THE Holden engine Is particularly receptive to a modification and can be encouraged to produce almost 140 bhp without becoming too inflexible or unreliable for normal driving.
For most purposes, however, an output of 110 to 120 bhp Is usually considered adequate, and is not difficult to achieve. Most of the well-known hot-up specialists have wide experience with the Holden en-gine and there Is a vast array of speed equipment available. In fact there is so much equipment that the inexperienced motorist may not select the "bits" best suited to his needs. Thus it is advisable to plan the hot-up well beforehand.
Engine modifying procedures generally fall into five categories — the cylinder block, cylinder head, valve train, inlet system and exhaust system. Engine modifying procedures generally fall into five categories — the cylinder block, cylinder head, valve train, inlet system and exhaust system.
CYLINDER BLOCK: One of the most common modifications is to overbore the cylinders so the engine has significantly greater capacity than In ' stock condition. Although some are overbored to 34 In. (and a few have been taken beyond that), the maximum overbore for a street engine is 3 3/1.81n. This increases the capacity to 2448 cc and usually presents no problems, providing the block originally had 31116 in. bores (3.0826) — as in the FE, EJ and SIC models. The overbore to 3 3/18 in. can sometimes be accomplished with earlier model blocks (those originally having 31n. bores) but only if the cylinders have been cast correctly. Unless a small-bore block has been precisely cast the overbore limit is 3 1/8 in, or 2388 cc. In either case It costs about £8 for the over-bore, plus about f:26 for a set of suitable pistons, gudgeons and rings. Because special pistons have to be fitted anyway, it saves time and money to fit those that raise the compression — Instead of later machining the cylinder head to achieve the same result. For normal use, with ordinary super-grade petrol, the maximum compression ratio should be about 8.6 or 9.0 to 1. Having a higher compression ratio than this demands a diet of high-octane fuel.
( below ): Norm Beechy Speed Shop offers complete changeover bored out Holden engine. Motor costs £65, Speco twin carby manifold £13.15. Competition clutch £10, lightened flywheel £7, rockert cover £7.28. These items alone are quite a good start.
Assuming that the modified engine is bound to be revved faster and worked harder than when standard, it is worthwhile installing steel supports for the two centre main-bearing caps. These cost about £2/10/-a pair, Naturally the crankshaft Journals must all be in good condition. It optimum acceleration is wanted the flywheel should be lightened. Most modifiers remove about six pounds of weight, a task costing about £4 a speed shops. Assuming_ that the modified engine is bound to be revved faster and worked harder than when standard, it is worthwhile installing steel supports for the two centre main-bearing caps. These cost about £2/10/-a pair, Naturally the crankshaft Journals must all be in good condition. It optimum acceleration is wanted the flywheel should be lightened. Most modifiers remove about six pounds of weight, a task costing about £4 a speed shops.
( Below ): From Sydney Speed Shop, special
valve keepers for competition Holden engines.
The smae shops wide range of Holden bolt on
bits include manifolds, special collets, pistons,
changeover heads and other items.
When an output of more than 90-100 bhp is wanted one should guard against clutch slip by installing a heavy-duty pressure plate. Some give N percent more pressure than the standard unit and cost £10 to £12. They are often supplied on an exchange basis, by which that the standard pressure plate is — in effect — traded-in on the heavy-duty plate.
The crankshaft, flywheel and clutch should be dynamically balanced — especially if they have been modified — to insure against vibration and undesirable blow-ups. The connecting rods and pistons should also be 'balanced — against each other — so that each assembly weighs the same amount.
CYLINDER. HEAD: Most speed equipment suppliers will arrange cylinder head modifications, sometimes on an exchange basis. The operations improve the ports and combustion chambers so the engine can breathe easier. Even when tho standard inlet and exhaust systems are retained a significant increase in brake horsepower comes from detailed work- on the cylinder head. There is a limit, of course, on how much can be done to the head with its standard Inlet and exhaust systems and beyond that point one must use multiple carburettors and a free-flowing exhaust. Most firms can supply a range of stages of head modifications. The least expensive, costing about £20, sees the ports and combustion chambers lightly ground and polished to remove sharp edges and burrs. Subsequent stages involve detail alterations of the ports and chambers to promote better breathing and more efficient combustion. The inlet and exhaust manifolds — whether they be the original or special components — are ground so their ports align precisely with those in the head. When the engine Is to have multiple carburettors, the modifications may include installing larger diameter valves of high-quality material.
