a smaller exhaust (which has higher back pressure) "increases" torque.
No, what actually happens is a smaller exhaust DECREASES back pressure at lower flow rates by its volume being more tuned to that flow rate/exhaust pulse frequency, and this also manifests as being off-tune at other RPM.  So people correlate increased back pressure (at high rpm/flow) with increased torque, when in fact, the best is zero or negative back pressure at any point.
Since fixed exhausts can have a limited number of resonances, typically, when it matters, designers will try to stack these in the power band, or have an exhaust with a broad resonance, but no anti-resonance features where it matters.

This matters the most on engines that require scavenging (2-strokes) where a tuned exhaust results in a negative pressure pulse hitting the exhaust port just as it opens, resulting in the same effect as the turbo situation I described above, where intake pressure is greater than exhaust pressure, even if the intake is at atmospheric.  This is called " on the pipe", and is the reason why two strokes have intricately designed expansion chamber exhausts, typically followed by small diameter, high velocity outlets.
The same goes on the intake (for 4-strokes)...when the intake valve is open, and the piston descending, the air is flowing into the cylinder at high velocity, which carries some ram pressure.  As the piston starts to rise, a positive pressure pulse starts propogating upward in the cylinder.  The key is to close the intake valve right before this pulse hits it, to trap more air in the cylinder than its displacement.
Same for the intake tract.
Combine all of these things and you can pack way more air into a cylinder than its BDC volume :)

One of the limits is how fast you can open and close valves--as the opening and closing times cut down on flow. In conventional valve trains, this is limited on opening by force to push against the spring, and on closing by how fast the spring can return the valve.  One of the reasons Ducati tends to get relatively insane torque/HP figures from its engines (in its twins, for example) is the Desmond system dispenses with springs, so the opening has virtually no resistance other than the inertia of the valve and lifter, and the valve is closed by the closing rocker, mechanically, which is why Ducati cams are closer to offset circles rather than ovoid patterns, their opening and closing rates are insane relative to conventional cams.
The price is complexity of course.

[RoadKingLarry]

When it comes to hotrods and high performance bikes the formula is HP=$$$.
There is a direct relationship. More $$$ = more HP.

[birdman]

When it comes to hotrods and high performance bikes the formula is HP=$$$.
There is a direct relationship. More $$$ = more HP.

Or along the lines of "no replacement for displacement"

"All speed costs is money, how fast do you want to go"

Or
"Displacement is measured in cubic inches, horsepower is measured in cubic dollars"

[charby]

Or along the lines of "no replacement for displacement"

"All speed costs is money, how fast do you want to go"

Or
"Displacement is measured in cubic inches, horsepower is measured in cubic dollars"

No kidding, even with the small engine crowd, it takes a lot of cash to increase the HP and Torque.

Like go-carts or lawn tractor pulling tractors.

[bedlamite]

There's way more to it than can be covered in a forum post. Here's a decent book on the subject:

http://www.amazon.com/Four-Stroke-Performance-Tuning-Graham-Bell/dp/0857331256

"All speed costs is money, how fast do you want to go"

I always heard it as "Speed costs money, how fast can you afford?"

[freakazoid]

Interesting stuff. Might need to check out that book. Found this site, http://www.epi-eng.com/piston_engine_technology/engine_technology_contents.htm which has a lot of useful information, even has a reference section of books that I'll also have to check out.

[BobR]

Amen to the More HP = $$$$$$$

This is what I have;



This is what I would love to have;



And for a mere 6K, it can be mine, all mine (+shipping across the country and back).

For 4400 dollars I can get 210hp.

So 4400 for 210hp, and for a mere 30 more hp it is another 1600 dollars.

