6 Appeal—Chapter 5

Every vintage race car restoration comes to a certain crossroads: Should the engine remain period correct, or is it better to shell out some extra dough and take advantage of modern technology?

We decided to follow the first path and return our 1969 Triumph GT6+ to its original race trim. We wanted to duplicate its exact state from the moment it won the Sports Car Club of America’s 1969 E Production national title. Every step of the way, in fact, we have tried to restore this Group 44 Inc. car to its original specifications.

Our research on the car turned up a good benchmark. When Group 44 Inc. wrapped up their Triumph GT6 program at the end of 1973, New England SCCA racer and engine builder Harvey Thompson bought one of the engines for use in his own Runoffs-bound GT6. Before leaving for that event, he freshened the engine and had it dyno tested at Coleman Racing Engines in Seymour, Connecticut. The engine made 162 horsepower at the flywheel.

Harvey Thompson now works for Vintage Racing Services and is still building engines. In fact, he’s one of the nation’s most noted builders of British engines. He’s been responsible for all of Kent Bain’s screaming Spitfire engines for the last 18 years. He can also put together a mean Lotus Twin Cam, six-cylinder Triumph, Formula Ford, or BMC A- or B-series powerplant.

He also built the engine for our GT6+. When strapped to the dyno, we saw a familiar figure: Maximum output was 162 horsepower at 6200 rpm. Folks, this is a vintage-legal engine.

RPM = Power

A vintage race car without a proper engine is about as exciting as an opera singer with laryngitis. It was time to give our Group 44 Inc. Triumph GT6+ a worthy heart.

When our car won its SCCA national title more than 40 years ago, things like billet cranks and Carrillo rods were not legal. As a result, engine rebuilds were common, and redlines were kept relatively low—6500 rpm was a widely-used figure.

Today’s trick equipment not only adds safety, but engines like ours can now enjoy another 1000 rpm of usable powerband. More rpm can bring more cam timing—although that creates the need for more carburetor. The Achilles heel of a vintage racing Triumph GT6 or TR6 engine is the stock intake manifold and Stromberg carbs. Weber carbs are usually substituted. A trick race engine will also feature about half a point more compression plus a camshaft designed for even higher engine speeds.

Harvey recently built an engine like ours that featured some modern updates. Even without a billet crankshaft, it produced 184 horsepower at 7000 rpm. (A billet crankshaft would have allowed even higher engine speeds—figure another 750 to 1000 maximum rpm, bumping output past 190 horsepower.)

However, that performance comes with a hit to the wallet. Figure about $5000 to $6000 for the parts and work needed to increase redline to 7000 rpm. Period correctness is also a factor, as the upgraded engine wouldn’t be true to the original.

Starting With a Solid Foundation

Our stock Triumph crankshaft was machined to accommodate MGB rod bearings, which are wider than the original Triumph pieces and provide about 20 percent more bearing area.

One of the keys to building a great engine is getting everything straight and flat. Just like a house, a race engine is only as good as its foundation.

Harvey started with the cylinder bores. If the holes are bad, they can often be machined or honed so they’re again perfectly round.

Our bores were straight and true. They had also been bored 0.040 inch over stock, a typical and legal practice during our car’s racing days. Harvey only needed to freshen the cylinder bores with a light honing.

Then he turned to the camshaft bearing journals. First, the surfaces were line bored. This process involves securely mounting the block to a jig so that all of the bearing surfaces are machined in succession. The result: perfect alignment. This makes for the truest possible engine and cuts down on wear and friction, which improves performance.

Our bearing surfaces themselves also needed some attention, as Triumph didn’t use cam bearings in their GT6+ engine; the steel cam simply spun on a film of oil inside the cast-iron block. We decided to optimize the clearances between the block and cam journals by adding a set of cam bearings. The bearings will improve engine life as well as oil pressure, especially at idle.

The Triumph Spitfire came with camshaft bearings, and they fit a GT6+ engine block that has been properly machined. Don’t forget to order two sets of bearings, since the Spitfire engine only features four cylinders and the GT6+ has six.

Finally, the top of the block was decked slightly—Harvey removed just 0.006 inch—so that it would be flush with the tops of the pistons when they reach top dead center. This is how Group 44 Inc. ran their engines during this car’s heyday.

Perfecting the Reciprocating Parts

We would have loved to use these beautiful Carrillo rods. However, the car raced on its stock GT6+ rods in 1969, and we wanted it to remain period correct.

The key to an inline Triumph six-cylinder is balance. The long crank combined with only four main bearings can allow this engine to vibrate itself to death when subjected to high engine speeds. We needed to take steps to prevent our engine from meeting such a fate.

