Conference terri::cars_uk

From my limited understanding of such things, the only sacrifice the twin
bank engine gives over to its in-line counterpart is smoothness of running
(ie lack of vibration), the primary reason for this design is to make the
unit more compact.  I stand to be corrected, though!

Chris.

>>    Now I'm no real expert at recent 6 cyl engines. Are you considering the
>>    new VW V6 ? the new Audi V6 ? the Alfa V6 used to be very smooth,
>>    torquy and powerful. 

>>    At this point I think the BMW straight 6's are among the best engines.

Well, actually I just bought a BMW 320i with 6 cylinder engine.
So its good to hear you like it.
I'm still running the engine in as they placed a brand new engine in the car
(previous owner tried driving without oil).

The reason I was wondering about the question is that I'm surprised about
the "power" being at high revs (from feeling, I haven't seen any graphs yet).
Compared to the Audi's 2.8 V6 engine that has nothing more exiting at high revs.

But this is not a true test, for the moment, as I don't dare reving my Beemer
to high for the moment.

Thanks,

Peter.

    The number of cylinders has much to do with the "harmonic" balance of
    the engine.  From what I understand (not an expert) an inline-4 has
    certain inherent roughness caused by secondary harmonic imbalances. 
    Mitisubishi puts balance shafts in the larger 4 cylinder motors to
    offset this problem.  Porsche uses something similar in the 944 (I
    believe).   These are not found in an inline-6.  A V-6 has some
    tendency not to be in balance because the "V" separates the firing
    pattern.  
    
    There are other characteristics which determine horsepower and torque. 
    The bore and stroke are important.  Generally, the larger the bore, the
    greater the torque.  The longer the stroke, the higher the horsepower. 
    There are also factors in connecting rod length which impact power.  I
    seem to recall some of the bikes using V-4's wanting long connecting
    rods to increase horsepower.  There are also intake and exhaust
    considerations.  The less restricted the breathing, the greater the
    power.  There is a lot being done with cars today to tune the inlet
    length to increase torque.  There are also variable length runners
    which open and close depending on rev's.  Then, of course, is variable
    valve timing.  Factors such a lift and duration can be set to optimize
    certain requirements.
    
    In general, a racing engine has a very steep curve for both power and
    torque.  More docile engines look to flatten out the torque curve and
    in fact boost it at low rpm's.  You may often hear of something like
    "90% of the torque is available at 2000 rpm" or see magazines test for
    top gear acceleration from 25 mph.  
    
    There is also something about surface area and fuel consumption, but I
    can't remember how that goes.
    
    BTW, until recently, German automakers opted for the inline-6 because
    it is "best" from a balance perspective.  
    
    Good choice of car!
    
    Jeff  

>Generally, the larger the bore, the greater the torque.  The longer the
>stroke, the higher the horsepower. 

I think you have this backwards.  Typically a long stroke gives lots of torque,
but limits the revs.  A shorter stroke and bigger bore will allow more revs and
higher hp.

Dave (owner of a 3.5" bore X 5" stroke straight 6 with max revs around 2000rpm)

>Dave (owner of a 3.5" bore X 5" stroke straight 6 with max revs around 2000rpm)

would that be your Studebaker by any chance?
Cheers,

Chris.

Yep, that's the engine in the '24, all 289 ci of it.  It's rated at 50bhp, but
can cruise around in top gear down to about 10-15 mph.

The straight 6 in the '26 is slightly smaller (241ci) but revs to 2500rpm, or so
I'm told since I don't it running yet.

Dave

    >the Alfa V6 used to be very smooth,
    
    is this unit no longer in production then? a fine engine.
    
    ric

    For balance I think an in-line 5 is one of the better ones.  Wasn't it
    Audi that used this arrangement in the '80s?
    
    One advantage a V6 has over an in-line 6 is the length and support of
    the crankshaft.  With a maximum of 4 main bearings the V6 c'shaft will
    be much les bouncy than an in-line 6 which has a maximum of 7 main
    bearings.
    
    The other consideration is the power:weight ratio which will generally
    be better for a V6.  There is then the acceleration of the rotating
    parts which will be lower mass on the V6.

I can remember that the advertising blurb at the time went along
the lines of `the power of a 4 with the smoothness of a 6'.  I
didn't believe it at the time, and still don't!

Chris.

    'The power of a 4' ?!?!?! As opposed to a six?! What utter tosh!
    
    Cheers,
    Dan

    
    I think it was the 'the smoothnes of a 6 with the economy of a 4'.
    