The Repco Hi-Power conversion cylinder head is one way of increasing the engine's power and flexibility. The Hi-Power head bolts straight on to a standard short-black assembly with very few modifications. The head can be classed as a cross-•ow type because the exhaust ports are on the same side as the standard head but the inlets are on the other. When fitting a Repco head and suitable exhaust manifold to the engine, the owner can virtually tailor the bhp figure by selecting from several camshaft and carburetion combinations. For example, if the standard cam is retained and two original-type carburettors are fitted 'the engine develops 90 bhp —which Repco regards as Stage T. In further stages a sports cam and Weber carburettors are installed. With 3 1/8 in. bores, 9.2 to 1 compression ratio, sports cam and two twin-throat downdraft Webers (which amounts to Stage 4A) the Repco-headed Holden de-livers 135 bhp and 145 pounds/feet of torque. Even in this guise It is smooth and flexible enough for normal day-to-day motoring. The Hi-Power kit com-prises the cylinder head — complete with 'valves, springs and rockers — lightweight pushrods, aluminium rocker cover, stub inlet manifolds and all necessary fittings. It costs £167 (plus tax) — to which must be added the cost of the carburettors and exhaust manifold.
VALVE TRAIN: The first requirement is a re-placement gear for the camshaft. The standard fibre gear is prone to failure and is usually replaced with one of metal — either iron, steel or aluminium, costing between £7 and £10. Because the camshaft largely dictates the finished engine's performance characteristics careful modifying is needed. For models up to and including the FC model the stock camshaft had this valve timing: inlet opens 4 degrees before TDC and closes 40 degrees after BDC, exhaust opens 46 degrees before BDC and closes 6 degrees after TDC. With FB and later models the valve timing was: Inlet opens 6 degrees before TOO and closes 48 degrees after BDC, exhaust opens 62 degrees before BDC and closes 12 degrees after TDC. A typical sports Cam has timing of: Inlet opens 18 degrees before TDC and closes 58 degrees after BDC, exhaust opens 58 degrees before BDC and closes 18 degrees after TDC. The extent to which the valve timing can be altered from standard depends on the engine's breathing ability, compression ratio, and inlet and exhaust systems. It is a mistake to specify a, wild cam if the engine has only moderately effective carburation and exhaust systems. In the interests of flexibility it is batter for the camshaft to be on the mild side rather than being too extreme. Thus because valve timing is vital, it is wise to allow one of the many specialist firms to choose the grind that best suits the engine. Most firms charge between £9 and £12 to regrind a Holden camshaft, and some operate an exchange system.
Next in line along the valve train are the cam-shaft followers, pushrods and valve caps. Lightweight replacements are available and these permit higher revolutions to be obtained — with springs of a given strength — than do the stock components. Sets of followers, pushrods and caps are priced at about E4/10/-, £71101- and £3 respectively. Inner valve springs, to raise the rpm at which valve bounce occurs, retail at about £2/10/- a set.
Pre-1956 cylinder heads were fitted with Inlet valves of 1281 in. diameter while the exhausts were 1.219 in. Later model heads have the same diameter exhaust valves but the inlets are 1.346 in. For hot street engines the original size exhaust valve can be retained with the inlets being replaced by valves that are up to 1.826 in. diameter. This is the absolute limit — over * in. larger than standard — unless expensive alterations are made to the head.
INLET SYSTEM: Several carburettor installations are employed by hot Holdens. The most popular of these are two or three original-type verbs, two or three SUB (either 1 ¼ s or 1 ½ s) and one or two downdraft twin-throat weber or Strombergs. There are manifolds and linkages available to suit all Installations with prices starting at £10 and rising to £20. Generally the carburettors are supplied separately.
EXHAUST SYSTEM: several firms produce dual exhaust headers for prices ranging from £11 to £15/10/-. These are usually made in cast Iron but special extractor systems may be fabricated from tube, to order. A complete dual system, with headers, pipes and sports muffler, costs about £27. There are also sports mufflers and over-size pipes to fit the original system.
