Car Modding, Car Tuning and the Science of Horsepower: The Mods
Your car lurches back and rolls slightly to one side as the longitudinally mounted monster in front of you revs back from 4000. You carefully feather the gas, keeping tire chatter to a minimum, waiting for that bite. There it is! You bring her up to wide open throttle and watch the tach. The needle rises… “Come on, come on!” 5500, 6000, 6400, and then you clutch and slam it into second — your left thumb twitches. As you watch the needle drop in slow motion, time stands still around you. It levels off at 3600, and you hit the juice! The 10 lb. bottle in your trunk hisses, releasing a 150 shot into the multi-port fogger and you’re sucked back into your seat. The world outside seems to lose its color like the wind is blowing it off. Your heart, like a metronome, keeps time… so that time doesn’t get away from you!
If you haven’t already familiarized yourself with the vocabulary of car performance, take a detour here first and come on back after you’ve skimmed through it. See you on the other side!
Now that we’ve gone over all of the textbook stuff, let’s have a little fun and talk about power adders that you can install on your car to begin that never-ending transformation from a car into a ride. The technology is tried and tested, but it’s up to you how you want to proceed. Do you want to do some light breathing mods or rip the engine apart and start replacing cams? Well, if you’re new to this stuff you won’t be taking engines apart any time soon, but that’ll come eventually, and when it does, you’ll want to know what your options are. Let’s get to it!
Breathing mods help naturally aspirated cars take in more air and expel it more efficiently for reduced losses and more power. They include work done to the intake, exhaust and most stuff in between. If air/fuel or exhaust flows through it, we’re interested in it. Each mod adds a little bit but if you do everything you get quite a big gain. There are a lot of mods though so be prepared to spend some money if you’re going all the way.
The CAI (Cold Air Intake)
This is the first mod everyone looks at installing. It’s fairly cheap, easy to do, it looks cool, and you get some small gains. The purpose of a cold air intake is to reduce the temperature of incoming air by drawing the air from a cooler place and by reducing restriction in the path of flow.
Why cold air? Cold air is denser than warm air. That means you can get more of it into your engine. Air is always the limiting factor. You can inject as much gas as you want, but without air, it won’t do a thing.
A cold air intake is usually made up of some polished metal tubing which goes from your throttle body to your air filter and you have to remove the stock sensors from your induction system so that you can put them on your new CAI. The stock air filter is discarded in favour of a higher flowing cone filter. Cone filters have more surface area and the filter media is a reusable fabric inside a mesh screen that you can wash when it gets dirty. A light coat of oil keeps fine particulate from getting through. You have to wash that off and replace it when you service the filter. The piping will come with straight sections and various adapters and elbows. The idea is to route the pipe in such a way as to avoid any hot parts of the car like the exhaust heat shield for example. Your destination? You want to put the end of the tube with the cone filter somewhere in the lower fender cavity or behind the headlight. If you have nostrils in the fascia that air can flow through, even better! Put the tube there for a slight “ram-air” effect! Some people have space restrictions and end up putting the filter where it fits. In that case you can sometimes quarantine the filter with a plastic barrier to keep radiant heat from raising the temperature of the air entering the filter.
Gains from this mod are quite modest, usually around 5-15 HP, usually on the low end if you don’t do anything else. The car’s computer will fully compensate for the extra colder air, so you don’t need to change anything else. Just make sure you hook up all the sensors just as they were before. Careful with the MAF too. It’s delicate and needs to be in a section of pipe where nothing too crazy is going on. These sensors like smooth, undisturbed flow to get a good reading.
This is basically a CAI that’s facing the front of the car and is exposed directly to oncoming air that’s hitting the front fascia or grille. Ram air designs also have a collector or funnel to channel a larger volume of air into a smaller diameter pipe, to get as much of a ram effect as possible. These are at least as good as a CAI and give you a bit better VE (volumetric efficiency).
The throttle body is the next restriction after the intake tubing. It has a narrowing in which the throttle plate is situated. You can buy aftermarket throttle bodies with larger openings and larger plates. This gives you much quicker throttle response and contributes to the whole better flow thing. These are a couple of hundred bucks but keep in mind that if you’re doing breathing mods, you won’t get the full effect unless you take care of all the restrictions since even one can choke your engine. You can get 5-10 HP from this mod.
