The march 2010 issue of sport rider states this about the new BMW S1000RR:
"With the most oversquare configuration in its class, we assumed that the BMW was going to give up a little midrange acceleration to its competition, even with the variable-length intake and various exhaust valves."
The S1000RR is 80.0 x 49.7 mm. For comparison, the CBR1000RR is around 76 x 55, the ZX10R is around 76 x 55, the GSX around 74.5 x 57.3, and the R1 checks in at 78.0 x 52.2.
so my questions are:
1) Is this comment a valid observation or is the reviewer just trying to sound like a badass, given that the differences are down in the mm range (as opposed to a huge difference, for example, between an I-4 and a V-twin)?
2) If this is a valid observation noticeable by a reasonably skilled rider, what are the mechanical specifics of what is going on in the relationship between oversquare and power distribution?
3) I noticed that the the bore and stroke has changed for some models over time, as has the compression ratio. Coincidence, direct relationship, or another element of my original question?
its super over square... 80mm to 49.7... but really hes just sounding like a badass.
typically an oversquare motor will produce more HP than torque (and be able to rev higher due to less piston velocity) and an undersquare (stroke longer than bore) will produce more torque than horsepower... but be able to rev no where near as high.
There may also be a "deeper" idea behind the engine layout - that is exactly what the new engine regulations in MotoGP say's regarding Bore X stroke !
It is widely accepted here in Europe, the FIM has chosen this layout, just to get BMW on the hook !
"Following talks between MotoGP’s governing body the FIM, series rights holder Dorna Sports and the MSMA, the Commission agreed to change the maximum engine capacity of the MotoGP class to 1000cc for the 2012 season. A limit of 4 cylinders will also be introduced, with a maximum cylinder bore measurement of 81 mm.
Mr Ippolito said: “The main changes we have decided on are new rules for the MotoGP class. We will have four cylinder engines, 4-stroke of course, with a 1000cc maximum, and the bore of the cylinders will be 81mm. This base will give all the manufacturers the opportunity to start work. At the beginning of next year we will produce the new rules in a more complete format, but that is the basis; 2012 will be the year of a new era of MotoGP.”
Mr Ezpeleta stated: “It was a very important meeting to decide the future of the MotoGP class. From 2012 the bikes will have an engine capacity of up to 1000cc, have up to four cylinders and the maximum bore will be 81mm. It’s a very important measurement because with this we can have all the characteristics of the engine. This has been approved and between now and the start of the 2010 season we will have another two meetings to define the rest of the specifications for this new class"
Let me put it this way, German motorcycle press is happy about FIM's decision as the right way to go (to allow "street engines" in MotoGP), while the Italian press sees it as a "conspiracy" against both SBK and their own favorites .
Anyway DORNA which organizes SBK is very clear in their voice around the goals with this particular engine regulations, and they think that MotoGP will profit from their success at first, trying to "steal" players from SBK to MotoGP, and by "mimic" the rules of SBK
No matter how it's put, SBK are overwhelming succesfull - while MotoGp are strugling the keep the team's in the sport...
The march 2010 issue of sport rider states this about the new BMW S1000RR:
"With the most oversquare configuration in its class, we assumed that the BMW was going to give up a little midrange acceleration to its competition, even with the variable-length intake and various exhaust valves."
The S1000RR is 80.0 x 49.7 mm. For comparison, the CBR1000RR is around 76 x 55, the ZX10R is around 76 x 55, the GSX around 74.5 x 57.3, and the R1 checks in at 78.0 x 52.2.
so my questions are:
1) Is this comment a valid observation or is the reviewer just trying to sound like a badass, given that the differences are down in the mm range (as opposed to a huge difference, for example, between an I-4 and a V-twin)?
2) If this is a valid observation noticeable by a reasonably skilled rider, what are the mechanical specifics of what is going on in the relationship between oversquare and power distribution?
3) I noticed that the the bore and stroke has changed for some models over time, as has the compression ratio. Coincidence, direct relationship, or another element of my original question?
Again, this is just because I am curious.
Thank you in advance for your time,
Jon
The best way to look at this is to try to keep it simple.
The larger the bore the more valve area you can introduce, the less quench surface area there is, and assuming the stroke is correspondingly made smaller re keeping a constant displacement - the higher your theoretical piston speed is and therefore higher RPM limit and therefore more power strokes per minute.
This is mostly peak horsepower talk so far.
