How to Build a 400HP Honda Civic on a Budget

Honda Civic is one of the most highly sought-after tuner cars on the market and that comes as no surprise considering the ridiculous amount of power you can squeeze from a little four-cylinder engine.

This article covers absolutely everything you need to know to build a 400HP Honda Civic without having to remortgage the house.

Install a Turbo on Your Civic To Boost Performance by 50%

If you want to make a Honda fast, installing a turbo is by far the easiest, cheapest, and quickest way to achieve that kind of power from a Civic.

And if you are wondering if can you put a turbo in your Civic, then the answer is yes, you 100% can put a turbo in your Civic with a lot less work needed than you may think.

After installing a turbo you can expect an increase in horsepower of up to 50% so long as you use the correct setup and get the ECU remapped by a reputable dealer who knows what they’re doing.

turbocharged b series honda

The reason a turbo increases HP so effectively is because of the velocity of air the turbo forces into the cylinders of the engine. The main ingredient in every combustion engine both petrol and diesel is air+fuel=power.

A turbo is bolted directly to your engine via the exhaust manifold. Once installed, the exhaust gasses which would usually exit your exhaust into the atmosphere will now be recycled through your turbocharger and back into your engine resulting in massive power gains.

A turbocharger can be split into two sides, the “hot side” and the “cold side” with the hot being the exhaust housing and the cold being the compressor housing.

The exhaust gasses pass through the exhaust side of the turbocharger which then spins a turbine inside the exhaust housing of the turbo, which in turn spins a turbine inside the compressor side of the turbo, which sucks cold air in from the atmosphere, compresses it inside the compressor housing and then forces that air into your engine at an extremely high velocity.

For a complete breakdown of a how exactly a turbo works and the different types of turbo to choose from you should check out this article to give you a solid understanding of how a turbocharger works.

When it comes to choosing which turbo to choose there is two options:

  • Buy a turbocharger specific to your needs and separately source the rest of the small bits and pieces needed to complete the build such as intercooler, piping, fuel system, ECU, etc. The benefit to this is that you have complete control over which parts you install on the car allowing you to tweak performance more so than if you bought a turbo kit, plus there is a far greater selection of individual turbos to choose from than turbo kits.

The downside to this method is that you need to be sure you are buying the correct parts that are compatible with each other. When it comes to choosing the correct turbocharger there are a lot of things to consider such as A/R, Trim sizes, etc.. and if your new to turbos it can become overwhelming, plus when you buy every individual piece it becomes expensive real quick.

  • Buy a complete turbo kit, this will save you mountains of time and money. Most good quality turbo kits will include everything you need to complete the build from start to finish including a fuel system, engine management system, intercooler, piping, etc.

The most important thing to remember when choosing a turbo kit is to buy the best quality, Iv seen too many cars blowing up because of cheap, poor quality turbos that disintegrate under stress.

The problem with buying a turbo kit for a Honda is that they are becoming harder and harder to find, that’s why I put together this article which lists 8 of the best turbo kits for a Honda to RELIABLY boost power, you should check it out, I think you will be surprised by the quality of turbo kits I found.

Upgrade Your Fuel System to Keep Your Engine Fed with Fuel

Upgrading your fuel system is an essential part of building a 400HP Civic, especially if you install a turbocharger, because as I previously mentioned air+fuel=power. So when you increase one you must increase the other or there will be an imbalance in the air/fuel ratio resulting in your engine running too lean or too rich.

When you install a turbocharger you also need to replace your fuel system to allow for more fuel to be delivered to the engine to compensate for the increase in air. If you decide to buy a turbo kit the fuel system is usually included in the high end kits.

Fuel Pump

The first component to replace would be the fuel pump. This pump is located inside the fuel tank and can be replaced by removing the rear seat and gaining access to the fuel tank there.

Upgrading to an aftermarket fuel pump will greatly increase fuel pressure and flow rate, meaning your engine will have all the fuel it could need and won’t experience fuel cutting or hesitation under heavy acceleration.

