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An Afternoon at Aldon

Dyno Testing a Couple of Dallaras at Aldon Automotive. This report is NOT about the result of the tests but about the process behind it.

The issue of Toyota 3SGE-based Piedrafita engines in Monoposto ("Mono F3") has been discussed for several years. The problem is that Monoposto engines in the class are defined by choke size and components, whereas the Piedrafita, whilst having a measurable choke size, is fundamentally a seal with an engine built round it. If you break the seal, you've either got a very expensive anchor for your boat, or you can take up hillclimbing and be uncompetitive. Until now we've not had enough information to do anything other than treat the Piedrafita as an F3 engine and impose the 25 mm restriction we use for all F3 engines. So if we want to decide what we can do to make it comparable (whilst not, for cost reasons, becoming the "must have") the only way is data.

Fortunately we have some people in Mono who are willing to make an effort for the club for little or no recompense. Nick Harrison and Ray Rowan volunteered, respectively, an F302 and an F305 with a Mono 3SGE and a Piedrafita 3SGE. Russ Giles got some sleeves machined up, and the Treasurer was anaesthetised for long enough to sign a cheque. And so on a cold February Monday we all met up at Aldon Automotive in Brierley Hill.

Aldon was started around 40 years ago by the current proprietor Alan Goodwin with a partner who has since retired. Alan was an ex-Austin apprentice, so was skilled in BMC A-series, a stalwart motorsport engine from the 50's to...well I can't say because it's still going. In fact, there was an A40 and a Spridget (both A-series powered) in the collection car park, together with a GT6. Younger readers can google them. All of us at the test recognised them. They've also developed a business servicing and tuning modern high performance road cars and competition vehicles, and even built their own sports racer some years ago which Alan still hillclimbs. And they have a parts shop too. But the reason we were there was to use their rolling road.

I've been incompetent in single seaters for over 30 years, so it's perhaps surprising that I've never encountered a rolling road in anger before. I'm not counting tow car MOTs. Aldon use a MAHA (Maschinenbau Haldenwang GmbH & Co. KG) dyno, in which the power is absorbed by eddy current brakes.  These are electromagnets which work on metallic rotors. The resultant heat is dissipated by air cooling. In case anybody is thinking of rolling-road testing their car, I will describe the process.

First of all, the car needs to be very firmly tied down to the dyno. There are tiedowns in the floor, but the main issue is finding somewhere on the car to attach the ratchet straps. Whilst a roll bar is ideal, it can be difficult to get a clear run for the straps. Other points can be used, but it's important to think whether they are strong enough in the direction they are being used. To this end it is wise to strip as much bodywork as possible off the car. Nick arrived with no sidepods, floor, or rear nappy. Incidentally, whilst it's against all modern aero ideas, the car looked great like this, reminding me of my favourite hillclimb car which ran in that configuration 25 years ago. The lack of under-car components is necessary because the car is loaded onto the rollers and then drops down into them pneumatically.

The test is run by Aldon's operator, not the car owner/driver. In our case, it was the hugely experienced Roger Bradley. After satisfying himself on the safety side with the tie downs, he warmed the car up. This involved running it against the rollers to run against constant resistance and then at constant speed. Around this time Roger calibrates the dyno so that, in the chosen gear, the recorded revs on the dyno match the revs on the car.  It's important to warm up both the engine (for obvious reasons) and the driveline because the latter needs to be in a steady state. This is because when the test is run, once maximum power is reached, the gears are disengaged and the car coasts. The dyno measures the resistance within the driveline by calculating the rate at which the rollers are slowed.

Warm-up screen

Power measurement screen. Note: this was an aborted run and is presented to show the graphs. Orange is torque, red is corrected power, blue is power at the wheels and green is the roll-out drag of the drivetrain.

Before any measurement, the airbox was blocked off to ensure that it seals. The engine stopped, indicating that it did and therefore the test should not be distorted by a leaky airbox. In the first instance, the test was cut short as the car (the 305) was climbing out of the rollers. The straps were repositioned and Roger decided that 5th gear was probably a better bet than 6th. The test itself is remarkably quick - probably around a minute or so once the preliminaries are complete. The PC and the dyno plotted a graph of power and torque against revs, and when Roger disengaged calculated the transmission drag and adjusted the power curve for the losses to give engine power. At this stage I won't give figures because that wouldn't be fair to Ray and Nick, and in any event they wouldn't be particularly meaningful as dynos tend to vary.

With the unrestricted benchmark set (31mm orifice), the test was repeated with 3 different sleeves in the airbox. We started with a restrictor a little larger than the current 25mm , and then ran 27mm and 29mm. Each was sealed as effectively as possible by being accurately machined and then by a ring of blu-tak.  The 305 was then replaced by Nick's 302 and the process repeated to get the benchmark figures.

I don't wish to trample on Russ's toes as he will be announcing the conclusion when it has all been ratified. However, a few points became clear from the tests:

  • the current restrictor cuts the power quite substantially
  • an unrestricted Piedrafita is more powerful than a Mono engine
  • the power is affected by how smooth the entry is into the airbox
  • power absorbed by the drivetrain is surpisingly high (to me at least) at around 20%
  • power absorption in the F302 and F305 were remarkably similar
  • the dyno needs to be properly set up for accurate power curves.

Many thanks indeed to Nick Harrison and Ray Rowan for providing the cars, Russ Giles for providing the sleeves and for managing the tests, to Roger for his patience, and to Alan Goodwin for providing a most useful facility at a very reasonable price.

Tony Cotton

Disclaimer: The above represents only the unofficial view of the writer and not of the Monoposto Racing Club in any way whatsover. Subheadlines and captions are not originated from the named author. We are unable to reproduce results due to copyright reasons. If any pictures are copyright and the owner wishes them removed please email us.




The Aldon premises
The MAHA dynamometer

A naked F302

Nick watches Ray fuel up the F305

Nappy fouled the mechanism at first trial

The Mono car showing the restraints
A restrictor in the airbox