In the olden days, cars were much more simple things. Vehicle manufacturers hadn't discovered crumple zones, steering columns were still basically spears that could impale the driver at the slightest whiff of a crash, and a radio was considered a 'fancy optional extra'.
On top of this, a lack of emission controls and care for the environment meant that cars were often slow, underpowered and stunk up the earth (re. pollution). In fact, throughout the 70's (due to the gas crisis), Malaise-era vehicles were regularly producing horsepower figures in the late 100's from vehicles with 6, 7 and 8 litre engines all while managing to break high scores for smog.
Obviously, car enthusiasts of the period were massively disappointed and a booming aftermarket formed for both minor and major upgrades. These upgrades would take the rackety boat anchors powering these cars and help them develop enough power to pull themselves along healthily.
The most common place to start was (and still is) the exhaust and intake.
In fact, for as long as cars have been around, exhaust, intake and camshaft packs have been the go-to way to pop some pep into otherwise powerless passenger cars. With manufacturers such as Hooker Headers, Edelbrock, Holley and Crane cams, it wasn't hard to find a package to suit.
Of course, all of these modifications came with other side effects too. These wouldn't just make you the "sickest" person on the block, but they also made cars significantly faster, louder and (somewhat surprisingly) more fuel efficient.
Why is this so?
At the time, manufacturers didn't really seem to care about the design of specific engine components as much. As mentioned in EP8 of the CarCar Podcast (shameless plug), most factory exhaust designers of the time were asked to meet 3 main criteria: cheapness, simplicity and packaging (i.e. making it fit in the car).
This seemingly daft set of priorities led to the most common intake and exhaust design throughout automotive history being 'lovingly' referred to as the "log".
It's easy to understand why they were named "logs" and (if you've got a little understanding of fluid dynamics) why there are some very big downsides to the basic design.
On the exhaust side, a log manifold means that the pulses of exhaust gas leaving the engine are forced to travel unequal distances and often converge at the collector point at the same time as each other. This means that exhaust backpressure fluctuates, flow is interrupted and the scavenging effect becomes none existent.
It was easy for aftermarket manufacturers to improve on these designs by making tubular manifolds that smoothly and evenly flowed exhaust gas. It wasn't uncommon for a 100HP engine to pick up an extra 10HP-20HP from this simple mod alone (or 10%-20%).
Though headers and exhausts made a massive improvement to power, the real gains often came through a good intake setup and a set of cams.
Engines are basically a giant air and fuel circulation pumps. Fresh air comes in through the intake, mixes with fuel, goes through the combustion chamber and out the exhaust. Increasing the flow rate of the air pump and the amount of fuel massively increases the power output and it all starts with the intake.
Historically, performance carburettors and intake manifolds were a staple of tuning up a car. Re-jetting or replacing a carburettor and switching out the intake manifold was a common way to achieve slightly better running.
You might not believe it, but you can still buy a (slightly more in-depth) "top-end kit" for a 1969 Mustang from Edelbrock that takes power from 250HP factory to 450HP, a massive 80% all by improving the airflow through the engine.
Now, here's where the whole thing gets a bit more difficult. As you've noticed, the title of this blog is "Is it still worth upgrading your exhaust and intake". The simple answer is no.
Throughout the 70's, 80's and 90's, manufacturers were forced to massively increase their fuel economy. As we mentioned earlier, one of the easiest ways to do this was to increase the efficiency of the intake system, exhaust and camshaft. This is also where we got such incredible innovations as VTEC, VVT, variable intake runners and even the regular use of turbochargers.
So what happened then?
Because of the massive leaps in efficiency and emissions control, most factory intakes and exhausts suddenly became incredibly efficient. Tubular manifold designs were much more common and (even better) exhaust piping was finally sized more appropriately from factory.
With all of these factors, modern intake and exhaust upgrades have honestly just become a noise-making exercise for otherwise stock cars. Just look at the fact sheets.
A set of headers on a Nissan 370Z (a modern-ish naturally aspirated sports car) advertise maximum gains of 23HP (6%) for the low, low cost of $2000; And there is absolutely no data readily available for a $600 cold air intake. All to make an otherwise perfectly good car sound like a rusty trombone.
It's even worse for factory turbo cars like the Audi RS3 with increase power figures from a combination exhaust and intake rumoured to be just 15HP (3%) total.
The worst part of all of this is that modern fuel injection and proper electronic engine controls make engines want to run within a mapped power window. No matter how good the flow is from a complete (and very expensive) set-up, most cars won't make any noticeable power gains without being properly tuned. These mods are likely to set the engine light in some cases.
What does this mean for you as an owner? On modern cars, these modifications really only serve two purposes. Firstly, for daily drivers, an exhaust and intake make a car sound a lot 'nicer' and can add the feeling of going fast to an otherwise very boring car. Secondly, they are supporting modifications for when you aim to make power. They help deal with the extra air added to the engine by big turbos, big injectors and big tunes.
If you want your car to sound louder, just admit it. It's not going to make your car measurably faster in any real-world situation so go out and drop some cash on a CAI (cold air intake) and a phat exhaust system and enjoy it for what it is.
If you want to have a power gain in a modern car, the best place to start is usually a tune. If you're a real connoisseur, you'll be starting with suspension, tyres and track days. After all, the cheapest part to improve in any car is the driver.
If you have any questions about this blog post, would like a second opinion from a mechanic or would like to find an honest mechanic in Brisbane, check out Kashy here.