Phil Irving - Conceiving the Highpower Repco Head

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A small article on the great man Phil Irving.  This is regarding the Repco High powered head for the grey motor from Phils autobiography.



Conceiving the Highpower Head

Staying out of the 1955 Redex was a good idea, because modifying touring or sports engines to screw more power out of them for racing had become a flourishing industry. When aspiring speedsters found that Charlie and I were prepared to tell them what to do, and where suitable or special components could be obtained from one or other of the many Repco branches, they flocked to our door. Even if the time was inconvenient we tried hard to be helpful and polite. Currently, Repco was competing for business with Rolloy, Poison, Cords plus several imported makes of piston and other automotive equipment, and Charlie instituted a scheme whereby selected drivers could be assisted by supplying them with parts of Repco manufacture free of charge, and I maintained a list of all the place-getters in major events in which our equipment was used, sending it each week to the advertising department. One of the many tuning articles from my pen which appeared in Motor Manual and Wheels was entitled (by the Editor) "Cam and Go" which explained how much the characteristics of an engine depended on its valve timing. The article stirred up a lot of interest and we co-operated with the ex-Repco technician George Wade to regrind camshafts to any desired specification, which meant a delay unless a spare shaft was on hand. When a smartly-dressed young man offered to sell us two dozen shafts which looked new but had minor defects, Charles bought the lot for £48, and some time later found that they had been stolen off a scrap-heap behind the General Motors factory. The best thing to do was to just say nothing, but Charlie was more wary in future.

Grinding out the three siamesed inlet ports of a Holden head was a slow, dusty process which was beyond the skill of those whose main skill with their hands was to pilot a car with enormous verve. Repco Research did not want to get into the business of porting individual heads such as some specialists were doing at a price, but there was no reason why we could not design and make a much superior article which anyone with the ability to wield a spanner could `substitute for his standard head over a weekend. We chewed the idea over for a while, and when Dave McGrath gave it his blessing, I was deputed to go ahead with the.project, although we were already deeply involved with the Maybach 3.

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In my final design, the inlet valves were arranged on one side at 23° to the vertical, while-the inlet ports sloped down at 15° from two shallow galleries, each one supplying three cylinders. The exhaust valves were vertical and slightly offset from the bores to provide room for the sparking plugs which lay at compound angles. The inlet valves were operated by short rockers and the exhausts by longer rockers, all being made of nodular cast-iron to avoid the initial cost of forging dies, but being so satisfactory, the material was never changed. For many details, I either copied or bought Vincent parts, including the duplex valve springs, light-alloy spring collars and the tappet adjusters. The rods were made, like Vincent push-rods, from quarter-inch silver steel with flame-hardened ball ends and, to reduce their length, the rods sat in cups in the tops of the cam-followers instead of at the bottoms. The main head casting was wider than the cylinder block, which enabled the pressed-steel push-rod cover to be replaced by a leak-proof cast-aluminium component extending up to the gasket face. The entire valve-gear was lubricated by internal pipes.

The combustion chambers were rather oddly shaped, but could be machined in three cuts, one being coaxial with the cylinder bore and the others coaxial with the valve-guide bores. The patterns were made by the Repco company Warren and Brown, and Russell's cast the heads, the rocker cover and the inlet manifold. The first head presented no moulding problems and, except for milling the top and bottom faces, all the machining was performed at Repco Research, using very simple plate and angle jigs which we made for ourselves.

Paul England, Frank Duggan and a new recruit, Bevan Fenner, were all keen to get an engine running, and when the first one was assembled with its own starter, a standard camshaft and a single carburettor on a mock-up manifold, there was great rejoicing when it fired up and ran perfectly, just sitting, on its own sump. I do not remember the actual date, but it was late in 1955, when we were also involved in the Maybach progress.

Paul England and his friend, Bill Hickey, were semi-privately building a "special" with Holden and Peugeot chassis components and an over-bored "full-house" three-carburettor Holden engine, claimed to develop 97 horsepower, and they were anxious to find out if the Repco head could effect an improvement.

Developing the Repco Highpower Head

A completely standard Holden engine provided a claimed 60 b.h.p. with its own head, but when fitted with our head, which we named the "Highpower", the output rose to 73hp; with two carburettors and a dual exhaust system, the power jumped to 90, an increase of nearly 50 percent. With two S.U. carburettors, 8.2 to 1 compression and a mild camshaft grind, 114 b.h.p. was obtained, which was enough to waft a sedan car along at well over 100 m.p.h. Further development produced 140 b.h.p. on 90 octane petrol and nearly 160 on 10 to 1 c.r. with alcohol fuel, which was about as far as we went in the early stages, and gave Paul's car, which he named the "Ausca", a remarkably sparkling performance. When several enquiries were received, the price was tentatively fixed at £140, excluding the cost of carburettors and exhaust system, but including inlet manifolds to suit the customer's choice of carburettors and a flange-plate to which exhaust pipes could be welded.

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As Stan Jones had no big car to drive of ter blowing up the Maybach, he forked out the air-fare for Charlie to go to the factory in Italy and purchase a Maserati 250F, plus a 3-litre spare engine.

Charlie also obtained the distribution rights for Weber carburettors, which were beautifully made, but very expensive instruments available in several types, and employed on nearly all Italian racers. One of their disadvantages compared with the single-jet S.U. carburettor was the multiplicity of chokes, air bleeds and main and pilot jets, which called for a vast stock of parts to arrive at the correct setting for a new design.

For fast touring, two down-draught compound Webers gave excellent results if mounted on long adaptors. The first customer to obtain this set-up was a South Australian contractor who hired teams of shearers to distant stations, and who often had to make a long journey in a hurry to settle some dispute between his men and the station owner. When he heard that we could make his Holden do about 104 instead of only 84, he arrived hot-foot with a bundle of folding money, a nearly-new car and a request to convert his engine as soon as we could. He drove off a couple of evenings later with instructions to take things easy for a couple of hundred miles, but next morning he arrived back with the car on a tow-truck and a dead engine. He insisted that he had not exceeded 70 before the engine failed but, later on, a Jaguar driver calling quite by chance espied the Holden in our shop and remarked that he had been dicing with it for some miles up the road at about 100 m.p.h., when it dropped back and was not seen again. • Faced with this evidence, the contractor admitted his fault and agreed to pay for any damage, which by good fortune was not extensive. The distributor shaft had seized, causing the teeth in the drive gears to strip, whereupon the distributor ceased to rotate and the engine just stopped firing. Reaming out the distributor bearing, replacing the stripped gear and providing more oil supply to the area cured the trouble, and became our standard practice from then on.

The contractor was highly delighted with his car and subsequently wrote to say that it was not only much faster than his old one but, speed for speed, was also more economical.