Is the format of an engine important?

[Andy Clayson]

This may be a really stupid question but...

 

I notice that BMW continue to use straight-6 engines, while many other manufacturers (whose cars have shorter noses) use V6 format. Some manufacturers (Porsche, Subaru) use boxer format. Why?

 

I can understand a V6 is smaller (longitudinally) and so can fit into a smaller engine bay. But why not use a boxer layout? I can't believe that BMW stick with straight configurations simply because they don't know how to make a V. yet they don't market themselves as using a straight configuration in the same way they market themselves as using rear-wheel drive. Similarly, if the V configuration is used in F1 cars so that the centre of gravity can be lowered, why not use a boxer configuration (or something close to it like an 80-degree V) and get ALL the weight low down.

 

I just don't understand...

 

Andy

[Peter Carmichael]

A straight six is a balanced configuration that balances second order forces. It is inherently smooth running. 90 degree V8s are also inherently balanced. V6s are not. Straight sixes are longer (obviously), so can suffer from being more fleixble besides the packaging issues.

 

Note that TVR's AJP engines are v8 (flat plane) and straight 6.

[Peter Carmichael]

flat fours have the cylinder heads a very long distance apart, giving block flexing problems and long timing belt runs - these have caused problems in Subaru's rallying campaigns when producing 300+bhp.

 

Edited by - Peter Carmichael on 17 Sep 2002 13:22:24

[Peter Carmichael]

As for formula 1, they experiment with the V-angle. A V gives you a stiffer block and remember that in formula 1 the engine is a chassis component, so a bendy engine gives bad handling. When Ferrari persisted with a V12 it gave better power (if peakier) but the extra length of the block gave packaging and flexibility problems.

[murph7355]

I also think F1 regs don't permit the use of anything other than a V10 at the moment, with presumably 'V' meaning the angle must be <180degs (think Renault are using 120 or something, for the reasons you note, but reliability was a hassle at first).

 

 

[Paul Ranson]

If you open the v-angle out then the centre of g is lowered, but if you make it too wide then the engine intrudes into the diffuser. This was one of Ferrari's problem during the ground-effect years with their flat-12.

 

Paul

[Old Septimus]

Peter, what are the advantages of narrow angle V configurations, like the old Lancias and some VWs? Is it purely to reduce the length of the block?

[MikeE]

When Ferrari persisted with a V12 it gave better power (if peakier) but the extra length of the block gave packaging and flexibility problems.

---

 

Are you sure that's right, I thought the V10 was a good compromise between out right power and efficiency. i.e it produced more power than an eqivalent sized V8 (the Zetec V8 of in the Beneton) and had less internal frictional losses than the V12 configuration.

 

 

Note that TVR's AJP engines are v8 (flat plane) and straight 6.

---

*thumbdown*I wouldn't use TVRs engineering prowess as an endorsement for a particular configuration

 

Edited by - MikeE on 17 Sep 2002 13:50:17

[clarkey]

I think the reason that many manufacturers use V6s is that they can be mounted transversely, so are suited to well-packaged front wheel drive applications. The BMW straight six can only be mounted lengthways, so is not suited to a front drive car.

I'm sure it is nothing to do with smoothness, power delivery, or anything else. Just a desire to build a car as economically as possible, by using exactly the same platform for each engine size and layout.

[Buda]

Don't porsche use a flat 6, the VW Beetles got a flat 4 and didn't the ferrari 512 have a flat 12, Ithought it was to do with space, i.e. a flat engine is not as high and so can be put lower in a sports car, in a beetle its just so it fits I think and a 911 is basically a beetle, there shouldn't be much difference from a straight six because the forces are both from the same plain i.e. horizontal? oooo I'm speaking crap again, I can feel it coming on, must go and lie down

[Mark Piper]

Zetec V8? wasn't it the Ford HB? The Renault's angle is 111 degrees I believe, but they can't get enough power out of it, can't dampen the vibrations enough or most importantly guarantee it'll last long enough when the one engine per weekend rule comes into being in 2004, so are going to resort to a more conventional V (possibly as early as next year ISTR).

 

I'm sure I read somewhere that Ferrari could get more power out of the V12 than V10 but stuck with the V10 (b4 they became compulsory) because of the better packaging it offered them.

 

Quote "911 is basically a beetle" ...ergo a Westfield's basically a Caterham isn't it?

[mark4newman]

seems like the top temas , don't want the one engine rule, so it wont be happening!

 

Su77on Se7enS

 

M100EOW....

