No Replacement for Displacement

[RobDET]

right... but acceleration is greater when torque is the same... that was my point... I'm speaking of the same motor in the same gear... the only variable in the S2k is RPM (torque changes but not mutch) Gearing is a factor but it doesn't have to be. If you ignore gearing the motor can still accelerate the car faster at 8K then it can at 5K even tho torque is pretty mutch the same... This is what you just said i think and what i ment by my previous post...

[s13sr20chris]

no that is one of those logic fowls... Because acceleration changes when horsepower stays the same does not mean that acceleration stays the same as HP changes...

The maximum torque is most motors happens before the 5,### rpm cross but some motors are still able to accelerate mutch harder past 5k Scope out the S2000 Dyno sheet forinstance... the torque curve on that car is flat as a pancake (except for the slight jump at vtec) but it is the most obvious case where torque doesn't really increase but acceeration does... BIG TIME

i guess we will have to agree to disagree here. i cant say that any na vtec motor seems to pull all that hard to me. that includes the s2k. i would attribute that to a lack of torque. yes, you can feel it pull harder after vtec but it is decieving because the torque curve is so flat. same prob with 350z. the car is fast for the money, but it does not feel all that fast. it has lots more torque than the s2k, but the curve is so flat. compare that to an old 300zx twin turbo. you can feel the torque curve as the boost builds and that feeling of power building up is just as decieving. it makes you feel faster that you are. the s2k is a fast car as are the old tt and the new 350z, but a different feel to them all and i think a lot of that is the different torque curve. the 350z torque curve is similar to the s2k, just a whole lot more at all times:). s2k has lower gearing and a higher redline to compensate. after this many times around the mullberry bush i dont know that we will ever agree on this subject. oh well, its fun to talk about anyway:ylsuper

[Nismo_Freak]

But engine specific volume is not a measure of efficiency.

Outputing X amount of power w/ X amount of displacement is a DIRECT measure of thermal efficiency. The engine is using more of the heat and pressure created to produce power and not absorbing it or losing it due to parasitic friction or usage.

[Onizuka]

pwned

[Nismo_Freak]

No, peak torque is where you will have the fastest acceleration in a given gear. HP is a function of speed and is actually 33,000 lb-ft per minute. So what this means is that even with less torque, at a higher RPM you can be doing more work than having more torque at a lower RPM. I can't think of a simple way of explaining this and proving it. But I can think of an easy to understand example that disproves that peak HP is where peak Acceleration occurs.

You've already agreed that torque multiplies through lower gearing. so lets say for a given motor we make 150 lb-ft of torque at 6000 RPM. With a 1:1 gear ratio, you'ld get 150 lb-ft of torque at the wheels. So the HP would be the same at the crank and at the wheel(leaving drivetrain losses out). This would net 171 HP. Lets cut the gear in half(2:1). So now we have 300 lb-ft of torque at 3000 RPM at the wheels. You have double the torque, but if you plug in the 300 lb-ft at 3000 RPM into the HP equation, you still get 171 HP. Lets take it a step further and cut the gear in half again(4:1). You will get 600 lb-ft of torque at 1500 RPM. Yet the HP still stays the same at 171 HP. BVut we all know and feel acceleration is faster in the lower gears. So if HP remains the same at the wheels, how can peak acceleration occur at Peak HP. In short, it doesn't. Peak accelration will always occur when the most torque is put to the ground. And for a given gear, besically where peak torque occurs in the motor itself.

1 HP is the ability to move 550lbs., 1 ft. in 1 sec. ... Horsepower is a measurement of POWER, that explains the amount of power exerted over a given time.

Torque is a measurement of rotational FORCE, not MOVEMENT. In fact torque is only calculated with delta horizontal distance (the angle following combustion in relation to center created by the center of the crank journal) in an engine.

[Nismo_Freak]

Outputing X amount of power w/ X amount of displacement is a DIRECT measure of thermal efficiency. The engine is using more of the heat and pressure created to produce power and not absorbing it or losing it due to parasitic friction or usage.

