Mercedes 300SLR

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The man we must thank for the beautiful and successful DBR1 has a high regard for the car he wanted to beat. Fate denied a head-to-head, but he knows the battle would have been tough

You man be wondering by the time you finish reading the article why I chose this car. It’s true, I have some concerns about it, things I would do differently, for every car is flawed. But that doesn’t stop it from being a masterpiece of engineering. The 300SLR was the best of its time: fast, reliable and, most important of all for a racing car, successful.

It was the brother of Mercedes’ W196 GP car. In fact, the official works names for them were W196 Rennwagen (F1 car) and W196 Sportwagen (sportscar). In many ways, though, the 300SLR was better. They had learned a lot with the GP racer that they ran in 1954, and incorporated these lessons into the 300SLR, which made its debut in 1955. It was their second bite at the cherry. Its engine is 500cc larger than the 2.5-litre F1 unit, but there is much more to their differences than an altered bore and stroke. The GP engine featured welded-up, sheet-steel water jackets, which is how they did it before WWII. The 300SLR’s power plant is all cast, with a one-piece block and head, like Bentley, and I would say this was superior to the Fl engine.

It only had one joint, where the cylinder barrel entered the crankcase, and it’s an oil joint at that, not a water joint; the GP engine had two joints. The 300SLR engine was certainly very strong.

And very expensive. I wish we’d had that much money at Aston. It’s all-roller bearing. Nobody uses these now as they are so costly. It also means you have to use a Hiirth crank, which is made up of 18 threaded pieces to hold them together. This is a no-expense-spared engine.

That said, it was perhaps a surprise they chose to build a straight-eight They had assessed a V8 and a V12, but decided that this was the best bet Straighteight engines have long, whippy crankshafts, with poor torsional vibration characteristics. To cure this, Mercedes took the power from the centre of the engine. This means there are two four-cylinder cranks, much stiffer and stronger. One thing I do not approve of, however, is its desmodromic valve gear. Nobody uses this today. Not because it is too expensive, but because it is inefficient. The system is mechanical and so does away with valve spring breakages. It can also cope with very high acceleration and deceleration forces. But the big problem is that it doesn’t put the valve back on its seat properly. It relies on the gas pressure to do that This means that the edge of the valve must have got very hot My guess is that they would have changed valves after every race, especially given that wear-rate is higher with desmodromic because it has more faces-to-pieces operating.

There were big advances in camshaft design just after WWII, multi-sine wave cams replacing threearc cams to provide much smoother operation of valves. This mainly stemmed from American and British engineers, and I imagine the Germans had not got on top of it by this time. Another aspect of the engine which the modern eye may find unusual is its wide valve angle approximately 90 degrees. But I did exactly the same thing in 1955.1 was once taken to task over this by Keith Duckworth, the master, who explained his narrow-angle-four-valve engines was the best way to do it. Wide angles, he said, create horrible combustion chamber shapes and do not generate enough swirl effect But he had years of extra technology to draw upon: the 300SLR engine was the best of its time.

They claimed 290bhp at 7600rpm for it, running at an incredibly high 12:1 compression ratio. Even by 1960, we couldn’t run any higher than 10.25:1 and that was only with the very best fuel we could find. A very tall piston is required to generate high compressions in engines with such wide valve angles, and I can only think that the Mercedes engine did not breathe very well at high revs. And Wits volumetric efficiency is only 75 per cent at maximum revs, then its effective compression ratio is reduced.

Engines were almost the be-all-and-end-all in this period. British chassis design was only just coming to the fore. But there are plenty more praiseworthy aspects to the 300SLR than just its engine.

Stirling Moss always commented how smoothly the car rode, almost like a big Yank. It had very good suspension. Its swing-axle rear end certainly gave it better traction, and was much better on bumpy surfaces, than its live-axled or De Dion rivals. It was not a swing axle in the true sense: it had two links locating each half-axle fore and aft. The only thing I would have changed is the centre line pivot point of the half-axles. I would have had two pivot points, the left-hand one operating on the right-hand wheel and vice versa. This would give longer arms, which would allow more scope to play with roll-centres.

The gearbox is a jewel, far better than anything we had at Aston Martin. Its a transaxle, which means the car had excellent weight distribution. The body was beautifully aerodynamic, extremely efficient for its time. And all of this served to make it very stable at high speeds. Braking must have been a different matter. Drums were already old hat in Britain, but Mercedes did not wish to use discs. They put their drums inboard to reduce unsprung weight, but this means the car was longer than it had to be. I would have put disc brakes outboard and made the car shorter. Of course, Mercedes used those amazing air brakes at Le Mans in 1955. They were fascinating to watch, and very effective, but

I think necessity was the mother of invention on this occasion. Let’s face it, squirting oil, via ‘trumpet valves’ on the dash, into the drums to cure a grabbing brake is hardly hi-tech or ideal. We shouldn’t end on a negative, though. People

have been kind enough to compare my DBR1 with the 300SLR. That’s very flattering. There is no doubt I drew inspiration from the Mercedes and Jaguar’s D-type. That’s only natural. It still happens today. Take all the liveries off modem Fl cars and see if you can tell which is which. The 300SLR is a car I looked up to. I would have loved to have been involved in the design of it. And the development of it. We had four years with the DBR1, making it better every year; Mercedes had just one with the 300SLR. Just think how good it would have been by 1958.

Ted Cutting was talking to Paul Fearnley

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