The basics of Turbocharging a 4.0 Mustang

Type: Info Guide

The following guide was written as a Informational/FAQ for the members and guests of the 4.0 Collective interested in Turbocharging their 4.0 or just want to know a bit about what goes in to such a project.

This write-up deals with power options but is targeted at Stock Block applications. If you want more than 400 HP, it is highly recommended you start out with a built motor. Everything outlined here can get you the rest of the way, but you will need to look closer at correctly sizing the turbocharger if you are putting it on an engine with modified heads, CAMs or Compression Ratio due to forged pistons.

Basic Parts: these are the absolute essentials required to turbocharge a car.

Hot side:

Turbocharger
Hot side piping
External Wastegate (you can use an internal but it is more costly and takes up more room)
Copper Spark Plugs

Cold Side:

Cold side piping – Aluminum
Bypass or Blow Off valve: determined by Blow-Through or Draw-Through MAF configuration.
39# Injectors (sub 400 HP)
Tuner
¼ inch vacuum line
5/8ths inch thick wall hose for valve cover breather relocation

Optional: Parts that will compliment the system, improve its efficiency and scalability

Hot Side

Boost controller
Wideband O2 sensor and gauge
Oil catch can set-up for PCV side of evacuation system

Cold Side

Intercooler
Boost gauge

Parts Brake down and Facts

The Turbocharger: The brain of the beast… yes I said brain. Turbo are full of air, just be sure it’s not all hot.

The .50 AR T3/TO4E Hybrid turbo bored out for a .57 trim compressor wheel is one of the best sized for the 4.0 Mustang if engine build-up is not in the cards and boost will remain below 12-15 PSI. If you are planning on running a built motor, then go with a T3/T4 .57 AR compressor housing or 60-Series turbo. A larger compressor wheel take more exhaust energy to spin up, meaning boost will come on higher in the RPM range, so if you go too big up front you’ll have lag. Same thing will happen if you go too large on the turbine side, as more exhaust energy will be expended spinning up the turbine, regardless of how well sized the compressor is. The draw back to the 50/57 is heat production at high boost. If you were to run more than 15 PSI, this turbo would not work well. It would just heat the air more and slide further outside the efficiency zone on the compressor map… meaning less power per PSI after about 15 PSI and would increase the chances of detonation. An IC can only do so much.

Please research Turbonetics, Garret, Precision Turbo, TurboSmart and other manufacturers. This way you will have an idea what is available and understand a bit better what the jargon means if you need further assistance in finding the right turbo for your application. All the information on turbo sizing and compressor maps are readily available on the web, you just have to dig a little. Happy hunting.

External Wastegate: The heart of the beast. So you want to know more?

The Wastegate is the most vital part of a turbocharged car. It’s the regulator of boost via exhaust gas bypass. It is where failures in turbocharged systems can potentially lead to the death of an engine. If the wastegate were to fail; be it minor spikes due to flow limitation, defect or a catastrophic failure causing unlimited boost, if you don't catch it in time, Boom. It could lean out the fuel system or push cylinder pressure past the point of head gasket integrity.

So now that that is clear, there is no getting around the need for premium quality when it comes to the gate. Get a $150.00 China turbo, use and after market cat in a before turbo configuration, or buy that $50 blow off valve, but JUST DON’T cheap out on the gate!

Note on internal gates: External gates are more accurate and cheaper than internal gates. They also allow for much higher boost because the vent port is not restricted by the size of the turbine housing. Internal gates also need a swing arm flapper configuration, which means a potential exhaust leak at the flapper.

So the wastegate works by limiting the amount of boost you run via a spring and diaphragm that is fed vacuum pressure from the manifold. The spring is rated at a given boost level; e.g. 3.5, 7, 10 PSI. When the valve opens, it allows the exhaust gases from the engine to be diverted directly into the down pipe, bypassing the turbo's turbine. If a 7 PSI spring is used, when the manifold see +7 PSI, so does the wastegate. The pressure on the diaphragm pushes on the spring and opens the valve allowing just enough exhaust to vent to maintain 7 PSI.  If the valve design and exhaust configuration is optimal, you will see your boost gauge hold very steady at the spring rated PSI level with no spiking.

