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When to hit the red button!

dynamometersThe author well remembers the first time he was given sole charge of overseeing the running in of an engine on the dynamometer of an un-named race engine manufacturer.

The engine in question was the first ever example of a Le Mans Prototype V8 and the author’s role was to do nothing other than warm the engine up on a base map which would be followed by a check over before the real mapping work commenced.

For around five minutes (no-one ever went through the data in much detail) everything went smoothly and nothing of any note happened; the engine hummed away and the hustle and bustle of the workshop continued apace in the background.

The world was a peaceful place and a lot of idling away was done, and as the author contemplated deeply exactly what was happening inside the engine, the engine built up temperature.

Then without any warning whatsoever the revs started to rise dramatically as if the engine had gone to full throttle. The engine continued to pick up speed and it was instantly obvious that is was in danger of over-revving and over-revving quickly; the author didn’t know exactly on the day (and still doesn’t actually!) how the rev cut strategy worked on that particular ECU.

A quick look at the throttle lever (this was well in the days of throttle cables) confirmed that it hadn’t moved and so there was only one thing for it.

As any dyno man will tell you there is only one reaction you can have in any unexpected circumstances; you find the big red button and you hit it!

The author did so and the engine died instantly. The soundproofing, being what it was in the day, meant that the regular dyno operator (along with most of the workshop) heard what had happened and came running.

Subsequent analysis of the data showed that the engine had over-revved but not to a point where anything had been damaged and after a borescope was deemed OK to continue. The data also confirmed that the throttle had not been opened.

Ten minutes later investigation of the dyno cell revealed the cause of the near disaster; an hydraulic oil return line from the dyno controller had come adrift, allowing the fluid to drain away until control was lost, which caused the dyno to lose all load during running. With no load on, a 4.0-litre V8 will happily spin up even on idle.

So the main lesson learned that day was the fact that anything can and at some point will go wrong.

Nowadays the world is a different place and a test cell can be rigged up such that an engine is automatically cut in the event of a problem but that is not always the case.

So if the author has one piece of advice for you; always know where your red button is!

Written by Tom Sharp.

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