    Isn't the Volvo 850 engine a 5?
    
    Mark

There's also a few flat-12's out there that are pretty, er,
interesting!  :)

Chris.

>There's also a few flat-12's out there that are pretty, er,
>interesting!  :)

180 degrees (flat) V-12 for the Ferrari Testarossa

Don't forget the flat 2's!  (2CVs and old Maxwells come to mind...)

Dave

    Does the V-8 not merit a mention?
    
    Brian Pituley
    

    
    Or the V10? :^)
    
    Mark

Or the 5-bank 30 cylinder unit (the `egg beater') as used in the
Sherman tank!

Chris.

Perhaps someone can explain why BMW have dropped the straight six engine 
for 3.0+ litre configurations in favour of V-8. Marketing reasons? Straight 
six is too big - but making it a V-6 looks as if they're copying other 
manufacturers?

Rupert

    
    Isn't there a sort of 'optimal' cylinder size of around 500cc per
    cylinder? I'm sure I heard/read this somewhere.
    
    Above that you start to build in extra problems (don't ask me what,
    I'm just a computer programmer :^)). Therefore a 3 litre 6 is about the
    limit along with a 2 litre 4 and a 4 litre 8. This ties in pretty well
    with most manufacturers engine designs.
    
    Maybe a 3.5 six wasn't too much of a problem, but a 4.0 was ?
    
    Mark 

    Did anyone read/here about that motorcycle engine which has something
    like 24 cylinders, each with a bore of about an inch, and a stroke of
    6mm ?? (Something in that order).
    
    This minute engine, total cc some pathetically small amount, can
    produce up to 200bhp, redlines at 450rpm, and can run on a mixture of
    water/fuel too ?!
    
    It was in MCN. Sorry I can't remember any more specific details, but it
    DOES exist.
    
    Cheers,
    Dan

    re .24
    
    Do you really mean 450rpm?
    
    Clive

    Yup.

    If it does redline at 450rpm, then it must have some phenomonal amount
    of torque to actually be of any use. In fact, given that torque is
    measured in (for example) ftlbs, and the stroke is only 6mm, then there
    must be a fair whack of force at the piston crown. Mind you, with 24
    cylinders, maybe not, although only revving to 450rpm implies serious
    gearing.
    
    Clive

    I agree, the engine sounded pretty amazing to me too.
    
    From what I can remember, the pistons were arranged like one of those
    plane engines - in a circle around a common 'crank'.
    
    Maybe the rpm figure is so low because of the number of pistons... I
    dunno, maybe my facts are wrong. I'll check it out tonight when I get
    back home.
    
    Cheers,
    Dan

    
    re . BMW 3.0litre
    
    I think the new BMW engine is a V8 not a V6 - and is available in both 3.0 
    and 4.0 litre designs.
    
    Richard.

RE: a few back...
This is old, old news. A guy, I believe an Australian, invented a 
multi cylinder engine where the gudgeon (sp) pins of the pistons run 
in the groove of a circular cam-plate. The camplate groove has 
several 'cycles' around its 360 degree path (this is well difficult 
to explain but obvious if you see one). So this engine has pistons 
but no connecting rods or crankshaft. Depending on the number of 
'cycles' in the 360 degrees of the camplate you can get multiple 
power strokes from an individual piston - the one I saw had a six 
cycle camplate so  for each revolution of the camplate each piston 
would produce 3 power strokes (it was a four-stroke engine). If you 
have multiple cylinders arranged around the engine in a radial 
fashion (say six cylinders) you get a lots of power strokes per rev, 
and therfore a lot of power/torque at very low RPM.

The beauty of this engine is if you bolt the camplate to the vehicle 
and put a tyre around the outside (!) it will propel the vehicle 
along at a reasonable span of road speeds with no gearbox required! 
Stopping and starting is apparently no problem, when you want to stop 
you just stall it, when you want go you just nudge the vehicle 
forward and it will pick up from virtually 0 RPM!

I'm sure there is a catch otherwise we would all be using them.

- John.

PS: I first saw this design at least 15 years ago.

    Sounds like the one, yup. Also, it's supposed to be dirt cheap to make.
    The particular one they were going on about was comparable to 500cc
    (ofcourse it would seem that wasn't it's *physical* displacement,
    surely?)....