Boost Controller:

Though not in the necessary parts section, I put the entry for the boost controller here because of its importance in relation to the Wastegate. It’s plugged into it and can just as well add an element of failure as it does control. This is another part that cannot be cheeped out on.

The function of the boost controller is to trick the wastegate into seeing less manifold pressure than is really present. There are a few different types of controllers, but I’m only going to deal with two of the manuals here.

Bleeder valve: This is one I do not recommend. As the name suggests, it bleeds off pressure from the line going to the wastegate. The problem with this is they bleeds it off to atmosphere unless it is routed back in to the wastegates bottom port; usually restricted to very high performance cars pushing 30+ PSI that have an extreme amount of exhaust flow that can sometimes pin the gate open. So if it does not get routed back, this type of valve literally creating a vacuum leak under load. Bleeder valves can also be an ‘open all the time’ configuration, thus the vacuum leak would also be there all the time. Would you create a vacuum leak on purpose? Further more, bleeders can bottle neck, and this backup can cause the wastegate to open before max boost is reached, contributing to turbo lag.

Gated Valve: This is an adjustable pressure restriction valve or "check valve” It regulates boost in the same way as the above valve, but uses a ball and tension spring to block the flow to the wastegate. Once the tension on the spring is overcome and the ball is pushed out of the way, pressure bleeds through the outgoing port to the wastegate and the gate opens once it is allowed to see the max spring rate. The more pressure put on the ball and spring via the tensioner; (this could be a screw, or dial or any number of things), the more boost the gate will allow before it’s able to “see” it’s wastegate spring rated pressure. Because of the quick reaction of the ball and spring configuration, there is no lag between shifts. Only electronic boost controllers are quicker and more accurate and some people even argue that..

Spark Plugs:

Side note: Some people are using plugs that are one or two steps colder from different applications. They lack the unthreaded portion of the plug that extends into the combustion chamber and I fear will not function properly under any condition for long periods of time. Plug depth is determined by cylinder head design and the use of a shorter or taller plug will move the gap out of the target A/F mixture path. This is bound to have a negative effect on the combustion process, contributing to fouling, incomplete mixture burn and poor performance. If you run a non-standard plug like this just to get 1 or 2 steps colder, do yourself a favor and check them often and change them ever 6K or two oil changes. They are bound to foul like nothing you've seen before. Trial and error on gapping for F/I applications will be necessary in order to find a gap that resists blowout but at the same time achieves as complete a fuel mixture burn as possible.

Our cars use platinum iridium plugs from the factory. These plugs have a wide gap and run hot by design, a cheap way of self-cleaning, in order to resist fouling. This allows Ford to claim longer service life between maintenance. Under boost this can lead to detonation, even if the gap is adjusted. The solution is a 1 step colder plug. Because an exact one step colder replacement does not exist, the next best solution is to change copper, which is inherently colder. Copper plugs have been the choice of F/I applications for years, and as it happens they are available for out cars. Your local auto store can cross reference the ford part number and find you a copper based plug. Some to look at are the Motorcraft AGSF24C, NGK TR5-1 or the TR55-1, that latter having a slightly larger electrode.

Note! The TR6 NGK plug, designed for the 4.6 2 valve engine has been tested on the 4.0 and despite it's shorter reach is now listed on NGK's site as a suitable replacement plug for the 4.0 V6. The great thing about this is it is a true 1 step colder plug than stock.

Hot Side Piping:

The hot side of the exhaust can be fabricated in stainless steel or mild (alimunized) steel and hot coated or for the budget conscious painted with B.B.Q grill paint which can take 600° F continuously. The configurations and pipe layout can be anything borne of your imagination, so I’m not going to go in to specifics on layout, just be sure to rout them away from plastics, wires and fluid lines and make sure they do not come in contact with anything, metal or otherwise.

