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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / January 2007What is the advantage of a V (or horizontally-opposed) engine over a straight engine?
I realise that a V or horizontally-opposed engine can be shorter because the left and right cylinders can overlap. But is there any other advantage in not having all the cylinders in-line, assuming the same engine capacity and the same number of cylinders in either case? In the late 60s, there was quite a craze for cars with V4 engines: I remember my dad had a Ford Corsair with a V4 and my friend's grandpa had a V4 Saab 99. And more recently my dad had a Citroen with a 4-cylinder horizontally-opposed engine. Since then, V engines have gone out of fashion unless you need to fit a 6- or 8-cylinder engine into a small space. Does the different timing of a V bring any advantages (or disadvantages, for that matter)? >I realise that a V or horizontally-opposed engine can be shorter because the >left and right cylinders can overlap. [quoted text clipped - 11 lines] >Does the different timing of a V bring any advantages (or disadvantages, for >that matter)? There are a multitude of considerations but, external packaging is a primary concern in the automotive world. There is some concern over engines with longer crankshafts particularly in higher speed engines because of the tendency to whip a little at higher speeds if they are not stiff enough. They can be stiffened but, this usually results in larger bearing journals with accompanyong higher bearing speeds which are not desireable. There is also the problem of the harmonics of torsional vibration with longer cranks. Many of these design problems are addressed using the shorter cranks of a "V" config. As fewer cylinders are used, many of these problems are greatly diminished as in the case of the inline 4 cylinder which has relatively low frequency power impulses compared to a 6 or more cylinder engine. Many of these problems re-surface at higher engine speeds. Most of these problems are addressed by design but, external package config is the major concern in the automotive world. As far as timing, etc, yes, engine design can be greatly influenced with timings and the basic engine config can greatly influence the power and performance characteristics. This can be particularly noticeable between engines like an inline 6 and a V8 or V12 of the same displacement. Even though the V's would generally have higher maximum horsepower output than the 6, the 6 would generally pull harder at lower engine speeds. This concept is extensively used in heavy duty trucks where inline 6 cylinder configs are the rule rather than the exception because of the higher low-speed torque production which can make the vehicle much easier to drive. The above is a very simplistic answer on a subject on which entire libraries have been written by people much smarter than I. I only hope I have offered some insite. Lugnut lugnut wrote in message 4rvhp25l1j2s5rebvntljnl7fr28fqmpse@4ax.com: >> I realise that a V or horizontally-opposed engine can be shorter >> because the left and right cylinders can overlap. [quoted text clipped - 31 lines] > external package config is the major concern in the > automotive world. I suppose also that it's easier to cool a V engine with two separate n-cylinder blocks than an in-line engine with a single 2n block. > As far as timing, etc, yes, engine design can be greatly > influenced with timings and the basic engine config can [quoted text clipped - 8 lines] > low-speed torque production which can make the vehicle much > easier to drive. Oh, so for the same capacity and number of cylinders, does the V engine develop more power but less low-end torque than an in-line engine? Didn't know that. Does a V engine run more or less smoothly than an in-line engine, given that in an inline engine the explosions occur at equally-spaced intervals whereas with a V engine the two banks of cylinders are offset by maybe 45 degrees. In an in-line engine with more than 4 cylinders, is it normal for *all* the cylinders to be in-phase (ie all at TDC or TDC+180 degrees) or is there an offset? For example, with an 8-cylinder engine, do two cylinders start on a power-stroke at exactly the same time, two on induction etc, or is one group of four cylinders offset from the other by 90 degrees so its power strokes will occur in-between those of the other group of cylinders, as if it were a 90-degree V engine? >lugnut wrote in message >4rvhp25l1j2s5rebvntljnl7fr28fqmpse@4ax.com: [quoted text clipped - 37 lines] >I suppose also that it's easier to cool a V engine with two separate >n-cylinder blocks than an in-line engine with a single 2n block. Cooling is a design problem. There is generally not a significan difference in a properly designed