Let’s face it, the world of performance is changing. More and more, we see automakers pushing vehicles straight from the factory with forced induction already built-in. And with more horsepower and better fuel economy—as well as a bevy of aftermarket advancements—it’s safe to assume that this appetite for boost isn’t going anywhere anytime soon. Naturally, many of us want to jump on that bandwagon and fit our home-brewed builds with turbos and superchargers.
It’s one of the most romanticized notions around engine-building—cheap boost. All of us think about it—and many of us go for it. I mean, the claims of radical power gains and real-world results are simply too loud to ignore, right? But despite what some kits advertise, simple bolt-on boost isn’t always that simple. For true, sustainable power gains, there are a lot of things to consider before simply throwing compressed air in your engine. So, when we say “bolt-on boost,” we’re referring to the aftermarket kits you can purchase to bolt right in place on the engine.
The question isn’t, “Do they work?” (Because they do.) It’s “What else do I need to consider before I pull the trigger on this upgrade?”
The Popularity of More Power
No doubt, modern advancements in engine hardware have completely changed the game of forced induction. “For the most part, today’s fuel-injected engines are very capable of being turbocharged for a 50-percent increase in power without making any real internal engine modifications. That correlates to about 7–8 lbs of boost. This is assuming that the engine’s duty cycle is relatively low, meaning that the high-horsepower potential is used only occasionally and for relatively short bursts,” states an SA Design automotive tech manual on turbocharging.
For example, the rotating assemblies of today’s engines make adding boost much less questionable. In the past, manufacturers of high-powered vehicles relied on cast internals for many of their engines. Mopar wedge engines, along with Ford and GM big block engines, could all be found with cast internals. Today though, the standards have risen. Third-gen Hemis, LS platforms, and Ford Coyote engines use stronger forged crankshafts and hypereutectic pistons straight from the factory. Yes, these types of internals also have a point of failure. But, throwing down 500-hp at the wheels is no stretch of the imagination, and boost is the perfect choice for getting there.
However—and this is important—not all engines possess the strength necessary to accommodate the additional power made by bolt-on boost. It’s important that before considering this upgrade, you take the time to read into exactly what your specific engine can handle. For example, a 5.7 Hemi and a 6.1 Hemi have different internals, and therefore will not handle the same amount of power.
Weigh the Installation Against Your Skills
Just because your engine can handle bolt-on boost, doesn’t necessarily mean you can. The installation of forced induction can vary in difficulty, so it’s important to be realistic about your skill set before you choose one. Sure, there are kits that include everything you need, but the process can still be lengthy and some are definitely easier than others.
For example, centrifugal supercharger kits, like those offered by Vortech, usually require the least amount of effort to install. This style of forced induction mounts to the front of the engine and is driven by an accessory belt that feeds air up to the throttle body or supercharger. Generally, this is a straightforward installation, but finding real estate under the hood can prove difficult. Additionally, foregoing a premade kit means you’ll have to fabricate your own brackets.
Roots-style blowers, like the Edelbrock E-force, are probably next in rank of difficulty. Installation will require the removal of everything from the intake manifold up. A roots-style supercharger sits on top of the engine and uses two rotors within to draw air through the throttle body or carburetor. Since you are tearing down most of the top half of the engine, this can be time-consuming and will require a trained hand.
Turbochargers are probably the hardest to install. Real estate and work space are the enemy here, as you’ll need to remove the intake manifold in order to install the manifolds needed to run the turbo. Turbos feed air into the engine like the centrifugal supercharger does, so routing the intake from the turbo to the throttle body or carburetor can also be a challenge.
But like most aftermarket mods, there are other things you want to consider both before and after you slap on some more boost. Fuel delivery, valve train components, cam grinds, and timing are all components you want to think about when it comes to adding forced induction to an engine. Throttle bodies, carburetors, and fuel injectors may all need to be upgraded. Cylinder heads in stock form may be restrictive and valve train components may not be up to par when it comes to dealing with the added stress. Be thorough in your quest for more power, young grasshopper, if you want that power to last.