Port & Polished Manifolds/Heads
After air gets past the throttle body, it goes into the upper and then the lower intake manifolds. These manifolds are usually cast and have a rough surface on the inside. The runners that carry the air to the cylinder heads are kind of narrow and have abrupt transitions that cause recirculation losses in the flow. A port and polish can be done at home with a Dremel tool, but most people will send them out to a performance shop because those guys have better tools and know what they’re doing. What they’re doing is widening the openings and smoothing out the transitions as well as grinding the inner walls of the runners until they are nice and smooth. They will clean up the heads as well. You’d be surprised what a difference a little roughness makes. Flow bench testing is the proof that a port and polish job can get more air into your engine faster! If you want to cheat a bit, you can sometimes purchase completely aftermarket but compatible heads and manifolds that are already higher flowing than stock. Gains of up to 20HP are possible with supporting mods.
Cams are long shafts with lobes on them, which are precisely timed and designed to actuate every valve in the engine at the correct time and to the correct depth. You can replace the cam in your car with a custom one which will give you more power, torque or both. Here’s how.
As I said, cams have lobes on them. These are like off-center oval-shaped pieces of metal that push the valves open. Valve springs return the valves to the closed position when the lobe has moved out of the way. The lobes themselves control 4 things simultaneously. The lobe position on the cam controls when the valve is supposed to open. The eccentricity or steepness of the lobe controls how quickly it forces the valve open. The height of the lobe controls how far the valve opens, and the width of the lobe controls for how long the valve stays open. You can get cams that alter any or all of these parameters. Sometimes you want to have the intake and exhaust open briefly at the same time for a scavenging effect. Sometimes you want them to open more deeply and for a longer duration to allow more air into the cylinders. Take care because you may have to change the springs to shut the valves faster than before or you’ll have problems, especially at high RPM where you can get valve “float.” That’s when the valve doesn’t have time to fully close at all. Aside from improving flow, cams with stiffer springs can allow the engine to rev higher and stay in a given gear longer, which gives you the advantage of more torquey gear ratio for a longer period of time. Modding your cam may require a PCM re-tune.
Normally you have a large collection manifold that picks up all the exhaust gas from all the cylinders at the same time. If you upgrade to headers, each cylinder gets its own pipe which is smooth, with large radii and the lengths of each pipe are tuned so that gas from each and every cylinder traverses the same length of pipe, no matter where it’s located. This makes it so that all the gas exits each pipe at the same time for improved flow characteristics. You want to dump the exhaust into the rest of the system all at the same time, not in spurts coming from each pipe all out of synch. This helps you achieve “bonus” power at the mid to upper end, where you tend to need it.
High Flowing Catalytic Converter
These mods are not terribly popular by themselves but are commonly combined in what’s called a “cat back,” which replaces everything from the cat, back. Cat back exhausts are purchased as a kit and installed all the way back to the tailpipe. You wouldn’t normally buy a cat without changing everything else at the same time unless you had a damaged cat. The increase in flow is marginal, but it works with the other exhaust mods.
This is the other main component of a cat back exhaust, but again, you can replace it alone if you want to avoid the work and expense of a full exhaust upgrade. Aftermarket exhaust comes in different flavours but a very popular one is called a “glass pack,” which kind of resembles the front of an assault rifle. There’s a straight pipe going clear through to the other side, but it has holes in it and a round baffle surrounding it. Sound waves go up through the holes and are damped out in the baffle. You keep much of the sound and all of the flow so there’s almost no restriction and the sound is amazing! This is good for a couple of HP, but if you do the full cat back, you’ll get closer to 10-15 HP in most applications.
None of the breathing mods are strictly additive. They don’t stack up so you can’t just add up the horsepower. Final results are hard to figure, but that’s part of the fun. Another thing to consider is that the intake and exhaust pipes CONTROL the flow and therefore they are “tuned.” At certain RPM values, you’ll get resonance within the pipes which will give you a small boost of efficiency and power. You can customize the geometry of your ductwork when you get to be really pro, so that you can exploit this resonance effect to get max power wherever you want it! One last comment is that just because you have a naturally aspirated car, doesn’t mean you can’t get a VE > 1. With correct pipe tuning, you can get a “mildly” boosted effect with a VE greater than 1. This allows you to exceed theoretical expectations for the engine at certain RPMs.
How Serious Are You About Performance?
How much are you willing to spend to make your car faster?