Then go the other way.
Small bore, long stroke. Less power, but more torque at lower RPMs.
We'll ignore things like rod angularity as a function of cylinder dimensioning and wrist pin locations out of it, which relate to mean, average and peak piston velocities that effect the intake, cylinder, and exhaust pressure profiles, which also has a effect upon the gas flow properties over the operating range of revs/load/throttle opening.
The best way to look at this is to try to keep it simple.
The larger the bore the more valve area you can introduce, the less quench surface area there is, and assuming the stroke is correspondingly made smaller re keeping a constant displacement - the higher your theoretical piston speed is and therefore higher RPM limit and therefore more power strokes per minute.
This is mostly peak horsepower talk so far.
Then go the other way.
Small bore, long stroke. Less power, but more torque at lower RPMs.
We'll ignore things like rod angularity as a function of cylinder dimensioning and wrist pin locations out of it, which relate to mean, average and peak piston velocities that effect the intake, cylinder, and exhaust pressure profiles, which also has a effect upon the gas flow properties over the operating range of revs/load/throttle opening.
I just caught an error I made and I'm not waiting for the number of people who will surely catch it and point out the needed correction.
Re larger bore.
Quench surface area increases at and near TDC with increased bore diameter, but is more than offset by the increased valve area allowed.
Using Harley as an example, look at a VROD and a Air Cooled cylinder side by side - You'll notice how much talled the air cooled cylinders are, due to the longer stroke.
Then, think about the air cooled machines being all low end torque monsters, for the most part, they are, the tractor of the motorcycling world.
And the VROD, it's a screamer in comparison. With much shorter cylinders - due to the shorter stroke -
The best way to look at this is to try to keep it simple.
The larger the bore the more valve area you can introduce, the less quench surface area there is, and assuming the stroke is correspondingly made smaller re keeping a constant displacement - the higher your theoretical piston speed is and therefore higher RPM limit and therefore more power strokes per minute.
This is mostly peak horsepower talk so far.
Then go the other way.
Small bore, long stroke. Less power, but more torque at lower RPMs.
We'll ignore things like rod angularity as a function of cylinder dimensioning and wrist pin locations out of it, which relate to mean, average and peak piston velocities that effect the intake, cylinder, and exhaust pressure profiles, which also has a effect upon the gas flow properties over the operating range of revs/load/throttle opening.
I had to look up quench, which seems to be the area where the piston would contact the cylinder head if there was zero quench height, so how does increasing the bore reduce the quench surface area? Or is the increased valve area subtracted from the quench surface area? Fewer hot spots and better cooling due to increased flows? What? What? What? Gotst to know!
I understand the concept of the shorter stroke allowing higher rpms, and I guess even though it seems like only 5 mm between the S1000RR and the the other bikes, it's still about a 10% difference which is substantial on any scale.
It's really just an extension of the same concept as V-twins developing/showing their power at the low end when compared to the I-4, but when looking at I-4 against I-4, a significant bore/stroke difference shows itself in the midrange?
Oversquare cuts piston speed which enables higher rpm.
Long bores give higher torque as combustion/expansion is spread over a longer distance. That's all I got for now....
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I had to look up quench, which seems to be the area where the piston would contact the cylinder head if there was zero quench height, so how does increasing the bore reduce the quench surface area? Or is the increased valve area subtracted from the quench surface area? Fewer hot spots and better cooling due to increased flows? What? What? What? Gotst to know!
I understand the concept of the shorter stroke allowing higher rpms, and I guess even though it seems like only 5 mm between the S1000RR and the the other bikes, it's still about a 10% difference which is substantial on any scale.
It's really just an extension of the same concept as V-twins developing/showing their power at the low end when compared to the I-4, but when looking at I-4 against I-4, a significant bore/stroke difference shows itself in the midrange?
Quench
Quench area is all surfaces that form the combustion chamber, so that would include piston tops, head chamber surfaces and valve surfaces facing the chamber, plus every other bit exposed surface - like the cylinder wall area above the top ring and the side of the piston down to that point. (one reason why rings are placed higher on the piston on high output engines)
The ideal shape for quench is a simple sphere. A sphere offers the least amount of surface area in relation to the contained volume. But a pure sphere shape combustion chamber would not be good for valve sizing and orientation (and other things as well but we'll leave that alone) The exposed quench surface area increases heat transfer of the containing metal, heat that would otherwise be used for generating power. Large bore engines end up with a more disc/slight dome shape shaped combustion chamber, so have much larger total exposed quench area in relation to the contained volume, as result.
