TECH: BS MOTORSPORT ENGINE DYNO
Story and photographs by Chris Horton
dynamometers are all very well, but if you want to know what your
flat-six is truly capable of then you need to bolt it to an accurate engine dyno like this
There are many facets to a successful engine rebuild, whether it be an entirely standard unit or modified for extra performance, but one of the most important – and often overlooked – is testing and fine-tuning the finished product for optimum power, economy and usability. For many of us (experts frequently included) that has traditionally meant – in very simple terms – refitting it to the car and driving it, perhaps with a few roadside ignition and fuelling adjustments, followed by another necessarily subjective and thoroughly unscientific road-test. It can be a slow, tedious and rather chaotic procedure. Hazardous, too, if you get it wrong, and (for instance) give the engine too much ignition advance and/or not enough fuel, and as a result blow a hole in a piston(s). Or worse.
Latterly, of course, we might well have taken advantage of a so-called rolling-road to assist in the process. The most obvious benefit of these now quite commonplace devices is a read-out (and ultimately a print-out) of the engine’s power and torque curves, as well as the ability almost immediately to see the effect upon them of any adjustments, major or minor, to the overall set-up. On even the most accurate of rolling-roads, however – and unfortunately both they and their operators can vary quite widely – the figures you see are by definition taken at the vehicle’s driven wheels. The engine’s true output, although invariably greater (even in a two-wheel-drive car the transmission and tyres can absorb as much as 25–30 horsepower), will always have to be extrapolated. There is also a limit to what can quickly and easily be done to address any mechanical issues, or to carry out any further modifications, especially in a car allowing such limited access to its engine as a typical 911.
It’s a basic fact of tuning life that had always exasperated Neil Bainbridge at independent Porsche specialist BS Motorsport in Westcott, Buckinghamshire, so three years ago he set about the ambitious task of putting together his own largely 911-specific test cell, in this case based around an American-made Land & Sea DYNOmite engine dynamometer, and the same company’s DYNOmax software. (More information on both at www.dynomitedynamometer.com.) The resulting system has now been running for about a year. Here, crucially, the crankshaft of any power unit under test is bolted directly to the input shaft of the standalone water-based ‘brake’ (see the panel on the right), and although the resulting readings are in the end still dependent upon the overall accuracy of any such system and its associated software, what you see is pretty much what you get. And that, needless to say, is what is going to give you the most accurate before-and-after picture of any modification.
It does mean, of course, that the engine not only has to be removed from the car (assuming it had progressed that far in the first place), but also separated from the transmission, secured to a special cradle, and finally connected to the many necessary life-support systems. ‘We charge our standard workshop rate – £65 an hour plus VAT – for the labour needed to get the engine out of the car, hooked up to the dyno, and/or back into the vehicle and running again,’ says Neil Bainbridge. ‘But we’re pretty good at that by now – we once had an engine out of a 911 and stripped before the crankshaft had even cooled down completely – so it can take as little as 90 minutes each way. Then you have the time on the dyno itself, of course, at £900 per day plus VAT. It sounds quite expensive, but some of these power units could easily have cost £25,000 or more to build, so Engine, complete with ancillaries, is lowered onto its cradle, and then with four bolts attached to shaped adaptor plate. One of three ‘flywheels’ is then fitted, although since the dyno itself acts as a flywheel (and also a starter motor) its purpose is mainly to allow the drive shaft to be connected. Machined lugs on cradle engage with fixed section of dyno, and the two are then secured by a pair of over-centre handles. Most important ‘life-support’ connection is Neil’s own thermostat housing (arrowed, opposite page), which sends failsafe signal to a big mechanical oil-pressure gauge. Fuel and oil systems all designed for maximum efficiency and safety, too. This engine had stood dormant for many years after a rebuild, so an accident, he still does more with just one than many of us manage with two – is never far from either the main throttle control or, in worst-case scenarios, the big, red emergency-stop button. And if it does all go horribly pear-shaped there are few better placed to undertake another rebuild.