However... you may be talking about BSFC which is Brake Specific Fuel Consumption which we all know the rotary engine is known to be poor at. Which is another way of expressing engine efficiency.

But, the manner of producing power is directly in proportion to the displacement in determining efficiency because of the nature of thermodynamics. Go ahead and try to argue that the stroke has no bearing in efficiency... cause I got the answer to that too.

[MrFox]

Outputing X amount of power w/ X amount of displacement is a DIRECT measure of thermal efficiency. The engine is using more of the heat and pressure created to produce power and not absorbing it or losing it due to parasitic friction or usage.

Power/Displacement ratio is mostly useless, unless you are trying to compete in displacement restricted classes. Its pretty much just a measure of how high an engine can rev. Power to weight is much more significant. You can argue that lower displacement engines generally weight less, but this is not always the case.

BMEP (Brake mean effective pressure) would be a better measure for thermal efficiency.

Rotaries might kick a$$ when it comes to power to volume, but try to calculate the BMEP for the 13B. It should be pretty much on par (I'm betting its slightly worse) than comparable turbo motors.

P.S. No need to make arguements to get a discussion going (re stroke/efficiency... I'm interested to know.

[Nismo_Freak]

I get...

BMEP = 194.44 (388.88) for the R26B making 700hp @ 9000 rpm. BMEP = 437.5 for a RB26 making 700hp @ 8000 rpm. BMEP = 253.90 for a JUN B16A2 producing 250hp @ 8000 rpm.

Since the R26B is essentially a 2-stroke engine you double the BMEP to get 388.88.

Now of course a naturally aspirated engine of the same displacement is gonna have a lower BMEP, thats because of it's lower VE as well. But you CANNOT deny the engine is not efficient ... add boost to the R26B and you'll have BMEP #s off the charts. Now compair the BMEP to the n/a B16... it's roughly 50% more!

To get the same BMEP as the R26B the B16 engine would have to produce 383 hp! ... which is insane.. and has never been done without boost.

[Spoolinz31SS]

Ok lets not get this topic going to 135 replys like the other car clubs are Doing....

[Nismo_Freak]

P.S. No need to make arguements to get a discussion going (re stroke/efficiency... I'm interested to know.

The longer the stroke the farther the piston is drawn down the cylinder both on the intake and exhaust side. This helps to improve low end efficiency due to the longer time the valves can be open on the intake side. Another aspect is that the increased stroke allows the engine to have a longer power stroke following combustion. It also means you amplify your torque to a larger degree because of the resulting delta rod angle.

It's simply why the KA has a strong midrange power potential, due to it's 96mm stroke. It alows the engine to be more efficient at specific RPMs. The same can be said for shorter strokes role in increasing RPMs... not exactly a more direct role in efficiency the longer stroke plays but it likewise allows the engine to rev higher due to lesser piston speeds and bearing loads.

[Nismo_Freak]

Ok lets not get this topic going to 135 replys like the other car clubs are Doing....

:pface

Dookiehead! ... we are having a good debate!

[Onizuka]

nothing wrong with a healthy technical debate!

[MrFox]

Since the R26B is essentially a 2-stroke engine you double the BMEP to get 388.88.

You can't do this. Its 194psi.

The x2 factor in 2-stroke is added only because it takes half the mean effective pressure in a 2-stroke to produce the same power output as a 4 stroke. The x2 is only added in parenthesis, and should not be expressed as a product.

There is nothing magical that can make a rotary have almost twice the mean effective pressure when compared to a normal recip engine. They are both 4-stroke engines operating on the exact same otto cycle principle. If they operate on the same fuel and similar compressions, they will achieve similar combustion pressures.

Rotaries actually have very poor thermal efficiency. The shape of the combustion chamber is long and narrow, resulting in large heat transfer losses from surface area quenching and poor flame propragation. This is reflected in your comparsion: 254psi for the B16A2, vs only 194psi for the R26B.

Rotaries do make up for this with excellent power to weight ratios, however.