Think Hard About That Stock Camshaft
Most of these related upgrades can be done without too much effort. However, dealing with a camshaft swap can be extensive. Yes, there are tons of accounts where builders have simply tossed a bolt-on boost kit onto their engine and continued on their merry way to enjoy excellent power all day long, without ever having to crack that far into the engine. But it’s important to consider the challenges a stock camshaft may face when paired with boost.
As our friends over at Super Chevy point out, “In a turbocharged engine, careful attention to camshaft selection can pay huge dividends in power, torque, and driveability. Because positive pressure in the intake manifold (boost) is force-feeding air into the cylinders, a turbo cam can often be very mild in comparison to a naturally-aspirated grind, needing less lift and duration to accomplish a similar horsepower goal. Also, because there is inevitably backpressure between the exhaust port and the turbo’s turbine wheel, careful attention needs to be paid to valve overlap. Too much overlap for the application can cause exhaust to backflow into the cylinder and heavily dilute the air charge.”
Essentially, the cam grind needs to be able to handle the air pressure. Addressing it up front will mean the engine can run healthy. Waiting to fix this down the road may not be an option, as you will be wrestling to tune the engine to run correctly. And speaking of tunes…
Never Underestimate the Power of a Good Tune
Despite how you feel about complementary upgrades, one thing’s for certain: the key to making reliable power with boost is a good tune. Achieving a decent tune with modern engines can be done with the help of computers, but older engines aren’t so lucky. And again: what makes that bolt-on boost possible is the factory equipment you are working with. (Those older engines are at a disadvantage, so upgrading cam grinds, fuel delivery, and ignition systems sooner than later will help you run boost with the best results.)
Low amounts of boost are easier to manage than high amounts of boost. But if you are like any other gearhead on the planet, a little will eventually become a lot and these are the kind of things that are worth being aware of, especially since the last thing you want is boost contributing to your engine blowing apart.
For clarification, we spoke with John Potucek of Keystone Automotive. Potucek has an extensive history of working with high-performance engines and that includes bolt-on boost kits. “Is there really a true ‘bolt-on’ option?” he asked. “Sure, there are kits that have all the parts you need—but what about the tuning? I know some companies offer a new ECU or re-flash your ECU with a new tune, but I’m skeptical. I’ve seen people buy these kits with a pre-flashed ECU and take it to the dyno and make more power when they actually adjust the tune for their car and/or conditions.”
We’ve established that fitting a naturally-aspirated engine with forced induction requires more thought than simply slapping on some bolt-on boost, but what about engines that are boosted from the get-go? It’s only natural to want more power, right? Upgrades are definitely available to increase boost. Whether it’s bigger turbos, smaller pulleys, an intercooler or water meth injection, you will need to come back to that tune. These engines will have a leg up in terms of the internals and valvetrain components, but a custom tune will be needed.
Keep Those Expectations Realistic
Bolt-on boost is possible. There are tons of examples out there of it being done—and being done well. But making power with forced induction is inherently different than making power with natural aspiration. It’s important to choose a kit that suits not only your engine, but also your budget, your skill set, and your will to tackle related mods.
Potucek advised that builders go forth with realistic expectations. “If you aren’t going after max power, the bolt-on boost kits are okay,” he said. “Stick with the big names; they spent all the money on R&D. For a supercharger, Edelbrock is a safe bet with its e-Force kits. For a turbocharger, the STS kits are well liked.”
Starting with a bolt-on boost kit is great, but John is right: if you want the best results, you will be looking at a genetic overhaul. It’s important to spend time building the rest of the engine around boost rather than simply adding boost. This isn’t to discourage you from attempting this sort of upgrade. In the quest for more horsepower, we say go for it. Pushing the limits and challenging yourself is what being an enthusiast is all about.