V Twin vs 4 (it matters not the layout of the 4, just the fact it's 4)
Assuming same total displacement.
Someone making a V twin instead of a 4, has just told you they are not looking for max bhp output, and don't mind having at least twice as many parts inside the engine. The practical layout of the twin is going to yield longer stroke than the 4. So, it won't be able to rev as high. The natural tendency of such a design is towards peak torque at a lower rpm, while also generating more torque at that RPM. Peak HP will occur at a lower RPM, and be less, all in comparison to a "typical" 4. Valve count and sizing, port sizing and lengths, fuel metering inlet area, exhaust layout, and cam timing, then come into play and are used to manipulate the RPMs where peak torque and peak hp occur, as well as what their respective amounts are.
They played with OVAL pistons some years back on a race big and put out a liminited edition rd version - V4 500 if I remember - their plan was to bypass racing rules that stated only 4 cylinders and their theory was 4 oval cylinders was giving them a cheats V8. 8 valves per oval cylinder, two conrods per piston.
Lots of effort, huge amounts of money for little result.
They played with OVAL pistons some years back on a race big and put out a liminited edition rd version - V4 500 if I remember - their plan was to bypass racing rules that stated only 4 cylinders and their theory was 4 oval cylinders was giving them a cheats V8. 8 valves per oval cylinder, two conrods per piston.
Lots of effort, huge amounts of money for little result.
What a nice read it is too !
Thanks for the link.
260 hp / litre, normally aspirated, gasoline, 30 years ago.
They called it oval, but they looked more like rectangles with nicely radiused corners. Lots of valve area.
It's too bad the oval design didn't work out, but hey, Fast Freddie still did OK when he transitioned to the 500 triple two stroke !
MCromo can you please site where you got your definition of quench from? I too always thought it was the area of the head that was not part of the combustion chamber. Wedge heads would have lotss of quench, hemis none or very little. Of coarse thiss is based off of car mags i've red decades ago.
As for why very oversquare engine are for top end power. Its more simple than what we are going into. One can look at just the short block and ignore the heads, cams,.........
There are two main stresses that govern the breaking point of an engine. Mean piston speed and break mean effective pressure (bmep). Too sate is simply, bmep is a pressure, so force/area is what creates it. We want more force (which produces the power) so we have to increase area (larger diameter pistons).
By definition bmep is power/(displacement*rpm). So another way to minimize bmep is to increase engine speed. Which is limited by mean piston speed (the other limiting stress factor). To minimize mean piston speed you increase piston area and decrease stroke.
Bringing up air cooling. Air cooled engines tend to be low end monsterss because the air cooling can only cool so much power. so the engine is power limited due to its cooling capacity. Therefore the engine designer makes his heads/cams and everything else to maximize torque within that limit of power that is available.
Thats why a 1200 form an 1198 makes 160hp and a 1200 HP2 only makes 126. Both twins, both 1200cc.
MCromo can you please site where you got your definition of quench from? I too always thought it was the area of the head that was not part of the combustion chamber. Wedge heads would have lotss of quench, hemis none or very little. Of coarse thiss is based off of car mags i've red decades ago.
As for why very oversquare engine are for top end power. Its more simple than what we are going into. One can look at just the short block and ignore the heads, cams,.........
There are two main stresses that govern the breaking point of an engine. Mean piston speed and break mean effective pressure (bmep). Too sate is simply, bmep is a pressure, so force/area is what creates it. We want more force (which produces the power) so we have to increase area (larger diameter pistons).
By definition bmep is power/(displacement*rpm). So another way to minimize bmep is to increase engine speed. Which is limited by mean piston speed (the other limiting stress factor). To minimize mean piston speed you increase piston area and decrease stroke.
Quench
My comments came from decades of interest, and there are a number of books in the basement too - but I just wrote from memory.
I will admit that most would probably say it's the zones where there is an extremely high surface area of boundry metal in relation to the contained volume. Read that as being the Squish Area. However, "quench" means "cooling", and every square mm of containment metal is part of the heat transfer area, which results in cooling, so is effectively part of the quench area.
The takeaway from all of this is that things that may cater to pure thermal efficiency, can be counterproductive in terms of valve sizing and layout, bore x stroke relationship, etc.
