Nelson Racing Engines
Any muscle-car enthusiast with access to YouTube knows of Tom Nelson and Nelson Racing Engines, famous for building twin-turbo, V8-powered cars. "My dad built a twin-turbo Pantera at home when I was about 11 or 12. Back then, that car was a lightning ship," he tells us. It also hooked him on turbochargers as his power-adder of choice. It has served him well, too, gaining Internet fame through dyno-room videos and in-car shenanigans in and around his modest Chatsworth, California, shop.
Tom recently introduced his own line of turbochargers—he calls them Mirror Image or Symmetrical turbochargers. The castings are available with left or right turbine inlets and compressor outlets. That way, you can build an underhood twin-turbo system for a V8 car with intake plumbing that is the same on the left- and righthand side of the car. Tom admits he did this mostly for aesthetics and ease of packaging, but there may also be a slight power advantage, as well. Either way, builders now have more options when laying out a custom turbo system. Tom's turbochargers come with billet compressor wheels and Inconel turbine wheels, and the design of the fins is more aggressive, which means they spool up faster. The pricing is in line with current high-quality turbo manufacturers' models.
Tom was less enthusiastic about using compressor maps as sizing guidelines for your particular application. "What I've fought for years is the notion that people think they need a smaller turbo. That's a total misconception. If the turbo is too small, all it does is become a heat pump," he says. We all know that hot air does not make horsepower, either. Tom says compressor maps can be deceiving, and that similarly sized turbochargers from the same manufacturer can operate quite differently when they are actually installed on a car. "The A/R ratio doesn't always correspond with performance. The best way to pick a turbo is to ask experienced people. Take advice from someone who's done it already."
Once you have turbos picked out, Tom recommends building the engine with the best parts you can afford. He likes 2618 aluminum-alloy pistons, "They are a little loose on start-up, but they take abuse; 4032 [alloy] is not as tough. Keep boost to between 6 and 7 psi with those pistons." For piston rings, Tom prefers 1⁄16-inch non-coated rings, and he sets the top ring gap at about 0.024 inch. He gaps the second ring a little wider than that, and he recommends using pistons with a V-groove between where the first and second ring lands. His reasoning is that with high cylinder pressure, you're going to have more blow-by than a naturally aspirated engine. The V-groove and wider second ring gap give blow-by gases a place to go. Otherwise, the pressure can build up behind the top ring and affect the way it seals to the cylinder walls. Tom also recommends using cams with 260 degrees of advertised duration or less for street engines. "Too much overlap takes the fresh charge and sends it out the exhaust," he says. For his custom cam grinds he uses large-base circle cams with special exhaust lobes that open the exhaust valve gently, allowing cylinder pressure to bleed down. Otherwise, a fast-opening exhaust valve will be hard on the cam and valvetrain because it has to fight the extra cylinder pressure of a boosted engine.
As impressive as their resumes are, none of the pros we've interviewed so far can claim to have put more turbochargers on engines than Gale Banks. He's been experimenting with turbochargers since 1966, when he started building twin-turbocharged, big-block Chevys for race boats. He described a twin-turbo, fuel-injected, 1,800hp 430 big-block running on alcohol that he built in 1976. He blames this engine for getting turbochargers banned from Off-Shore boat racing for decades. Success in boat racing led customers to his shop asking for turbochargers for their cars, and Gale branched out to all forms of motorsports as well as high-performance street engines.
Gale believes turbos are finally here to stay. “I was lobbying the OEs in the ’80s during the second oil crisis,” he says. Now, Ford and Chevrolet are rolling out turbocharged 4- and 6-cylinder engines across their model lines, not just on a few limited-production models. For the aftermarket, Gale tells us he’s working on a compound (turbocharged and supercharged) LSX engine package. The twin-turbo small-block in this picture is a package Gale has offered for a few years. The turbos force-feed a port fuel injected manifold. Though an intercooler is available, the base package doesn’t include one. Instead, Gale, recommends a water/methanol injection kit to cool the intake charge. Power levels range from 800–1,100 hp and this engine can be daily driven. Another cool feature is the cast-iron exhaust manifold design. The narrow design places the turbochargers close to the engine in a neat, compact package that should fit in nearly any Chevrolet from the muscle-car era.