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As promised, some pictures i took when viewing the engine. The workmanship on this engine is tremendous!
The builder was invited to the Porsche factory to show the engine. The workers that build the aircooled engines all rushed to the scene to see the engine run.
Everything on the engine is an exact 1:3 scale, down to the distributor cap, spark plugs, valves and carburetors. Only the chain for the distribution and the spark plugs are off the shelf parts (spark plugs were milled down etc.) the rest has been fabricated by himself.
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Frits Hofman was infected with the virus when he was a Porsche 911 purchased in 1967 from 1965. At the time this instrumentenma- ker, who works at the National Air and Ruimtevaartlaboratori- um, a cross sectional view of the engine came to see was his leisure completed for the next ten years. And not to build miniature steam engines, such as did many of his colleagues, but a scale model of the air-cooled six-cylinder boxer such as those housed under the hood of his own 911.
However, there was one problem, his hands can make what his eyes see but the aluminum block to ennoble so that it actually lives, you need to know that there Hofman
that time had not ready. His project began with the collection of so much information.
Measuring and calculating backwards
To the scale by the real block 911 to make it appear he took as many dimensions on his own six-cylinder. But for the details you need to actually separate the motor coach and since Hofman Porsche used for commuting was not really an option. His former Porsche dealership brought this respect outcome, which had somewhere a block demolition lie that he could use for measuring. But this block was not complete, in particular, there was the prime mover. Luckily there were people of Pon Porsche im-
importer, with him. They voorza- gene him a crankcase with crank shaft. In any case, Hofman was at work!
Before the block metal daad- was actually processed, the instrument maker had to reflect on the scale. Because he took off from the start that the block had to run, he hereby is guided by the smallest (elementary) component that he could still scale. In 911 it was the cover story steal in the ratio 1: 3.2 are real from the lathe.
Surface-content relationship
As we get further into the story is the complexity of the whole becoming more apparent. Hof- man wielded the ratio
In 1968, Fritz Hofmann himself was the trotstebezittervaneen Porsche 911. He was so gilded art that he decided to rebuild the engine to scale. And he made it absolutely is not easy: the engine had to sound like a real 911.
1: 3.2 and could without too much trouble handling the measure lining of appearance. For the performance of the engine, it is a different story, it turns the surface content ratio play a major role. After all, the surface is a square, while the content is a third-power. Practically this means that once you get everything Reduce by the same factor, the surface area relative to the inhoud is much bigger. For the course conditions this extremity is teraard ideal, the cooling ability and the strength of the engine block are fine. But for the internal friction is a totally different story, bearing surfaces are relatively large so high demands are placed on the lubrication. If we further consider the dimensions of the various components in the block it is striking that particularly the oil pump almost at once (in proportion of course) is as large as the original.
Furthermore, he is as much as possible based on the Porsche measures lining; for example, the crankshaft are all oil drilling and oliekana- cells identical to the big expense. And crankshaft can really be a paragon of Johnston; it is manufactured from one piece of metal. And in his own words that went right the first time.
For this part, he does other things being appealed to the engineers at Porsche. Its sizing crankshaft gave, without cutting the cable pot, do not expose the subcutaneous tunnels. At that stage, he contacted the Porsche factory in Germany with a request to provide structural information. And was apparently one particular gold- of the operations of the instrument maker; he not only got the blueprints, no-one even turated him to come and show the model of the Porsche stand of the IAA.
Problem problem
Very characteristic of this project is the patience with which Frits Hof- man has gone to work. After all, he has spent 6,000 hours over 10 years to his pas- sion. But if we turn what deeper into matter than diving is actually surprising that he saved it in ten years. Especially if we take into consideration how long it takes for an engine manufacturer to develop a new engine line. And remember that a large number of specialists in-house and also another may rely on expertise from
Hofman possessed in 1968 itself such 911. The difference between the two engines is only the size, the specific air-cooled boxer sound share them.
Small, bigger, biggest. In terms of technique is the block 911 in the ontzet- evolved over the years and current, the base, however, all this time remained the same.
Fantastisch to see how truthful Hofman has recreated the look of the motorcycle. Even the nuts and bolts were made to scale. And what about the capsule to guide the cooling air to the cylinders, lifelike but the color appears as the 'Porsche-profiles "is not entirely accurate because this is supposed to be black.
gene (the contact start to hover at 16,000 r / min) lovely walks around. And the instrument maker claims to have the camshaft but have to adapt once.
A plume of Porsche
In 1976/77 was Hofman far as 911 'lived'. In the initial phase of his project he had shown the Porsche staff where he was doing and then received universal praise. At a later stage, when the engine actually ran, he has been back once and probably him that yielded the greatest admiration that a Porsche profile itself may consist think a bevy Porsche employees who are breathless
the past. Hofman for his project itself must collect all the coal from the fire.
The most serious problems under dervond Hofman sash of his motorcycle. His claim that the block had to run and sound and work as a real 911 took the necessary headaches. Had to be given to each elementary component. We mentioned earlier the lubrication of the piece that actually makes just enough Communities could be a, relatively, very large oil pump.