EDIT:For a comparasion of BMEP in slightly less insane engines:

N/AF20C: 240 @ 8300 RPM: 188psiKA24DE: 155 @ 5600 RPM : 150psiRenesis: 238 @ 8500 RPM : 140psi

Turbo:13B-REW: 255 @ 7000 RPM: 182psiSR20DET: 202 @ 6000 RPM: 218psiRB26DETT: 280 @ 6800 RPM: 206psi

[Nismo_Freak]

You can't do this. Its 194psi.

The x2 factor in 2-stroke is added only because it takes half the mean effective pressure in a 2-stroke to produce the same power output as a 4 stroke. The x2 is only added in parenthesis, and never expressed as a product.

There is nothing magical that makes a rotary have twice the thermal efficiency when compared to a normal recip engine. They are both 4-stroke engines operating on the exact same otto cycle principle. Since they operate on the same fuel and similar compression, they will achieve similar combustion pressures.

Rotaries actually have very poor thermal efficiency. The shape of the combustion chamber is long and narrow, resulting in large heat transfer losses from surface area quenching and poor flame propragation. They do make up for this, however, with excellent power to weight ratios.

I think the rotary operates more like a 2-stroke than a four...1. It has no valves2. It fires once every revolution3. You can turn a rotary engine upside down and mechanically it would still work in the same harmonics. A piston engine would not.

The fact that it does fire once every revolution is the reason you double the BMEP. Since it's mechanical operation is more efficient by producing 2 power "strokes" per 1 piston engine power stroke.

You even give the 4th example of why the rotary is a 2-stroke.. it's power to weight ratio.

In the end the rotary engine is effective in producing power per revolution in relation to the SAE displacement... hence why I believe it is highly efficient. I don't think you'll find anyone who will argue that the 787B's engine is not efficient... you'll be hard pressed to find someone who thinks a B18C engine isn't efficient.

IMO, turbo engines are a whole different ballgame in efficiency. You can't really compare a turbocharged engine to a naturally aspirated one, the turbo engine's VE's are gonna be through the roof if it's got any serious power. Forcing an engine to breathe and making one breathe are two different games.

Try making 700hp w/ a 2.6L engine ...

[MrFox]

The fact that it does fire once every revolution is the reason you double the BMEP. Since it's mechanical operation is more efficient by producing 2 power "strokes" per 1 piston engine power stroke.

MEP = (P*n)/(V*N)

where:P = powern = # of output shaft revolution per power stroke per combustion chamberV = displacementN = RPM

Even though n=1 for both rotaries and 2-strokes, there is no justification for a x2 multiplier to be applied to the rotary. It may share a lot of similar characteristics with a 2-stroke, but a rotary engine does operate on the 4-stroke cycle: Intake, compression, power, exhaust... its all there.

I can agree that a rotary is mechanically more simple than a reciprocating piston engine. But they simply cannot compete from a thermal efficiency standpoint (how efficiently it converts the fuel's chemical energy into motion)

For turbo vs N/A, see my previous post for addtional comparasions between normal and turbo induction engines.

[Nismo_Freak]

Well... it's thermal efficiency thus sucks... but it still fires 2 times, and has 3 moving parts... so it's mechanical efficiency is king!

[MrFox]

The longer the stroke the farther the piston is drawn down the cylinder both on the intake and exhaust side. This helps to improve low end efficiency due to the longer time the valves can be open on the intake side. Another aspect is that the increased stroke allows the engine to have a longer power stroke following combustion. It also means you amplify your torque to a larger degree because of the resulting delta rod angle.

Long stroke engines are torquey, and operations at low RPM minimizes frictional and windage losses, improving efficiency. But the stroke length of an engine of given bore and displacement is limited by its compression ratio. Atkinson/Miller cycle engines uses a long throw crank, a supercharger, and delay intake valve closing to produce an engine with a very long power stroke and good efficiency.

[MrFox]

An argument FOR large displacement engines:

Generally, the thermal efficiency of an engine will increase with an increase in cylinder displacement. This is because a large volume to surface-area ratio will reduce the amount of heat loss during combustion, allowing the max amount of energy to be converted into cylinder pressure. Hence - engines like the "OMG straight 10" and Porsche 968 are born.