That almost takes care of the engine but there are a few more points to be considered. For instance, the standard distributor's advance curve is unsatisfactory if the engine is modified comprehensively. Speed equipment suppliers can arrange to have the advance curve altered to suit the new requirements, at a cost of about £3. Sometimes, when an engine has been thoroughly worked over, it may be necessary to install an oil cooler to help keep the temperature at a safe level. These cost about £15 complete with pipes and fittings. And don't forget sports-type air cleaners at between £2 and £4 each, for the engine will not last as long as it should if it is free to inhale dusty air.
Modifying the engine is only a part of building a fast car. It has to be roadworthy, too. There are a number of ways in which the roadholding and stability can be improved. The ideal solution to most brake problems would be to fit discs at the front wheels as the owners of some racing Hoidens have — but this is an expensive operation. Dunlop calipers and discs are available but they have to be individually adapted, for conversion kits are not yet produced. Repoo's transversely-finned brake drums, for all models through to and including the FT, are a satisfactory alternative to discs for most normal motoring purposes. The Repco drums are more fade-resistant than the standard components, because the fins assist cooling, and cost g6/81- each. The next step is to fit heavy-duty brake linings at about £4 a set. To gain the full benefit of the competition linings it Is some-times necessary to Incorporate servo-assistance so that brake pedal pressure does not become too high.
( below ): One of the first steps to better handling,
apart from lowering is a Panhard rod which
particualuray in the case of the Holden locates
the live rear axel better. This one a home made
job runs from axel housing to sub frame.
Drilling the backing plates and fitting air-scoops is not recommended for street cars, for dust and grit enters and accumulates, causing premature wear of the linings and drums.
Lowering kits can be supplied for an models, with the maximum practical reduction for street machines being about 1.5 in. Blocks are installed between the rear springs and the axle, while the front springs are shortened either by cutting a coil off on each side or by compressing the springs so they are shorter than usual. After the car. has been lowered it is vital that the front suspension be re-aligned so the esistor. camber and steering geometry are to original sped-fleations. When the existing dampers are in poor condition, or a lot of hard driving is intended, It is ad-visable to fit heavy duty shock absorbers — at £22 a set of four.
Axle tramp on acceleration and cornering can be minimised with torque rods fitted between the axle easing and forward spring mounts, while a Panhard rod — installed transversely between the axle casing and chassis sub-frame — helps locate the axle positively and decreases body sway. More responsive, though slightly heavier, steering is obtained with a steering conversion. This reduces the steering to approximately two turn’s lock-to-lock. The necessary modifications cost £121101- including fitting and re-alignment of the front wheels. The required components can also be supplied In kit form. Anyone modifying a Bolden should decide at the outset whether the car is to be raced or retained solely for street use. This will determine the extent of the modifications and the budget limits. Also, some modifications make a .Holden ineligible for Appendix J racing — such as fitting a Repeo conversion head. All these things must be considered. Additionally, one must ensure that the engine Is In good enough condition to withstand modifying. It Is pointless to work over the top end of a motor without making sure that the bottom end is robust enough to take the extra power. Tyres to match the extra performance are also necessary, and most of the high-speed Continental tyres are available in Holden rim sizes.
Most of this modifying equipment can be bought over the counter. There are a number of Australian sources for it.
Speed equipment shops have mushroomed In this country in the last three to four years. The logical explanation for this boom lies in the increasing Interest In motor racing and the improving economic status of the younger members of the community. Be that as it may, it is notable that the bigger shops — Eddie Thomas, Peter Manton/Monaro Motors, Sydney Speed Shop, Lynx Engineering, Prank Klein*, John Malcolm Motors, SAS and others — are doing more and more business every week. New shops are opening, too. Sydney's Lancaster Motors tentatively opened a small equipment shop in August, and were so impressed by the reaction that they started enlarging it immediately. Now they carry not only a big range of bits for their normal .BMC franchise, but also much equipment for other makes.
So for the modifier, whether he have a Holden, Cortina or Mini, the way is made quite easy. We wish him happy hot-ups. #
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