A stock Honda fuel pump has a flow rate of 65-70 LPH (liters per hour) which is more than capable for a stock engine, but when comparing this to the flow rate of an aftermarket Walbro fuel pump (Amazon link) which has a rate of 255LPH its obvious that the Walbro pump would far out work the stock pump and supply the engine with far more fuel.

walbro fuel pump

Even though the pump is rated at 255 LPH that doesn’t mean you will be using more fuel, your engine will only use what the ECU tells it to use, that is why adding loads of performance parts is pointless unless you are planning on getting the the ECU remapped.

This is because the stock ECU is only ever so slightly variable, meaning it can compensate and make minor changes to the fuel system and ignition timing if it detects changes in air flow, temperature, load etc.. but to get the full benefit from any performance parts you install you will need to get the ECU chipped and remapped or buy a mappable standalone ECU and go from there.


The next thing to do is to replace your stock fuel injectors with aftermarket injectors. A fuel injector is an electronically operated solenoid that opens and closes at an incredibly high speed, when open a very fine mist of fuel is released into the cylinder.

There are four injectors in total, one per cylinder, and all four are synchronized to open and close at the exact perfect timing to each other, if this timing is out by even 0.01 of a milli second it will wreak havoc with your engine, and drivability.

When your choosing which injectors to use there is a huge range to choose from and selecting the correct size is crucial. Injectors work off what’s called a duty cycle which is the percentage of time the injector will be “open” or “on”.

You want the injector to be working at 80% maximum, it’s important to not go over 80% duty cycle. Anything above 80% will result in the injector basically being open all the time resulting in gasoline just being dumped into the cylinder and flooding the engine, causing a misfire.

Injectors are rated in cc (flow rate) and come in a range of sizes, a stock Honda injector is 240cc however this is far too small to keep up with the demand a turbo would put on the fuel system. The most common injector to use with a turbo set-up is a 550cc injector.

grams 550cc injectors
Grams 550cc Injectors

This will give you a slightly bigger cc than you need, but don’t worry going oversized will not have any negative effect, its only, when you go too small is when you exceed the duty cycle due to the injector not being able to keep up with the fuel that’s needed.

If you want to be 100% sure you can use this handy, easy-to-use fuel injector calculator which will tell you exactly what size injectors you need to use, all you have to do is put in your specific car, its specs and the tool tells you everything you need to know.

Check out these 370cc injectors on Amazon

Fuel Pressure Regulator and Rail

The fuel pressure regulator is attached to the end of the fuel rail and is an important element of the fuel system because its responsible for maintaining a constant stable fuel pressure in the fuel rail at all times.

99% of petrol cars built in the 90s were designed to have a fuel pressure of 3bar or 43.5 PSI in the fuel rail. When you install a turbo it creates positive pressure in the intake manifold causing more resistance on the fuel pressure, meaning you need to increase the fuel pressure to overcome this higher resistance.

If you don’t maintain the correct fuel pressure your engine will run lean, meaning it won’t receive enough fuel and will leave air unburned in the cylinder which may cause a knock in your engine resulting in engine failure if it’s severe enough.

That’s where a fuel pressure regulator comes in, with an upgraded adjustable regulator you are in full control of your fuel pressure so you never have to worry about your car running lean and causing a knock at full boost.

That’s another reason why it’s so important to get your ECU mapped after tuning your fuel system, by getting the car mapped and properly set up on a dyno you find out the exact sweet spot for your fuel pressure and any other little tweaks that may need to be done to get the full potential from your motor.

Replace the Intake Manifold and Throttle Body to Double Air Flow

The basic principle of an engine is to take air in and push gas out, and the faster you can do both of these things the faster your car will be. That’s why replacing your intake manifold and throttle plays an important role in producing big power gains due to the high volume of air the bigger intake manifold will allow into your engine.

The intake manifold is bolted to the cylinder head and it’s responsible for delivering cold air into the cylinders of the engine so it goes without saying that the bigger the manifold, the more air it can hold.

