There have always been a lot of posts about turbos and SC's out there. Hopefully this will be made a stickey and help you guys answer a few questions you may have about installing a forced air induction system. If there are any errors, factual or even spelling, feel free to point them out. I only want you guys to know the best.
Marcin's Guide to Forced Induction Systems for Gasoline Engines
This reference is just a guide to understanding the basics of forced induction system of a car. It is not to be considered the definitive how-to for installing such a system onto a car, and it is not to be considered an invitation to do so. Though the information provided here is true to the author's knowledge, he claims no responsibilities for inaccuracies in the information. The author, his family, his college, his friends, his club, the fourm/webpage this is posted on, it's host and other related parties TAKE NO RESPONSIBILITY FOR ANY MISINTERPRETATION OF ANYTHING WRITTEN FROM THIS POINT ON. THE INFORMATION PROVIDED HERE IS FOR EDUCATIONAL PURPOSES. WHAT THE READER DOES WITH THE INFORMATION IS SOLELY HIS OR HER RESPONSIBILITY. This document can be copied and reproduced at will, but the author retains all copyright privileges.
In English: This information is true to the best of my knowledge, but I will not sign my life away to prove that point. The information here is for you to learn, but I'm not telling you to do anything with your car. If you go ahead, install something on your car, and mess up, it's YOUR fault and YOURS ALONE. You should have done more research. I, and everybody related to me, claim NO RESPONSIBILITY for what you do, no matter what your age is. Anybody can copy this at will, just don't say that you wrote it, or I'll do very bad things to you.
It seems like every day you see a post saying "I want to supercharge/turbocharge by car. What do I need?" There are a million instantaneous replies: "well, it's more work than it's worth"; "go for it, ask someone"; "it shouldn't be too hard in theory"; and my favorite "there should be a sticky about this." Well this is meant to be that sticky- the almost complete guide to forced induction systems for gasoline engines. Not all engines are the same- there is definitely a difference between a lawnmower engine and a Nissan SR20DET, but the theory is the same, more or less. So what you read here can be applied onto multiple engines.
This guide is meant to be a starting point. It is by no means exhaustive. I can't tell you how to put a turbocharger on an engine- I haven't seen yours, I don't know what you've got running on your system... there are just too many variables. I hope that with this guide, though, that if you feel like taking the next step, you'll know what you're getting into. Throughout this guide, I assume you know the basics of engines, their parts and how they (basically) work. You don't need to know air/fuel ratios and fuel curves for your engine, but if you don't know what an intake manifold is, this probably isn't for you.
What will this guide do for you? It is here to give you a basic understanding of what forced induction is, to tell you how it works and why it works. It will set you straight on the myths and the realities of supercharging and turbocharging, and maybe even start you on the path of retrofitting your car with a turbo or a supercharger. What it will not do, however, is tell you how EXACTLY to install a system. There are to many variables, and something always arises. This is where you'll need to engineer and tinker a little. This is not a guide to welding, cutting, machining and mechanical work, but an introduction and an overview of what forced induction systems are, and the basics of adding it to your car. Any car.
What is forced induction?
What does it mean to be naturally aspirated? What does it mean to run boost? What is vacuum, and how does a car produce it? These are all very important concepts in understanding forced induction.
Engines are like people: they need to breathe. In order for combustion to occur, two things must be present, oxygen and gasoline. I'll spare you the chemistry, but the stoichiometric ratio of air to fuel is roughly 14.7 : 1 (usually referred to as "stoic"). That's where combustion is close to "perfect": no excess gas (running rich). Air does not come with the gas, so the engine needs to "suck" it in. Most engines nowadays are naturally aspirated, that is, they suck in their own air with no outside help. When the pistons move downward on their intake stroke, they create a vacuum throughout the intake system. As you remember from basic chemistry, gasses want to equalize pressure, so as a result, air is sucked into your engine for combustion.
That is the way most engines work. Vacuum lines are also run from your plenum throughout your car to control many things-- brake boosters, evap
purge canisters and a bunch of other things use vacuum to run.