Give Me a BOOST
Boost is slang for forced induction. It’s when you force air into the engine instead of letting the engine suck it in. Gains are huge, and so are the price tags. You’ll spend a few thousand and the install isn’t easy, but you’ll get somewhere between 40-60% more torque on average. If you are good enough to design your own boosted configuration, you can get far more than that but a word of warning. Adding more than 40% to your car puts it at risk of mechanical failure. You would have to reinforce everything in the engine to take the punishment, which means forged and heat treated internals like connecting rods, pistons, crankshaft, main bearing caps, etc. More $$$. When adding forced induction, you will also need a chipped PCM, or you’ll have to program it yourself, primarily to modify the MAF fuel table for the higher pressures and also adjust the PE AFR a little lower. There’s more to change, but those are the big ones.
I love superchargers. They’re not as efficient as turbos, but that’s why I love them… cuz they’re manly, burning all that gas for nothing yeah!!
There are two main types of supercharger: the “Roots” style and the centrifugal style. The Roots-style, also known as “positive displacement” is an old design that was originally used to move large volumes of air quickly for industrial, not automotive applications hence the name “blower.” They did a really good job at that. They are quite inefficient however when you use them to push air across a large pressure gradient, like when you’re taking air at 14.7 psi and trying to make 23 psi. They work by transporting “parcels” of air from the low-pressure side to the high-pressure side in much the same way as an airlock would transfer an occupant between 2 different pressure zones. The problem is it moves sealed volumes of low-pressure air into a high-pressure area so as soon as it opens up on the high-pressure side, you get all this backward flow trying to push the air back the way it came. The supercharger doesn’t care and keeps going but it builds up a lot of heat in the process, and this wastes a ton of energy. What energy is it wasting? Well, all superchargers are driven by belts which are connected directly to the engine. Therefore the engine wastes a lot of horsepower just to run the blower, and it gets you your 40% but at the expense of God knows how much it took to run the thing. As you might guess, they chew through gas.
Why use them then? Well, they are really really good at providing instant and linear boost. You hit the gas, and the car goes. No questions asked. The harder you hit the gas, the more boost you get, nice and even. They’re popular for drag races because of this. Time is everything there, and you can’t miss 1/10 of a second.
The other type of supercharger is the centrifugal type. It looks like a snail. It draws air in through the middle and spins it outward really fast so that it all piles up on the walls and exits at high pressure. It’s also belt driven, but it’s a bit more efficient. The problem here is that it doesn’t have the instant uummph!! that Roots does. It makes up for this by giving you more boost at the top end and with less waste. This is better for the less serious car nut.
Turbos are different in where they get their power from. While a super runs off the engine, the turbo runs off the exhaust. It recycles in a sense. The exhaust is hot and has lots of energy in it. A turbo places a turbine in the way of the exhaust so that the gas has to go through the turbine blades. This causes them to spin up faster and faster. There’s a shaft that couples the turbine to a compressor that is basically a centrifugal supercharger. The turbine gives its power to the compressor, and the compressor delivers boosted air into the car’s intake.
Benefits are fuel economy and top end power. The more you hit the gas, the more exhaust you make, the more boost you get. It’s a very nice buildup. The process is fairly efficient, and it’s using waste gas instead of engine power so you won’t break the bank driving with this every day. Disadvantages are mostly a lack of low-end torque and “turbo lag.” As I said, the exhaust needs to spin up a turbine. This takes some time so for the first fraction of a second you get nothing… it’s just motor. Then you get everything at once like someone lit a rocket under you. It feels awesome, but dragsters tend to favour the Roots super.
There are other types of turbos, but I could talk all day, and they’re not as common anyway.
This rather obscure mod is actually nothing special. It's just a regular supercharger powered by an electric motor and independent battery bank instead of a belt coupled to the engine. The really attractive feature of this mod for me is that it costs no energy (from the engine) to run, so the engine doesn't have to work any harder to get the boost produced. While 5 psi might not sound like much, people often forget that it's 1/3 of atmospheric pressure and that the 8 psi they're running on their conventional supers is being partly wasted just to operate the supercharger. That energy is energy LOST which has to be made back again to break even...and then some more to get a gain. Therefore electric superchargers are not only more efficient, but they put less strain on the engine which means you can get more spark timing and more power at lower cylinder pressures and temperatures. Add to this the fact that you can turn the unit on and off any time you like, and it's something to have a look at!
Juice it Up! Nitrous Oxide
I like this almost as much as superchargers. You press a button, your car goes fast! What could be more awesome? Maybe if there was a bulldog in the passenger seat, a shotgun in the trunk and you were drinking a beer at the time… (don’t do that).
