19 replies to this topic

[David Birchall]

This is a minor question I admit but one that intrigues me; Why did so many manufacturers produce engines of 2600cc? It fitted no racing class that I am aware of. Off the bat I can think of Alfa Romeo, pre and post war; Aston Martin-Lagonda; Austin/BMC; English Ford and I am sure there are others. Why the odd capacity?
David B

[byrkus]

Probably not true, but it just hit me. These were/are all (more or less) british cars, and they used non-metric units. If you put imperial units into metric, this is what you get:

160 cubic inches = 2622 cc - which is more or less capacity of Austin-Healey, Lagonda, etc. I'm not saying that's the reason, it's just curious enough.

[David Beard]

The Ford 6 cylinder engine in the Zephyr was a 6 cyl version of the Consul engine. The C series BMC engine was (I think) a 6 cylinder version of the B series. But I'm not sure if that helps... :
Something to do with rationalisation of parts used in a largish (for UK) four, tended to result in that size of six?

[petefenelon]

I forget how the RAC "hp" calculations were performed, but seem to recall that it involved number of cylinders and bore - so does six cylinders at a particular stroke lead to a particular RAC classification (12 RAC hp? 15?) - and picking an efficient stroke for that lead to about 2.6l?

[Michael Müller]

For Alfa-Romeo (post war) it was the 1750 cc 4-cylinder enlarged by 2 cylinders to 2600 cc.
Postwar it was the 6C-1750 6-cylinder + 2 pots to create the 8C-2300, which then was enlarged later to 2600 cc.

[David Beard]

Originally posted by petefenelon
I forget how the RAC "hp" calculations were performed, but seem to recall that it involved number of cylinders and bore - so does six cylinders at a particular stroke lead to a particular RAC classification (12 RAC hp? 15?) - and picking an efficient stroke for that lead to about 2.6l?

Bore I think was considered in the HP rating...and stroked was ignored...very strange. Did it hold back the over square motor for years?

[petefenelon]

Originally posted by petefenelon
I forget how the RAC "hp" calculations were performed, but seem to recall that it involved number of cylinders and bore - so does six cylinders at a particular stroke lead to a particular RAC classification (12 RAC hp? 15?) - and picking an efficient stroke for that lead to about 2.6l?

Dug up the formula -- RAC hp = cyls * bore * bore / 2.5

Having looked up the formula, I get a "square" 82mm bore and stroke giving 25 RAC hp from a 2.6 litre six - does that fit with most of the engines of that class?

[petefenelon]

Originally posted by David Beard


Bore I think was considered in the HP rating...and stroked was ignored...very strange. Did it hold back the over square motor for years?

Possibly in the UK yes - there is an interesting page on http://www.designcha...fhoundRACHP.htm

[David McKinney]

I think RAC horsepower was irrelevant by the period we are talking.
So were exact engine sizes as far as people like BMC and Ford UK were concerned. They didn't design engines for racing classes. They wanted a "medium-sized" engine for their family cars so built one which happened to be about two and a half litres. The first Ford Zephyrs were 2262cc, the Mk2s 2553cc. The equivalent BMC four of the same period was 2660cc, and its replacement six 2639cc.

[petefenelon]

Originally posted by David McKinney
I think RAC horsepower was irrelevant by the period we are talking.

Taxing cars on RAC horsepower went out in '47. You're probably right!

[David Beard]

Originally posted by petefenelon


Taxing cars on RAC horsepower went out in '47. You're probably right!

But the terminology, and many people's visualisation of engine size, stuck for a long time after.

[D-Type]

Originally posted by David McKinney
I think RAC horsepower was irrelevant by the period we are talking.
So were exact engine sizes as far as people like BMC and Ford UK were concerned. They didn't design engines for racing classes. They wanted a "medium-sized" engine for their family cars so built one which happened to be about two and a half litres. The first Ford Zephyrs were 2262cc, the Mk2s 2553cc. The equivalent BMC four of the same period was 2660cc, and its replacement six 2639cc.

I think that's the key. After all the Ford Consul Mk 2 was 1703cc and the Ford Ten was 1172cc

Bykrus,
We never used cubic inches in Britain so it won't be that.

The RAC Horsepower taxation was a major contributory factor to the tradition in Britain for long stroke engines. But a long stroke does have the technical advantage of low piston speed.

[David Beard]

Originally posted by D-Type
But a long stroke does have the technical advantage of low piston speed.

Are you sure about that???

[Roger Clark]

Originally posted by D-Type


The RAC Horsepower taxation was a major contributory factor to the tradition in Britain for long stroke engines. But a long stroke does have the technical advantage of low piston speed.

Obviously not.

