Look at the smoke! Turbocharging...
Look at the smoke! Turbocharging might be a great way to gain solid horsepower from your street car. Under the hood, the pipework routes pressurized fresh air to the carb.
The old adage "Speed costs money; how fast do you want to go?" still rings true. If you want to play, you're going to have to pay. For Kevin Alexander, or "Feets" as he's known on Moparts.com and Pentastarpower.com, there were several performance options he wanted out of his '65 Plymouth Belvedere II, with economy to boot.
"The idea was to get three things out of this project," says the 30-year-old Dallas native. "I wanted it to top end at 130 mph in the quarter, I wanted an engine that could make 650 horses, and it needed to run on pump gas. Here in Texas, it gets real hot in the summer, so big cams and big fuel systems are out the question. Forced induction was the only choice."
Weighing the options, Kevin knew Roots-type blower systems would rob a lot of horsepower and dump large amounts of heat into the boosted air, and the modern centrifugal units were a bit better but still make plenty of heat. Turbocharging seemed to be the way to go. Unlike the others, turbos are driven by exhaust forces, meaning they don't rob horsepower off the crank except by creating minor backpressure. The silent running nature of turbos is a big bonus for a street-driven car. Since the 440 in the big, black Plymouth was mildly tweaked, Kevin researched what it would take to rig a set of cast-iron hair dryers to the motor. He obtained most of his information from the book Maximum Boost by Corky Bell, published by Cartech.
"There isn't a lot out there on doing turbochargers on an engine this big," says Kevin. "I read as much as I could to get an understanding to make good choices. Turbo science, especially on a motor with this much displacement, can be a hit-or-miss proposition."
Here's where it begins: through...
Here's where it begins: through an air filter mounting inside the front wheelwell. The pressurized air runs through the pipe, dropping down to the right. The turbine, which is spun by exhaust pressure, is inside the fenders.
Kevin says the idea is to get a large-enough turbo that won't restrict flow, yet small enough to quickly spool up to maximum boost pressure. If the turbo was too small, the engine would choke because it couldn't push exhaust out quick enough. If it's too big, the exhaust gases could past the turbine instead of spinning the turbine wheel quickly enough to get boost at an usable rpm (turbo lag). The result of this mental deduction came via Garrett Research Products through Majestic Turbo in Dallas, where Kevin specified a T3-sized turbine housing (which handles the exhaust charge action) coupled to the larger T4-style compressor (which pressurizes the intake side). The turbine for the exhaust and the impeller for the compressor are mounted on a single shaft; this is how the turbocharger makes power. After he finished, Kevin admitted he was probably a little too conservative on the turbine side, though the idea was to get units that would reach peak efficiency by 98,000 rpm (many won't get to peak efficiency until 130,000-plus rpm). Low efficiency means high heat in the intake charge and big detonation problems.