Peugeot 604 Turbo Diesel

Introduction

During the era of the 604 (and based on figures we have found for 1980), the diesel market in France was a not inconsiderable six per cent, second in national percentage only to Belgium (seven per cent) and ahead of West Germany and Italy (both five per cent) and America (one per cent).

By the late 70's Peugeot had already been producing diesel cars for a long time, these being mainly their medium and small car offering, the 504 and 304. It was during the 1979 Geneva Motor Show that they announced diesel versions of the 305 (the 304's replacement) and the 604. With the 305, Peugeot wanted to go one step further than Volkswagens class leading Golf diesel.

The Peugeot engine was an all-alloy affair, while the Golf used an alloy head but had a cast iron block. To help lug the extra weight of the 604 around, Peugeot opted for a turbocharger version. 504 engine - something they needed to do if they were to compete with other manufacturers, such as Mercedes-Benz, who had started to offer more powerful diesel options for their 2-litre-class cars.

After the five-cylinder 80 bhp 3-litre Daimler-Benz diesel appeared in the 240D 3.0 in July 1974, Citroen replaced the 66 bhp CX 2200 in the autumn of 1975 with a 75 bhp 2500 (February 1978), and in 1978 Volvo launched their 82 bhp 2.4-litre version of the 244 (using the six-cylinder Audi-VW top-of-the-building-block-range unit). We cannot be sure, but we think it unlikely that Peugeot, through their tenuous link with Volvo via the PRV engine tie-up, ever considered going the same way as Volvo.

They could at the outside have perhaps converted the all-alloy PRV 2. 7-litre V6 to diesel, but it seems likely that the strengthening needed to cope with the higher inertia and compression loads of a diesel had not been built into the Oouvrin unit as it had for VW's engines. The relatively straightforward 2.3-litre diesel used in the 504 was a long-established one, with plenty of strength in hand.

Even though stretching it further was going to be difficult, exhaust turbocharging was relatively easy. It would be comparatively easy to increase the 2.3·s 70 bhp to around 80 bhp using a modest turbocharger - without adding greatly to weight or, thanks to the fact that a turbocharger unlike mechanically driven blowers uses some of the waste heat energy of exhaust gas, fuel consumption.

Peugeot went to Garret AiResearch of Pheonix. Arizona, then a well-known subsidiary of the Signal Co. conglomerate, as Mercedes have done for their 115 bhp turbo version of the 3000. AiResearch opted for different turbo casings but used the same turbine, in effect "tuning" the turbocharger to give it 16t of power at peak, or, less peakily, to start working low down with some sacrifice of top end poke but a better spread over the range.

Together with an integral waste-gate which limited boost to a maximum of 0.6 bar - 8.7 psi-maximum power went up from th 504's 70 bhp at 4,500 rpm to 80 bhp - a 14 per cent increase - at 4,150 rpm. But that maximum boost was first achieved with the engine on full load at 2,000 rpm,: continuing at the same level tailing a turbocharger on an engine with exhaust and induction on the same side of the block was much simpler than other contemporary designs.

On the down side, it meant that the turbo was sandwiched in the vee formed by the underside of the 20-deg inclined cylinder block with the side of the engine compartment - those old enough to remember the Turbo Saab 99 and 900 will well remember the trouble they went to locating the blower unit away from the engine, in front nearer a supply of fresh air. Turbine cooling being achieved via oil, Peugeot followed common practice in adding an oil cooler to the water radiator. In addition, the usual Peugeot thermostatically clutched engine-driven main fan - which according to their road tests used a massive 7 bhp (8% per cent) if it engaged at peak power speed - was supplemented by an electric fan in front of the radiator.

The waste gate was neatly integrated with the turbine casing and it worked in the usual way, its poppet valve opening to allow exhaust to by-pass the turbine when, via a diaphragm, it sensed inlet pressure rising too much. To ensure that the pistons were properly cooled, Peugeot provided oil jets placedsingly in the outer and as a pair in the middle crankshaft main bearing housings which directed oil at each piston's underside - instead of relying on the more usual finger hole drilled in the root of each connecting rod.

We have not been able to obtain specific weight figures for the turbo setup, but the overall kerb weight of the Turbo 604 went up by nearly 60lb, and we will guess that this was the basis of a corresponding increase in front axle loading - weight distribution changed from the petrol 604's 51.0/49.0 to 51.7 /48.·3 front/rear - so it seems to us rather obvious that the alloy-headed, iron-block four-cylinder diesel weighed a bit more than the all-alloy V6 - if you think we are wrong you can always write your review below. For most countries the transmission choice was either a five-speed manual gearbox or a three-speed automatic, however in France you could option a four-speed - but we don't know why you would.

Interestingly, in spite of the extra torque and extra car weight - the latter went up by 10 per cent - the turbo 504 engine took with its 504 gearboxes to the 604. The five-speed was of course the four speed with an indirect fifth added, and the automatic a ZF unit, not the GM Strasbourg one used in the petrol 604. Final drive ratios differed by one tooth - 12/43 (3.583 as on all forms of the petrol 604) for the five-speed and 13/43 (3.308) for the automatic (and four-speed). This meant that fifth on the manual would return a maximum of 99.6 mph @ approx 4,200 rpm. The automatic was slightly undergeared; its less than tidy maximum was around 93 mph at @ 4,250 rpm.

As with all earlier type turbochargers, it was very easy to destroy a turbochargers bearings by revving the engine hard when the oil was still cold. Peugeot recommended that, after the engine had been started, you should wait "at least 30sec before accelerating to allow for the lubrication of the turbocharger." Starting was a key-only matter; there was no separate glow-plug switch.

The 604 made the usual diesel noises to about 40 mph., but beyond than it would be difficult to tell the difference between the oil burner or petrol variety. Things changed again when you would it out past 90, when the engine noise would remind you that you were driving a diesel.

But perhaps the most remarkable thing about the 604 was how difficult it was to notice the car was turbocharged. We are not being sarcastic either - sure the 604 was not a performance machine, but unlike the petrol turbos of the era where the usual response time from throttle closed to wide open with the engine already revving at well abovethe minimum speed at which turbo effect started was usually measured in seconds, what delay there was on the Peugeot diesel at least seemed far less.

Quite apart from the fact that the installation was designed to give turbo effect from comparatively low down, it is worth remembering that where the petrol engine's output was controlled by varying the flow of intake gas, the diesels air-flow-through was not interfered with other than by the variations due to crankshaft speed; you controlled the diesel only by varying the amount of fuel injected. That meant that when you cut the power on a diesel, you didn't cut the through-flow of air; therefore although the temporary loss of exhaust heat when you decelerated affected the turbo somewhat, there was still the kinetic effect of that air to keep it spinning fairly quickly.

The overall effect was of a surprisingly pleasing power unit with no real vices. There was enough power for all normal purposes, and combined with the well known and considerable virtues of an excellent chassis, it seemed Peugeot had a winner. Today we remember the 604 as the first production turbo-diesel car, and a reliable one at that. However, there was one one major problem. Like many diesel engines of the time they were hard to start in the cold weather, and the 604 was amoung the worst. It was a very difficult car to start and some ensured it was parked on a hill to avoid this problem. In nearly all cases the problem could be overcome by some minor tweaks to the glow plugs and compression. This problem in itself was not enough to tarnish the 604 Turbo-Diesels reputation, but sales were never particularly strong. The last 604 rolled off the production line in 1985. Peugeot's next major executive car, the 605, was launched in 1989.