[Buda]

I thought the Beetle was developed by Mr Porsche, Mr Porsche developed the 911, ergo he stuck with what he knew, would you build a sports car with the engine out the back? thats what I was trying to say thats all

 

Edited by - Buda on 17 Sep 2002 14:27:12

[caterhamnut]

I *think* one of the problems with the Ferrari V12 was that is was very thirsty. If you look at the F1 cars of that era they were often very flat but also very wide at the rear - in fact the width of the body seemed to be quite consistant front to back. Now the bodywork at the rear curves in sharply, to give the coke bottle shape. This is possible because of the tiny proportions of the V10's, and results in a much cleaner air flow around the engine, gearbox, through the rear wing, and through the diffuser.

 

V10 formula is fixed by the powers that be - many people think it should be open, then we would see a mixture of design layouts. It would be interesting to see what the optimum layout would then be with all these top engineers given a free reign.

 

Renault have been using an engine with a V angle of about 110/111 degrees, mainly so that they can lower the C of G as has already been mentioned. Unreliability was caused by flexing of the block I believe, and also excessive vibration causing component failure. The Renault drivers had a much lower rev limit for a while to limit failures, and had to endure a nightmare season last year whilst the engine was developed under a very public spotlight. If you saw any of the pictures at the begining of the season it is a beautifuly packaged thing. The shame is that just as this engine, which was one of the few slightly innovative things in todays ever controlled F1 environment, is coming on song it seems that Renault will revert to a more traditional engine V next year, as there are fears about reliability under the new 'one engine rule' which is due to come into force. Shame.

 

😬26,000 miles in 13 months!

angus@tinyworld.co.uk

[caterhamnut]

Mark P - you beat me to it!!

 

😬26,000 miles in 13 months!

angus@tinyworld.co.uk

[kjp]

90 degree V8's are not balanced (second order moment)

[Joe 90]

Everone else has contributed, so I might as well. V6 production engines are currently en-vogue because they package up well and deliver smoother power (more firing strokes per revolutio) then fours. Modern distributor-less ECUs mean that you can have any V angle you like without too many problems and you can map out problems caused by different length induction systems, see VW VR6 for an extreme example. Straight six engines have perfect dynamic balance , so they are, and probably always will be smoother than V6s. A down side of the straight six is that the long crankshaft limits maximum RPM.

 

On the subject of flat engines, there are two types.

Firstly there are the true "boxer" engines such as the BMW bike twin, VW beetle flat 4 and Porsche 911 flat 6. Boxer engines have good balance, even as 2 cylinder units

Secondly there are the 180 degree V engines, such as the Ferrari. The 180 degree V does not have such good intrinsic balance, but with 12 cylinders it doesn't matter. It is smaller and has lower losses than the true boxer.

 

In either case, a major headache is the exhaust routing on a flat engine. If you stick your engine over your gearbox, you will have room, but you compromise C of G , as per Ferrari 512 etc.

 

99,000 miles so far

[Peter Carmichael]

I found this interesting.

 

and I found a goldmine here:

 

Section 1

Section 2

Section 3

Section 4

Section 5

[Highlander]

Call me technically challenged, OK thick, but surely the length of the crankshaft should have no bearing on the max engine speed. Rather the length of the con rods and hence piston speed that determines 'termial' velocity.

[Mark Piper]

Buda, not intending to pull your chain, just fed up with 15 years of being told that my 911s were just Beetles in drag. You're quite right too, although persevering with the design concept was more a desire for Ferry Porsche to prove that it could work, rather than sticking to his knitting.

[Old Septimus]

It was different generations of Porsche who did these things. The old boy did the Beetles, Auto Unions, Tiger tanks, Porsche 356s etc and his son did the 911.

[Peter Carmichael]

Highlander,

 

If, as I think, you are referring to the VR6 description please appreciate that this is not written in the authors first language and I think he meant the "stroke of the crankshaft". His comment is then more appropriate.

[Highlander]

Peter C

If Olivier was refering to crank stroke, then I understand the comment.

I wasn't aiming to lambaste someone elses comments, merely to confirm if my thinking was correct.

[Miraz]

I think the report is correct, it's very difficult to build a long engine that will sustain high rpm - the rigidity of the block and the management of vibration/balancing of the crank will eventually result in a bottom end failure. It's much easier to build a high speed engine with a teeny, short little crank.

 

I may have the wrong end of the stick....does anyone know of any exceptions?

 

Miraz

 

 

Edited by - Miraz on 17 Sep 2002 17:20:15

[AMMO]

Nope.

 

All high speed engines I know of have short cranks. BMW with the M3 tried building a relatively high rpm engine with a longish stoke crank. I've been told that they are falling apart.

 

AMMO