By definition bmep is power/(displacement*rpm). So another way to minimize bmep is to increase engine speed. Which is limited by mean piston speed (the other limiting stress factor). To minimize mean piston speed you increase piston area and decrease stroke.
The mean effective pressure is a quantity related to the operation of an internal combustion engine and is a valuable measure of an engine's capacity to do work that is independent of engine displacement[1]. When quoted as an indicated mean effective pressure or imep (defined below), it may be thought of as the average pressure over a cycle in the combustion chamber of the engine.
Let,
W = work per cycle in joule
P = power in watt
pmep = mean effective pressure in pascal
Vd = displacement volume in cubic metre
nc = number of revolutions per cycle (for a 4-stroke engine nc = 2)
N = number of revolutions per second
T = torque in newton-metre
The power produced by the engine is equal to the work done per operating cycle times the number of operating cycles per second. If N is the number of revolutions per second, and n_c is the number of revolutions per cycle, the number of cycles per second is just their ratio. We can write
W = {P n_c \over N}
By definition:
W = pmep * Vd
so that
p_{mep} = {P n_c \over V_d N}
Since the torque T is related to the angular speed (which is just N 2 π) and power produced by
P = TN2π
Then the equation for mep in terms of torque becomes,
p_{mep} = {T n_c \over V_d} {2 \pi}
Notice that speed has dropped out of the equation and the only variables are the torque and displacement volume. Since the range of maximum brake mean effective pressures for good engine designs is well established, we now have an engine displacement independent measure of the torque producing capacity of an engine design (a specific torque of sorts). This is useful for comparing engines of different displacements. Mean effective pressure is also useful for initial design calculations; that is, given a torque, we can use standard mep values to estimate the required engine displacement. However, it is important to remember that mean effective pressure does not reflect the actual pressures inside an individual combustion chamber—although the two are certainly related—and serves only as a convenient measure of performance.
Brake Mean Effective Pressure or bmep is, as usual, calculated from measured dynamometer torque. Indicated mean effective pressure or imep is calculated using the indicated power; i.e., the pressure volume integral in the work per cycle equation. Sometimes the term fmep (friction mean effective pressure) is used as an indicator of the mean effective pressure lost to friction (or friction torque) and is just the difference between imep and bmep.
[edit] BMEP typical values
* Naturally aspirated spark-ignition engines : maximum values are in the range 8.5 to 10.5 bar (850 to 1050 kPa; 125 to 150 lbf/in2), at the engine speed where maximum torque is obtained. At rated power, bmep values are typically 10 to 15% lower.
* Turbocharged automotive spark ignition engines : the maximum bmep is in the 12.5 to 17 bar range (1.25 to 1.7 MPa; 180 to 250 lbf/in2).
* Naturally aspirated four-stroke diesels: the maximum bmep is in the 7 to 9 bar range (700 to 900 kPa; 100 to 130 lbf/in2).
* Turbocharged automotive four-stroke diesels : the maximum bmep is in the 14 to 18 bar (1.4 to 1.8 MPa; 200 to 269 lbf/in2) range.
* Two-stroke diesels have comparable values, but very large low speed diesels like the Wärtsilä-Sulzer RTA96-C can have bmep up to 19 bar (1.9 MPa; 275 lbf/in2).
For example, a four-stroke motor producing 160 N·m from 2 litres of displacement is going to have a bmep of (4π)(160 N·m)/(0.002 m³) = 1,005,000 N/m2 =1,005 kPa (10.05 bar). If the same engine produces 76 kW at 5400 rpm (90 Hz), its torque is 134 N·m and its bmep is 8.42 bar (842 kPa). As piston engines always have their maximum torque at a lower rotating speed than the maximum output, the BMEP is lower at full power.
The above is a straight copy from Wikipedia, I did not write it or copy if from elsewhere, and it saved me from having to look for my college test lab notes from 1972 when we all had to so BMEPs and Fuel Specific curves from a single cylinder test engine in the lab.
Geeze. And I was just thinking of scanning a page out of a text book. I did over simplyfy my explination of bmep (I left out a constant, oops). But I think what you put in there covers it.
I see on the quench explination. Thank you. I tried looking it up and found what I was looking for. But as you stated, it was called squish. I guess those old HOT ROD and Car Craft articles wern't quite accurate with their terms/definitions.
