Number of Cylinders

[uzael]

Back in the early 90's, all manner of engines were run, V8's, V10's and V12's. There was always the discussion of torque vs hosepower, but since each is a function of the other I am confused as to what the advantage of each might be, given the same displacement, wherether it be 3L or 3.5L. Could someone enlighten me on this?

[West]

Back in the early 90's, all manner of engines were run, V8's, V10's and V12's. There was always the discussion of torque vs hosepower, but since each is a function of the other I am confused as to what the advantage of each might be, given the same displacement, wherether it be 3L or 3.5L. Could someone enlighten me on this?

Let's use a 3.5L V10 vs a 3.5L V8. Using division, a 3L V10's displacement should be around 350cc per cylinder while the V8 will have a little more displacement (I didn't calculate it, but it should be obvious to anybody here). With this bigger cylinder, chances are that the stroke will be bigger in the V8 than in the V10, should the cylinders have the same, or almost similar, bore. A bigger stroke leads to more torque, but at the cost of higher RPM limits (the longer stroke adds vibrational and balance penalties to the crank, limiting its effectiveness). Try spinning an 8-track with your finger near the center of the record, and then after a while spin it backwards. Do the same with your finger at the edge of the record.

If we use a 3.5 V12, the size of the cylinders is even smaller than that of the V10, and its safe to assume that the stroke will be even smaller than that of the V10. It is possible that this V12 will use a smaller, and hence relatively, lighter connecting rod, which will make it easier for the crank to rotate. Of course, with this smaller stroke, the torque will suffer.

[joseff]

A V8 would also be lighter & more fuel efficient compared to a V10

[Stu]

One of the other considerations other than just pure horsepower and torque is the size of the engine and the heat which must be dissipated. Back in the day ('91 I think!) The Ferrari/Honda/Lamborghini V12's were always 30-40mm longer than the V10s/V8's and as John Barnard spent many years moaning about at ferrari always needed larger radiators and obviously created more Drag through the larger sidepods.....

Stu

[NickT]

Looking good.

V10 were settled on as they were the best compromise sitting squarely between the torque and economy of the V8 and the higher peak power, weight and size of the V12

As for vibration, well "Theoretically, the best V-angle is 72°. Like two inline-5 mated together, there is no vibration in vertical and transverse directions, but there is vibration from end to end of the engine, thus require a balancer shaft install in the V-valley for best balance. However, there is no vibration between bank and bank because pistons in both banks are in the same positions." - Autozine technical school

The other area that has to be considered is friction and packaging. Generally the more cylinders you have the more power you can produce. However there is a corresponding increase in friction, overall weight and size to overcome which means that the returns are diminishing with each additional cylinder.

I hope this answers your question

Cheers

[Becker4]

i thought it was only for v10s that best v-angle was 72, for other engines, there are different angles . . . is this incorrect?

[joseff]

a 72deg V10 would mean an even firing pulse without the need for a complex crank.

because a 4-stroke engine fires once every 720deg, 720/10cyls = 72deg
(ignoring the units)

OK a question for the mech engineers out there: do the current non-72deg V10s (eg. 90) have a single-plane or 2-plane crank?

[Becker4]

so a V8, for example, has an ideal angle of 90? if so, then that would be another advantage of the v8: better firing at a lesser angle, giving a better C of G with less severe vibrations at high revs. also, what is difference between single plane and two plane crank?

[Scuderia_Russ]

the V-10 is the best compromise among rpm,weight,fuel consumption,size shape,structural integrity and driveability,and a V-10 will not reach its crankshaft limitation until about 19,000 rpm whereas a V-8 is limited to around 15,000 rpm by secondary torsional vibrations in its crankshaft.When rpm was in sight of 19,000 a few years ago,Audi experimented with a twelve cylinder engine,not in V,but in W config.The lengh was shorter than that of a V-8 of the same capacity and potentially stiffer,without a dramatic size increase that would have affected rear aerodynamics,maybe realising all the advantages of a twelve cylinder engine without any of the drawbacks.As we know tough,we won't see any more than ten cylinders until after 2007!

[joseff]

When you say "W12", would you mean a double-VR6 (narrow angle 6) or a 6+6+6 (like in the veyron concept)?

I can't see how you can fit a twincam head on a VR6 and make it work at 19000rpm

Btw I think a V8 can work at 15000+rpm, Ducati's new V4 runs at 16500 IIRC.

If a W12 as a double-VR6 is *that* good, what's stopping current engine manufacturers from making a double-VR5-W10?

[Scuderia_Russ]

I mean three banks of four cylinders.Audi abandoned their project before Volkswagen did combine two VR6 engines to create their first W12,going on to create a W16 for the 623 horsepower Bentley.VW might have used a W config in the Passat,can't remember.When i say 15,000 rpm i mean an F1 engine in the mid 90's,not a motorcycle engine from '03/'04.
Although a size saver,you would have the extra weight of pistons,valves,gear etc. and possibly a CG problem.I'm sure someone on here can tell us about design implications/solutions for reaching 19,000 rpm with such an engine.I can't becase "engines aren't my bag baby!"

[Roy]

..... A bigger stroke leads to more torque, but at the cost of higher RPM limits (the longer stroke adds vibrational and balance penalties to the crank, limiting its effectiveness). Try spinning an 8-track with your finger near the center of the record, and then after a while spin it backwards. Do the same with your finger at the edge of the record...

Generally I agree. Bigger stroke leads to more torque. But the total torque of V8 and V10 shall be almost the same since the total torque is a function of total piston displacement. So, whatsoever, logically V10 will produce more power than V8.

[marcush.]

anyone who has had a look into the combustion chamber(Piston design) of a VR engine knows ,that these are a child of compact packaging and cheap production and all out performance was not a design factor .

[Carbon]

Just going back to Becker4's last question, can any of you explain the 2 plane and 4 plane crankshaft design? I've read that some of Ferrari's road cars have 2 plane designs, but I don't know what that means.

[Guest]

the w12 isnt three banks of 4 cylinders but rather 4 banks of 3 cylinders. think of it as 2 v6 engines placed very close to each other. it has only 2 banks of cylinders, with varying cylinders on each bank.