Make it Sing: 10 Steps to Performance-Tuning Your Favorite Classic


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By Tim Suddard • Photography by the author

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?

Changing Carbs

The Stromberg carburetors found on many British cars aren’t exactly universally loved, and that’s because they’re barely adjustable. In fact, they pretty much only allow you to raise and lower the needle, which fine-tunes the air/fuel mixture.

Sadly, the Strombergs fitted to 1968-’69 Triumphs are no exception. These carbs were set to run very lean in order to help the rather crude TR6 engine meet increasing emission standards.

Raising our compression ratio, bumping up our timing, and running a slightly hotter cam only made the problem worse. The dyno said that we were running a bit lean, too, with an air/fuel ratio just above 15:1 at higher rpm. Lean can be fast, as it usually generates a bit more horsepower, but it can also be dangerous. The engine runs hot, it starts to detonate, and then bad things can happen. We needed to fix this problem.

The easiest solution on a TR6 is to replace the Strombergs with older-style SU carburetors. There are other options–-Webers, fuel-injection conversions–-but the SUs bolt to both the TR6 manifold and the original air cleaner. SUs are also readily available, either new or used.

To keep the swap quick and clean, we sourced a new set of SUs from Moss. Their TR6 conversion kit retails for a little less than $1000. You can find used carbs at a swap meet or on eBay for less money, but installing worn-out, 50-year-old carbs may hurt more than it helps.

We topped off these carbs with some cool velocity stacks from The Winner’s Circle that fit perfectly inside the stock air cleaner housing. Running velocity stacks smoothes the airflow into the carburetors and can make a difference in power. Installing the SU carburetors was a very straightforward, hour-long project.

Installing a Rebuilt Distributor

As a vehicle puts on years and miles, its distributor begins to wear. It can rotate unevenly and cause a miss, especially at higher rpm.

Advanced Distributors rebuilds older distributors, including all of the popular Lucas units fitted to these older British cars, to as-new condition. Figure most of their Lucas rebuilds start somewhere between $130 and $200.

We ordered a Lucas distributor that had been rebuilt, recurved and fitted with just a mechanical advance. Most distributors have both centrifugal and vacuum advances. Using just the centrifugal makes more controllable power, as the vacuum advance doesn’t kick in when it’s not wanted.

Factory advance curves are often a compromise between performance, drivability and emissions. Considering our slightly higher compression, desire for maximum performance, and use of premium fuel, we asked Advanced Distributors to bring in full advance by about 2500 rpm.

After receiving our new distributor, we replaced the stock points and condenser with a Pertronix ignitor–about $100 for the parts and just a few minutes to install. This system uses rotating cobalt magnets to create a Hall effect to trigger the ignition. Once set, this ignition doesn’t require any adjustment. We’ve used Pertronix ignitors on most of our project cars for years and have had very good luck with them.

Upgrading the Exhaust

The final step in our TR6 modification involved the exhaust. What goes in and gets ignited must come out, right?

An early TR6 like ours uses a cast-iron exhaust manifold paired with a single exhaust system. Starting in 1972, most likely to reclaim some power lost to the lower compression ratio introduced that year, the TR6 received a dual exhaust manifold. That twin-pipe manifold was met by twin exhaust pipes.

According to the Triumph community, the dual-exhaust system offers more performance. We found a used 1972-and-up manifold and ordered the later exhaust system from Moss Motors.

Actually, we ordered a pair of systems from them: their stock replacement as well as the all-stainless Tourist Trophy model. To mount either of these systems to an early TR6, you’ll need the corresponding late-style exhaust hanger bracket that attaches to the transmission.

The Tourist Trophy model is beautiful. The fit, finish and design make it unquestionably nicer than the stock replacement. And with a list price of $569.95, the Tourist Trophy exhaust only costs about $30 more. It’s a no-brainer.

We tried both systems, and while slightly louder than stock, the Tourist Trophy system delivers a very pleasing exhaust note. We didn’t find it objectionable for high-speed touring, either. It’s the one we kept on the car.

The Dyno Does Lie

We always tell folks that the dyno doesn’t lie, but in this case it did. Well, we’ll explain.

Our peak numbers didn’t change. Despite all of the work, the engine’s max horsepower remained constant during the entire session. At wide-open throttle, the engine still made the same horsepower peak, with 2 or 3 more horsepower produced in the meat of the powerband.

Here’s the big improvement, though: Our TR6 now drives so much better than before, it has simply come alive. The hesitation, ignition mis and general lack of zing have been banished. It starts easily, warms up quickly, revs nicely, and runs flawlessly in all conditions and at all speeds. Our once-sour TR6 is now an absolute joy to drive.

So what made the difference? Our worn-out distributor certainly wasn’t helping, so replacing it with a rebuilt unit was a must. Plus, the new carburetors work better with our slightly warmed-over engine. And that Tourist Trophy exhaust delivers the perfect note for a classic sports car. Finally, our TR6 runs as good as it looks.

1.

None

We tested the Triumph at Balanced Performance Motorsports, a dyno facility located just outside metro Atlanta. Longtime Triumph racer J.K. Jackson handled the tuning, and Redline BMW Performance’s Rennie Bryant did the driving. Our initial runs revealed that our mildly built TR6 preferred 36 degrees of total ignition advance.

2.

None

Like so many British cars of this era, our TR6 came from the factory sporting Stromberg carburetors. Thanks to their lack of adjustment, our slightly modified TR6 was running a bit lean for our tastes.

3.

None

We replaced those Strombergs with a pair of SU carburetors–-standard equipment on British cars built just a few years earlier. This was truly a bolt-on installation, and Moss Motors had the parts in stock.

4.

None

We paired our SUs with short air stacks sourced from The Winner’s Circle.

5.

None

The early Triumph TR6 came with the single-runner exhaust manifold paired with a single-branch exhaust system. In 1972, Triumph started to fit a twin-branch system. In theory, the twin-pipe system performs better.

6.

None

Ever the perfectionist, Jackson port-matched the new twin-branch exhaust manifold before installing it. This step provided a totally smooth passageway between the manifold and the cylinder head. Here’s how to do it: First, use the mounting gasket as a template to mark the openings of both components. Then, grind open both passageways to match the gasket. In the end, both the cylinder head and exhaust manifold will feature matched ports.

7.

None

The two exhaust systems used on the TR6 correspond to the exhaust manifolds: The early setup features a single branch, and the 1972-and-up one uses a pair of pipes.

8.

None

Moss Motors offers a pair of exhausts for the 1972-and-up Triumph TR6: the standard setup and the upmarket Tourist Trophy. For about $30 more, the Tourist Trophy system gets you a show- quality setup that sounds much sportier without being too loud.

9.

None

Now this is what the back of a TR6 should look like, featuring the classic twin pipes of the Moss Motors Tourist Trophy exhaust. The fit and finish are fantastic.

10.

None

Despite receiving all of these modifications, our Triumph’s max horsepower remained the same. Was the session a bust? Hardly. What was previously an unhappy little car now hums along smoothly.


This article is from a past issue of the magazine. Like stories like this? You’ll see every article as soon as it's published, and get access to our full digital archive, by subscribing to Classic Motorsports. Subscribe now.

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Comments
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mikecortina
mikecortina New Reader
3/7/19 4:37 p.m.

I've used Advanced Dist for my Lucas dist...great place and he had the Pertronix I needed in stock.

Gvillamizar
Gvillamizar None
3/8/19 10:07 a.m.

Hello,

 

‘’would sure love to get a solid recommendation for a tunning outfit somewhere near me (NYC.) for my carburetored Fiat 124!

 

gavillan@hotmail.com

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