Correct me if I'm wrong. But from the bmep definition brings up a good point about torque and engine volume. Its independent of stroke. I' guessing this is because from a static evaluation, and keeping volume constant making the stroke longer would necesitate making the piston surface propotonatly smaller. Wich would make the force generated on the piston propotonatly smaller making the actual torque on the crank come out in a wash. Double the stroke, half the force due to halving the area. Or the other way around, double the piston area thereby doubleing the force acting on the piston, but with the stoke cut in half torque stays the same.
But there is advantages to having a longer storke for a low rpm high torque engine. I assume this comes into play when looking at the dynamic situatiions of air flow, burn time and I'm sure other things that are over my head at this point. For example if shooting for low end torque high rpm piston speeds aren't a worry. So, go for a longer stroke which alows for a smaller diameter piston that can allow for complete combusion more quickly. Or faster piston speeds at lower engine speeds which allows for better filling of the cylinder. These are all slightly educated guesses at this point. You sound like the guy to answer them.
This special for touring919 .......... he DID ask !
I'm not going to directly answer all his questions, but will say this.
One calculates the BMEP from dyno generated Torque results.
Engine dimensioning is not a factor in the equations, just displacement.
Remember that the calculation of BMEP is derived from dyno results, so the calculated BMEP is automatically a reflection of the characteristic of the engine.
I found my Feb 11, 1973 Thermo Lab report. We did two engine tests, one diesel, the other gasoline. They were dedicated lab engines. Those engines had cylinder pressure sensing devices that were tied to an oscilliscope, and we used printed out info that when combined with other data and subsequent calculations permitted us to determine the Mean Effective Pressures for a range of engine loads. Brake ahead of Mean just means after losses from inefficiencies. BMEP relates to torque at the crankshaft flywheel, while MEP relates to inside the cylinder before losses Fascinating stuff, I say, and you DID ask !
More.
1
Did some more BMEP fishing for you.
You have the Widipedia info.
Now go to www .factorypipe.com/t_brake.php for more decent info
2
Some decent engine theory that to a certain extent deals with your question about torquers vs revvers.
Keep in mind that engines can be designed to do different things, and be spooked into doing things that at first glance seems out of place. The point being, you can build a big twin that makes big power, and you can build a high cylinder count motor that makes good torque down low.
OK, go to www .hotrod.com/techarticles and find the January 2004 Hot Rod Magazine Article "Engine Power Delivery - Torque Vs. Horsepower , Grunter or Screamer:What's The Difference?
The article is by Marlan Davis of Superflow Corp.
So, touring919, have some fun with some really good info !
Let us all know how you find it.
There's sure to be others just as interested but not asking out loud like you do.
I was too busy reading this stuff to notice! No harm no foul!
I actually stumbled across the Hot Rod mag article by accident. I did an initial search on Top Fuel Engine Design, being a ancient fan badly out of touch with current tech. I saw a Hot Rod mag reference, went there, and then say the Grunter or Screamer article as a related piece, so went there.
I used to read Hot Rod back to the 60s, but drifted away in the 80s. Like many mags, it has done a shape shifter routine over the years. I now see it has some excellent tech articles again, so maybe it's time to at least starting looking at their website. I have never found the bike mags to be anything remotely good as engine tech info sources. Historically, it was Hot Rod, Car Craft, Popular Hot Rodding and Circle Track Magazine (Smokey Yunick articles in particular) that were the best. Popular Hot Rodding was doing an "Engine Masters" series of publications that had good info as well, but I don't know if they still do.
I still go back to a most insightful, and easy read, namely Bill Jenkins's "The Chevrolet Racing Engine" as published in 1976. That book is packed with concepts and info and while it's based on a wedge chamber two valved push rod V-8 with carbs, it's still a good read. It was the definitive book on Chev small block pro stock engines in its day, actually the only one I ever came across.
Thanks MC. I had a good understanding of both articles. They are very well written. I wish I could put my thoughts into words that well.
The Hot Rod article did confirm a couple statements above. The main one being that chaning bore and stoke would have little to know effect on torque. As far as the sort block is concerned its a distplacement dependant thing, not bore or stroke. And it also answered my question above. Smaller bore and longer stoke is used to help make better powere/torque in low rpm engines. thiss is because of better flow due to higher pistons speeds, not because the longer stroke directly makes more torque.....Better everyone read the articles MC kindly brought to our attention. my wording is going to make it more confusing that what it is.
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