Intro to Turbocharging

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Forced Induction: Turbocharging​

The purpose of this thread is to give a basic walk through of turbocharging a Honda. It is neither a guide, nor an exact build list. It was designed merely to get new people pointed in the right direction of making some power.
First, we'll start off with some basic knowledge. These are things you should know and understand (in my opinion) before attempting to turbo your car.

  1. Understand what a turbocharger is, and how it works. (How do turbochargers work? | Who invented turbochargers?)
  2. Understand the difference between CFM and PSI, and also know that neither designates a power level (HP). CFM vs PSI Q's and T3 Or T3/t04e, Which Pushes More Cfm's @ 20 Psi
  3. Once you have a basic understanding, learn how to read compressor maps. (Compressor Map Reading)
  4. Now you're ready to choose a power goal. Choose this level in HP (example: I want 450whp out of my B18c1.)
  5. Using your knowledge of compressor maps and your personal preferences, you can choose a turbo that is just right for your application. You will be able to almost pinpoint where it will make the power, and a ballpark number of how much you will be capable of making.

Basic Parts List​

(notice, I said basic, not complete):
  • Manifold flanged for your turbo/wastegate setup
  • Turbocharger
  • Oil and/or Coolant lines for the turbocharger
  • Wastegate
  • Intercooler
  • Intercooler piping (as well as couplers and clamps)
  • Blow-off Valve
  • Boost, oil pressure, EGT (Exhaust Temp), wideband o2 sensor and gauge
  • Upgraded fuel system (fuel pump, injectors, depending on your power goal)
  • Exhaust (typically you will want a larger than stock diameter to allow your car to breathe properly)
  • Filter for the end of your turbo
  • Vacuum line for gauges and compressor signal for the wastegate, blowoff valve, and other misc pieces (boost controllers, etc)
  • Last and most importantly: a means of tuning the vehicle for the new setu


When you add a turbocharger, you are forcing more air into the engine. To compensate for this added amount of air, you need to add more fuel. There are several methods for tuning. One way is to use a free program, such as CROME (< C R O M E >). This is one of the most common programs used and it is recognized by many tuners. Hondata is another option. Though quite expensive, this program is more in depth than CROME.

Keep in mind that in order to use CROME, Xenocron, ECtune, etc. you'll need an OBD1 ECU that is chipped/socketed.

If you are a driven soul and fancy learning how to use CROME, or another free program, more power to you. I will say that your first build is NOT a good place to be testing out your skills with tuning. Your car is in better hands with a tried and true tuner who has had decent experience with CROME, Hondata, Neptune, Turboedit, or whatever program you decide to use. This is the most important aspect of your build. Ask around your area and find the most reputable tuner, or even look out of your area if none are readily available.


Stock Honda injectors are fairly weak (averaging about 240cc's overall). Stock injectors are typically suitable for builds under 180whp. Even then, upgrades may be necessary depending on the setup and tuning. Upgraded injectors are needed for higher horsepower applications.

For this, you can turn to DSM (Mitsubishi, Eagle) injectors as a cheap solution. A set of 440cc injectors can be had for anywhere from $25-$150 used.

If your build demands a larger injector than 450cc's, you will most likely find yourself turning to an aftermarket manufacturer. RC, Precision, etc all make injectors ranging from 310cc's all the way up to 1600+cc's. Keep in mind that larger injectors are usually more difficult to tune with.

There are two types of injectors: Saturated, and Peak & Hold.

Peak & Hold will require the use of a resistor box in your vehicle. Some Hondas already come with a resistor box in the factory wiring (typically OBD1 cars, IIRC), so if you have one of those you're in luck.

Saturated injectors do NOT require the use of a resistor box.

Most aftermarket injectors larger than 450cc's are typically going to be peak and hold. There are some injectors on the market (for example, Injector Dynamics) that are larger sized and do not require the use of a resistor box.
Editors Note: There are larger saturated style injectors in 2020, as high as 860cc is common.

Read more about Injectors in our Honda Injector Guide

Now that you have an injector to support your power goal, next part to consider is the fuel pump. OEM Honda fuel pumps will most likely not support your power goal (anything over 200whp, and its a good idea to change the pump). For this, most turn to Walbro for a cheap solution. $100 gets you a brand new 255lph pump and installation kit. There are other solutions, but again, Walbro seems to be the most common.


Lets talk about the engine itself. Your first concern should be reliability. Any time you tamper with the stock internals, you obviously will be tampering with the reliability as well. How much that reliability is affected is in the hands of the builder. Your engine should be properly built for the power goal you have selected. If you are looking to make over 400whp, you should be heavily considering going with an aftermarket set of sleeves. Stock sleeves are a risk above that level in my eyes.

Reliability will be a direct product of the parts in your build, and just how much time and effort you have spent to make everything absolutely perfect. If you lack experience in this field, its a great idea to find a machine shop and have them do the work.

Another aspect of the build that is most commonly overlooked is drivetrain and suspension. The more power you put to the pavement, the faster you're gonna go. The components that should be looked at here are:
  • Differential
  • Axles
  • Engine mounts
  • Struts/Springs
  • Traction bars

I focused most of my effort in this department of my build. I added solid mounts, an LSD, upgraded axles, suspension, and a traction bar to ensure that I was getting my power to the pavement. A decent set of tires, mounts, suspension and axles will usually suffice for builds under 300whp. Over 300whp, you should be considering an LSD (Limited Slip Differential), and traction bars.

A good set of suspension is also key to getting decent traction. Even if you have a set of cheap coilovers, a stiff suspension will help you to handle your car safely at higher speeds.

