20 replies to this topic

[FordFan]

I noticed, in looking at the specs of various engines, that most of them have cylinder angles of 72 degrees, except for Ferrari, which is 80 degrees. I'm told the greater the angle, the lower the center of gravity. There must be some disadvantages, though, or the other manufacturers would be using that configuration as well (unless they can't do it technologically).

So, why only Ferrari with 80 degrees, and what's so special about 72 degrees such that everyone else uses it?

[Jonathan]

Without resorting to "split" crankshaft journals the ideal balance for a V8 engine is 90 degrees and for a V12 is 60 degrees, therefore one would assume that 75 decrees might be ideal for a V10 (right ?).

My guess is that the angle of the v shape is not based so much on an ideal balance so much as for (1) packaging efficiancy and (2) what provides the lowest centre of gravity with out (3) compromising aerodynamics.

Perhaps Ferrari is mostly inderested keeping the height of their engine as low as possible so as not to interfere with the airflow under the rear wing ?

[Ray Bell]

72 degrees - 80 degrees! What is that going to translate into in overall height? 1mm or 2mm?
Width will not be terribly different, either.
But there will undoubtedly be a reason - probably relating to some design parameter the team set when they had a white sheet of paper.
Did you know that the C of G of a horizontally opposed F1 engine is generally through to be higher than that of a V?

[tak]

The Bosch Automotive Handbook shows 72 degrees to be the best V-angle for engine balance. It has to do with 5 power pulses per revolution (360/5 = 72). If you do this for a V8, you get 90, and so on. BTW, an inline 6 cylinder engine has perfect balance, so a V-12 has perfect balance at any V-angle...
Any 180 degree engine (boxer) needs an oil pan (or dry sump pan) BELOW the cylinders--this helps prevent the pistons from slapping the oil ("windage"). The result is that the oil system raises the whole motor (and the resultant CG).

[sunil]

Tak,

Do you know why inline 6 has perfect balance?
I happen to have a M3 (which got a i6) and one of my friends asked me why they use I6 instead of V6 which will be more comapct and my answer was better balance but could come up with a reason.

[Ray Bell]

An inline six does need a harmonic balancer at the front of the crank, however, to take out the harmonics (sort of balancing up the weight of the flywheel at the other end) - keeping the crank all in a straight line.
And doesn't an inline 6 have a nice howl?

[DangerMouse]

Ray, the thing you mention isn't really a balancer but a damper to reduce the tendancy of natural harmonic frequencies becoming destructive at certain revs.

I suppose perfect natural balance isn't as important these days as overengineering other parts to deal with excessive vibes without wasting too much in terms of weight is probably acceptable, the only reason however for running slightly different V angles I can think of is possibly to optimise the intake path, and the power increase from that outweighs the power drain/slight weight increase from out of balance configurations.

Might be tosh of course!

[Art]

Ray Bell.

How about giving me some Tec. talk on how and why a V has a lower C ov G Than a flat opposed engine. If the center line of the crank is the same distance from the road surface on both engines.

Art NX3L

[Ray Bell]

Just draw a diagram of the engine looking from one end. The datum figure is the flywheel diameter.
You'll find that be the time the exhausts (or the inlets!) have room to fit under the heads that you have lifted the crank centreline higher. Just can't be done without it. Maybe a very wide-angle Vee - say 150 degrees, would be the optimum for c of g, but then you have width destroying your airflow and getting in the way of the suspension.

[Art]

Ray Bell.

Both engines have to have a flywheel so we can eliminate that. Now for the intake & exhaust? We re design the heads intakes between the cams W196 style and switch sides of the heads with the exhaust. We gain body width but eliminate the large air box and can run a much lower body profile behind the driver. The exhaust headers will protrude through the body which looks nice anyway eliminate engine room heat and can be aimed at the rear wing better. So the C ov G is the same and we have a different looking car. But it may be equal to the V engined car and the aero package may be the same or better.

Art NX3L

[desmo]

With the included valve angle being so small in a modern engine, there isn't any room between the cams for a port anymore.

[This message has been edited by desmo (edited 02-23-2000).]

[Art]

Desmo.

What angle are the valves? Are they running a near flat combustion chamber?

Art NX3L

[Art]

Where can I find a picture of the valve thane and combustion chambers? I have never been able to find any.

Art NX3L

[Ray Bell]

By the way, the clutch diameters are around 8".
Exhaust pipes also need neat and gradual bends - it's all a minefield down there.

[Art]

Ray Bell.

I was surprised the first time I saw an F1 clutch it is very small. And with my idea you could use almost straight exhaust pipes like the old Auto Unions. It is nice that we all can get in and discuss each others ideas.

Art NX3L

[desmo]

I wouldn't go any further than to say that the included valve angle in an F1 motor is <20 degrees. The combustion chamber can hardly be described as flat though. The actual shape of the combustion chamber at TDC is extremely complicated. Much of the volume is, of necessity, in the reliefs of the piston domes for valve clearance. This is far from the ideal of a sphere or at least a lenticular shape that would be much better for efficient combustion. Much of the blame for the tortured shape is due to the extremely oversquare bore to stroke ratio required to spin a four stroke up to 18K (or whatever it is). It is incredible to me that such a massively compromised design works as well as it does. It is simply the best compromise that present circumstances allow.

[This message has been edited by desmo (edited 02-24-2000).]

[Yelnats]

I thought the flat twelve that Ferrari used in the eighties had a low center of gravity, at least that was the claim at the time. In any case ground effects spelled the end of the flat twelve cause it interferred with venturis and diffusers.

[tak]

Sunil-
I'm afraid I can't explain why an inline six is perfectly balanced without using diagrams. Head to your local library and look up the "Automotive Handbook" published by Bosch. In the section called "Function and Dynamics of Power Transmission Components", there is a 7 page description of engine balance, starting with a single cylinder example, and then expanding it to most common motor layouts.
You are right about the better balance answer though! Sorry I'm not more help!

[Racer]

Just some info, Ferrari use 90° for their 2000 challenger.
And a clutch is 97mm in diameter today for a F1-engine.

[Blackhawk]

I was just looking at some old pictures from the 70's (around 78 I think) and noticed Ferraris V12. If you can call it a V12, its more like a boxerengine. Strange. Any thoughts about this?

[desmo]

It was a boxer (horizontally opposed). As the clutch diameters got smaller, and the crankshafts lower there was no longer room for the exhaust plumbing with this design. Ray, I believe that clutch diameters are now down to 4 1/2" or less!