system. It is normal, however, for the cylinders at the rear of an engine to run a bit warmer than the cylinders closer to the cool water at the pump. >> As far as timing, etc, yes, engine design can be greatly >> influenced with timings and the basic engine config can [quoted text clipped - 12 lines] >develop more power but less low-end torque than an in-line engine? Didn't >know that. Not necessarily. It depends on which component of "power" you are talking about. They have different useable characteristics. An engine with lots of torque at lower speeds will be easier to drive in everyday driving but, the engine that produces more horsepower at higher speeds may have better maximum acceleration characteristics. A small truck with only a 100 HP inline 6 cylinder engine may be able to drag a 400 HP honda Civic around backwards all day because of it's torque advantage at low speeds while the Civic can run off and hide on acceleration because it's horsepower advantage. The nature of the work to be done should be the guide when selecting an engine for a specific job. >Does a V engine run more or less smoothly than an in-line engine, given that >in an inline engine the explosions occur at equally-spaced intervals whereas >with a V engine the two banks of cylinders are offset by maybe 45 degrees. No. They both can be designed to be very smoothly. Just because the cylinders appear to be offset has nothing to do with the timing of the power impulses. >In an in-line engine with more than 4 cylinders, is it normal for *all* the >cylinders to be in-phase (ie all at TDC or TDC+180 degrees) or is there an [quoted text clipped - 3 lines] >will occur in-between those of the other group of cylinders, as if it were a >90-degree V engine? No. The crankshaft is made so the the cylinders are offset from one another resulting in even power impulses. You may want to pick up a book on basic engines at the library to see this. Start here for very basic intro: http://auto.howstuffworks.com/engine.htm Lugnut > No. The crankshaft is made so the the cylinders are offset > from one another resulting in even power impulses. You may [quoted text clipped - 6 lines] > > Lugnut I am going strictly from memory, and there may be those who find fault with my perception of the subject but, as I remember the practice versus theory, all engines do not have even power pulses. In particular, some of the early Buick V6 engines did not. It required a special crankshaft design in later versions to get the even fire operation. The oddfire versions were tamed with motor mounts,and other techniques, and gave surprisingly good durability. The ability to balance an engine varies a lot with the engine design. Some configurations cannot be balanced perfectly, while others can. Thanks, Lugnut, for you comments on engine design. >> No. The crankshaft is made so the the cylinders are offset >> from one another resulting in even power impulses. You may [quoted text clipped - 12 lines] > not have even > power pulses. I believe the Viper's V10 is another one like that. http://en.wikipedia.org/wiki/V10_engine Honestly, I'm no mechanical engineer or automotive designer... but I'm pretty sure that 90% of the layout of a modern automotive engine comes down to marketing and packaging. (and by modern, I mean since about 1960.) A V8 is more "impressive" than a 6, which is "better than" a 4. Inline 6's were "old", so a V6 was newer and therefore "better." American musclecars have always (Buick 3.8 turbo excepted) had V8's, so even if you could make 400hp from a V6, it probably wouldn't sell as good as the V8 version. Once you've invested a lot of engineering $ and tooling $ into a certain design, you're generally not inclined to toss it. They've tried a couple of other designs too, like VW's VR6 and W8... http://www.autozine.org/technical_school/engine/smooth5.htm They all try to claim each design is better... I don't buy it. I have a Subaru with a flat-4 - according to them it should have a lower CG than an traditional inline, but I'm not sure if I buy that, because once installed in the car, it's not THAT much lower and definitely a LOT wider. (I bought the car for awd, not because of the engine, and it's not a sports car, so a 1/2" reduction in the CG isn't going to make a huge difference.) Ray >>> No. The crankshaft is made so the the cylinders are offset >>> from one another resulting in even power impulses. You may [quoted text clipped - 17 lines] > I believe the Viper's V10 is another one like that. > http://en.wikipedia.org/wiki/V10_engine The Viper and Dodge Ram truck V10 are a very special case. Unlike the early Buick V6 or the Harley-Davidson twin that are truly "odd firing" in that there are gaping holes in their firing pattern, the V10 has pairs of cylinder that fire "close" and pairs that fire "farther apart," but a "close" pair is ALWAYS follwed by a "far apart" pair and vice-versa so that overall, the engine runs perfectly smoothly. But it has an odd double-toned exhaust note as a result. >>>> No. The crankshaft is made so the the cylinders are offset >>>> from one another resulting in even power impulses. You may [quoted text clipped - 25 lines] > vice-versa so that overall, the engine runs perfectly smoothly. But it > has an odd double-toned exhaust note as a result. And I believe the reason a Viper has a V10 instead of a V8 is because of Moore's Law. If some is good, Moore is better. The current Dodge Charger SRT8's 6.1L V8 Hemi makes more power than the original 8L V10 Viper engine. But a V10 is more cylinders, therefore it's better. And all the car companies are guilty of that kind of stuff - how well would a V6 Corvette sell? Ray >>>>> No. The crankshaft is made so the the cylinders are offset >>>>> from one another resulting in even power impulses. You may [quoted text clipped - 30 lines] > Charger SRT8's 6.1L V8 Hemi makes more power than the original 8L V10 > Viper engine. But a V10 is more cylinders, therefore it's better. A) The 6.1 Hemi didn't exist when the Viper came out. It wasn't even on the drawing board. The biggest engine Chrysler made at the time was the 360 (5.9L) v8 at only 230 horsepower and tuned for maximum low-RPM grunt because it was only used in trucks. The v10 is loosely based on the 5.9 architecture with two extra cylinders. B) The V10 is going away in a couple of years, in favor of (you guessed it) the Hemi. There is a downside, at least for the hardcore Viper enthusiasts. The V10 is EXTREMELY under-stressed in factory trim. The thing is just loafing when its putting out 500 rear-wheel horsepower, and many aftermarket tricks (both with and without forced induction) easily put it in the 1000 rear-wheel horsepower range. The 6.1 Hemi is a GREAT engine, but whether it can match that potential is very questionable. >> No. The crankshaft is made so the the cylinders are offset >> from one another resulting in even power impulses. You may [quoted text clipped - 12 lines] >not have even >power pulses. You are correct. My response is intended to be very general for the OP who appears to have extremely limited knowledge od how the engine works. There are exceptions to almost every rule and the Buick engine was one of them. There are other oddballs out there that did not work nearly as well but, the Buick had some natural feature to overcome. You may also want to look at the Radial 9 aircraft engines for some interesting features. Lugnut >In particular, some of the early Buick V6 engines did not. It required a >special crankshaft [quoted text clipped - 8 lines] > >Thanks, Lugnut, for you comments on engine design. > of the subject but, as I remember the practice versus theory, all engines do > not have even > power pulses. True, but I look with such derision on those engines that I hardly call them "engines." :-/ Odd-firing is a half-assed cheap way out of building a more complicated crank. But it does work, or Harley-Davidsons wouldn't run at all :-p > In particular, some of the early Buick V6 engines did not. It required a > special crankshaft > design in later versions to get the even fire operation. True of any 90-degree v6. The oddfire > versions were tamed > with motor mounts,and other techniques, and gave surprisingly good > durability. Because the crankshaft was WAY overbuilt for the low power they put out, yes. It would never have survived the power levels that it got to later in even-firing form in the turbocharged Buick GNX and the later supercharged FWD Buicks and Pontiacs of the 90s. > The ability to balance an engine varies a lot with the engine design. Some > configurations > cannot be balanced perfectly, while others can. As long as you can make an engine EVEN FIRING (the discussion above) you can take care of the rest of its balance idiosyncracies through crankshaft counterweights or additional balance shafts driven by the timing chain or belt. The proof of that is that one of the inherently WORST engine layouts in terms of inherent balance is the inline 4-cylinder- but look at how many gadzillions of them have been built and continue to be built. Its arguably the most common engine layuout for cars. Also look at the popularity of 90-degree v6 engines in even-firing form. They have a lot of inherent imbalance, but its all 2nd and 3rd order stuff so long as the are even-firing. > In particular, some of the early Buick V6 engines did not. It required a > special crankshaft > design in later versions to get the even fire operation. The oddfire > versions were tamed > with motor mounts,and other techniques, and gave surprisingly good > durability. Yeah, they were of course, V8s with 90 degrees between banks, with the back cylinder removed on