I think I could be happy at 210. But he is working on a naturally aspirated 280hp version. Wonder what that will cost. 

bob

[drewtam]

So I've been trying to figure out a few things. How do you figure out how much an engine can theoretically put out for torque, horse power and RPM. What is it that gives it those numbers? Stroke? Displacement? Through my reading I did discover that the Octane you should use is regulated by the compression ratio, that's pretty neat.
I've been trying to look it up but all I can really find is HP=RPMxTorque/5252. Ok, so how do you find torque?
Well torque=HPx5252/RPM.

I do performance research & development on diesel engines as a MechE.

Torque is best measured by a steady state dyno. The engine spins, the dyno resists that torque (water brake, eddy current, electric motor, etc). That resistance pushes against a load cell (which is calibrated regularly using traceable standards.) The load cell puts out an electric signal is recorded by a computer.

Torque = Force x Lever arm distance

Force is measured by the load cell - electric signal.
Lever arm distance is a measured constant.

Power = Torque x Rotational velocity

Torque is calculated from the above.
Rotation velocity is engine speed converted to proper units. This is also measured.
Now you have the measure of engine power.

The next question is much more difficult. The power of an engine is dependent on 1 - how much fuel it can consume, 2 - the energy content of the fuel, and 3 - how efficiently is converts that chemical/heat energy into mechanical energy.

1 - depends on what kind of engine. Gasoline runs close to stoichimetric, diesel runs very lean. In either case, these engines are generally limited by available air for combustion.
So for the same displacement, a diesel will run less fuel. A turbo can increase the airflow. Displacement increases the airflow. Improved head, port, and manifold flows will improve volumetric efficiency and thus a little bit of air and decrease pumping losses. Increased engine speed will increase airflow (but has the side affect of increased friction power).

2 - Except for multi-fuel engines this is pretty consistent. Be careful that energy by mass and energy by volume can be very different. Hydrogen has best energy/mass and worst energy/volume. Diesel has very good energy/volume but lower energy/mass.

3 - Injection timing, ignition timing, compression ratio, pumping losses, engine friction, heat rejection characteristics, etc interact to affect this last and essential parameter. Typical high speed diesel thermal efficiency peaks at ~42%. Gasoline peaks ~38%. Gas turbines peak ~35%. Of course it all depends on engine size and design details. For all engines, the thermal efficiency goes to 0% as it goes to idle.

[birdman]

Bob, what bike?

Mine did 160hp/73ft-lbs
(Note, that dyno reads lower than usual, superbike store ran the same config and got 174 on theirs)
NA, just a LEO full system and full bazzaz.
CBR1000RR

[BobR]

It's a Rocket 3 Touring. It has a tractor engine. Three cylinder with a displacement of 2300CCs. Each cylinder displaces over 700CCs. The Roadster makes closer to 145hp, the Touring came from the factory pretty restricted. So far I have only done aftermarket slip-ons and a new MAP in the ECU.    

How they are made.

http://www.youtube.com/watch?v=HKEuzxC4eGc


I have a distant relative to the CBR1000RR, I have a 1988 CBR1000F hanging out in the shed.

bob

[birdman]

It's a Rocket 3 Touring. It has a tractor engine. Three cylinder with a displacement of 2300CCs. Each cylinder displaces over 700CCs. The Roadster makes closer to 145hp, the Touring came from the factory pretty restricted. So far I have only done aftermarket slip-ons and a new MAP in the ECU.    

How they are made.

http://www.youtube.com/watch?v=HKEuzxC4eGc


I have a distant relative to the CBR1000RR, I have a 1988 CBR1000F hanging out in the shed.

bob

I remember reading about that triumph when it first came out. 
What kind of revs does it do?  Like 6-7k?

[BobR]

I remember reading about that triumph when it first came out. 
What kind of revs does it do?  Like 6-7k?

I believe it has a rev limiter set at 5800rpm from the factory in 1-4, 5th has a fuel shutoff that starts to kick in @ about 6000 so you don't get the abrupt shutdown. The MAP I loaded into my ECU runs the revs out to 6300 before hitting the rev limiter. It gets there PDQ in 1st and 2nd.

bob