The flywheel, damper, crankshaft and clutch pressure plate were balanced by Valley Auto Machine. They got every piece within two-tenths of a gram of perfect balance.

Even though we’re using the stock crank, it has been machined to fit MGB rod bearings. This move will provide about 20 percent more rod bearing area, as the MGB pieces are wider than the Triumph units.

Modifying the Triumph crankshaft to fit the MGB bearings is a complex operation, however. The tabs on the MGB bearing shells must be narrowed, while the crank needs to be cut down by 0.001 inch.

We’re still using the original Triumph connecting rods, but Harvey first checked each one for straightness and imperfections. He then balanced the set: The lightest rod was pulled from the set, and the others were machined to match.

We threw out all of the original internal Triumph fasteners and replaced them with new hardware, including ARP rod bolts and main cap bolts. Our pistons are forged Venolia units, as most Triumph engine builders agree that the stock cast pieces can’t withstand the rigors of racing.

Even with the modified and balanced pieces, Harvey still recommends that we keep the engine revs below 6500 rpm. Yes, Group 44 Inc. turned similarly built engines beyond 7000 rpm on a regular basis, but they also tore them apart after nearly every race weekend and replaced the connecting rods after every two or three races. We aren’t seeking the national championship or being paid to race, so we’ll just go a bit easy on our engine.

The Power Is in the Head

ARP head studs and mild springs (225 pounds of pressure, open) finish off the head. The porting work amounted to simply cleaning up what Group 44 Inc. had done some 40 years ago.

They say that power is made in the cylinder head, and ours received much attention. First, 0.140 to 0.150 inch was cut from the bottom. This raised the compression ratio and ensured that the head’s mating face was perfectly flat.

Combined with our Venolia pistons and shaved block, our compression ratio is 12.5:1. If our compression were any higher, it would negatively affect engine longevity.

Naturally, our head features quite a bit of port work. Harvey told us that he only had to clean up the ports, as Group 44 Inc. had already reshaped them to match the round-tube exhaust headers.

Group 44 Inc. crew chief Brian Fuerstenau experimented with port shape in the early days, but supposedly it didn’t make much difference. On the typical Triumph engine, which uses a non-crossflow head, working on the intake ports will improve low-end torque while working on the exhaust ports will improve top-end horsepower. Unfortunately, the two are somewhat mutually exclusive, so decisions must be made.

Another sign of Group 44 Inc. tinkering: deep relieving found in the valve spring area. We’re told that Group 44 Inc. had been experimenting with some serious valve springs, hence the added machine work.

We shimmed this area and went with more common Isky performance valve springs. Valve spring pressure can be a camshaft’s enemy, and we weren’t willing to risk increased camshaft wear in the hunt for just a few more horsepower. Our valve spring pressure is set at 225 pounds open and 85 pounds closed.

A period-correct Kastner cam was in the car when we got it, and Harvey had Cam Techniques cut it to his specs: 0.525 inch of lift (at the valve) and 262 degrees duration (at 0.050 inch of cam lift). Conventional pushrods and rocker arms were used, as they would have been legal in 1969. We finished off the valvetrain with a double-row timing chain for safety.

Black Gold

Mocal makes an oil cooler that’s dimensionally identical to the original GT6+ unit. Any engine builder will warn you against using an unknown oil cooler on a fresh engine.

Oil is the lifeblood of any engine, and Group 44 Inc. took several measures to provide extra oil and control its flow. These steps aid cooling and extend engine longevity.

One of their tricks was a deeper oil pan. The original pan was sectioned so a 1-inch strip from a second pan could be welded into place. This was a great modification for extending oil capacity by an extra quart or two. However, the oil pump pickup needed to be modified accordingly.

During the rebuild, we blueprinted the oil pump itself to improve pressure. This process would fall under the heading of selective blueprinting, as we simply purchased several oil pump rebuild kits and used the one whose clearance between the body and outer rotor measured closest to 0.004 inch. If you can’t find a pump with that exact clearance, consider 0.006 inch to be your maximum.

The 0.004-inch clearance will yield the highest oil pressure, especially when combined with our cam bearing installation. We should see 30 to 40 percent more pressure, even when the oil is hot.

After a bit of research, we also wound up reusing the original catch tank. At first we were told that the piece wasn’t original, so we removed it. Thank goodness we didn’t discard it, as we later found a photo showing that exact catch tank on the car when it was originally raced. We cleaned up the tank and mounted it back on the firewall.

Brian Fuerstenau had designed an oil filter adaptor for this car, and we simply reused it. Our new Mocal oil cooler and lines came from our good friends at BAT.