Indeed, safety – of both engine and operator – is paramount. The cell itself, which Neil was fortunate enough to buy second-hand from one of the large UK-based car manufacturers, is heavily sound-insulated (as required by legislation, although an engine-only dyno is considerably less noisy than a rolling-road which has two or four big tyres running at high speed), with all connections to the external fuel and water tanks through specially sealed ‘ports’. (The water is primarily to run the dyno itself, not for cooling the engine, although liquid-cooled units can be tested.) There is also the usual ducting for exhaust fumes, and two large ceiling-mounted blowers to maintain the cell at more or less any desired temperature, and thus ensure the full repeatability of any power run. The whole place is brightly lit and scrupulously clean and tidy, and two high-definition CCTV cameras stare down like a basilisk on the areas not easily visible from the separate and routinely darkened control room. There is even a polished tray beneath the engine, partly to catch any leaking oil (or coolant, where relevant), but also to provide a quick and convenient means of seeing where it might actually be coming from. There are naturally plenty of fire extinguishers on hand, as well.
For no less obvious reasons Neil has spent a considerable amount of time and money perfecting the lubrication system. Specially designed and made for him in the US, the 25-litre aluminium tank required for the air-cooled 911’s ‘dry’ sump can be opened for easy deep-cleaning when necessary (Neil normally runs it with the typical air-cooled 911 motor’s standard 11–12 litres of oil), and although individual connections vary, is always linked to the engine by pipework capable of flowing at least as much as that in the car itself. The screw-on, 911-pattern filter, which is in the outlet from the engine to prevent contamination of the entire system in the event of a blow-up, is renewed before each new installation. The oil itself is either the customer’s own preferred brand and grade (if Neil agrees its suitability) or the relevant Valvoline product, and is again drained off after each finished test for the customer to take away and use if required. Neil can even offer an external oil-analysis service to assess bearing and piston-ring wear.
Fuel is supplied from a 100-litre foam-filled safety tank outside the test-cell. Again Neil is happy to use whatever brand and/or suitable octane rating the customer specifies (and ideally brings with him, too; see again the panel on page 91), but by the same token can also supply it himself from a local filling station. Be warned, though, that a typical session can easily get through at least that amount, and quite a lot more if any running-in and/or endurance testing is involved – see below. The large primary tank feeds a smaller wall-mounted so-called day tank inside the cell – also foam-filled for safety – and from this the petrol passes to the engine via an easily switchable low- or high-pressure pump as required by either the carburettors or the injection system.
Not surprisingly given the nature of the 911, much of Neil’s time in the control room is spent looking for additional power and torque, which at this stage in a typical engine’s life will most likely mean tweaking fuelling and ignition, either by remapping the electronic control unit (for later engines Neil is a big fan of Australian-made Wolf or Motec ECUs; in earlier ones, with mechanical fuel injection, he’ll rely on rather more traditional techniques), or possibly altering the camshaft timing or even changing the camshafts themselves – which given the ready accessibility of the cylinder heads with the engine out of the car is a relatively simple task. Exhaust and induction systems, too, can often be modified or changed in a matter of minutes, making it easy (and thus relatively cheap) to see what works. ‘Or more likely what doesn’t work,’ suggests Neil with a knowing smile. Indeed, he quickly ‘found’ an additional 15bhp from the engine shown here simply by discarding the single tailpipe extension.
But the dyno, which by its very nature can place an infinitely variable load on the engine (or even no load at all), is ideal for initial running-in, too. The software that runs the system is more than capable of automatically monitoring and managing the power unit for the critical first few hours of what one hopes will be its long and reliable life (and if necessary shutting it down), but such is Neil’s attention to detail that it’s rare for him to leave them to their own devices for more than a few seconds. The engine shown here – an effectively brand-new 2.2-litre 911E unit, with ‘S’-specification barrels and pistons – was finally fired up at 6pm one day, but Neil and its owner, Sean Guest, were in the control room until one the following morning, and then back in at nine for further running-in and finally a full-power run. (Customers are welcome to watch the entire process if they wish. And assuming they can keep up with Neil himself...) This also means, of course, that the engine can be given its first service while still on the cradle – valve clearances can be adjusted in minutes, the oil and filter changed in little more than seconds – and thoroughly checked for leaks and any other minor issues before it’s even fitted to the car. And then, within reason, driven as hard as you like from the outset.