[RobDET]

:alcoholic :alcoholic :alcoholic :puke :puke :puke

If you don't think hondas "feel that fast" you need to ride in a better one... There are some that are that fast and ALL of the NA Vtec motors increase their pull a LOT as RPM increase...

If you say that hondas don't feel fast that sounds kinda like misplaced hate to me... but i've had one hell of an evening so i'm not sure...

[s13sr20chris]

Power/Displacement ratio is mostly useless, unless you are trying to compete in displacement restricted classes. Its pretty much just a measure of how high an engine can rev.

cha ching!

BMEP (Brake mean effective pressure) would be a better measure for thermal efficiency.

ba da bing!

P.S. No need to make arguements to get a discussion going (re stroke/efficiency... I'm interested to know.

he is most definately hot tonight

[s13sr20chris]

The longer the stroke the farther the piston is drawn down the cylinder both on the intake and exhaust side. This helps to improve low end efficiency due to the longer time the valves can be open on the intake side. Another aspect is that the increased stroke allows the engine to have a longer power stroke following combustion. It also means you amplify your torque to a larger degree because of the resulting delta rod angle.

It's simply why the KA has a strong midrange power potential, due to it's 96mm stroke. It alows the engine to be more efficient at specific RPMs. The same can be said for shorter strokes role in increasing RPMs... not exactly a more direct role in efficiency the longer stroke plays but it likewise allows the engine to rev higher due to lesser piston speeds and bearing loads.

you most definately know your stuff bro so im not gonna do one of these

:bsflag

but i come from a different school of thoughtthe valves will not be open longer because rpm is rpm. the open time will not change "at a specific rpm"(i dont know if you are intent on specific rpm or not). what changes is piston speed. the higher piston speed actually causes higher pumping losses by causing the initial vacuum to be higher(more negative). also according to my school of thought the power stroke is not longer(in time that is) at a specific rpm, but the piston speed is higher. this results in less pressure exerted on the piston and more wasted trying to keep up with the piston.

none of this is an effort to contradict you; only something to consider as it comes from the mouth of an uneducated bufoon.

[s13sr20chris]

You can't do this. Its 194psi.

The x2 factor in 2-stroke is added only because it takes half the mean effective pressure in a 2-stroke to produce the same power output as a 4 stroke. The x2 is only added in parenthesis, and should not be expressed as a product.

There is nothing magical that can make a rotary have almost twice the mean effective pressure when compared to a normal recip engine. They are both 4-stroke engines operating on the exact same otto cycle principle. If they operate on the same fuel and similar compressions, they will achieve similar combustion pressures.

Rotaries actually have very poor thermal efficiency. The shape of the combustion chamber is long and narrow, resulting in large heat transfer losses from surface area quenching and poor flame propragation. This is reflected in your comparsion: 254psi for the B16A2, vs only 194psi for the R26B.

Rotaries do make up for this with excellent power to weight ratios, however.

EDIT:For a comparasion of BMEP in slightly less insane engines:

N/AF20C: 240 @ 8300 RPM: 188psiKA24DE: 155 @ 5600 RPM : 150psiRenesis: 238 @ 8500 RPM : 140psi

Turbo:13B-REW: 255 @ 7000 RPM: 182psiSR20DET: 202 @ 6000 RPM: 218psiRB26DETT: 280 @ 6800 RPM: 206psi

im afraid i have to agree with all of this. rotary engines qualify as a two stroke in my book for calculation of displacement but not for caculation of bmep. and it is a darn shame about all that surface area inside a rotary combustion chamber.

[s13sr20chris]

Well... it's thermal efficiency thus sucks... but it still fires 2 times, and has 3 moving parts... so it's mechanical efficiency is king!

no doubt. i especially like how it is a rotating design and not a reciprocating design.

[s13sr20chris]

Long stroke engines are torquey, and operations at low RPM minimizes frictional and windage losses, improving efficiency. But the stroke length of an engine of given bore and displacement is limited by its compression ratio. Atkinson/Miller cycle engines uses a long throw crank, a supercharger, and delay intake valve closing to produce an engine with a very long power stroke and good efficiency.

ok here i take issue. i think long stroke engines are tuned to be torquey because they are unable to rev high. just like a pushrod motor is tuned that way for the same reason.

