Here I will attempt to address a lot of the most commonly asked questions specifically regarding turbocharged Mustangs.  If you want to learn more about turbocharging in general please check out the Turbocharging Bible and the links page.  I also recommend that you look into some of the most popular turbocharging books
The latest book on turbocharging was just released and the author used some of the people from the forums to help with parts of the book, the book is called Street Turbocharging by Mark Warner.  Order it here. 
"Maximum Boost" by Corky Bell and "Turbochargers" by Hugh McInnis.  You can also pickup any book on thermodynamics to learn more about why turbochargers work.  Please read the turbo bible that is on this site too.

If you have something to add or a correction, please feel free to email me: trelken@gmail.com

What is a boost controller? What is boost spike?
Answer: external wastegate or internal wastegate actuator has a base spring setting. For the sake of description lets say it has a 5 psi spring. That means that when 5 psi boost hits the diaphragm the wastegate opens. The boost controller is installed inline with the hose that leads to the pressure side of the wastegate and the other side of the boost controller is a vent. When the boost controller is in the closed ( You cannot blow through it ) position, all the boost pressure goes to the wastegate and you have a stock boost level. As you open the boost controller, boost pressure that would have gone to the wastegate now diverts through the boost controller. What this does is fool the wastegate. If you bleed off 5 psi on a 5 psi system it will take 10 psi to open the wastegate resulting in a 5 psi boost increase on your boost gauge and a lot more power from the engine. This is the simple version and results vary with the system, the size of the hose being used, the sensitivity of the wastegate spring. Manual boost controllers are also very prone to boost spikes. This occurs when the boost controller is open all the way and small diameter hose is being used. The boost pressure builds faster than the hose can flow which lets the turbo spike up big boost numbers until the pressure fights its way through the small hose to the diaphragm, then the boost drops back down. This is a dangerous situation since the spike can blow up your engine before you know what happened. The best way to minimize spike is to keep the manual boost controller located under the hood with as short a length of hose as is possible. This is easily demonstrated by you picking up a piece of ¼" hose 4 feet long and trying to breath through it. Go ahead, try it. Pretty tough isn't it. Now cut the hose in half and try it. Much easier. Your turbo and wastegate feels the same way.

What is boost creep?

Answer: As greater exhaust output is created from higher levels of engine performance, the stock internal wastegate actuators begin to lose their effectiveness because the amount of exhaust flow to be bypassed is now beyond their intended operating range. As the result of exhaust flow being greater than the valves’ capacity to discharge, more exhaust flow is directed to the turbine and additional boost is created, which is commonly referred to as boost creep.

I want to make blah blah horsepower, which turbo kit should I get? or Which turbo kit is best?
This question will get you lots of ridicule right away because NOBODY can tell you which turbo kit to buy for your car.  This decision has to be made by you.  Each kit has it advantages and disadvantages.  That is why I created the Ultimate Turbo Kit Guide, it contains all the information on every turbo kit out there, even discontinued ones.  The great thing about turbos is that just about any kit on the market will make more than enough horsepower to split a stock Ford 302 block in half.  Just do a little research, determine your car's goals and buy a turbo kit from a reputable company.  Customer service is a huge factor when determining where to buy your turbo kit.

Which gears should I get?
Turbochargers rely on exhaust gasses to drive the unit.  Useable Exhaust gas is created when the vehicle is under a load.  This is the reason many people recommend 3.27's or 3.55's for a turbocharged street car.  These less aggressive gear ratios place a higher load on the car for a longer amount of time per gear.  Of course for a straight drag car you want to pick the set of gears that puts you in your powerband for every gear and so you are passing through the traps at about redline in your final non OD gear.

How fast will my car go with xyz?
This is a pretty stupid question because all cars and combos are different.  But if you want to know how fast your car will go first estimate how much power it will make.  (Just about every turbocharged Ford V8 will make over 380rwhp)  Once you figure out your power estimate plug it into a HP or track calculator like the one you can download here.

What size turbo should I get for 300, 400, 500, 600, 700, 800, horsepower?
It is hard to answer such a vague question.  Proper turbo sizing requires an actual scientific method using several mathematical equations based on the needs of the vehicle and the airflow ability of the powerplant.  But if you want some broad guidelines here goes:
300rwhp- Single T44, most single turbo kits come with the T44 as the base turbo.  Twin- ??
400rwhp- A Single T44 will get you there but a T60 or T64 would be a better choice. Twin- ??
500rwhp- A T64 is operating fairly efficiently at 500rwhp, if you want more power upgrade. Twin- ??
600rwhp- A T72 or T74 will get you there no problem.     Twin- ??
700rwhp- T74 or T76.                                                   Twin- ??
800rwhp- T76 or Garrett GT42.                                     Twin- ??

Where should I get xyz part?
When purchasing parts for your car please look first to our sponsors.  All of the sponsors of our site are reputable companies and it is their sponsorship money who keep the forums alive.  Please check out the sponsors page for more information.