You probably get the idea by now – with further clues, we hope, in the accompanying photos. Proper dynamometer testing – as opposed to a casual run on a rolling-road – is neither cheap nor particularly quick. So it is highly unlikely to be taken up en masse by the hot-hatchback brigade, or even the owners of many front-engined Porsches, unless perhaps as a prelude to the initial installation of the engine. For enthusiastic owners of air-cooled 911s, however – and those, perhaps not surprisingly, are what BS Motorsport specialises in – it is just about the most scientific and cost-effective way of finding out what is really going on inside those hard-working combustion chambers, and then doing something meaningful about it. Add the proven track record of the man who effectively designed and built – and continues to modify and improve – this particular system, never mind the almost spiritual passion with which he pursues Porsche engines’ sometimes hidden potential, and we have a feeling that Neil Bainbridge is going to be busy for a long time to come. He certainly deserves to be.
BS Motorsport is at Unit 421, Westcott Venture Park, Buckinghamshire HP18 0XB; tel: 01296 658422; e-mail: firstname.lastname@example.org. The company’s website, at bsmotorsport.co.uk, has more details about its dynamometer and other repair and restoration services, including ‘house rules’ for dyno customers (see also the panel above), and a useful on-line, real-time calendar showing the system’s current availability.
endoscope (below right) was used to check inside all six cylinders before even turning it over. Better to be safe than sorry TECH: BS MOTORSPORT ENGINE DYNO spending another £1500–£2000 or so getting them running reliably and at maximum efficiency is a good investment.’
Reliability? Maximum efficiency? You’d better believe it. The system, itself fine-tuned over the last 12 months to incorporate Neil’s own carefully considered requirements, and in many ways still under development even now, routinely monitors (obviously) not only power and torque output, but also precise exhaust-gas composition, oil pressure and temperature, turbocharger boost (where applicable), and even piston-ring blow-by. (See also the panel on page 90.) That, and his many years’ experience, both building his own engines and repairing others that have blown up, allows Neil to spot problems almost before they occur, and no less importantly to do something about them. His hand – and, despite having lost an arm in an
WHAT THE SYSTEM MEASURES
This could quickly become a long and very complicated part of the story – the system can tirelessly monitor something like 75 different individual signal inputs – so we’ll stick (and in no particular order) to the bare essentials. Automatically logged are throttle position, knock (ie detonation), inlet and outlet oil temperature, ignition advance, cylinder blow-by, and air/fuel ratio (usually abbreviated to lambda; see the photo below). The exhaust gas is constantly monitored, too, for carbon monoxide, carbon dioxide, hydrocarbons and oxides of nitrogen, all of which can give an expert such as Neil a very good handle on what’s really happening – and what might be further achievable. Overall exhaust-gas temperature offers a further glimpse inside the combustion chambers, and if using his own specially adapted headers Neil could even take a reading from each individual cylinder. He’s also working on a refinement to monitor cylinder pressure via a special spark plug, and later adding a four-channel oscilloscope to show the real-time spark voltage at each plug. Oil pressure – the lifeblood of any engine – is shown on the main PC screen (which flashes up warnings on that and most of the above parameters when necessary), but as a final, irrefutable safeguard is also displayed on a simple, large mechanical gauge in the test cell (see below again). It’s no wonder the set-up looks like a cross between a hospital intensive-care unit and NASA ground control.
WHAT IS A ‘BRAKE’?
A dynamometer is in very simple terms a device for measuring the torque produced by an engine, electric motor or some other prime mover at any given rotational speed. From this can be calculated the benchmark figure beloved of performance-car enthusiasts the world over: its power output.