each side. Cheapest way to come up with a "new" V6 using existing tooling. So they went bang bang bang ___ bang bang bang ___ bang bang bang ___ bang bang bang ___, etc. > Does a V engine run more or less smoothly than an in-line engine, given that > in an inline engine the explosions occur at equally-spaced intervals whereas [quoted text clipped - 7 lines] > will occur in-between those of the other group of cylinders, as if it were a > 90-degree V engine? Most engines are designed to fire at evenly-spaced intervals. A four will fire every 180 degrees of crankshaft rotation, a six every 120 degrees, an eight every 90 degrees, a 12 every 60 degrees. Whether it's an inline or vee or opposed makes no difference.The engine is designed internally to get the even firing. The Harley-Davidson engine is one example of an engine with uneven firing, giving it the distinctive lope. Inline sixes can pull better at low speeds because their redlines are often lower due to the longer, more flexible crank and larger bearing diameters, so the designers get the required power by making them less oversquare ("square" meaning that the cylinder bore diameter and stroke are the same measurement, and "oversquare" meaning that the diameter is larger than the stroke). An engine having a relatively longer stroke will generate more torque and lower RPM, just as a bicycle with longer pedal cranks will climb better. I once owned an Auster aircaft. This airplane had a deHavilland Gipsy Major engine in it of around 6 litres displacement (350 cu. in.), all in four cylinders. The bore was 4 5/8" and the stroke 6 1/2", making it way undersquare. It delivered 145 hp at 2600 RPM, giving it a torque rating at that RPM of 293 ft-lb, rather awesome for an engine of that displacement. Horizontally-opposed engines are naturally balanced, eliminating the need for massive counterweights and making the engine lighter, though some larger opposed aircraft engines do have counterweights that are loosely mounted so that they can move slightly on the crank to reduce some forms of harmonic vibration. An opposed engine has a short, stiff crank to make things safer. An opposed engine has a low profile, making it ideal for the front of an airplane or the engine compartment of a low car. Opposed engines in aircraft are commonly found in 4, 6 and 8-cylinder versions, and Lycoming once built a 12-cylinder engine that was never produced. Most of them are air-cooled. A liquid-cooled opposed engine has no need of cooling fins so the cylinders can be placed closer together, shortening the crank further. Liquid-cooled V-12s were used in many bombers and fighter aircraft of WWII. The best was the Rolls-Royce Merlin, a 1647 cu-in. engine that produced more than 1500 hp, and a version of that engine was run for 15 minutes while producing 2640 hp. The V-12 block was mostly aluminum with steel cylinder sleeves, and was light and fairly narrow to fit in tight cowlings. It was geared so that the engine ran at 3000 RPM and the prop turned at less than 2000. (Big propellers can't be run at high RPM. The tips must be kept below supersonic speeds, and centrifugal forces get too high at higher RPM.) Dan > Horizontally-opposed engines are naturally balanced, > eliminating the need for massive counterweights and making the engine > lighter, though some larger opposed aircraft engines do have > counterweights that are loosely mounted so that they can move slightly > on the crank to reduce some forms of harmonic vibration. Horizontally opposed six and twelve cylinder engines have a high degree of balance. Same for inline six and twelves. The same is not true for horizontally opposed twos, fours, eights, etc. > > Horizontally-opposed engines are naturally balanced, > > eliminating the need for massive counterweights and making the engine [quoted text clipped - 6 lines] > > The same is not true for horizontally opposed twos, fours, eights, etc. Better qualify that. The textbooks disagree with you. Dan > > The same is not true for horizontally opposed twos, fours, eights, etc. > > Better qualify that. The textbooks disagree with you. > > Dan Of course there are qualifications... Here is a general clip from Wikipedia, however "The straight-6, flat-6, and V12 designs have none of these forces or moments of vibration, and hence are the naturally smoothest engine designs. (See the Bosch Automotive Handbook, Sixth Edition, pages 459-463 for details.) Engines with particular balance advantages include: a.. Straight-6 b.. Flat-6 c.. Flat-12 d.. V12 Engines with characteristic problems include: a.. Flat-4 boxer and straight-4 have no better kinetic energy balance than a single, and require a relatively large flywheel. b.. Crossplane V8, which requires a very heavily weighted crankshaft, and has unbalanced firing between the cylinder banks (producing