7 replies to this topic

[Macca]

Looking through spec sheets for 1960s Ferraris, it struck me that some 3L and 4L engines had the same 77mm bore, but strokes of 53.5mm, or 71mm with a taller block. So if the the valve size is limited by the bore(assuming both have the same number of valves and both use fuel injection), how can you get a third more mixture into the cylinder to develop a third more power?

Would the 17.5mm greater stroke suck more mixture?

Would a longer stroke allow higher-lift camshafts to push the valve in further or for longer?

If more air can get in with the longer stroke, would the injection sort out the mixture automatically, or would it need a different cam?

What would be the likely effect of the different angularity of the conrod; and would the conrod and piston have to be heavier to handle greater acceleration at the same revs?

Bearing in mind that I am technologically inept, can any kind person help out in words of one syllable?


Paul M

[Deepak]

Even though i consider myself poor in practical knowledge of engines i decided to have a go at what i think might produce more power

The longer stroke would mean more volume of fuel+air mixture (assuming bore dia is constant) and hence more of the F+A mixture is burnt in one stroke and hence more power but a lesser mileage.

I think the longer stroke can allow for more lift of camshaft but that can he controlled depending on cam profile. So i would say the option for more lift is opened up with a longer stroke.

Thirdly the mixture would have been sorted out by the carbeurator(that is from my knowledge of old road cars).

As far the angularity conrod and piston i have no clue but i would assume from basic SOM that greater accelration leads to more loads and hence conrod and piston have to be stronger.

Please correct me if i was wrong guys

[Engineguy]

Typically, max horsepower is almost completely dependent on bore size (and hence valve size) and even a stroke increase of this magnitude will show the same horsepower, but at a lower RPM. This is assuming the valvetrain can tolerate the RPMs needed to get the shorter stroke engine to that HP level. The longer stroke engine will get to the same HP at a lower RPM but even if its bottom end can tolerate a higher RPM the valves can't flow enough to match the HP/L of the short stroke engine at higher RPMs. You didn't say, but I doubt the 4L had a third more HP than the 3L, all else being equal.

[dovatf]

This subject is extensively treated under
http://www.auto-inno...ent/power2.html

Quote:

"Mechanical loads on the moving parts, as well as friction losses in the pistons and their segments against the cylinders walls, increase roughly with the square of the piston speed. The energy lost in friction is transformed into heat and this heat is mainly transmitted to the lubricating oil. In addition to accelerated wear and increased specific fuel consumption, sustained high rpm with MPS in the order of 20 m/s quickly cause lubricating oil overheating, unless the engine is equipped with a properly sized oil cooler. This is why engineers seek to limit piston speeds. For that purpose there are two possibilities only, namely decrease the revs and shorten the stroke.

As a reduction of the revs lowers the power, to reduce the stroke while increasing the piston area to compensate seems to be an appealing alternative.

There are two ways of shortening the stroke for a given displacement :

1. Multiply the number of cylinders. Smaller cylinders obviously have a shorter stroke.
2. Increase the bore and so decrease the stroke/bore ratio.

By multiplying the number of cylinders:

- due to scale effect, the surface/volume ratio of the combustion chambers worsens
- the friction losses grow with the number of cylinders
- the weight and dimensions of the engine increase
- more complexity means less reliability
One needs more main bearings, more crankpins, but the principal increase in friction losses comes from the surface that the pistons and segments circumference travels against the bores, surface which grows along with the number of cylinders for an identical displacement.

As the deterioration of the surface/volume ratio of the combustion chambers increases the thermal transfer to the walls, the thermodynamic efficiency decreases together with the reduction in displacement per cylinder.

By decreasing the stroke/bore ratio:

- a similar problem of deterioration of the surface/volume ratio of the combustion chamber is encountered
- the flame front propagation also worsens due to the widening out of the combustion chamber
- it becomes difficult to obtain a sufficient compression ratio, especially since it is necessary to arrange recesses for the valves on the piston heads
- the untreated toxic emissions increase

The designers are thus confronted with a dilemma, even if at identical BMEP and MPS, the power is proportional to piston area - as the stroke is reduced, the revs can be increased in the same proportion for the same mean piston speed. There are always unavoidable compromises to compose with. The best engine is the one which presents the best compromise for its intended operating conditions.

The stroke/bore ratio thus varies somewhat according to the requirements, but also quite randomly along with the designers' judgment. The engines produced until the beginning of the Sixties usually had a stroke longer than their bore. When, in September 1959, Ford UK presented the new Anglia, its innovative 105 E engine flabbergasted the experts by its largely "oversquare" stroke/bore ratio of 0.6, from a bore of 80.96 mm for an extremely short stroke of 48.4 mm.

(...)"

[McGuire]

Originally posted by Macca
Looking through spec sheets for 1960s Ferraris, it struck me that some 3L and 4L engines had the same 77mm bore, but strokes of 53.5mm, or 71mm with a taller block. So if the the valve size is limited by the bore(assuming both have the same number of valves and both use fuel injection), how can you get a third more mixture into the cylinder to develop a third more power?

Actually you can't...not quite. The Colombo Ferrari V12 was built in a nearly unlimited number of different tunes in both the 3.0 liter and 4.0 liter versions, so it is hard to say anything with any specificity (and there are folks here happy to argue from exceptions). But *in general* the 4.0 liter versions make more torque and power, but the 3.0 version will make more hp per liter. That's mainly due to the limitations in valve area and port volume as limited by the bore diameter -- just as you suggested.

[Wuzak]

The Colombo V12 started life as a 1.5l in the late '40s, developed through 2.0, 2.3, 2.6, 3.0 and 3.3l versions (IIRC).

Did they actually make the Colombo engine with a 4l capacity?

The 3.0l version - the famous "250" engine, had a bore and stroke of 73.0mm x 58.8mm. The 3.3l version, the "275" had the same bore, but a longer stroke.

There were also the larger V12 engines being built alongside the Colombo ones, designed by Aurelio Lampredi (sp?), which had a larger capacity from the beginning.

[McGuire]

Originally posted by Wuzak
The Colombo V12 started life as a 1.5l in the late '40s, developed through 2.0, 2.3, 2.6, 3.0 and 3.3l versions (IIRC).

Did they actually make the Colombo engine with a 4l capacity?

The 3.0l version - the famous "250" engine, had a bore and stroke of 73.0mm x 58.8mm. The 3.3l version, the "275" had the same bore, but a longer stroke.

There were also the larger V12 engines being built alongside the Colombo ones, designed by Aurelio Lampredi (sp?), which had a larger capacity from the beginning.

Sure...the engines in the 330 models are 77mm x 71mm, or 3967cc. There were also some 4.0 liter GTO cars on the end of their model run (the "330 GTO" and the 330 LM Berlinetta). This is also the engine used in the 400 Super America (contrary to Ferrari's system of designating models by individual cylinder displacement). These engines are all based on the original Colombo layout. There was even a 4962cc version in the 500 Superfast, which creates some confusion as its dimensions are the same as the Lampredi V12 used in the 410 SA (88mm X 68mm). The Lampredi design is distinguished by cylinder sleeves which screw into the cylinder heads, Hispano-Suiza style. Ferrari 3.0 liter V12s were produced on both the Colombo and Lampredi patterns.

[McGuire]

I forgot to add: the 275 engines were 77mm x 58.8mm, 3286cc (the bore of the 4.0 liter with the stroke of the 3.0 liter).