Saturday, September 29, 2012

Less is more

US-market 'Federal' spec GT6s were a bit different from the versions sold in their homeland. Oh, Triumph nailed the steering wheel on the other side, but there were extra features such as running lights, a seatbelt reminder light and a buzzer that sounded if the door was opened while the key was still in the ignition. For 1972, that was fully loaded!

Triumph were also selling cars in a market with tighter legislation governing emissions, and so the Federal GT6s' engines were in a lower state of tune. Low compression engines and a different camshaft meant that they were about 20hp down on GT6s sold elsewhere. So, I decided that my GT6 would get a bit of a kick on the pants performance-wise, and swapped the 2L crank for a 2.5L version. Because the stroke is increased, the engine is tuned for torque rather than revs. To stop it being a lazy slug, I've added a few goodies to retain the sporty feel.

The bottom end's away getting balanced, and includes a lightweight Bastück steel flywheel. It should be back in a few days. More exciting, a set of 60-overbore forged pistons arrived this week, so I can move forward and get the block bored. I ordered them a couple of years ago, as soon as I stripped the engine, but production delays mean that they've arrived just when I need them. Below are a few photos, with a Nüral 40-thou cast piston for comparison. The stock cast pistons are nice, but the forged ones look, and feel, even better.

Nüral 40 thou piston, including gudgeon piston and rings - 415g

Forged 60 thou piston with gudgeon piston but without rings

The crowns of both pistons

Side view. Note that the cast piston has large slots in the sides, while the forged piston only has small drillings behind the oil ring groove.

The undersides. There's a lot more material in the cast piston - it's quite chunky by comparison.


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