While the car world is obsessed with everything boosted these days, many still yearn for the smooth power delivery and sonorous tone of a naturally aspirated engine. Of course, everyone still wants to go fast, so here’s how you go about getting more power out of your car without bolting on a big turbo or whining supercharger.
Intakes: This Can Get Pretty Invovled
The intake is one of the first modifications made by many budding car enthusiasts. Throwing on a chromed intake pipe with a big pod filter was the mod to have back in the Fast and Furious era. Power gains can be had, though typically these are minor – on the order of 5-10 horsepower at most. It all depends on the car in question. A BMW M5 V10 was designed for high performance, with a highly advanced intake with individual throttle bodies from the factory. It’s unlikely any eBay parts are going to unlock horsepower that BMW’s engineers didn’t already find. Conversely, early Mazda Miatas are known to have a restrictive intake, largely due to the flap-type air flow meter. Replacing this with a freer-flowing setup has merit.
Intake mods can range from simple to complex. With many modern cars, it’s a case of removing the stock factory parts and bolting in whatever shiny new pipes you bought online. These intake kits usually bolt in front of the throttle body, leaving the stock manifold as-is. Alternatively, particularly if you’re working on an old carby V8, you may be replacing the whole manifold entirely. This generally involves a new set of intake gaskets and some fresh sealant in some cases. At the other end of the scale, one can go as far as installing a full individual throttle body kit, requiring modifications to linkages, fueling, and even braking systems. These are best attempted by those willing to suffer for their build.
Exhaust: A Bit More Beginner Friendly
If you crave more rumble, this is the mod for you. Exhaust modifications range from a simple muffler swap at the rear of the car, to a full kit from headers to tailpipe.
There’s often some small gains to be had by upgrading to a freer-flowing exhaust system. Factory parts are often made with an eye to ease of manufacture and cost, and may not be the most efficient design. Additionally, the average motorist likes a nice, quiet car. Swapping these parts out for something less restrictive that makes more power and noise is a no-brainer for a true enthusiast. Gains are generally on the order of 15hp or less, but it’s an important modification to make on the quest for bigger power numbers in concert with other mods. Plus, you want other people to be intimidated by the growl of your engine as you idle through the McDonald’s drive through, right?
Exhaust mods are usually an easy job, though modern cars with tighter engine bays can prove more difficult to work on. It’s usually a case of undoing a few bolts, removing the stock parts and installing the new ones. New gaskets are key to avoid leaks, and bring plenty of WD40 if you’re working on an older or rusty vehicle. Make sure to use a good socket set, too. Exhaust bolts have a habit of being tough nuts to crack, and if you snap a stud on the engine, you’re in for a world of hurt.
Cams: When You Crave Some Risk in Your Modding Projects
The camshafts in a piston engine are what control the opening and closing of the intake and exhaust valves. By altering the amount the valves are opened (lift) and how long they’re opened (duration), it’s possible to alter the engine’s characteristics. Increased lift and duration lets more air into the cylinder, creating more potential power.
However, there’s always a tradeoff. Greater lift can cause problems with valve float at high RPM, where the valve spring can no longer keep the valve in touch with the cam. This can result in catastrophic damage if the valve contacts the piston. Greater duration can create greater overlap – the time at which both intake and exhaust valves are open at the same time. This can hurt performance at low RPMs, and give the engine a lopey idle. Additionally, it’s important to consider the proper supporting mods. Often a cam change may require upgraded valve springs to deal with the new profile.
Generally, a cam swap enables gains to be made in high end power or low end torque, but rarely both at the same time. Often, they’re discussed in terms of application — street cams, race cams, and so on. A race-oriented cam may give great top end power, but very poor performance low in the RPM range, which would make it awful for driving around town. Being realistic about your build’s application is key to making the right choice.
Heads And Porting: Delving Into the Jobs For the Pros
For some engines, mostly classic American V8s, it’s possible to buy new cylinder heads off-the-shelf as a performance upgrade. Additionally, in some cases, it’s possible to swap heads between different engines of the same family, as is often done with Honda B-series motors in the JDM scene.