the distinctive and much-loved V8 "burble"). c.. Flatplane (180° offset crankshaft) V8. In modern multi-cylinder engines, many inherent balance problems are addressed by use of balance shafts." Balance is an interesting subject.. A lot of things can influence the way you choose to balance a particular configuration. > lugnut wrote in message > 4rvhp25l1j2s5rebvntljnl7fr28fqmpse@4ax.com: [quoted text clipped - 54 lines] > develop more power but less low-end torque than an in-line engine? Didn't > know that. Uh, no. Not really. That depends more on the camshaft and valve train design than on the V or inline . > Does a V engine run more or less smoothly than an in-line engine, given that > in an inline engine the explosions occur at equally-spaced intervals whereas > with a V engine the two banks of cylinders are offset by maybe 45 degrees. "Maybe" 45 degrees? There's no "maybe" about it! A typical American or European v8 engine's banks are offset by 90 degrees, and the cylinders fire perfectly evenly, just like a straight 8. V6s are ideally built with the bank angle 30 degrees for even firing, but you can build a 90-degree v6 (or a 60-degree v8 for that matter- eg the Ford/Yamaha SHO v8) if you build the crank with offset bearing throws to make the cylinders fire evenly. And, half-assed as it is, you can also just let a 90-degree v6 fire UN-evenly, too. GM once did that with the very early Buick 3800, but quickly revised the crank to make it an even-firing engine. > In an in-line engine with more than 4 cylinders, is it normal for *all* the > cylinders to be in-phase (ie all at TDC or TDC+180 degrees) or is there an > offset? A 4-cycle inline 4 has two pistons moving up in unison (one on its compression stroke and the other on its exhaust stroke) while the other two move down in unison (one on its intake stroke, the other on its combustion stroke). Ditto for a flat-4, or a V-4. However the cylinders are arranged, the crank is designed to make the pistons move this way. > For example, with an 8-cylinder engine, do two cylinders start on a > power-stroke at exactly the same time, two on induction etc, or is one group > of four cylinders offset from the other by 90 degrees so its power strokes > will occur in-between those of the other group of cylinders, as if it were a > 90-degree V engine? The cylinders are timed so that the combustion cycles occur at uniform angles of crank rotation. Cylinders do not fire simultaneously. So if you look at a V8 frozen at an instant in time when a cylinder is at top-dead-center (TDC), you'll actually find two cylinders at TDC (one firing, the other at the end of its exhaust stroke/ beginning of its intake stroke), two cylinders at bottom-dead-center or BDC (one just having fired, the other just having completed its intake stroke) and 4 others halfway down the cylinder- two of them moving downard (one combusting, the other on intake) and two moving upward (one compressing, the other exhausting). It gets really fun in V16 engines, or if you're a real masochist the 28-cylinder R-4360 radial airplane engine! :-) >I realise that a V or horizontally-opposed engine can be shorter because the >left and right cylinders can overlap. >But is there any other advantage in not having all the cylinders in-line, >assuming the same engine capacity and the same number of cylinders in either >case? Have you sized an inline 8 or 12 lately? Unless you want a hood that is twelve feet long, it makes sense to put them into a V configuration. There other option is a horizontally opposed config, but it is wider than a V. you all should just be cool and get rid of piston moters because it is all about the rotory moter! >you all should just be cool and get rid of piston moters because it is >all about the rotory moter! The rotaries I've seen are niether fuel efficient, nor, big on low end torque when compared to piston engines outside a relatively narrow operating range. This may cease to be as much of a problem as transmission development advances that will provide for operation in that relatively narrow range. Rotaries, in general, are still in need of lots of development to compete with more traditional offerings in the mass markets. The piston engines will go only when/if anyone ever comes up with a viable replacement. That is still a tall order even as outdated as some think the piston engine may be. Lugnut > I realise that a V or horizontally-opposed engine can be shorter because the > left and right cylinders can overlap. [quoted text clipped - 11 lines] > Does the different timing of a V bring any advantages (or disadvantages, for > that matter)? I've just skimmed the responses, so if this has been stated before I apologize. The V engine (and by extension, the H engine) are significantly shorter in 6-cylinder and up applications. this is a big bous for