Highlander Posted September 17, 2002 Share Posted September 17, 2002 Hmm. Well according to the article Mr. C points to above an inline 6 is inherently balanced vertically and end to end, so theoretically length (so to speak!) shouldn'y make a difference. The only long 6 cyl engines I can thing of are huge and hence speed limited on crank throw. Unless of course anyone else knows different. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 17, 2002 Share Posted September 17, 2002 Sorry, mixing up my references. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 17, 2002 Share Posted September 17, 2002 There are two things here. Length of stroke and length of crank. Stroke gives rise to reciprocating forces that are large, so have a direct effect on revs capability. Length of crank and indeed block might give some problems with torsional rigidity of the crank, but that is all I can think of. Link to comment Share on other sites More sharing options...
Jimbo Posted September 17, 2002 Share Posted September 17, 2002 I understood a key reason for the increase in Vees over straight 6s is rather more depressing. In our modern society crashing seems to be the most important design criteria. The relative shortness of a v engine gives body engineers a lot more chance of creating the necessary crumple zones to absorb impact. This means that complete with 14 air bags, pre-tensioned seat belts and brake assist, a completely useless driver can endanger pedestrians, (motor)cyclists and caterham drivers without fear of getting hurt. Oh dear I can feel a rant coming on… Link to comment Share on other sites More sharing options...
Paul Ranson Posted September 17, 2002 Share Posted September 17, 2002 Well according to the article Mr. C points to above an inline 6 is inherently balanced vertically and end to end, so theoretically length (so to speak!) shouldn'y make a difference. I think the flywheel and power take off being at one end makes a difference. Paul Edited by - Paul Ranson on 17 Sep 2002 21:24:58 Link to comment Share on other sites More sharing options...
Highlander Posted September 17, 2002 Share Posted September 17, 2002 Why should flywheel position have any effect on engine vibration as it's centre of rotation is in the centre of the crankshaft. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 17, 2002 Share Posted September 17, 2002 The theoretical view is that the crankshaft is rigid. It is far from rigid. For the power pulse from cylinder 1 to reach the flywheel, it has to be transmitted down the length of the crankshaft. In this regard, the crankshaft acts as a large torsion spring. The frequencies and modes of vibration of the crankshaft will have a frequency characteristic and a longer crankshaft will probably have lolwer frequency resonant vibration - this is torsional vibration in the crankshaft rather than out of balance vibration of the whole engine. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted September 17, 2002 Share Posted September 17, 2002 I've got a 3-D plot of crankshaft deflection along its length over time somewhere at home. serves to illustrate and explain the point nicely... HOOPY R706KGU See you at Cadwell Link to comment Share on other sites More sharing options...
Smokin Joe Posted September 17, 2002 Share Posted September 17, 2002 I use a 60 degree motor in my 7. This gives you a firing order of 123456 and is extremly smooth (see Peter C's excellent post earlier on this thread) The 90 degree V6 is really just a V8 with the front 2 cylinders lopped off, in any state of tune can be very "Lumpy" V6 *eek*60 degreeV6 *thumbup* Forget Cukes! Ban Cheeze 😬 Link to comment Share on other sites More sharing options...
Joe 90 Posted September 17, 2002 Share Posted September 17, 2002 What a lot of debate ❗. A long stroke limits an engine's maximum rpm, as mentioned in various postings. A long crankshaft also limits maximum rpm because it twists more easily when number 1 cylinder (at the opposite end from the flywheel) fires. When the firing pulses match the torsional resonance of the crankshaft, trouble ensues. This is why straight sixes and V8s are fitted with vibration dampers at the pulley. You can make your crank rev higher by making it stiffer, either by reducing stroke or by increasing the journal diameters. The obvious drawbacks are reduced capacity and increased weight ☹️ V6 engines have been produced in a number of V angles from 120 degrees (Ferrari dino 1.5 litre F1 engine of the 1960s), 90 degree cut down V8 (Rover metro 6R4), 90 degree even firing (Peugeut/Renault/Volvo 3 litre),65 degrees (Ferrari dino 2.4 litre road engine), 60 degrees (too many to list, popular with Ford, Alfa worth mentioning), and sub 60 degree stuff. These engines cover a huge range of performance and smoothness, depending mostly on the skill of the designers 99,000 miles so far Link to comment Share on other sites More sharing options...
cdg Posted September 17, 2002 Share Posted September 17, 2002 The BMW straight 6 M20(?) engine in my good friend's ALD Group C Le Mans car (just sold unfortunately) made 450 bhp from 3.5litres on the Dyno. It had the biggest crankshaft damper I have ever seen.... Rev limit was a very scary 8300rpm. I hate to think what was happening to that crank at those engine speeds. It did sound wonderful on an open pipe though... Chris Link to comment Share on other sites More sharing options...