Forced induction engines work much the same way as naturally aspirated engines do... well, at least the basics are the same. Stoic is still 14.7, the engine is still four stroke, gas is burned, etc. The only thing that differs is the intake system. If naturally aspirated engines are like you breathing normally, then a forced induction system is like you breathing with a compressed air hose in your mouth. When a car runs a turbo or a supercharger, there is a blower that forces more air into the engine. Your engine will be able to breathe faster while it's at higher RPMs (also referred to as "up high') due to a pressure in the system, called "boost." This extra air in the system allows the car to run stoic with more fuel up high, and thus gives you more power. Also, since it ensures a good air/fuel mix, combustion is usually more efficient.
One common misconception is that a forced induction engine runs constantly under boost. It does not, and it cannot. When RPM's are low, the engine's pistons can suck in enough air on their own to make a decent amount of power, it is only up high when boost is needed. This is important to remember later on. Also good to remember is that the more boost your car is making, the less efficient it is. Why? Less pressure means that the car is burning less fuel to achieve stoic.
A blow-off valve (BOV) is used to relieve pressure in the intake system when a shift occurs. When you run your engine up high and shift gears, your car kicks into a lower RPM
range. When it goes lower, the engine will require less boost, but you have a problem: you have too much compressed air in your system. This can cause many headaches, such as blowing off your intake pipes, among other things. A blow-off valve helps to alleviate this problem. It is mounted on your intake pipes.
In it's simplest form, a blow-off valve is two cylinders- one inside the other, with a spring on one end, and holes around some part of the valve. Normally the spring pushes one cylinder down, covering the holes drilled into the outer one. Coming out the top of the blow-off valve is a vacuum line. Under normal operation, the pressure on both sides of the interior cylinders is the same, and therefore it stays closed, letting air circulate through your intake system. When the RPM's dip, however, there is pressure on one side, but a vacuum (or at least a lower pressure zone) on the other. The higher pressure air pushes the valve open and escapes until the pressure on both sides of the valve is equalized.
Though it is not necessary to have a blow-off valve, it is a very good thing. At a lower RPM
, the fans spin slower, producing less boost, but the continued pressure in the system is a "shock" to the turbo/supercharger. When running low boost you may not see that big of a difference, but when running high boost, this is a great way to bust a fan blade. The blow-off valve is probably one of the cheapest things you can get for a forced-induction system, and it will be well worth the cost.
As you all probably know, when a gas is compressed very quickly, its temperature rises significantly. As you also know, the colder the air is in an engine, the better it runs (once again, I'll spare you the chemistry). If a forced induction system compresses air quickly, it get ______.
Hot, yes. It gets very hot- sometimes you can't even touch the pipe with the compressed air in it. So what can you do? You use an intercooler- basically a radiator which air passes through. Usually they're mounted in front of the car, and can drop temperatures significantly. Unless you are adding a huge turbo or supercharger to your car, you will not need a HUGE intercooler, actually, usually one of the cheaper aluminum aftermarket or even a stock intercooler found on a mass-produced car will suffice.
There is a debate between top and front-mount intercoolers and which is better. I personally tested this on an engine dynamometer, and I can tell you that there is little to no difference between a top and front-mount intercooler, granted that the top-mount has a hood scoop. Heat soak is very negligible, and is only an issue when you're standing still, idling/revving for 2-3 minutes. When the car is moving, you won't be able to tell the difference.
You'll need to redo your path of air to the engine if you add a forced induction system to your car. This does not have to be the hardest part of your job, but you need to do it right. It is from my experience that aluminum pipes will do the best job while cutting down on your weight. ONLY USE MANDREL BENT PIPE. Otherwise, you will not get a smooth flow of air, and everything will be messed up. This is easily enough obtained from places like Burn's Stainless <http://www.burnsstainless.com>, and you can buy silicone couplings to hold the pipe together from HoseTechniques <http://www.hosetechniques.com>. Invest in a good set of hose clamps too, you don't want your intake blowing apart.