packaging. There are some engines that have good inherent balance. An I-6 or V-12 has almost perfect natural balance. A V-8 is pretty good. A V-6 is awful. So an answer as to one layout is better than any other depends on how many cylinders we're talking about. The one thing that I haven't seen mentioned is center of mass. The crankshaft will almost always end up in the same place in the chassis, so the horizontally opposed engine will provide the lowest center of mass when installed; the V-engine next, and the inline worst (unless it is slanted, as a certain American manufacturer famously did a couple decades back.) nate > I realise that a V or horizontally-opposed engine can be shorter because the > left and right cylinders can overlap. > > But is there any other advantage in not having all the cylinders in-line, > assuming the same engine capacity and the same number of cylinders in either > case? A shorter crankshaft is more rigid, less prone to torsional vibrations, and generally stronger. Inline sixes are about the longest practical crankshaft length for car-sized engines (IOW, you can go a lot longer in a locomotive engine where you don't CARE that the crankshaft weighs 4000 pounds). Inline 8 engines and V-16s were obviously used back in "the day," but even then they were running up against the limits of the crankshaft as horsepower levels increased. > Does the different timing of a V bring any advantages (or disadvantages, for > that matter)? Most V-type engines are actually a little less inherently well-balanced than their inline counterparts. A notable exception is the V12, which is just two inline sixes and therefore just as smooth as an inline six- commonly considered the most "naturally balanced" engine configuration of all. A typical V8 is NOT timed like two inline 4s, and for good reason- inline 4s SUCK from a vibrational viewpoint. That's why so many inline 4s are hobbled with balance shafts- to cancel out the remaining undesirable flex and vibration modes caused by having the inner two pistons going up and the outer two going down in unison. The so-called "90-degree crank" v8 used in virtually all passenger car v8 designs is much smoother than a 4-cylinder, though not as nice as a straight six. There are "180 degree" or "flat-crank" v8s that are timed like two siamesed 4-bangers, but they are not used in production cars because of the vibration problems. They are used in some racing series (IRL used them for a while) because of desirable breathing characteristics and manifold designs allowed by the timing, but they are just too rough for daily use. Steve wrote in message HuSdnRfFUOtPewfYnZ2dnUVZ_r-onZ2d@texas.net: > A typical V8 is NOT timed like two > inline 4s, and for good reason - inline 4s SUCK from a vibrational > viewpoint. That's why so many inline 4s are hobbled with balance > shafts - to cancel out the remaining undesirable flex and vibration > modes caused by having the inner two pistons going up and the outer > two going down in unison. So a straight 8-cylinder engine has its pistons arranged equally about 360 degrees - ie one every 45 degrees? And a V engine has them *effectively* at the same spacing, if you allow for the angle of the V. Fair enough - makes sense. Given this, I've always wondered why 4-cylinder engines don't have the cylinders every 90 degrees, instead of two at 0 degrees and two at 180 degrees. Would it cause even more vibration if successive cylinders counting from one end were at 0, 90, 270 and 180 degrees rather than 0, 180, 180 and 0? Either way you avoid a travelling wave of vibration (0, 90, 180, 270 or 0, 0, 180, 180 would be a Bad Thing!). One other thing. Someone mentioned radial engines, as used in aeroplanes. Am I right I thinking that some radial engines had the propeller attached to the engine block and rotated all the cylinders about a stationary crankshaft that was attached to the fuselage? Have I really understood that correctly? If so, you'd think that getting the fuel fed through what is effectively a commutator (in electric motor terms) from stationary fuel supply in the fuselage would have been a little bit tricky, even if you had rotating carburettors and separate exhaust pipes for each cylinder. Why did they do it this way rather than having the cylinders fastened to the fuselage and rotaing the crankshaft and propeller? > Steve wrote in message > HuSdnRfFUOtPewfYnZ2dnUVZ_r-onZ2d@texas.net: [quoted text clipped - 8 lines] > So a straight 8-cylinder engine has its pistons arranged equally about 360 > degrees - ie one every 45 degrees? Nnnnnnno. You're forgetting that most car engines are 4-cycle engines. An 8 cylinder engine fires only *FOUR* cylinders for each turn of the crank, or a combustion cycle every 90 degrees of crank rotation. The remaining four cylinders fire on the next turn of the