Turbocharging A Carburetor Isn't As Ridiculous As It Sounds

If you're the proud owner of a classic or specialty car, you've no doubt had the mental debate between retaining an old-school carburetor or modernizing the fuel injection. With electronic fuel injection, there's extra wiring to contend with and potentially, modifications required for the vehicle's fuel system. For example, some EFI systems require a second fuel line for returning unused gasoline back to the tank. However, you'll be rewarded with improved performance and fuel economy, along with self-tuning capability for improved drivability in all sorts of environments.

That all sounds attractive, but the great equalizer between the two fuel delivery methods is budget. New and used carbs are cheap and plentiful, not to mention that you might already have a perfectly good one installed. But what about when boost, like turbochargers or superchargers, comes into play? That $200 "eBay special" turbo doesn't sound so good anymore if you're obligated to buy a $1,500 EFI kit to go along with it. So, does turbocharging your vehicle automatically mandate eighty-sixing your faithful old carb? Actually, no.

During the late 1970s and early 1980s, several major American automakers combined turbocharging with carburetors, so it's definitely a thing. A couple of examples are Pontiac's Turbo Trans Am and the early turbocharged Buick Regals, which would later morph into Buick's Grand National. Of course, OEMs have the resources to engineer things correctly. For the shadetree mechanic, certain modifications to the carb will be required. You can't just slap a turbo hat atop your Holley and call it good. 

Carburetors can be combined with boost in either draw-through or blow-through configurations. The former situates the carb ahead of the turbo, while the latter pushes the already-pressurized air through a carb in its original location. Focusing on the more common blow-through applications, the first order of business will be sealing up your carburetor. 

Surprisingly, carburetors can have large openings for boost to leak out, such as where the choke linkage passes through the body of the carb. These openings can be filled with a gasoline-resistant epoxy. And speaking of the choke, you'll also need to remove the choke horn, if equipped, by milling or grinding. On a typical Holley, that's the rectangular, tent-like structure atop the carb that would prevent the turbo plumbing from fitting correctly. 

At the risk of boring readers to death with specifics, suffice to say that a host of other subtle modifications like new power valves are also required for mating a turbo to a carb. The good news is that this type of work isn't terribly expensive if you're up to the task of doing it. Several years ago, the staff at Hot Rod magazine built a killer blow-through carb rated for up to 600 horsepower with just $48 worth of new parts. There's an old saying that a task can be accomplished fast, cheap, or good — pick any two. With some elbow grease, hanging onto your old carb in boost applications just might check the "cheap" and "good" boxes.