Fitting a chin spoiler for better cooling

A summary of Mike Taylor's "Stag aerodynamics", from his Driver's Diary in Classics Monthly, September 2017. The full article, with photos, is in that issue.

Why bother

The Stag's grille, bumper and number plate partly block the air going into the radiator, and much of the air that does arrive goes over the intake and under the car. Dave Wardle's evaluation of the Stag's cooling, printed in the UK Stag Owners Club magazine, found a front spoiler brought down both coolant and oil temperatures, especially at speed. A spoiler under the valance creates low pressure behind it and helps pull air through the radiator.

Some owners fit a hidden deflector between the grille and radiator instead. Mike couldn't find much about that approach, and with an electric fan and an air conditioning condenser in front of his radiator there wasn't room, so he went for a chin spoiler under the front valance rather than a deep splitter.

Making a TR6 spoiler fit

There's no spoiler made for the Stag, so Mike used a fibreglass copy of the TR6 rubber spoiler. It needed real work to suit the curve of the Stag's valance:

• Trial fit it with a single bolt through the centre of the valance, mark the high spots, and use card templates to close up the gap.
• Sand off any release agent and shape the top edge with a flap wheel.
• Build up the low areas and the mounting flanges with glass fibre and resin, reinforcing the flanges with steel strips set in the resin.
• He also filled the curled-over front lip, which would have trapped water and dirt, with expanded polystyrene wrapped in plastic film, then glassed over it.
• Fix it with M6 screws: three in the middle where you can reach nuts behind the valance, and stainless rivet nuts at the two outer ends where you can't.

He finished it in matt black acrylic rather than body colour. Blair's '74 in the Showcase wears a TR6 front spoiler too.

Fitted one and measured the difference? Tell us in Tech Q&A.