Big Bore/Small Bore Model A Engine Block

M

markwilltoo

Junior Member
In the engine serial number listing, a small bore (14 HP) and a large bore engine blocks are referenced. What are they referencing? Was there really a 14 HP model A engine used in the UK?
 
I the picture the small bore is on the top, look closely at the distance between
the cylinders and you can see the difference.


Bob
 

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It was about "taxable " horsepower, a formula using bore and stroke, the way it works is smaller bore made for less tax,
 
I think they rate HP differently in the UK than we do in the US. Can't remember what my Morris Minor was rated at when I was there for a couple of years but I know the engine was only 918 CC. It was a flat head 4. Not a lot of HP
 
The rated HP was used for the annual taxation as has been said. It was based on the total area of the tops of the pistons. The stroke wasn't considered. That's why manufactureres back then kept the bores small and the strokes long. A Model A with the same engine as was used elsewhere would have incurred a prohibitive tax so Ford reduced the bore so they could sell cars. IMO, that system held back engine development for years.
 
the so-called 14.9 hp of the small bore engine was the "fiscal" or RAC rating horsepower. this was ((diameter of cylinder in inches ) squared x the number of cylinders )all divided by 2.5 . This formual was devised in 1909 by the Royal Automobile Club and gave at the time a good approximation of the horsepower on an internal combustion engine. Of course engine design improved and the formula was no longer a good approximation but the UK goverments of the times kept using it until 1947 as a basis for an annuala road tax levy on vehicles . This gave rise to the Model A 3.3 litre (200 cu in)engine being rated in the UK for tax purposes at 24hp using RAC formula, whist actually producing 40 bhp ,( both large bore and small bore engines were available in the Model A's later years) . Furthermore other European countries used a similar but not identical system for annual vehicle tax. Thus ( from Sam Roberts book History of the Y and C) the European Ford Y was actually producing 22 bhp, but was rated in UK for tax at at 8 hp, in France at 6CV ( chevalvapeur) and in Germany at 4 PS (pfered starke).
 
I believe all the large trucks sold in UK were big bore? The small bore also added 5 pounds more to the cars price ; why?
It is little known that Ford Canada could provide the small bore engine which they supplied to Singapore & some other markets. There was a link between Ford Canada & Britain, so it may have been the British made engine. Cheers
 
Tudortomnz said:
I believe all the large trucks sold in UK were big bore? The small bore also added 5 pounds more to the cars price ; why?/QUOTE] yes, all AA trucks were large bore, lightweight vans ( 10 cwt ) could be either . (Commercial vehicles had different road tax regime )
Cars initially were all small bore But in summer of 1930 cars began to be offered with either small bore or large bore at the same price, but by Oct 1930 the 14.9hp ( small bore was £5 extra eg a contemporary ad for Oct 1930 has the prices listed ranging from Tudor Saloon 3.3 litre (24 hp) at £180 to Cabriolet (24hp) £210 with in small print for all the car range for the 14.9 hp £5 extra.
I think the price differential was just a marketing ploy- Ford car sales in the Uk were a disaster by this stage anyway.
Did all the Singapore cars have the small bore engine- I've seen a Canadian parts catalog with the small bore components listed and had always wondered why that was-
Click to expand...
 
Back in the Model A days, we used a system very similar to the English one but I'm not aware of any small bore engines coming here. They would have been just as much a disaster as English cars were (some of the larger, expensive ones excepted.)
 
John, Canada supplied both large bore & small bore vehicles to Singapore plus only small bore to Nyasaland which I think was in East Africa.
This was in 1930 & '31 with the majority being the large bore [ 300 s.b.] for each year to Singapore. These are recorded in the Ford Canada export shipment records that were at Oakville Ontario. So only a small number of small bores. Thankfully there was no 'tax' on engine size in NZ & Model A's were the most popular new car in NZ in that era. Cheers.- Tom.
 
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