crank. For a 4-cycle engine with an even number of cylinders to fire at uniform crank rotation, the cylinders have to move in pairs. One of the pair is on its combustion stroke while the other is on its intake stroke. And a V engine has them *effectively* at > the same spacing, if you allow for the angle of the V. Fair enough - makes > sense. Given this, I've always wondered why 4-cylinder engines don't have > the cylinders every 90 degrees, instead of two at 0 degrees and two at 180 > degrees. See above. A 4-cycle 4-banger needs to fire a cylinder every 180 degrees. >> Steve wrote in message >> HuSdnRfFUOtPewfYnZ2dnUVZ_r-onZ2d@texas.net: [quoted text clipped - 25 lines] > > See above. A 4-cycle 4-banger needs to fire a cylinder every 180 degrees. The other advantage to engines with numbers of cylinders greater than 4 is that a 4-cylinder, 4-stroke engine has no overlap between power pulses so power delivery esp. at low RPM will always be a little rough. A 6- or 8-cylinder engine does not have this problem, so power delivery is creamy smooth. most of the cars I've owned have had 4-cylinder engines simply because they're more economical (generally,) but I do miss my '67 Dart and '86 BMW... a well tuned straight six is a wonderful thing. nate  Signaturereplace "fly" with "com" to reply. http://home.comcast.net/~njnagel -- Posted via a free Usenet account from http://www.teranews.com > Steve wrote in message > HuSdnRfFUOtPewfYnZ2dnUVZ_r-onZ2d@texas.net: [quoted text clipped - 26 lines] > it this way rather than having the cylinders fastened to the fuselage and > rotaing the crankshaft and propeller? Yes, indeedy. This was the original "rotary" engine. Had a few advantages; 1) very smooth; if you diagram it out, you would see that in fact both the cylinders and the pistons/conrods merely rotate in two circles, with the centers offset, so there is no reciprocation at all!!! 2) very efficient air-cooling obviously, 3) with the cylinders spinning, you don't need a flywheel, so you save ??? a hundred pounds? just a guess, which in a WWI aircraft was quite a chunk. 4) centrifugal force serves as your valve springs, which was a bonus in those days of crummy metalurgy. Fuel and oil delivery were actually pretty easy; again centrifugal force. The pistons had flapper valves on top, the fuel came in through the crankshaft and found its way up through the piston into the combustion chamber. Obviously, this also moved quite a bit of oil into the combustion chamber, which required replacing during operation. Similarly, oil got pumped up into drivetrain by centrifugal force, and just blew off rather than being recycled as in a modern engine. Very messy and smoky process. Note also: no throttle. Engine is either full on or full off, generating characteristic vroom sput sput sput vroom as pilot attempts to modulate speed via ignition kill button. Problems were immense gyroscopic forces; as the rpm of engines became higher, this became impossible to ignore. >>One other thing. Someone mentioned radial engines, as used in aeroplanes. Am >>I right I thinking that some radial engines had the propeller attached to [quoted text clipped - 6 lines] >>it this way rather than having the cylinders fastened to the fuselage and >>rotaing the crankshaft and propeller? That was the early "rotary" type radial engine, not a "modern" (as in 'used in WWII and later') type radial. The rotaries started out as 2-strokers, and later were adapted to 4-stroke using special "flapper" valves. Fuel delivery was imprecise at best, and the fuel was mixed with castor oil to lubricate the engines. The fuel/oil was delivered through the cranshaft and through the crankcase- no "commutator" or multiple carbs. Radials are much more conventional- the crankcase is stationary and the propellor either hooks directly to the crankshaft (in smallish engines) or to planetary gears in the nose case which are then driven by the crank (big engines). And they don't mix their fuel and oil either. > >>One other thing. Someone mentioned radial engines, as used in aeroplanes. Am > >>I right I thinking that some radial engines had the propeller attached to [quoted text clipped - 13 lines] > castor oil to lubricate the engines. The fuel/oil was delivered through > the cranshaft and through the crankcase- no "commutator" or multiple carbs. Go here to see an animation of a four-stroke rotary: http://www.pilotfriend.com/aero_engines/aero_rotary.htm To see a radial engine animation, go to http://www.turbosquid.com/FullPreview/Index.cfm/ID/211544/SID/211222/blFP/1 And click on "Stream." Or try http://commons.wikimedia.org/wiki/Image:Radial_engine.gif Other interesting animations: http://www.keveney.com/Engines.html Even better: http://www.pilotfriend.com/aero_engines/aero_recip_eng.htm Click on the different inline/rotary/radial/wankel etc. names