    Re. Number of cylinders vs capacity
    
    You're right. It has to do with the bore and stroke. Automobile engines
    must be very clean. The way to get a 'perfect' combustion at a certain
    top rate (function of rpm) will inevitably limit the capacity of the 
    cylindres. Ferrari used to make 250cc displacement per cylinder as an
    ideal number back in the early 60's. Engine technology has surely made
    a lot of progress when you consider the most recent Porsche engines
    (3.8 ltr boxer or 3ltr inline 4). The recent Ferrari engines work very
    well with cylinder capacity almost double the 250cc magic number.
    Listen to the new F355 ... while it is a V8, it sounds pretty good.
    
    Back to BMW. Yes, the reason to make inline 6's then V8's and V12's at
    the top has to do with cylinder capacity. 

The problem with this type of engine (I think it's called an Orbital 
engine) and rotary engines (the Wankel) is - how do you define its 
capacity? Is it simply the sum of the cylinder swept volumes, or do 
you have to take into account that the cylinders will 'sweep' their 
volume several times per revolution? Norton had this problem with 
rotary engines in their racing machines when competing against 
conventionally powered machines.

- John.

BTW - I just heard on the radio that Norton have just gone bust 
(again).

I thought that the engine capacity would be the sum of the maximum
displacement of all combustion chambers regardless of the number
of revolutions involved, but of course there's little chance of
such a simplistic approach actually being applied!

Re optimum cylinder sizes, what must the designers of the Merlin
27 litre V12 have been thinking?  :)

Chris.

>Re optimum cylinder sizes, what must the designers of the Merlin
>27 litre V12 have been thinking?  :)

This engine has a great sound.
Quit often used for Tractor Pulling.

    re.30
    
    This is the one, I think, yes.
    Some details I have...
    
    It has ports, not valves, and the engine example I read about had 48
    pistons for a total 'capacity' of 500cc - 24 pistons fired
    simultaneously for every 15% turn of the engine! Each turn of the
    output shaft means each cylinder fires 12 times - 576 firings per turn!
    
    The 500cc example was capable of producing 260bhp. There was no
    specific mention of bore or stroke, but I remember from another source
    that my previous figure of a 6mm stroke was about correct.
    
    It was also capable of running on 30% water.
    
    Cheers,
    Dan

The only demonstrator I saw was a six cylinder four-stroke engine of 
undefined capacity (but was about 25cc per cylinder) mounted inside 
the rear wheel of a strengthened bicyle! It went really well!

There was also a static demonstration with an eight (I think) 
cylinder two-stroke engine which when run up to about 2000 RPM made a 
glorious sound :-)

- John.
 

    
    was it one of these orbital engines which was shown on Tomorrows World
    a few years ago ? They demonstrated an engine which drove a central
    shaft, to get more power another engine could be put onto the same
    shaft. The units they user were pretty small - the whole setup ran on a
    table-top/bench affair.
    
    Graham

    
    That sounds about right, I remember some mention of it running on a
    water mixture as well...
    
    G

    Very interesting ! 
    
    I still prefer the tri-phased linear electric motor ... top "torque" at
    zero and low speeds, no vibrations, no refueling, no grease, ....
    
    Nice week-end everyone !
    

    Pah!
    
    All this talk of V6's and V12's .. rubbish engines the lot of them.
    
    Who remembers the best engine of all? The Ford V4!!!!
    
    Yes indeed, all the smoothness of a carthorse on cobblestones with the
    impressive fuel economy likened only to a Saturn V rocket. The power of
    2 2CV's roped together. A truly impressive contender for the 'Best V
    engine' award.
    
    I believe the V4 was put in the 2 litre transits back around 73 and
    then Ford thought it would be a good idea to put it in their 'luxury'
    car range, so they gave it to the Granada (Consul?).
    
    I was unfortunate enough to own one, it was nice and comfy, but I
    couldn't afford it for long. It seemed to have a permanent steering
    fault, every time it passed a petrol station it veered sharp left!
    
    Stuart

    
    The (t)rusty V4 even made its way into the Marcos GT in the late 60s.
    
    Nearly everyone with a V4 has dumped it by now and dropped in the V6,
    but there was a V4 at last year's rally which has been owned by the
    same person for over 20 years (he may even be its only owner).
    
    However, even he wasn't glowing in his reports of the V4 :^)
    
    Mark

    
    re .42
    
    Showing your age :-)   The V4 could also be found in Zephyrs and
    Corsairs and maybe even the earliest Capri - probably long before 
    your time!
    
    Richard.

Didn't Saab have a V4 in one of their cars?