Another story is the breathing
ment of the block. The in / uitklep- pen have a diameter of respectively 11 and 10 mm. Proportionally this great values hence Hofman has reduced and reduced overlap the lift of the valves. Unit only, how do you know for example, before the camshaft is turning and how great those values must be exactly? No one has experience with such projects!
Yet Hofman has made good assumptions. The breathing of the engine is such that the both stationary and on full power
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TECHNIEK
From block to metal working miniature model
te look and listen at the time that the mixture burn. A similar experience we may experience during the photo shoot for this article; the showroom of the Porsche dealership in Amsterdam was empty at the time when Hofman 911 started in the workplace, even the 'status' Porsche drivers were shut out of this piece of engineering beauty.
Hans Doornbos:
Hofman has really recreated everything, camshaft, valves, rocker arms, you name it. Even the adjusting nuts on the rockers are not lacking. The spark plugs are originally derived from a Honda generator, obviously Hofman has the appearance adapted to the Porsche standard. Fortunately for him turned to adjust the heat range of the spark plugs in well with his 'passion'.
911 scale 1: 3.2 has 6 Solex 40 PI downdraft carburetors. And you'll believe it or not: they are made from a single block of brass.
Distributor, rotor, ignition name it, it all fits in detail. Hofman was incidentally much cooperation from the Porsche factory Germany, in the sense that he was original bouwtekenin- gene disposal stelde.Van both Solex booster pumps could not do that, they were copied from a set of originals.
De 911 engine Frits Hofman still exists
technique, a modern version of the 911 is packed with electronics and is liquid cooled. Nice detail, also Hofman for 'his' 911 special tools to develop.
mainly of mechanical
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In the background an original plan of a Porsche connecting rod. In the dispensing of the milling machine version for the small 911.
From the black and white era
Over 10 years, Frits Hofman about done to build the smallest rotary motor 911 in the world. During that time he spent 6,000 hours on the project. All his works are well documented and recorded on film. In this photo collage you can see how a piece of duralumin 5kg begins to take shape and eventually a small, exact copy of a 2-liter 911 engine.
Here, the clock out of a camshaft. Naturally, high demands on the material. Hofman chose nitriding. Equally important is the lubrication of the parts. Till now the practice has proved that Hoffman has made the right choices, both camshafts keep just fine and show no traces of wear, while the block already has the necessary hours turned.
The cams are 'machining' applied to the camshaft (even this part is not cast). Therefor it was necessary that man Court- the lathe in a special way instituted. To the engine block over a broad speed range acceptable to run, he should do the breathing zone concessions: the light of valves he has reduced and the overlap is less. In addition, the carboxylate of the venturi burateurs 20% smaller.
Het sump begins to take shape and dimensions. None of the components are cast, so this crankcase is not. Base was a lot duralumin machined so that was that it lived up to the manufacturer's requirements. And that was in Johnston case the appearance truthful happened and that the engine block at the end of the 'ride' could 'walk'.
The two booster pumps the fuel delivered in principle quite difficult because even Porsche had no bouwte- accounts of the part. The plant has when Hofman two 'real' Solex driven pumps which he could count.
So it looks close out. Look at that little socket screws of the valve cover, everything to perfection in accordance with the original. But still large- re homage harvest the builder if the cube is gestart.Want shows that he can not only recreate, but the proportions and adjustments as well knock the block fantastic responds to the gas, "smoothly" running, even at idle and no holes through accelerates to the maximum speed of 16 000 r / min.
The Solex downdraft carburetor 40 PI tors have been recreated to scale. The fuel collects in a central float chamber (one per bank) and flows (over) to the carburetor. To give you an idea of the dimensions: the stationary nozzle has a diameter of 0.15 mm. And the other holes are so small that the fuel system is quite sensitive to impurities.
To give you an idea of the precision and patience of the instrument maker: manufacturing of the valve cover with the text "Porsche" took 10 hours. And those characters are not drawn stick! It was not later than after the manufacture bead blast to get the original surface structure.
The cooling fins on the cylinders are firing set on the lathe, the ribs on the heads are fitted with a saw mill on the milling machine. The chain camshaft drive are derived from the store. Hofman rather have to experiment with the tensioners but it is not strange because Porsche also considerable variations tensioners used in the 911 block.
In one piece and in one time. Fortunately could Hofman when turning the crankshaft using the original dimensions of Porsche and this against recalculation to its scale. And as you by the slide rule (who knows those things yet?) Can see, the crankshaft has a length of 15 cm.
Het block without gear was finished in 1973. Hofman has presented at the Porsche stand in that year at the IAA. In 1977, he was satisfied that the motor and when he turned the Porsche factory employees in DuitseWeissach astound zijn'hobbywerk. Especially the sound (higher in frequency but unmistakable air-cooled six cylinder boxer) garnered much awe.
Merging crankcase and crankshaft. Hofman the flywheel, of course, has also been added to the whole. In the flywheel is a special coupling which he operates by hand. This component is required for starting, which is of an electric motor of a jig saw are spent. And to convince yourself of the assumptions Hofman did during the conception and execution of the project: the small 911 starts in an instant.

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Flat six engine....