The way this works is that the air enters the engine through your intercooler piping coming from your turbo, and then as you press the accelerator the throttle flap inside the throttle body opens which allows the air to then pass through the throttle body and into the intake manifold and lastly into the cylinders.

This is also the same if your car is NA (naturally aspirated) or non-turbo, the only difference is that the air enters through the air filter rather than the turbo.

skunk2 ultra series intake manifold

Increasing the size of your intake manifold and throttle body will give you an increase in power of up to 10 BHP which doesn’t sound like much but it all adds up in the end.

A stock B series Honda engine comes with a 63mm throttle body, I replaced mine with a 70mm Skunk 2 throttle body (amazon link) and it made a noticeable difference even before I got the car remapped.

I coupled that with a Skunk 2 Ultra Series intake manifold with a 74mm throttle body opening just in case I ever need to go bigger than the 70mm I installed, this manifold is also designed with long high-velocity runners which force the air in a concentrated flow into the cylinders rather than some oversized manifolds that let the air dissipate rather than directing it.

Install a Catback Exhaust System to Clear Out Your Engine Faster

Installing a bigger diameter Catback exhaust is just as important as installing a bigger intake manifold because the more air the engine takes in means the more gasses it will let out and if you don’t have a sufficient size exhaust system fitted your engine will get choked up and bog down due to the exhaust gasses being severely restricted by the catalytic converter and the stock exhaust system.

The correct size exhaust depends on a few factors but the diameter exhaust I most commonly use for turbo conversions is a 2.5-2.75 inch pipe with a D-cat pipe to match. Anything bigger than 2.75″ isn’t necessary unless you are planning on going over the 400 HP.

The main thing is that your engine can expel those exhaust gasses as quickly as possible and not get choked up.

Get Your ECU Remapped to Unlock Your Motors Full Potential

Like iv said before, you can install all the performance parts you want, but unless you get your ECU professionally remapped you will never get the full benefit from those parts or your engine.

A MAP is a data table that is programmed into your car’s ECU (Electronic Control Unit) by the manufacturer.

The problem is that the ECU is programmed to keep your engine safe and reliable while improving the overall lifespan and longevity of the engine.

But when it comes to tuning your engine the ECU doesn’t have enough variability to make the changes needed to facilitate the likes of an upgraded fuel system or turbo installation, meaning that even though your engine may be getting far more air, etc.. the engine doesn’t know what to do with it because the ECU doesn’t send the signal to use more air or fuel.

That’s where getting your ECU remapped comes in. There is a couple of options when it comes to programming your Honda ECU, you can either buy a programmable chip such as Neptune or Chrome and get it installed into your stock ECU and get it mapped that way or you can buy a standalone engine management system.

The preferred choice would be the standalone engine management system purely because it gives you absolute control over every input and output on the ECU plus you can add outputs such as launch control, shift lights, etc.. the only downside to this system is that an AEM standalone ECU will set you back at least $1400 but it really is worth every cent, especially with a turbo set up.

ecu remapping

Now once you have your ECU sorted you need to find a reputable shop that does remapping services and that has a dyno (rolling road). This is super important because for one if they have a dyno it means they are serious about their trade, and two, a dyno is the only way to tune a car correctly, road or track tuning will never give you the accuracy a dyno will.

That being said, road and track tuning are perfectly fine and probably the best way for some applications such as track or rally cars, because you might need to simulate the actual driving conditions but for a road car, a dyno is by far the better option.

There are a lot of auto shops out there claiming to be capable of doing a remap but really all they are doing is installing a generic base map that they use for every car of that model. A map needs to be specific to the car’s needs and ability, so be sure to shop around and find a shop you can trust.


If you follow along with this set up you will be pushing 400 HP safely and reliably without any problems and will cost you less than $6000 including getting your ECU mapped, but if you do decide to build a 400 HP rocket you need to check out this article on how to make your car more stable at high speed, because if you have 400 HP on tap you will need it.


With over twenty years worth of experience in the motorsport industry and many happy customers you can rest assured that the information you get here on is 100% free, reliable and without the fluff.

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