Now you have a vehicle that is well built, makes a power level that you want WHEN you want it, puts it to the pavement, and is tuned well. This is just a basic overview obviously. Things will vary somewhat depending on your specific situation.

Other bits of info:​

Static Compression VS. Effective Compression​

I read a lot of questions on this topic. The static compression of your engine is basically when your car is bone stock, no add ons. Each time you add boost/pressure to the equation, you increase what is called the effective compression.
Example: Bone stock B18b1 sitting at 9.0:1 compression. We add boost to the equation, say 10psi, and the effective compression ratio will be in the neighborhood of 12.0:1-15.0:1. So we see the importance of building your engine for your power goal. Set the static compression too high, and you won't have room for too much more. The good thing about a higher static compression ratio is that it will take less additives to make the same power level as a lower static compression engine.
For further detail on this, we can look to a thread found right here on Hondaswap. (Static vs. Effective Compression)

Air-Fuel Ratios in more detail​

You'll here this more often than you want to, but tuning is absolutely key in this process. You MUST compensate for the turbocharger with more fuel. My recommendation to you is to start by learning what an air-fuel ratio means exactly, and why it is so important.

Most will tell you that an air-fuel ratio is simply the mass of air present in the combustion chamber in relation to the mass of fuel present in the combustion chamber. Well, just about anyone could have figured that one out. Say you have a wideband gauge (AEM, Innovate, etc. all make them) and you want to know "How does this help me? What do these numbers mean?" On a wideband gauge, you can think of it this way. ___times the mass of air to fuel. Fill the blank in with the number shown on your gauge. For example, say your car is showing a 12.0. That would be 12.0 times the mass of air to fuel.

Now, how is this useful? The whole reason you put this turbo on your car is to make more power. Using the air/fuel ratios accompanied by the other gauges in your setup, the tuner will now be able to tune your car properly (provided he/she knows what they are doing.) The "ideal" mixture is 14.7, but many tuners will have different variants of this number. 14.7 is commonly heard of and referred to as "stoich". Anything wildly below that number is considered "rich", and anything wildly above it is considered "lean".

Most tuners will run your car slightly richer than where you would like them to. This is simply because rich is safer than running the car lean. Running a car too lean creates heat, which we all know is the enemy of any internal combustion engine.

The difference between narrowband and wideband o2 sensors and gauges is this: Narrowband reads only 14.7 and a small range above and below it. Whereas a wideband gauge and o2 sensor will read ratios from ~10.1-~17.0 depending on the brand.


To those out there who are considering a turbo build for the first time:

1. Set your goals LOW. Many people underestimate even a 250whp Honda. Consider not only power, but also the power-to-weight ratio when doing one of these builds. It does NOT take much to get a 2500lb car moving quickly.

2. Make sure you have the suspension and brake setup to handle the power you are going to have. Stock suspension and brakes will work, but are not ideal for a car with 250-300whp. This is very commonly overlooked in builds and can get you into some trouble if you plan on autocrossing the car or doing anything but running down the strip.

3. Take your time. I've watched several builds come apart because people rushed building the bottom end, or didn't take the time to tighten the clutch bolts properly.

4. Keep as close to OEM as possible in your bottom ends. Honda engines are known for reliability and longevity for a reason. Its because they are put together well from the factory. If you can keep the bottom end stock and make your power goal, do it. Don't build if you don't have to.

5. GET YOUR SETUP TUNED. I don't mean with a FPR, or other hoaxy means of tuning. Get CROME, Hondata, Uberdata, Neptune, whatever. Something that changes the map inside the ECU. Have it tuned for your setup, even if it is just on the streets. Hit the dyno if you must know the power you're making.

FAQ's of Forced Induction​

In this section I'll cover some of the questions most commonly answered in the Forced Induction section.
1. Can I boost this engine?
The answer is yes. You can turbocharge any Honda engine. The difficulty of the job is going to vary based upon the engine, and the parts used. Higher compression engines typically take more attention to detail. A higher static compression means an even higher effective compression when in boost, which means that one small mistake could lead to catastrophic failure.

2. Is low compression required for Forced Induction?
No. As stated above, compression does not matter. Most will say that it is better to have lower static compression for ease of tuning. Lower compression also helps eliminate the worry of high cylinder pressures. Higher compression engines will make more power on the same amount of boost/nitrous/etc. than a lower compression engine.

3. Should I upgrade my cams and valvetrain?
Depends on the build. VTEC applications see a decent cam profile at start. If you are DOHC or SOHC non-VTEC you may want to look into a different cam, or maybe even a head swap.

4. Do I need an oil catch can?
Yes, if you want to do things properly. An oil catch can will relieve the positive crankcase pressure created by forced induction by ventilating it to the atmosphere. Another bonus is that you don't spill oil all over the track, causing a nightmare for someone else.

5. Should I sleeve my engine?
If you have to ask this question, you probably should. OEM sleeves do not have a set limit, but most will not last long at 400whp+. This is very dependent on tuning, obviously, but 300-350whp is generally a good area to stay in on stock sleeves for decent longevity and reliability.

6. How big of an exhaust do I need?
Generally, for a street turbo setup, 2.5" will be plenty. If you are looking to go 350whp+, 3" should be suitable. Most race applications will feature a straight 3" or 4" downpipe that exits out the side of the front bumper or behind the front wheels.
Exhaust size is going to vary slightly dependent upon your turbo setup, goals, and desires out of the setup. For quicker spooling, smaller is generally better. This applies more backpressure on the turbo to increase spool time, but will also restrict the engine's breathing more than a larger diameter exhaust.

Any comments/criticisms are welcomed. Feel free to post them here or PM me. Linkbacks are welcome as well.

Continue the conversation here: Comments on Intro to Turbocharging Article


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