Installing a high-performance head on your engine can be a major performance gain, and is often done along with a cam change to make the most of the better flowing part. A performance head will have less restrictive ports, and may also slightly change the compression ratio of the engine, depending on design. Often, larger valves may be fitted than stock, further helping flow. For those with older iron-block motors, there’s often an extra benefit to be had, too. By fitting a modern aluminium head, there’s a huge weight saving along with the power gains.
An alternative to buying a new performance head is modifying a stock part. A head can be ported, where the intake and exhaust ports are carefully machined out for better flow. On some heads, there’s also scope to fit larger valves, once again by machining the original part. These jobs are often performed by skilled machinists, as tolerances are tight and getting things wrong can destroy an engine very quickly.
Head swaps can be a more intermediate level job. It involves removing manifolds and often accessories from the engine, as well as timing gear. Making mistakes in reassembly can cause valves and pistons to collide, causing major engine damage. Dilligence is key to make sure your motor doesn’t end up overheating or smashing itself to bits.
Building an Engine: Down the Rabbit Hole We Go
If you’re hunting for ultimate power in a naturally aspirated engine, you’re generally looking at building a motor. This involves disassembling the engine, and putting it back together with fresh parts to completely change its performance characteristics. Building an engine is not for the faint of heart, but opens up options like stroking and boring which can provide major power gains for serious builds.
The “stroke” of an engine is the distance the pistons travel up and down within the cylinder. Stroker kits involve swapping out the crankshaft, rods, and sometimes even pistons, to give the engine a greater stroke length, and thus displacement. This greater displacement allows the engine to suck in more air, creating more power, and the pistons have greater leverage on the crank, creating more torque.
The bore of an engine is the diameter of the cylinder. Increasing this dimension increases displacement, and allows the engine to suck in more air, creating more power. Boring out an engine requires new pistons to be fitted, and can cause issues with cylinder walls cracking if taken too far. .
When replacing pistons, crankshafts, and associated parts, there’s also the option to choose parts to change the compression ratio. Increasing compression ratio produces more power from the combustion reaction, but also increases the risk of the fuel-air mixture detonating, which causes engine damage. This can be staved off by running fuel with a higher octane rating, which obviously comes at a cost.
Building an engine involves choosing a large number of very specific parts which have to be exactly right in order to all spin together at thousands of RPM for thousands of miles without destroying themselves. Additionally, assembly requires the utmost attention to detail and the use of specific, high-quality tools. Tolerances of tiny fractions of an inch must be measured accurately, torques set just so, and lubricant applied properly to all the relevant areas. Miss one step, and it’s possible to turn thousands of dollars of precisely machined metal into a boat anchor in seconds flat. It’s a job that is achievable by the home mechanic, but requires serious dedication and investment of both time and money.
A Note On Tuning
When making changes to the way air flows through your engine, it’s important that the fueling changes in kind. Otherwise, you’re not making any more power, and you’re risking detonation and damage. The tuning your car will require depends on a number of factors, from the parts you’re fitting, to the way your engine manages air and fuel.
For modern fuel injected cars, oftentimes, simple mods like an air filter kit or new exhaust won’t require any changes. The sensors attached to the engine’s ECU can detect the amount of air coming in to and leaving the engine, and adjust fueling to suit. Sometimes, even a sneaky cam change can be pulled off without modification. A great example is the original Mazda Miata, which runs very rich in the high RPM range. Aftermarket companies noticed this, and supplied mildly hotter cams which flowed a touch more air up top, taking advantage of the extra fuel already there to make more power. However, generally if you’re doing more than some basic bolt ons, you may need to get your stock ECU tuned, or even replaced entirely with an aftermarket unit.
For carburetted builds, the story is much the same. While a mild change to a new muffler likely won’t require any changes, a full exhaust or cam change will demand a retune. At this point, it’s time to get out the carby jets and the timing light, or take the car to a shop that can do it for you. Without doing this crucial step, it’s likely your mods will simply make the car run worse, not better!
Making big power gains in a naturally aspirated build is more complicated than just buying an eBay turbo and slapping it on in a weekend. However, for some, the effort is worth it, for the incomparable sound and smooth power curve that is only available with such an engine. Whatever your automotive journey, may it be a good one — with as few trashed engines as possible!