Photography By Tim Suddard
You’ve rebuilt the engine, redone the body, and rejuvenated the suspension. Your latest restoration project is ready for the open road, right?
Not always.
Sometimes the driving experience can still be underwhelming–even miserable. Such was the case with our Triumph TR6.
Ours is a very early 1969 model, and yes, it’s beautiful. This Laurel Green car has been completely restored and outfitted with just a few modifications: a tan leather interior, a Tourist Trophy leather-wrapped steering wheel from Moss Motors, 72-spoke wire wheels fitted with Vredestein tires, and anti-roll bars sourced from Good Parts. The stiffer springs came from J.K. Jackson’s English Automotive.
Under the hood, the original, numbers-matching engine has been completely rebuilt to nearly stock specifications. In the interest of improving performance, while the engine was apart we did a little bit of port-matching and shaved the head to bump the compression ratio from 8.5:1 to 9.0:1. A Good Parts mild street cam replaced the stock piece, too.
After all that work, however, our TR6 never ran that well. It felt a bit lean, and its engine acted as if it were choked down–it even missed a bit on occasion, especially at highway speeds. There was work to be done.
To monitor our work, we packed up our TR6 and did some testing at Balanced Performance Motorsports, a dyno shop located just outside Atlanta. There we could run the engine in a safe, controlled environment.
First, a baseline run. Triumph rated the factory engine at 106 horsepower, and we were pleasantly surprised at the initial dyne results: 99.59 horsepower and 126 ft.-lbs. of torque at the rear wheels.
Why were we happy to see less horsepower than the factory promised? Driveline loss. Factory numbers record the power made by the engine–and, depending on the year, with or without the engine accessories. Once the car is put on a chassis dyno, driveline loss comes into play. As the engine’s power moves through the transmission, rear end and other systems, friction takes a bite.
A common rule of thumb is to expect a 15-percent driveline loss. Following that logic, our car is doing better than stock–and, in fact, most stock TR6s produce close to 85 horsepower at the wheels.
With our baseline recorded, it was time to start making improvements. First we reset the ignition timing, an easy fix. In theory, the dyno would reveal the ideal setting. In our case, 36 degrees of total advance yielded the best performance: 100.2 horsepower at 5000 rpm.
Although we gained a bit more power, something still wasn’t right. The car just didn’t drive as it should. Before our test day, we identified a few specific areas that needed work: carburetors, distributor and exhaust. Could fixing these three weak spots cure our drivability ills?