Cold side piping:

Any aluminum intake piping will do fine so long as it’s not too thin of a wall. Welding aluminum is an art and a TIG is vital unless you can route your piping in such a way that there are few connection points and silicone couplers will do the trick. This is hardly possible with the 4.0 unless you use pipe layout to determine turbo location.

Bypass or Blow Off: That is the question.

First, the point of the bypass or blow off is to prevent intake air that is being forced into the engine from bouncing back off the throttle plate on lift and rushing back into the turbo - the wrong way. This causes compressor surge. It has two ill effects; it slows down the compressor, creating lag during spirited or WOT shifts and the sudden slow down and speed up of the compressor wheel can damage the turbo over time.

There are two ways to run the Mass Air system on cars equipped with Forced Induction. The first and more common is the draw through system. This places the MAF sensor  in the piping before the turbo charger and the IAT sensor after the turbo and IC. In this configuration, the pressure release at throttle lift needs to be provided by recirculation of the intake air to before the turbo inlet, but after the MAF. Most blow off valves can be used in a recirculation setup. Most bypass or recirculation specific valves are open under vacuum, thus open at idle, and cannot be used in a Blow Off configuration.

Fuel System: 39# Injectors.

Surprisingly, the only thing that needs to be added to the stock 4.0 fuel system to achieve over 300 horse power are larger injectors. The stock fuel pump seems up to the task of supporting in excess of 360. If you are planning on going beyond the 350 HP mark, however, I would recommend a Kenny Bell Boost-A-Pump or some other alternative that will ensure reliable fuel delivery under the extreme conditions the car will be subjected to.

On line injector sizing calculators show that 350 RWHP is the top end of the 39# injector on a 6 cylinder application. This is very conservative, as some cars have hit over 360 with them, but I would not recommend taking chances like this. Specially if the 4.0 is your only car. If you are going to go well beyond the 350 mark, it would be in your best interest to just get 55# injectors right away. 55# will support over 500 RWHP and that is well beyond what the stock bottom end will likely handle.

Tuning it all in: XCALIBRATOR 2, LIVEWIRE, Diablo Predator

As tuners go, there is not much to say about them that has not already been said. There are a lot of people that are brand loyal and others that don’t care. Just get the tuner you like and find a Dyno Tuner to set up your car after you’ve built your kit, or get the PRO Racer Packages that allow you access to all the tuning parameters in the ECU. There is a learning curve to tuning. It’s a lot of information, but it gives you quite a bit of insight on what’s going on in the ECU and you can improve on your tunes all the time or create entirely new tunes when it’s time to up the boost or change the injectors down the road. It really depends on how ‘hands on’ you want to be.

Vacuum lines:

Buy a roll. It’s cheaper in the long run than getting a few feet from AutoZone.

Looking under the hood of your 4.0, find a vacuum line. Not as easy as it used to be is it. So much more is controlled by electronics today that vacuum lines are almost extinct. There is still need for manifold pressure measurements, it's just most of that is accomplished via electronics. Thanks to the returnless fuel system and a little fuel rail sensor that replaced those big old regulators, we still have a line to tap coming from the manifold. Look for the line coming out of the center of the manifold on the driver’s side. That’s the line you can tap. You can build a vacuum tree right here if you want to get fancy. You will need a minimum of 2 ports and a max of 5 depending on how many things you decided to attach to the system.
 
5/8ths Heater hose or braided steel line:

This line is required due to the elimination of the stock air box and intake hose and subsequent loss of the driver side valve cover vent line that is plumbed into it. You will need to replace this line with heater hose or braided steel. Though the PCV side of this system is actually more critical, it is not actually mandatory and is covered under optional parts.

Optional:

Boost Controller: This was covered right after the Wastegate due to their relationship. If you are going to get a controller, get a good one and use common sense when you dial up the boost.