Dave

    See... a V4 supporters club is forming.
    
    I hadn't realised Ford had stuck the lump in the Capri. I suppose it
    was a case of, lets make the British public think they've got an
    American car, we'll stick a V engine in it.
    
    I *DO* remember both Corsairs and Zephyrs, my uncle used to own a
    Zephyr. A real car, no need to get in the backseat with your
    girlfriend and no gear stick to get in the way ;*) (Bench seat and
    column shift for those who don't remember)
    
    Stuart

    
    	The Corsair 3000E was a lurrrrrvley car. My uncle had one (just
    	before he got a Lotus Europa - ultimate joke car! It was always
    	breaking down...).
    
    	The Corsair went like the proverbial. Only problem seemed to be
    	getting it to go where you wanted to go, and with stopping in a
    	hurry.
    
    	Andy.

    
    A friend has a Corsair 2000GT (1966?ish) with the V4 engine, lovely
    motor, all original etc.
    
    G.
     

re.48:

How much?

Ex-Corsair owner.

Yes the Saab 95/96 started off in life with an 850cc 2 stroke, but then the 
fitted the Ford 1500 V4.

Trouble was they fitted it to the old gearbox, so A) you could fre-wheel it, 
great for changing gear without the clutch!, and B) it was fitted forward of 
the front wheels which made it a bit wallowey if you chucked it around 
corners!. Graet fun though!

Richard

    
    My brother had a Capri 2.0 GT V4, Auto,  was alright 'till the big-ends
    went.
    
    Richard

    I had a V4 Tranny about 18 years ago, that ran its mains and ends;
    common problem on the V4.
    
    Laurie.

    Yes indeed, it actually used to win rallies back in the 70's
    made an odd noise like a muffled lawnmower, looked a bit
    teardrop shaped. The norsemen ran them in the snow with
    razor thin tyres and left the Ford Escorts with fat tyres
    scrabbling around like fools... ah them were the days.
    Also may have been aircooled? not sure.
    
    Matt_remembering_RAC_rally_197?
    

    err that is the Saab I meant...

    A number of things need to borne in mind when talking about engine
    horsepower and smoothness. All engines will develop harmonic
    frequencies when running. This will follow an improving trend as you 
    increase the number of cylinders from 1 to 4. after 4 cylinders the 
    next smoothest engine is a 6 then 8 cylinders then 12. 5 cylinder
    engines slot in somewhere between 3 and 4 cylinders  and 10 cylinders
    slot in some where between 6 and 8. If you look at a 3 cylinder engine
    for example the firing order MUST be either 1,2,3 or 3,2,1. This
    obviously sets up a rocking moment as each cyclinder fires. This is
    countered by balance weights on both the crankshaft (and/or pulley) and
    also the flywheel. if we take two three cylinder engines and arrange
    them in a v formation then the obvious result is that we have two
    rocking moments which can (to a certain extent) be cancelled out. 
    Unfortunately, as the two rocking moments are operating at a number of
    degrees (typically 60 but can be as low as 15 (VR6 volkswagen)) from
    each other these rocking moments cannot in themselves be completely
    eliminated. If you look at the internals of a V6 engine you will see
    large counterweights on the flywheel, crankshaft, and crankshaft
    pulley, just as you would on a 3 cylinder engine. If we narrow the
    angle between our two 3 cylinder angles then the counter balance
    weights get progressively smaller until with a straight 6 they are
    virtually eliminated. A straight 6 still has some harmonics but they
    are primarily secondary harmonics that occur at around 6500 rpm
    (typically). This is why there the counter balance weights do not
    vanish altogether. If on the other hand we increase the V angle, the 
    balancing weights get larger until we pass 90 degrees where they start
    to get smaller again. Increasing the angle to 180 degrees (a la
    porsche) provides what is probably the best balanced 6 cylinder
    configuration as the distance between firing pulses can be kept very
    small, hence reducing the need for large counter balance weights. The
    other benefit of a flat 6 is that the crankshaft can be kept very short
    and thus reduce the amount of rotating mass as well as reducing the
    amount of 'whip' in the crankshaft as different cylinders fire.
    Following this logic through, we can easily see why 5 cylinder engines
    are inherently not as smooth as 4's or 6's.
    All of the above is assuming all other things to be equal. (i.e
    bore/stroke ratios, engine capacity, maximum rpm, BHP etc)
    The prime consideration for developing high horsepower is the ability
    of the engine to ingest large volumes of (cool) air and fuel. Large
    bore / short stroke engines will (again all other things being equal)
    develop more power than smell bore / long stroke engines purely because
    there is more room to fit larger inlet and exhaust valves. This is why 
    the very high powered F1 engines are all relatively short stroke, 
    large bore. Turbocharging, supercharging and Nitrous oxide injection
    all force feed the engine with a larger volume of air than the engine
    can normally ingest by itself. An important factor when dealing with
    forced induction is the effect of compressing a gas. When the air is
    compressed by a Turbo or Super charger it becomes hot (Boyles law is
    it?). This will decrease the density of the gas hence the need for
    intercoolers to cool the mix and thus increase the number of molecules
    of air in a given volume (hence my reference to cool air earlier). 
    In earlier times water injection either with or without meths
    accomplished the same thing. Nirous oxide injection works diferrently,
    in as much as it is not only very cold when it is depressurised,
    but NO2 is also a carrier of large quantities of oxygen (approx 68%
    oxygen (by mass) as opposed to the 21% that we can obtain out of the
    atmosphere - less in cities!!). The main drawbacks to large bore, large
    valve, smallish capacity engines are the lack of low down
    power and torque (the two are related). This is due to factors
    such as the gas speed through a valve / port combination and the way in
    which the gasses combust during the ignition phase. The larger port and
    valve surface area will slow the gas speed and lose the effect of
    inertia inherent to a column of moving gas. It will also therefore,
    cause poorer mixing of the air and fuel (less turbulence within the
    combustion chamber). 
    I hope that this will clarify some of the threads that have been posted
    here.....
    