Nitrous oxide or N2O is a molecule carrying 2 nitrogen atoms and 1 oxygen atom. If you get 2 nitrous molecules and decompose them you get 2N2 and an O2. This is exactly what happens when you put nitrous in a high temperature environment. It breaks apart. This makes it safe right up until the combustion is actually happening and it’s why we don’t put straight oxygen into an engine. The principle with nitrous is to dump extra oxygen into the engine and with it, extra fuel. The fuel can be adjusted by the car’s computer (I’ve chosen this route) or you can inject extra gas from an additional fuel injector on a switch. The former is known as a dry kit, the latter is a wet kit. Dry and wet refers to the manifold because in the first method you’re only pumping nitrous into the engine without fuel. In a wet kit you spray fuel into the intake manifold with the nitrous and this “wets” the manifold. It also makes it possible for your manifold to explode and punch a hole through your hood :D Dry kits are less popular and aimed at lower gains because the car’s computer just isn’t set up to detect the presence of nitrous. It doesn’t know how to compensate. Dry kits sometimes come with a new PCM or offer programming services and if you want it to work reliably you have to trigger something in the computer with your button directly so the computer knows to compensate. Dry kits are also a pain because the stock injectors can’t flow much extra fuel so the wet option really is the better way to go, if you can sidestep the whole exploding manifold thing.
Gains are virtually unlimited. You get as much as you put out. You control the flow of nitrous using metal orifices called jets and by getting bigger flowing solenoid valves on the bottle. You can get different sized bottles and you can jet the fuel line as big as you need to as well. The limit on power is the limit on how much the engine will take without exploding. This is dangerous because it means YOU are the last line of safety since you decide what the gains will be. Take my advice. Start with a 50 shot (+50HP) unless you own a decent V8 and work your way up. Don’t forget to tune your PCM or buy a chipped one to handle the extra O2 when you juice. You will also need bigger injectors, a new fuel pressure regulator and colder spark plugs.
CHIP: Powertrain Control Module
The last power-adder on my list is the PCM itself, the brains of the operation. I plan to spend an entire hub on this alone but suffice to say you can change every parameter in the car and easily add 10% or more just from programming alone. Even if you don’t like the idea of loading new settings to your car, you can’t get away from it. If you want to do any of the more serious mods above you’ll have to either buy a PCM, pay someone to program yours or do it yourself. It’s cheaper to do it yourself and infinitely better. If there’s one thing I know, it’s tuning, and you cannot get a proper tune from a guy hundreds of miles away claiming to have special settings just for you. You have to drive your car 50 or even 100 times to zero in on the perfect tune. The store-bought PCMs are fine to support your mods but not to get the perfect tune so if you just want to bolt on a super and have it work, you can buy one. Otherwise, don’t bother.
Do it yourself tuning requires a tuning module which is a few hundred bucks but it pays for itself with what you can do with it. It’ll work on any OBDII car you register and you can program it over and over again however you like. There are hundreds of things to change and just learning what you’re doing will make you an engineer of sorts.
GRIP: Traction Mods
While not considered power-adders, mods that hold your car to the road are as important, if not more important than power-adders. Having a fast car is a delicate balancing act between grip and torque. Gaining 50HP could make your car slower if you suddenly can’t hold the road. Upgrading all season tires to summer tires or better yet, drag radials is a great idea and increasing the tire width will really help too. Special rubber compounds are available to grip dry asphalt better than any stock tire, and a bit of research will help you find what’s right for you, and what fits.
The other grip upgrade you can opt for is a limited slip differential. Differentials transfer power from the engine to a pair of wheels but allow them to spin at different speeds, depending on how much the car is turning. That’s what they’re there for. They allow the car to turn without losing grip since the outer wheel wants to go faster than the inner wheel during a turn. During a race in a straight line, you don’t care, and you’d rather have the wheels locked so that if one slips, the other will take over. A limited slip differential uses a torque sensitive clutch to achieve the best of both. It locks the wheels up when you floor it, and it slips when you’re doing a turn (hopefully you’re not gunning it through the turn).
How a LImited-Slip Differential Works
Let's Wrap This Up
That’s all for now in the mods department. The industry is rich, and you can buy a ton of mods for your car. Hopefully, these descriptions have given you a taste of what’s out there and what you can look forward to. I encourage you to check out my other car performance hubs and do whatever research you need, to know this stuff inside out. Better that than have a really expensive explosion on your hands (unless you enjoy expensive explosions).
Keep your wheels on the road!
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
© 2012 chriscamaro