DanB Posted September 18, 2002 Share Posted September 18, 2002 I was wondering the other day why Renault didn't extend their 'wide V' format to its logical conclusion and use a boxer engine. Apart from any regulatory reasons, it occurred to me that if you use a boxer engine, and the cylinder heads have the induction on the top (as you'd assume they would) they exhausts would be underneath the engine. Assuming that the exhausts are above the floorpan, this means that the crankshaft is higher than in a V has the exhaust has to go underneath the engine rather than alongside it as in a V, even a wide one. Since a considerable part of the weight of the engine is in the crankshaft, bearings and block, it seems to me that a boxer engine wouldn't necessarily have a lower CoG than a wide angle V. Anyone care to model it? Dan Link to comment Share on other sites More sharing options...
Tony Martyr Posted September 18, 2002 Share Posted September 18, 2002 I think everything from an automotive engine has been said. From my prospective of engine development I think that the space an engine produces now within the vehicle is begining to dominate. modern NVH techneques and electronic management can deal with a not of the inherent problems of designs that are not inherently balanced. Lots of design effort is now spent on working out just how the driving belt route can be optimised to drive all these wiggets attached. In bigger engines we have series built up by adding cylinders in the straights, typically 5, 7 and 9 cylinder units and pairs 12, 14 and 16 in the Vees. The V 16s can cause some wonderful and weird vibration problems because of the flexibity of the crank shafts which cause resonances when coupled with certain devices - these are problems of such complexity - like 4 and half order vibration - that they are very difficult to predict and give rise to shafts failing because of torsional resonances giving torques over 10 times rated. A new phenomena is now evedent with electronic controlled engines in that some of the systems are so fast that they are seeing and inappropriately reacting to transient vibration and distortions. These are an asolute bugger to sort out as we have the electronic guru blaming the mechanical and vice versa - Oh happy new world Link to comment Share on other sites More sharing options...
Morls Posted September 21, 2002 Share Posted September 21, 2002 Ultimate traction is maybe a little harder to get from the small contact patch of a bikes's back tyre than the big things on the back of cars. Maybe this is why the V (or firing) angle on bikes has been the subject of so much debate... Harleys have been brilliant at flatrack racing (like faster speedway) for years as the 45 degree V angle produces lumpy, grippy, power pulses to the back wheel, as opposed to the smooth seamless delivery of a straight 4 which would help perpetuate any loss of rear wheel traction. V engines of 90 degrees or less also dominate Moto GP, WSB and BSB. The "big bang" 500cc V4 strokers even fired the cylinders as close togather within the 360 deg as poss, to replicate this lumpy delivery. While plenty of gearboxes broke, the race times dropped. For the non-bikers... the difference between the "feel" you get from the back tyre of a single/twin/vee and a straight four is huge. It seems that the throttle can always be opened that bit earlier and that any movement of the tyre is less terminal. Maybe it's less noticable on cars tho? Mark Link to comment Share on other sites More sharing options...
alicat Posted September 21, 2002 Share Posted September 21, 2002 Lots of talk about V's, Flat and straight engines. What about W's ala Passat from mr VW 🤔 Link to comment Share on other sites More sharing options...
PACR Posted September 22, 2002 Share Posted September 22, 2002 The VW VR6 engine is a narrow V config, much like a straight 6 with the cylinders 'squeezed' together - Imagine a row of 6 pennies, to shorten the overall length offset the pennies from the center line a little bit. If you have two seperate rows of 3 pennies you have the normal V6 config. The block casting is thus more like a normal straight engine than a V engine. I believe this makes casting and machining costs cheaper. With two of these 'bolted' together on a common crank you get 12 cylinders and 2 blocks like a normal V engine. And hence a W 12 (but I suspect it's not quite as simple as it sounds....). Piers Edited by - PACR on 22 Sep 2002 19:45:03 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 22, 2002 Share Posted September 22, 2002 The links I gave earlier in the thread gave detaols of the VR and W configurations. Link to comment Share on other sites More sharing options...
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