By C. D. F. Buckler
Part II.– Tuning the Engine.
The Ford Ten engine has four very desirable qualities:–
(i) Light weight.
(ii) The ability to “rev.”
(iii) A low b.h.p. per sq. in. of piston area.
(iv) Low initial and maintenance costs.
From the competition angle the ability of the engine to rev. is of major importance.
The standard engine gives its peak figure of 30.1 b.h.p. at 4,000 r.p.m. but will exceed 5,500 r.p.m. The addition of double valve springs will enable 6,000 r.p.m. to be reached, whilst the incorporation of a higher compression-ratio and attention to the ports raises this to 6,200 r.p.m. A reasonably well-designed twin-carburetter inlet manifold will give a further increase in the rev. range up to around 6,500 r.p.m. Incorporation of these modifications raises the b.h.p. approximately 30 per cent., at around 5,000 r.p.m. It should be clearly understood that at any speed over 5,000 r.p.m., the b.h.p. is dropping, but these extra revs. are nevertheless very useful in avoiding additional gear changes in sprint events. Owing to, presumably, the rigid cast-steel crankshaft employed, the very excellent rev, range given can be consistently used. The writer, having had no small experience of these units at speed, is convinced that it is virtually impossible for them to blow up, no matter what revs. are used. As however, a crankshaft period sets in at around 5,400 r.p.m. (76 m.p.h. with normal axle-ratio and tyre sizes) but disappears at 5,600 r.p.m. (79 m.p.h.) it is advisable to avoid maintained speeds in this range.
Whilst the compression-ratio can be readily raised it should be stressed that the highest usable ratio is determined by the octane rating of the fuel, the axle-ratio and tyre diameter (standard wheels permit of four variations in tyre size), the weight of the car and, to a lesser extent, its frontal area and shape. The higher the axle-ratio and the heavier the car, the lower the compression-ratio permissible on a given fuel. Owners of Prefect saloons should not use a higher ratio than the standard manufacturer’s setting of 6.1 to 1. The following Table shows the writer’s recommendations for average speeds fitted with the standard 5.5 to 1 axle-ratio:–
Unladen Weight Compression-ratio Pool (70 Octane) Compression-ratio 50/50 (80 Octane)
15 cwt. 6.1 to 1 7.1 to 1
14 cwt. 6.3 to 1 7.6 to 1
13 cwt. 6.6 to 1 7.8 to 1
12 cwt. 7.0 to 1 8.0 to 1
11 cwt. 7.6 to 1 8.2 to 1
10 cwt. 7.8 to 1 8.5 to 1
These are the highest possible ratios, and with them “pinking” will be apparent on full throttle at low speeds in top gear. With decarbonised engine and any rough spots in the combustion chamber removed, set the ignition to give cessation of “pinking” in top gear at 30 m.p.h. on flat roads. With a 4.7 to 1 axle ratio (sometimes obtainable but not a Ford product), reduce listed compressions by approximately 0.75 per cent. of a ratio. As it is advisable never to drive with the engine “pinking,” a change to a lower gear should be undertaken for full throttle work under 30 m.p.h.
To obtain the above and other compression-ratios proceed as per the following chart:–
6.1 to 1 Standard Ten cylinder head and standard C. & A. gasket.
6.3 to 1 Standard Ten cylinder head and 18 G copper gasket.
6.6 to 1 Standard Ten cylinder head and 22 G copper gasket.
7.0 to 1 Standard Ten cylinder head and 22 G copper gasket but with 0.020 in. machined from head face.
7.2 to 1 Standard 8-h.p. cylinder head with C. & A. plus 24 G copper gasket.
7.6 to 1 Standard 8-h.p. cylinder head with C. & A. gasket.
7.8 to 1 Standard 8-h.p. cylinder head with 16 G solid copper gasket.
8.2 to 1 Standard 8-h.p. cylinder head with 18 G solid copper gasket.
8.5 to 1 Standard 8-h.p. cylinder head with 20 G solid copper gasket.
8.6 to 1 Standard 8-h.p. cylinder head with 21 G solid copper gasket.
8.9 to 1 Standard 8-h.p. cylinder head with 24 G solid copper gasket.
9.0 to 1 Standard 8-h.p. cylinder head with 26 G solid copper gasket.
9.2 to 1 Standard 8-h.p. cylinder head with 0.010 in. machined from face and 26 G copper gasket.
9.5 to 1 Standard 8-h.p. cylinder head with 0.020 in. machined from face and 26 G copper gasket.
Whilst it is normally inadvisable to machine substance from the cylinder-head face this may be done providing a head with above average thickness of metal on the face is chosen. Even so 0.020 in. is considered the maximum amount that should be removed.