The air will have to get sucked in before the compressor. Your stock airbox sucks and won't allow enough flow. I highly suggest using a K&N cone filter- they may be pricey, but they're worth it. Also, running a "cold-air intake" or "ram-air intake" with a forced induction car is just pointless. Your compressor will heat up the air so much that the cold/rammed air that your filter just took in does next to nothing. You may see 0.5HP at the flywheel, which translates to NOTHING. Your intercooler does a better job of cooling the engine. Let it.
Introduction- What Turbos are and how they Work
A turbocharger ("turbo") is one of the two devices used in a forced induction system. Usually found in diesel engines, it is placed by the exhaust manifold and is run by exhaust gasses. There are three parts to a turbo- the "compressor," the "turbine" and a shaft connecting the two. Both the compressor and the turbine are nearly identical, both looking almost like seashells. Inside both sections there is a "fan", and both fans are connected by a shaft, so when one spins, the other spins. Exhaust gas enters the turbine section, circles around, spinning the fan, and exits. This spinning fan spins the shaft it is connected on, which in turn (no pun intended) spins the fan over in the compressor section. This fan spins, pulling in air from your intake, and forces it down intake pipes over to the intake manifold so it can be used in combustion.
Turbos come in all shapes and sizes, from tiny little things that you can hold in your hand to massive monstrosities which you can stand next to. Smaller turbos don't have the ability to make as much boost as larger ones, but they "spool up" (get up to operating speed) quicker due to the fans having a smaller moment of inertia.
When a turbo is making little boost, it doesn't need to spin as fast as if it were making a lot of boost. The usual top speed of todays turbos is an impressive 150,000 RPM
, so there is usually little room for error. You do not want to push your turbo too hard, or else something might explode and you'd be screwed, so you want to prevent your turbo from making more boost than it's supposed to. This is achieved by a "wastegate." The wastegate is a separate path for the exhaust to take, instead of flowing through the turbo. When a sensor called a "boost control solenoid" (which is run by a vacuum line) detects that the boost in the system is much too high, it opens up the wastegate enough so the right amount of exhaust gas can escape the turbo, thus preventing overboosting and blowing up your turbo/engine.
When an engine uses more than one bay of pistons (the V-engines and W-engines), it is not uncommon to see twin turbochargers. Each turbo powers and is powered by its own bay of pistons. The benefit to this is that you can run the same boost with two smaller turbos instead of one large one. The two small turbos will be able to spool up quickly, and life will be good. On an inline engine, twin turbos are generally a very stupid idea, adding weight and complication unnecessarily. Sometimes two different sized turbos are used in an installation, one small one to spool up quickly, and the larger one to produce more boost. The turbos switch roles somewhere down the line, but this is for hardcore racers, and is usually pointless.
Design and Installation of a Turbo onto an Engine
A turbocharger should be as close to the exhaust manifold(s) as possible. It will do you no good whatsoever to have it far down the exhaust pipe- though it is a closed system, the closer your turbo is to your engine, the better. More pipe means more backpressure, and that will reduce the gains you will see.
To put a turbo onto an engine, you will definitely have to redo your exhaust system. For the engine I'm used to working with (Nissan SR20DET), the turbo is mounted right onto the block- the exhaust manifold empties right into it. This would be ideal for an install of a turbo. Ideal and what can happen are two different things, though. In theory, one can put the turbocharger where the exhaust manifold(s) meets the exhaust pipe. This will require an adaptor plate with a purchasable wastegate, and unless a kit exists for your engine, it will need to be custom. Ideally you could make your own custom exhaust manifold so that your turbo can mount right onto your block.
Both of these things will require some fabricating skill. To begin with, they MUST be made of a material with a very high melting temperature, usually HIGH QUALITY steel, and ideally stainless steel. An adaptor plate will need to be pretty precise so that it can mate up to the turbo and the exhaust manifold snugly, but the new exhaust manifold extremely so. Always use gaskets: copper is what needs to be used for those parts due to the temperatures involved.