But for many years it was believed that piston speed was the limiting facotr in engine design. If that is so, then stroke and engine speed (in revolutions per minute) are interchangeable. This was why several early racing formulae limited cylinder bore but not overall capacity. You can also see it in Pomeroy's "Grand Prix Car" where he assesses engine efficiency in terms of power per square inch of piston area.

[Geoff E]

Originally posted by David McKinney
They didn't design engines for racing classes.

Apart from the 2.5litre world championship class (for which, I presume, Ford and Austin engines were not entirely suited) what other classes were around at the time?

Nowadays, all engines seem to be a couple of cc below 1300, 1600 etc but in 1955/56 there was

Austin 803
Austin/Morris 2639
Rover 2638
BMW 2580
Ford Consul 1702 (which gave 2553 when enlarged to 6 cyl)
Hillman 1390
Humber 2267
Standard 2088
Vauxhall 2262
Volvo 1414
Ford (and Morgan) 1172

[Paul Newby]

Here in Australia we had the Holden "red" 6 cyl engine in original 161 cu inch configuration (2638cc) as seen in the first Torana GTR. Also local was the Mitsubishi "Astron" 4 of 2600 as used in Sigmas and Magnas.

In Europe there was the Alfa Romeo Montreal V8 of 2593 cc. I'm not sure how they arrived at that as the racing V8 it was loosely based on were 2 and 3 litre plus the 2.5 Tasman spec. Maybe it has something to do with the 80mm bore size as used on contemporary "1750" 4 cyl engines.

Plus there was the "Cologne" Capri RS 2600. I guess that was a "German thing."

[soubriquet]

My understanding (I have been known to be wrong) is that the Montreal is a 105 series Alfa, and the V8 (2593cc) comprises two 1300cc blocks and heads on a common crank case. Not related to the competition engines.

[RTH]

Originally posted by David Beard
The Ford 6 cylinder engine in the Zephyr was a 6 cyl version of the Consul engine. The C series BMC engine was (I think) a 6 cylinder version of the B series. But I'm not sure if that helps... :
Something to do with rationalisation of parts used in a largish (for UK) four, tended to result in that size of six?

I think this is much the most likely explanation it was a period when car makers were very much more cost concious about new designs.

There is a parallel today , when the present F1 engine makers were consulted about a regulation change to reduce power outputs BMW in particular requested if there was to be a change at all it should be to 2.4 litres - so in design terms all they had to do was cut off 2 cylinders from a 3 litre V10 to make a 2.4 V8 which for them would be the cheapest option - so far the FIA have not had the courage to do anything.

[Ray Bell]

Originally posted by David Beard
.....The C series BMC engine was (I think) a 6 cylinder version of the B series.....

The 6-cylinder version of the B-series was actually the 'Blue Streak' six that was put into production in Australia for the Austin Freeway and Wolseley 24/80.

On the other hand, the C-series was unrelated to any other engine and had some unique features... and as David McKinney posted...

.....They wanted a "medium-sized" engine for their family cars so built one which happened to be about two and a half litres. The first Ford Zephyrs were 2262cc, the Mk2s 2553cc. The equivalent BMC four of the same period was 2660cc, and its replacement six 2639cc.

Well, not exactly... the 'family car' of the BMC range was the A70, which was about 2260 or something... it was the A90 'sporting' saloon/convertible range (and the Austin Healey and the Austin Champ civilian version...) that had the 2660cc engine. But the A90-six was a bigger car, so probably merited the 2639cc engine on that basis. It was later enlarged, of course, to 2912cc.

There was a 6-cylinder version of the bigger four, which was the truck engine and was used in the Sherelines and Princesses (A125 was a designation, I think), but it was created before the more modern family of engines and didn't have any designation that I know about in the manner if the A-series/B-series line.

In the case of the Zephyr, it replaced the V8-60 powered Pilot...

[Patrick Italiano]

Originally posted by soubriquet
My understanding (I have been known to be wrong) is that the Montreal is a 105 series Alfa, and the V8 (2593cc) comprises two 1300cc blocks and heads on a common crank case. Not related to the competition engines.

Err, I feel compelled to correct that!

The Montreal is a 105 as far as drivetrain, suspension and body construction are concerned, and of course for its internal designation. Note that the 33 racer is also a 105, its code number being 105.33

But the Montreal engine is a detuned version of the 33 engine, with an odd capacity. Why 2593? probably as result of the use of an existing piston (thus fixed bore) and a geometrical fixed value of the bore x stroke ratio.

In Italy, many exact capacities of engines were dictated by tax rules, but I on't remeber anything like that for the Montreal. But there was also the straight-six engine of 2600 from 1962 to 1967.

See http://www.alfamontreal.info/ as excellent reference site on Montreals.