[s13sr20chris]

:alcoholic :alcoholic :alcoholic :puke :puke :puke

If you don't think hondas "feel that fast" you need to ride in a better one... There are some that are that fast and ALL of the NA Vtec motors increase their pull a LOT as RPM increase...

If you say that hondas don't feel fast that sounds kinda like misplaced hate to me... but i've had one hell of an evening so i'm not sure...

i promise its not hate. i love honda like a sister(gross). but i love nissan like a wife. if that makes any sense. i just have not been impressed by the "feeling" of a honda powerband. i love the way it looks on paper and the results it produces though.

sorry about the post whoring. i am too busy to post everyday so i have to get on when i can and offend people in bulk. i also dont know how to quote multiple posts in one post of my own or else i would address everyone at once.

[RobDET]

No biggie man... if you don't like it you don't like it... But what i was saying is that torque stays the same but acceleration increases.

And as far as the undersquare = torque motor check again because that isn't always the case... There is only 1 B series honda motor that is over square and thats the B16.

Yah i get off on dispeling myths... Just because somehting is "usually" true doesn't make it fact. Mr Wizard used to have the best saying "You'r right but for the wrong reason" I think that that is VERY common in the automotive world...

where the motor makes peak horsepower has more to do with intake manifold design than anything...

[C-Kwik]

right... but acceleration is greater when torque is the same... that was my point... I'm speaking of the same motor in the same gear... the only variable in the S2k is RPM (torque changes but not mutch) Gearing is a factor but it doesn't have to be. If you ignore gearing the motor can still accelerate the car faster at 8K then it can at 5K even tho torque is pretty mutch the same... This is what you just said i think and what i ment by my previous post...

That is exactly what I am saying is NOT the case. In any given gear, If you make 150 lb-ft of torque at all RPM's, it will accelerate at the same rate in that gear at all RPMs.

[C-Kwik]

1 HP is the ability to move 550lbs., 1 ft. in 1 sec. ... Horsepower is a measurement of POWER, that explains the amount of power exerted over a given time.

Torque is a measurement of rotational FORCE, not MOVEMENT. In fact torque is only calculated with delta horizontal distance (the angle following combustion in relation to center created by the center of the crank journal) in an engine.

550 lbs x 60 seconds = 33000. No disagreements here. We are talking about the same thing.

I'm thinking you were just agreeing with me, but it seemed like a response to contradict my post.

[C-Kwik]

:alcoholic :alcoholic :alcoholic :puke :puke :puke

If you don't think hondas "feel that fast" you need to ride in a better one... There are some that are that fast and ALL of the NA Vtec motors increase their pull a LOT as RPM increase...

If you say that hondas don't feel fast that sounds kinda like misplaced hate to me... but i've had one hell of an evening so i'm not sure...

I urge you to attach a G-Tech meter to any car and watch how the G-forces change directly with torque changes you experience while going through a gear. This goes for any motor, including Honda VTEC motors. The laws of physics do not change because you have VTEC or can rev high. My guess is you've never actually felt what a sharp increase in torque feels like. VTEC will feel nothing likesharp rise in torque. VTEC motors just keep pulling almost the same until redline. And I have been in enough of them to know.

[C-Kwik]

Yah i get off on dispeling myths... Just because somehting is "usually" true doesn't make it fact. Mr Wizard used to have the best saying "You'r right but for the wrong reason" I think that that is VERY common in the automotive world...

where the motor makes peak horsepower has more to do with intake manifold design than anything...

You can't dispell fact or the laws of physics. Nor anything that is "Always" true.

Where a motor makes peak power are dependent on a lot of factors. But I'd say cams and port design will have the biggest single effect on a given motor's torque curve characteristics. The B17 VTEC motor only used a cam change. The B18 VTEC motor made an additional 10 HP over the B17 VTEC using both displacement and a staged intake runner set-up.