Adding something like that into your system will undoubtedly mess up your current exhaust pipe- it will have to be cut short at least, and probably redone. One of your worst enemies in a turbocharged car is backpressure. The exhaust is being spit out of the turbo at relatively high speeds, so the exhaust needs to be as free flowing as possible. Thus, it is suggested that when you run a turbocharged car, you have an exhaust system whose pipes are NO LESS than 2.25" in diameter, preferably 2.5". This is the entire exhaust system too, not just the exhaust tip.
Also remember, since the turbo is spinning at very high speeds, it needs to be cooled and oiled. Make sure that you take that into consideration when designing the system. The turbo also MUST BE MOUNTED SECURELY. If it is not, bad things can happen. Safety first, and second, and third. You do not want a fan blade breaking loose. At best it causes your turbo to explode, at worst, your engine.
Needless to say, a retrofit of an engine which was not designed to have a turbo is a lot of work. It will require access to a machine shop and a lot of custom fabrication (of brackets, adaptor plates, gaskets, exhaust pipes/entire system, etc...). You will also need to make intake pipes, and find a way to package all of that neatly into your engine bay. A thorough knowledge of cars is key- you MUST know what you are doing or else you will bust your engine. The easiest part of the project, quite possibly, would be taking out the engine from the car.
Introduction- What Superchargers are, their Types and how they Work
The one BIG difference between a turbocharger and a supercharger is that a supercharger is powered ("driven") by a belt instead of exhaust gasses. A belt is run from the crank pulley to the supercharger (also called a "blower"), and the belt spins a fan inside. That fan compresses the air and shoots it out to the intake manifold. Its main advantage is that, unlike a turbo, there is NO spool up time, boost is ready immediately. This makes superchargers very popular with dragsters who haven't got the time to wait for a turbo.
There are three types of superchargers, but only two that matter: roots and centrifugal.
Roots: Pushes out an almost constant volume of air for every RPM
(don't ask me how that works). Main advantage is that you get full boost early, aka more power right off the line.
Centrifugal: Pushes out a volume of air proportional to RPM
of engine. Most common blower out there.
The supercharger has a disadvantage to the turbocharger- it is less fuel efficient. Since it is belt driven, it takes away power in order for you to make more. This is where the concept of "parasitic drag" comes in. In short, you use more fuel, but you get more power off the line.
Design and Installation of a Supercharger onto an Engine
The supercharger also beats out turbos in another aspect: ease of installation. Since you do not have to monkey with your exhaust, this makes the installation a lot easier. Though you may still have to remove your engine from your car, you are not required to do nearly as much machining as you would have for a turbo.
First off, you will need to find a place for your blower to be mounted. Remember, since it is belt driven the pulley MUST be DIRECTLY ABOVE your crank pulley. Any deviance and you've got yourself a bent belt, which can and will jump right off. You'll also have to find the right sized pulley wheel for your supercharger, especially if you're using a centrifugal blower. Blowers have different max rotational speeds, so I cannot tell you what final pulley ratio you should get. Your pulley ratio can be found by this formula-
diameter of crank pulley
------------------------------- = Pulley ratio
diameter of SC pulley
The reason it is written as such is basic geometry, I'll spare you the math. Take your max engine RPM
(should be around 6000) and multiply that by your pulley ratio. This number will be the max RPM
of your blower. It is better to underdrive than to overdrive- throwing a fan blade is NOT COOL.
After you find a place to securely mount your supercharger, everything else should be relatively easy. After all, it is just connecting the blower with your intake pipes, and you will be set. The install is much, much easier than a turbo install.
Pros/Cons of Turbochargers and Superchargers
* Increased power (30-40%)
* Increased fuel efficiency
* No parasitic drag
* Parts are cheaper
* Installation is extremely difficult
* Require wastegate/boost control solenoid
* Require redoing of exhaust system and overall widening of exhaust pipes
* Some require redoing of cooling system so they can be cooled (it's on the exhaust manifold for crying out loud!)