    Alastair.
    oxygen   
    

    Doesn't the short stroke also benefit from lower linear velocity for
    the pistons, and hence more easily achieve higher rotational speeds,
    resulting in a higher 'rate of doing work' i.e. power?
    
    Chris 

    Yes this is true also, but another factor wich can have a greater
    impact in todays world of hi-tech materials is the weight of the
    reciprocating masses. Obviously the larger the bore the larger the
    piston hence heavier. To get the optimum design you need to consider
    not just the linear velocity of the piston but the momentum of the
    piston/con-rod unit as whole. Piston speed used to be a major factor in
    causing piston ring wear, but modern materials have virtually
    eliminated this as a major concern.

    Thanks for the very detailed explanation Alistair.
    
    One, unresolved, question is about boxer vs boxer. The Porsche flat-6
    is a boxer ie opposite pistons move in opposite directions. The Ferrari
    flat-12 is not a boxer ie opposite pistons work in same direction. 
    
    What's best ? The Porsche boxer has a longer crankshaft, how about
    balancing ?

Someone noted that the Ferrari was actually a 180 deg V12 as opposed to a true 
flat 12.  The firing order or something was the key I believe.

Dave

>Someone noted that the Ferrari was actually a 180 deg V12 as opposed to a true 
>flat 12.  The firing order or something was the key I believe.

yes, I think that's right, something like (this could be totally wrong!) 
because cylinders from different banks share a common crankshaft bearing.  Or 
something.

Chris.

    The boxer engine to my way of thinking would probably be better
    inherently for balancing as the two pistons are always moving in
    different (opposing) directions. This would tend to reduce harmonics 
    and to a certain extent offset the longer crankshaft that would be
    required. I think (but am not by any means sure) that the Ferrari flat
    12 as used in the 512 has pairs of pistons connected to a common
    crankshaft big end journal (as is the norm in most V8s).This
    arrangement gives a more compact powerplant than the boxer where every
    conrod has its own journal. One thing of interest is that flat 4
    engines do not generally speaking run any smoother than an in-line 4.
    
    
    Alastair 

    re. Ferrari flat-12, boxer vs boxer
    
    The confusion came from the fact that Ferrari called their initial
    coupe using that engine the 365BB, BB for Berlinetta Boxer. In Ferrari 
    Club ranks you hear people talk about boxer engines, which is wrong.
    
    Apart from spawning confusion Ferrari went even further into crazy
    design when they located the above-mentionned flat-12 on top of the
    gearbox and differential. Needless to say, this is not the best
    balanced combination. The various BBs (365, 512, TR, ...) have shown
    regular improvements in roadholding but are still miles behind real
    midship engine racers (Lotus Esprit, Venturi, ...). 
    
    The Porsche boxer engine while being located at the far rear end of the
    car enjoys a dry sump lubrication system, meaning that it is located
    very low in the car ... yielding an unexpected good roadholding.