at the left. Dan > I realise that a V or horizontally-opposed engine can be shorter because the > left and right cylinders can overlap. [quoted text clipped - 11 lines] > Does the different timing of a V bring any advantages (or disadvantages, for > that matter)? First, packaging; when cars changed over from the old style with the engine sitting above the frame in a long skinny "doghouse" between outboard front fenders, to a wider engine bay with fenders built in, with the engine nestled down between the front wheels, long skinny engines became more of a pain. Secondly, crankshaft vibrations. Double the length of the crank, you've either got to add more support or you'll see a lot more wiggly worming which has nasty results, and as engines started to turn more rpms that became significant, Adding more main bearings to an engine means more oil passages, more places needing precision machining, more $$. z wrote in message 1167854962.558973.280910@s34g2000cwa.googlegroups.com: >> I realise that a V or horizontally-opposed engine can be shorter >> because the left and right cylinders can overlap. [quoted text clipped - 25 lines] > means more oil passages, more places needing precision machining, > more $$. Is it much of an advantage for a four-cylinder engine, which is what my original question was about? I appreciate that for a 6, 8 or 12 cylinder engine, you'd need a very long engine compartment (or a very wide one if the engine was transverse), and there may also be crankshaft vibration problems due to the greater length. But is there any advanatge of V4 or H4 over straight 4? If not, why did they go through a phase of trying it in the late 60s, I wonder? People have mentioned vibration of certain engines. How about engines with an odd number of cylinders, like the 3-cylinder engine that's fitted in my mother's Daihatsu and some Daewoos, or the 5-cylinder engines that (I think) Audi made in the 1980s. My mum's Daihatsu is surprisingly good, though its automatic transmission has the gearchange thresholds set at very high revs so the engine spends a lot of time at high revs (which makes it noisy) - presumably to get decent power out of a mere 900 cc engine! Maybe I'm biassed because I'm used to my 2-litre diesel which rarely goes about 3000 rpm and accelerates fine in third gear on a roundabout at 1000 rpm. > Is it much of an advantage for a four-cylinder engine, which is what my > original question was about? In terms of vibrations, yes. A "boxer" 4-cylinder has some residual imbalance, but not NEARLY as much as an inline 4. > Is it much of an advantage for a four-cylinder engine, which is what my > original question was about? I appreciate that for a 6, 8 or 12 cylinder [quoted text clipped - 4 lines] > But is there any advanatge of V4 or H4 over straight 4? If not, why did they > go through a phase of trying it in the late 60s, I wonder? Ah, good question. Lots of V4s in European cars then, I recall; Ford for instance. Never did understand why. Certainly with 6s, you're already getting into packaging problems in-line, which accounts for the appearance of 5 cylinder in-lines by Audi and Honda, at least. > People have mentioned vibration of certain engines. How about engines with > an odd number of cylinders, like the 3-cylinder engine that's fitted in my [quoted text clipped - 5 lines] > biassed because I'm used to my 2-litre diesel which rarely goes about 3000 > rpm and accelerates fine in third gear on a roundabout at 1000 rpm. Balance in odd cylinder engines is actually not a problem, as long as they are spaced around the 360 degrees of crankshaft rotation correctly. As in the 5 cylinders you mention. In fact, once you get up to 5 cylinders you've avoided the inherent second harmonic shake of big four cylinder engines that balance-shafts were designed to counter. I imagine a three cylinder would also not have that problem, since the pistons' accelerations aren't in sync. all i really know about the subject is if u took the same number of pistons and stroke and bore the inline motor will have a lower redline increasing the torque at lower rpms while the v will more often that not have a higer redline and move the power further up in the rpms. Signaturemidgetracing28 http://www.automotiveforums.com > all i really know about the subject is if u took the same number of > pistons and stroke and bore the inline motor will have a lower redline > increasing the torque at lower rpms while the v will more often that > not have a higer redline and move the power further up in the rpms. That would really depend on the cam, the weight of the rotating assembly, manifolding, and lots of other things. There's absolutely no *fundamental* reason that an inline of the same cylinder configuration would have a lower torque band. |
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