* Some require oil pumps to stay lubricated (they only spin at 150,000 RPM
* Require time to spool up before boost is delivered
* Increased power (20-35%)
* No spool up time: power right off the line
* Installation easy when compared to turbo install
* Parasitic drag decreases efficiency
* Parts are very expensive
* Rather bulky, adding weight and clutter to engine bay
Issues with Forced Induction
There are many questions to ask yourself before you go about adding forced induction to your car. Here are some of the most important that will let you decide if you are up to the task-
Do I have a spare car I can use for a month? For a year?
Do I have money required to do a project like this? (Turbo will be around $1,000, Supercharger around $2,500. Both easily more.)
Do I have the patience to do a project like this?
Will it be easier and/or cheaper to buy a better car?
Is there a kit available for my car?
Will I be safe with the new car?
Do I have access to specialty tools such as an engine hoist or a pulley puller?
Can I weld? Can I machine? Do I know somebody who does?
Do I know somebody who can help me with this project?
Can my car handle the extra power produced?
The last question is a very important one. Sometimes you may have the skill do do something, but your car does not have the capabilities. If your transmission will explode if you add 10 HP, then what good is the extra 50 that you're going to add? Naturally aspirated engines were designed to make as much power as they make stock, with some exceptions. Some internals will not handle the stress of more power- you may throw a rod! Be very careful and wary of doing something as drastic as this to an engine. If you are unsure that your car can handle it, BUY NEW INTERNALS! Just about everybody sells forged internal components these days. Buy those and rebuild your engine, and maybe it'll handle more power, but only to a certain point where the whole block will explode. Also, engines are VERY precise nowadays. Flat surfaces are important to the engines of today. There are very tight tolerances. When doing something this drastic to your engine, "good enough" is not "good enough." Only the best workmanship will have your engine run. If you feel as if you are not up to the job, or feel like cutting corners, DON'T DO IT. Only the best, most precise work will give you a decent engine. Half-a**ed work will wreck it.
Don't let this scare you, however. Anybody can learn about cars and their mechanics easily. There is a wealth of information in your local library. Read up as much as you can, it is how I got my start. Then slowly work your way around your car, getting to know pieces and doing your own repairs. Only when you feel comfortable around your car will you be able to do a big project like this and do it well.
If you do go ahead and decide to do something crazy to your car, you'll need to deal with the aftermath. You just made a very big change to your engine: it will behave very differently. You will most likely need to get a performance chip or an EEC
tuner. My suggestion, however, is a bit more drastic, but a bit more fun. Instead of somebody else doing the tuning for you, tune your engine yourself. There is a marvelous product out there made by Electromotive <www.emi.cc> called the TEC3 (Total Engine Control 3) which replaces your ECU
(for any car). It is a bit on the pricey side, about $2.5-3k for a setup, but it gives you complete control over your engine- over your timing, air/fuel mixture, and a lot more. You install the TEC3 sensors onto your engine, and are able to monitor all of its functions REALTIME. You can see the manifold absolute pressure, check the exhaust gas temperatures and check the coolant temperatures, amongst a plethora of other things. The TEC will plug into any serial port and you will be able to monitor and change things realtime as you drive. It even comes with a tuning guide! Some of the other cool things you can do include switching your electric coolant fans on and off.
Aside from retuning the engine, you also have to remember to use premium gasoline. You have to use this to prevent premature ignition and knock, both big problems in and of themselves, and doubly so with a force-inducted engine.
Forced induction is a great way to add 50~100 HP to your engine. The not so great thing is that the install, especially a custom retrofit, will cost a lot of money, take a lot of time and effort, require you to retune your engine, and your emissions will begin to suck (don't plan on passing any smog tests with a new, powerful car. Sometimes it gets really bad). Custom fabricating will be key in every step of the way. If you do go for it, Supercharging is the easiest, but most expensive.
Don't let anybody get your hopes down. If you are motivated enough, you can do anything. You can supercharge or turbocharge any car you want. I hope that if you want to go down that path, this was a good beginning. You'll need to do a lot more research, but at least you'll know where to look. Good luck and Godspeed.