Knowledge is Power, or A Day At The Dyno
There's an old saying that “knowledge is power”. If that's the case, then I've often thought that it would be interesting to have a bit more knowledge about power, specifically the power of racing car engines. The way to measure power directly is, of course, a dynamometer, but usually people are pretty secretive about the process. So it was quite a surprise when, with the engine owner's enthusiastic permission, I was invited to watch the dynamometer testing of a Toyota 3S-GE engine on carbs and DTA ignition that Ray Rowan was having run at the test facility operated by Paul Knapton's X-Tec Engineering. X-Tec is, of course, very well known to Club F3 racers and historic racers and have been responsible for building some pretty exotic kit. The dyno has run such diverse engines as Hyabusas, Matra V12s, DFRs, F3s, Touring Cars, Mercedes Group C and Porsche GT1. The latter was described to me as “a big enough engine which looked like it was covered by one of those metal spiders from Mars, there's so many pipes and wires.”
The dyno itself is by Heenan Froude with a capacity of up to 1,000 bhp and 13,000rpm. (Paul commented here that “we've never had anything that went beyond that, so I have to say that's the capacity!”.). It has been installed at the Aldridge test house for about 5 years, and before I talk about the test, the installation of the machine bears some examination. The dynamometer itself is a fairly small green box which provides a load to the running engine by pumping against water pumped in under pressure. The pressurising pump is obviously very powerful, and is assisted by static weights for the more powerful engines. To absorb the power of a 1000bhp engine takes a lot of water, so there's a 5,000 litre tank in the bay next to the dyno. The water has to be de-aerated before it can enter the dyno and in part this is done by two big, linked drop tanks, much the same size and shape as cattle drinking troughs that the water pours into from the dyno. If you've seen white water rapids, you'll have a bit of an idea what the troughs look like when the system's running with a 2 litre Mono engine. With the more powerful stuff, a flood isn't unknown.
The heated up water settles in these tanks and is pumped outside to 3 large water to air heat exchangers in the car park. There are fairly beefy fans on top to get a breeze through them, with the aim of keeping the water around 30 degrees. During the test I felt the pipe (on a day when ambient was around 5C) and I can confirm it was warm though only just. The fans weren't needed.
As can be imagined, the watchword on everything is safety. A lot can go wrong, and it's catered for by the test cell being in a separate room, very heavily isolated for sound by acoustic panels under a thick pre-stressed concrete roof. Placards warn against entry by unauthorised persons, everything is very heavily built, tested, and tested again. I can confirm that from the outside there's just an industrious hum during the Mono engine test, and certainly a lot less noise than comes from a small engineering shop. As the neighbours don't complain even when there's been a V12 Matra running up (ask one of the older Mono members why I chose that one), I think we can assume silencing is good.
Moving to the engine, Ray explained that the objective is to have it as close as possible to the car set up. The car exhaust is used and (by adaptors) leaves the test room through trunking. The full car wiring loom was used to connect up the ignition box, which confirms another variable, and the fuel and oil systems were as near as possible to that in the car. Only the engine cooling was different in that instead of radiators the water feeds into twin heat exchangers which transfer the energy to the dyno water. Temperature can therefore be controlled by the valves to the heat exchangers. The flywheel is bolted to a driveshaft with a CV at either end driving the dyno itself.
The control and reporting systems are a curious mixture of technologies. As the pumps and cooling arrays are basically heavy industrial machinery, there are heavy electrical switches to control them. But the “Texcel” dynamometer control unit is a straightforward looking box, reminding me a bit in appearance of a 1970's British HiFi. It reports the revs and the dyno water temperature and allows maximum revs to be set. This stops the engine from over-revving during tests. The actual opening of the throttle can be programmed to be done automatically so that a cycle can be run with nobody present. However, Paul prefers to operate the throttle manually with a big aluminium lever connected by bowden cable to the carbs. “I can feel anything begin to go wrong through that and shut off straight away. It's amazing what you can detect.”, he said. It isn't the only sensory detector, though. There is a microphone attached to the engine which plays through headphones to detect detonation (see Martin Cliffe's article for a description of detonation). Normally, there's just the gentle clickety-click of the tappets, but any major noises mean an immediate cut.
A lambda sensor is fitted in the exhaust and reports through a separate unit. The lower the number, the richer the mixture, but remember that however much we would like to save the planet,the objective is maximum power without engine damage, so emissions aren't a priority. A reading of around 0.9 under load is regarded as reasonably optimal for this sort of race engine.
Finally, there's the really interesting bit, the Froude Consine Texcel V10 software running on a standard Windows XP computer (display, left). This gives engine water temperature in and out, engine revs, oil pressure, torque, and power. When I visited it was set in imperial pound-feet and bhp, but I believe metric can be switched in.
The test lasted just over an hour. With the engine firmly bolted to a sturdy frame, it was warmed up and run in at around 2800rpm. This in itself gave me my first surprise. At around 2,700rpm the engine was giving little over 30bhp and 60lbft of torque. This is, of course, cruising along at 55 on a flat A-road, and would be pretty economical in a road car. With a bit of warmth, the testing started. Apparently it's traditional for predictions of engine power to be made at this point. It's also traditional for the owner to look nervous, and adopt the same panicked expression that people get when the engine note suddenly changes on your Easyjet A320. For example, somebody leaned over the engine as it was running, blocking the carbs and almost stopping it. Cue owner turning white.....
The power runs themselves were fairly undramatic. Paul tried a few different settings on the DTA box, controlled from a separate laptop which (reassuringly) repeated many of the rpm and temperature readings from the Texcel software display. The box comes as standard with 10 degrees at 800 rpm, rising to 33 BTDC at 3000, then steady to 8,000. This was changed, but not by a lot. Since Paul makes his living from programming such boxes (amongst other things) I won't reveal his secret, but suffice it to say he found the optimum to be pretty much the same as most other near-road tune engines he's seen. “You need to be able to increase the compression or boost the engine for the ignition map to make a big difference” he commented. As the throttle was moved up through the rev range, we watched the power and torque. Ray warned: “Don't take too much notice of the bar graphs during the runs. They can be like a needle flicking up and giving a high reading. The software will take a series of averages at points in the rev range and give more reliable figures in a report at the end. We've had engines in here where the owner was delighted to see 580 – but that was misleading and the true figure was nearer 515. People often have an optimistic view of power. We once had a track day man in here, very disappointed that his engine was nearly 100bhp down on what he thought it should be. When pressed, it turned out that “everybody in his club knew” those engines should be the higher figure, but nobody had actually tested one before. I think that may apply to a lot of quoted power figures.”
The tests were over fairly quickly, with everybody being quite pleased at both the maximum power and how it was delivered. Rather than quote a load of numbers, here's a graph plotted from the results. I've asked our Excel man to plot both the readings and smoothed curves, and I'll leave you to decide where reality lies, with Texcel or Excel.
If you are thinking of dyno testing your engine, or want to get the
map optimised, the dyno is available (with operator – you can't
play by yourself) by calling X-Tec (01922 454 858) or via xtecengineering.co.uk.
Toyota engine (right) on the Heenan Froude dynamometer (green, background). Overflow tank just below, behind
Paul Knapton of X-Tec at the mechanically connected throttle (F). Pump and Electrical controls (A), Texcel software on XP PC (B), lambda sensor ( C), Texcel dynamometer controls (D), and laptop running DTA ignition box setup software (E)
DTA screen gives many engine parameters. Overlaid window sets / displays ignition timing
5,000L tank in ante-chamber
Remote, external heat exchangers and cooling fans
Rob Barnsley makes some setting up adjustments. Tank right is oil supply.