There are many different types of dynamometer, but in an automotive context essentially just two: the rolling-road or ‘chassis’ dynamometer, and the engine dyno. The former measures output at the wheels, extrapolating as best it can the inevitably higher output from the engine itself, but a good engine dyno, linked directly to the crankshaft, is by far the more accurate.
In all dynamometers the torque is measured by applying a known force to try to prevent the crankshaft turning. The means of doing that, too, varies widely from one system to another, but most rolling-road and engine dynos use what is known as a water brake absorber – essentially a fluid coupling with a housing restrained from rotating. Think of it as a water pump with no outlet.
Water brake absorbers – such as Land & Sea’s DYNOmite unit – are relatively common, having been manufactured for many years, and are noted for their high power capability (here fully 2000bhp), small size, light weight, and relatively low cost. Their main disadvantage is that they can take a little time to ‘stabilise’ the load they apply, and they also require a constant supply of water to the brake housing for cooling purposes.
How does it work? Water is added until the engine is held at a steady speed against a known load, and then maintained at that level by the continual draining and refilling needed to carry away the heat created by absorbing the horsepower.
The housing attempts to rotate in response to the forces produced within it, but is restrained by a special metering device (here arrowed) that measures the torque – and from this, as we’ve said, can be calculated the horsepower.
|Engine, complete with ancillaries, is lowered onto its cradle, and then with four bolts attached to shaped adaptor plate. One of three ‘flywheels’ is then fitted, although since the dyno itself acts as a flywheel (and also a starter motor) its purpose is mainly to allow the drive shaft to be connected. Machined lugs on cradle engage with fixed section of dyno, and the two are then secured by a pair of over-center handles. Most important ‘life-support’ connection is Neil’s own thermostat housing (arrowed, opposite page), which sends failsafe signal to a big mechanical oil-pressure gauge. Fuel and oil systems all designed for maximum efficiency and safety, too. This engine had stood dormant for many years after a rebuild, so an endoscope (below right) was used to check inside all six cylinders before even turning it over. Better to be safe than sorry|
There is, it seems, a kind of basic etiquette for both users and suppliers of dynamometer services, and Neil Bainbridge, using his own long experience in both roles, has put together two helpful leaflets and a disclaimer form outlining both what he will provide and what he expects of his customers. The underlying but obvious principle – also explained on his website – is that the engine must be in a serviceable condition to start with, and if it does go bang then it’s the owner’s responsibility, not his. Quite right, too. Neil also makes the point that, since time is money, you need to be prepared with all of the materials (fuel and oil, for instance) and relevant spare parts (spark plugs, fuel injectors, gaskets, specific fasteners etc) and any tuning hardware likely to be needed during the session. You will not be charged for any delays caused by Neil’s own system, and all test data, as the property of the customer, will remain strictly confidential. If you want to tell the world what your engine produces that’s up to you, but no one will hear it from Neil or his staff without your permission. On a related note, incidentally, the BS Motorsport dyno can currently handle vehicle and inboard marine engines up to 2000bhp, and outboards to 500bhp. Neil has a bit of a thing for boats, too, but that’s quite another story.
|External fuel and water supplies are brought into cell by top-quality braided hoses. Lockable cabinet houses selector board for low- or high-pressure fuel pumps – and pumps themselves for easy maintenance. This engine’s headers had to be drilled for oxygen sensors – they were later sealed with threaded plugs. Usual exhaust probe measures precise content of waste gases. Earlier test session shows Turbo engine getting exhaust system red-hot under load – but never unduly bothered. On this more recent occasion the 2.2-litre motor wouldn’t even fire, but basic diagnostic checks traced that to a faulty CDI box. Fortunately Neil had a couple of dozen spares in stock... Once running satisfactorily after its long lay-up it clocked up enough ‘miles’ on the dyno to be fully run in. Owner Sean Guest (below right) followed the entire process|