Wideband O2 Sensor and gauge:

This is optional because it is used more for tuning in your WOT A/F than anything else. Some people that do not tune their own car may still have a wideband gauge as an insurance policy against leaning out under any driving condition. With some options as low as $270 shipped, it’s actually worth the expense.

A Wideband will help you if you are running lean at a given Load/RPM consistently, have an issue a some points in the power band, or some other intermittent failure is causing a lean condition and you are lucky enough to catch it before it results in serious failure or damage.

The reality is pushing the power limits of the stock block drastically shrinks the margin for error. A seriously lean condition under WOT in a post tuning environment (as in not on a Dyno) means it’s likely too late. Wideband gauge or not, you may not even know it’s happened… Ask yourself how often you actually look at your gauges. Then think about going WOT and staring at you WB instead of the road.

PCV Catch Can: Truth is it’s not mandatory to make a Turbo system work – but it will help your engine last longer. It has been shown by many members of the 4.0C that this car likes to eat it's own oil even under N/A conditions.

The passenger side valve cover houses the PCV valve. It’s a simple check valve with a lead weight in it that is supposed to allow the passage of gases when enough pressure is present to push the weight out of the way. It’s not a check valve and in fact I wouldn’t call it a valve at all. I don’t even think I would give it a name beyond POS.

NOTE: A cheap work around for some has been to cap the intake and run the PCV hose to the ground. This system is closed loop, meaning it’s part of the entire metered air system and venting to atmosphere is like having a vacuum leak. This can mess with the accuracy of the air/fuel mixture and is NOT a good idea.

Even in stock form, the PCV system on the 4.0 lets oil get sucked through this hose and into the upper intake. This has a net result of reducing your fuels rated octane level. e.g. you put in 91, but once it reaches combustion it’s more like 89-90, perhaps even worse.

In a F/I application this issue is multiplied many times. What is a few drops under high load NA, ends up a 5 pointer under F/I. If you have aggressive timing and run more than 10 PSI, you are going to detonate. You may not feel it or hear it, but if it’s there, it’s going to break your pistons.

The catch can is a simple reservoir that traps the oil that is missed by the POS in the valve cover. It is cheap insurance considering what it does and is highly recommended for people running 7 PSI or higher. Please check out the install articles in the write-up section of the 4.0 Collective. A larger can or the oil/water separator used in my article is recommended.

Intercooler:

The intercooler is much like the other optional components talked about here. It is not required to make a turbo work; it just makes it work better. The compression process heats air, and the IC brings it back down closer to pre compressed temps before it enters the engine. This helps reduce the chance of detonation and makes the entire system more efficient. You can run less boost, meaning less stress and still get the same power out of the car.

NOTE: An intercooler is not a power adder. It cools the air, thus increases the density and makes it look like it produces power. In reality, depending on how your boost is regulated you will either see less manifold pressure and get the same power or get more power at the same boost levels. 7 PSIG of hot air look the same as 7 PSIG of cool air, one just has more density and thus more oxygen molecules than the other. It’s that oxygen that makes for the extra power.

Boost gauge:

Both the cheapest and least important component of a F/I system.

This is just a cool pressure gauge that shows you how much pressure is in the manifold above what can be used in the combustion process. It’s what is referred to as BOOST and though it’s not actually a measurement or indication of power, is usually interpreted that way. This is the one component above all others that serves no practical purpose other than to look cool. Some will argue that it’s necessary to make sure boost spikes are not happening or an over boost or open boost situation is not occurring. My thought on that is if you can’t tell there is an issue in the event of a spike or open boost, you are dead from the neck down.  In the case of the latter, we are talking about a 20 to 50%  power increase. 15 PSI in the 4.0 feels like someone hit you in the chest with a sledgehammer. It’s actually more obvious than the night and day difference from N/A to 7 PSI or 7 to 10 PSI because of the torque output. It would put you so far back into the seat you would have to be dead not to notice it. If you leave your foot in it, you blow your engine. It's that simple. 




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