The final piece of the oiling system is the oil itself. After break-in we filled the sump with Red Line 20W50 oil. We have had such good luck with this product, and while the experts at Red Line told us we could run even lighter oil, we decided to stick with the tried-and-true 20W50.

Tackling the Last Few Systems

The carbs and air horns were original Group 44 Inc. pieces that we rebuilt and saved.

Before the engine could go back into the car and again mix fire, fuel and air, we had a few more systems to tackle. As always, we aimed to preserve the original work done by the Group 44 Inc. crew.

When we purchased our car, it fortunately still had its original exhaust headers—a set designed by Group 44 Inc.’s Brian Fuerstenau. They were works of art, and we wanted to keep them that way. We lovingly cleaned them and sent them to Swain Tech Coatings for treatment. We’ve found Swain Tech’s coatings to be very durable, and they noticeably lower exhaust temperatures.

Our flywheel and clutch came from Spec. We’ve had good luck with their units, and their lightweight flywheel was beautifully made and similar to what would have been used back in the day.

For the sake of originality, we retained the original Stromberg carburetors and intake manifold. While Strombergs aren’t our favorite carbs, they are what the teams had to run: Back then, racers were only allowed to minimally clean the stock carburetors. Our car still even had the original velocity stacks, although we added some new air horn screens sourced from Pierce Manifolds.

When we got our car, its stock Lucas alternator featured an oversized pulley. We wondered if that was the original race setup, and our answer came in the form of an underhood photo from 1969: That exact pulley was mounted to the alternator.

We replaced the alternator with a new stock one and retained the larger pulley. We have since learned that Group 44 Inc. ran the big pulley to slow down the alternator so it wouldn’t fail at race speeds.

We did make one concession to reliability and ease of maintenance: We replaced the distributor’s original points and condenser with a PerTronix ignitor. We run this simple, inexpensive electronic ignition system in pretty much all of our project cars and have never had one fail.

Okay, make that two concessions: We also installed a modern high-torque starter sourced from Gustafson Specialty Products. Like the PerTronix igniter, this modification has no real downsides. The modern starter weighs less than the original and has no problem turning over a high-compression vintage race engine. This is another go-to part for our project cars.

Radiator Runaround

Griffin fabricated a perfect replica of our stock radiator out of lightweight aluminum. BAT oil lines offer improved functionality compared to the originals but still have a period-correct look.

Our car came with what looked to be a big Corvette radiator. Lanky Foushee, who joined the team the year after our car won its SCCA title, told us that the piece was original. He explained that the team had been playing around with radiators during this period in the interest of improving the cooling.

We spent $600 to have the radiator re-cored at a local shop, only to later find some pictures of our car sporting the original piece. Maybe our car eventually ran this huge radiator, but early on it used a stock unit. Switching gears at the 11th hour, we asked if our friends at Griffin Thermal Products could duplicate an original GT6+ radiator in lightweight aluminum. They said yes.

Instead of carrying a 42-pound monstrosity at the front of our already nose-heavy car, we now have a lightweight Griffin unit that weighs 25 pounds less. The Griffin piece fits perfectly, and we simply painted it black to give it a stock look. On track, we were rewarded with cool water temperatures—almost too cool. We would recommend this move for any race car or hot street car.

Repeat Transmission

Our dyno chart shows a healthy, happy inline six.

We mated the engine to a rebuilt transmission, and we’re now on the home stretch. Soon we can start sorting our GT6+ and making high-profile appearances at the Amelia Island Concours and the Monterey Historics. There are still a few loose ends to wrap up, however. Look for the next installment in a future issue of Classic Motorsports.


ARP Hardware (800) 826-3045 arp-bolts.com

BAT Mocal oil cooler (941) 355-0005 batinc.net

Cam Techniques Cam modifications (941) 727-5552 camtechniques.com

Coleman Racing Engines Dyno testing (203) 522-0417

Gustafson Specialty Products Starter (978) 281-2012 gustafsonmachine.com

Griffin Thermal Products Radiator (800) RACERAD griffinrad.com

PerTronix Performance Products Ignitor (909) 599-5955 pertronix.com

Pierce Manifolds Air horn screens (800) 874-3728 piercemanifolds.com

Red Line Oil (800) 624-7958 redlineoil.com

Swain Tech Coatings (585) 889-2786 swaintech.com

Valley Auto Machine Machining and balancing (203) 881-9713

Venolia Pistons Pistons (323) 636-9329 venolia.com

Vintage Racing Services Harvey Thompson, engine building (203) 377-6745 vintageracingservices.com

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View comments on the CMS forums
GregW Reader
2/1/12 12:45 p.m.

Did you use a stock or aftermarket torsional vibration damper? Some six cylinder crankshafts can self destruct due to torsional resonances.


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