Having dealt with the compression ratio the next step is to smooth away all rough spots in the ports, cylinder head and manifolds. This is best accomplished by using rifling files or, where an electric hand-drill is available, rotary files or small grinding stones. The latter is expensive on stones as speeds of 20,000 r.p.m. should be used. It is important that the port shapes be not altered, but providing care is taken on this point they can be opened out by approximately 1/16 in. The valve seatings should be radiused, as should the seating faces on the valves. Whilst that portion of the valve guides protruding into the ports can be smoothed to blend into the gas flow, it is inadvisable to cut these down in length. Fitment of double valve springs necessitates machining the guides to give a proper purchase for the inner springs. Double valve springs also necessitate the use of heavier valve retainers, but as these are non-standard, they are not normally available from Ford dealers. Genuine Ford valves are advisable and in the writer’s experience have shown that they stand up to competition stresses long after valves of other makes, even of special steels, have failed. Removal of the inner one or two sparking-plug-hole threads in the head will obviate hot spots likely to cause pre-ignition. Owing to the fine degree of initial balancing given by the makers to the crankshaft any further balancing is not considered a worthwhile expenditure for the average user. Smoothing and polishing the con-rods will increase fatigue-life, but they should not be drilled or otherwise weakened. As Ford pistons are fitted with what most people would call racing-section rings no gain is to be achieved by any alteration in this direction. Whilst the writer has never used other than standard camshafts, a gain in power can be obtained with correctly-designed racing cams. As such camshafts give a gain only over a limited rev.-range and actually less power at other engine speeds (they are in any case prohibited for use in 1,172 Formula events) only a limited advantage would be obtained by their use. What is important is that no excessive play be countenanced in the camshaft bearings, as any undue loss of oil at these points will result in a below-normal volume and pressure of oil to the main and big-end bearings. As volume of oil to high-speed bearings is an important factor in cooling the bearing surfaces, which in turn plays an important part in giving bearing life, extra attention to correct camshaft bearing fits is well worth while. These bearings are normally direct in the cast-iron of the cylinder block and providing they be not worn the fitment of a new camshaft will give the correct running clearance.
Oil pressure is normally released to give a running pressure 30 lb. per sq. in. but at sustained speeds of over 4,000 r.p.m. is likely to fall to 15-20 lb. This is caused through temperature rise and whilst a loss of ultimate engine life must arise, sustained full-throttle use for 10-15 minutes at a time has shown no detrimental effect. The use of a larger non-standard sump will give a gain, and is sufficient to cope with the position for all normal, and average competition, use. For cars capable of really high cornering “Gs ” in track work, a special non-standard oil pump shroud is necessary to avoid oil surge starving this unit on left-hand bends. For “specials” with a limited volume of cooling water in circuit, fitment of a water pump will allow for momentary excess temperature conditions, but any sustained high temperatures can only be overcome by increased radiator cooling area or a larger fan. The standard Ford Anglia export water-pump (Part No. E 493 AFS 8501) is very easily fitted and, if required, a four-bladed fan is a standard Ford part. Both these consume power and should not therefore be used indiscriminately for competition work.
For unsupercharged engines with compression ratios up to 8 to 1, Champion L10 plugs are preferable, with L10S advisable for higher compressions. As the Ford standard coil ignition system has been found to give every satisfaction up to the highest engine speeds obtained, the fitment of a magneto is considered both a needless strain on the camshaft drive as well as a source of power loss.
Twin carburetters of 1-in, bore will give a few per cent. power gain over a single carburetter at the loss, but not a large loss, in m.p.g. With the standard single Ford Zenith carburetter an increase by 5 in the compensating jet size will sometimes be found advantageous, as will removal of the hot-spot and a cool air supply to the intake. [We believe that some 1,172 Formula fans employ two 1 ‘ S.U. carburetters and achieve about 80 m.p.h.–Ed.]
A correctly-designed four-branch exhaust manifold will give reduced exhaust valve temperatures under high engine speed conditions, although the standard manifold is adequate for normal competition work.
The Ford Ten Engine
Bore: 63.3 mm. Stroke: 92.5 mm. Capacity: 1,172 c.c.
Firing order: 1, 2, 4, 3.. Normal b.h.p.: 30.1 at 4,000 r.p.m.
Torque: 46.4 lb./ft. at 2,400 r.p.m.
Normal compression ratio: 6.03 to 1; De Luxe; 6.6 to 1; Prefect. 6.16 to 1.
Maximum compression pressure: 157.3 lb./sq. in.
Pressure at cranking speed; 104 lb./sq. in.
Cylinder offset: 0.125 in. Grade of oil: S.A.E. 30.
Sump capacity: 4 pt. Oil filter capacity: 1 pt.
Oil pressure: 30 lb./sq. in.
Oil pump capacity: 0.75 gall. at 1,000 r.p.m.
Piston weight: Short, 177 grms.; long. 192 grms.
Valve lift: 0.2825 in.
Valve springs: Free length 2.96 in.; test length 11/32 in.; test pressure: 29.32 lb.
Valve timing: Inlet opens 9 deg. 30 min, before t.d.c., closes 50 deg. 30 min. after b.d.c. Exhaust opens 53 deg. 30 min. before b.d.c., closes 6 deg. 30 min.after t.d.c.
Carburation. standard jets: Idler 55, Progressive 100, Diptube 140, Main 85, Comp. 75, Starter 105, Choke 22 mm., Float level 21/32 in. to 43/64 in. below top of bowl.
Main bearing clearance: Up to 0.0025 4; wear limit, 0.005 in.
Big-end bearing clearance: 0.001 in. to 0.0025 in.; wear limit. 0.005 in. End float on pin, 0.004 in. to 0.010 in.; wear limit, 0.015 in.
Camshaft bearing clearance: 0.002 in. to 0.0035 in.; wear limit, 0.005 in.
Makers: Ford Motor Co. Ltd., Dagenham. Essex.