Which boost controller should I get?
Any manual boost controller valve (air compressor valve) will work fairly well at controlling boost.  The $90 Turbo XS manual boost controller probably is a little more reliable and steady.  For electronic boost controllers many people go with a Greddy Profec B.

Which turbo timer should I get?
A turbo timer is a fairly simple device, get whichever one suits your fancy.

What is the difference between a BOV and bypass? How do they work, are they necessary?
A BOV is a Blow off Valve.  These horn shaped device is mounted along the intercooler piping somewhere between the turbo and the throttle body.  It will open up once the throttle blade is closed in order to bleed off all the air in the system between the turbo and the throttle blade.  The blown off air is simply blown into the atmosphere.
A bypass valve looks very similar to a BOV and many BOV's can function as a bypass valve.  The difference being is the air that is blown off from the bypass valve is recirculated via a hose back into the air intake system somewhere between the MAF and the turbo.  A bypass valve and not a BOV is necessary on draw through MAF cars, otherwise you would be blowing off metered air.  A Draw through MAF is where the mass airflow meter is mounted in front of the turbo.
There is no definitive answer if a BOV or bypass is necessary. However many people agree that utilizing a BOV or bypass can extend turbo life and increase spool time between shifts.

How does a wastegate work?
A wastegate is mounted in the exhaust plumbing before the turbocharger.  A wastegate functions as a boost regulator by diverting exhaust gasses around the turbo once the turbo has reached the desired boost level.  They are simply a large valve backed by a spring.  Once the exhaust gas has reached the capacity of the spring the valve starts to open, diverting the exhaust gas around the turbo and back into the exhaust and out the tailpipes.

What exhaust should I buy?
Turbos HATE backpressure.  You want the highest flowing exhaust system you can fit. The main item here is mufflers.  You do not want chambered style mufflers like flowmasters.  You want a "straight through" type muffler like the dynomax super turbo, ultraflo or any other straight through design muffler. Chambered mufflers will cost you at least 20hp minimum.  If you are running a single exhaust 3" is the minimum, for dual exhaust 2.5" will be fine. 
The overall exhaust system is up to you, like I said the larger the better.  If you can fit dual 3" then do it.  The turbomustangs.com project car is running a 3" downpipe which U-s out to a standard 2.5" catback and this basic setup has been good for 700hp.

What is Turbo Lag?? 

Turbo Lag is the time it takes from when you smash the "go" pedal to the time the turbos are making an appreciable amount of boost.  For some reason people have it stuck in their mind that it takes 10 minutes for the turbos to respond.  That is simply not the case.  Most of the single turbo kits are making FULL BOOST before 3000 rpm or less (try that with a centrifugal supercharger).  Sure, if you mate up a T76 to a stock 5.0 then yes, there will be some turbo lag.  But when you get a turbo that is designed to work with your combination then there should be very, very little lag.  Twin turbos have even less lag, the power is there right after you hit the gas basically.  
You can even launch off the line under boost with a 5 speed if you get a two step.  I have made 10 psi at 5000 rpm with my single turbo kit and a simple MSD two step.

What are the main differences between a Single and Twin Turbo setup?

First off, you can make as much or as little horsepower as you want with either a single or a twin.  The main differences between the two are the turbo sizes and the complexity of the entire package.  With a single turbo you only have to deal with one of everything, one turbo, one wastegate, one downpipe, and one set of plumbing.  With a twin turbo of course you have two of everything so that makes it a little more complex.  With a typical street twin setup you use fairly small turbos therefore there is very little turbo lag.  Now that Incon is pretty much out of business there is no place to get a highly engineered twin turbo kit for fox body Mustangs.  However there are a few places that are coming out with cheap do it yourself TT kits based on junkyard designs that people have been using for years.  If you are interested please check them out, so far the feedback for them has been very positive.
Personally, I prefer the single turbo setups because I think they are a little easier to work on because everything on the non-turbo side is just like a stock mustang.  So plug access and everything else is unaffected on that side.  Also it is pretty easy to swap out a single T60 turbo for a T72.  Just loosen a few bolts and bolt on the new turbo and you now have a turbo that can support 850 hp.

I want to make 650+++ horsepower, where do I start?

If you want to build a Mustang with anything over 500 reliable rear wheel horsepower then you are looking at spending some serious cash, basically every major stock component of the car is subject to breakage at this point and will need to be upgraded.  The main areas are drivetrain, fuel, powerplant and power adder.
   First is the drivetrain.  You can't expect a stock T5 designed for 225 horsepower to stand up to 3 times that amount.  Assuming this is a street car the best choice is the Tremec TKO or maybe a T56 if you are a high roller, along with a STAR Spec III or IV clutch or perhaps and McCleod twin disk setup.  These two components can handle that much power, but even the TKO is only rated at 550 ft/lbs of torque, so if it blows up don't blame them.  If it is a drag car most guys use a built up C4 automatic.  You also may want to throw in a lakewood bellhousing, you will need it when you run 10's anyway.  You will also need to upgrade your rear end to a 31 spline or even 33 spline setup.  I use a detroit tru-trac differential with mine, I am very happy with it. You will also need to stiffen the chassis with a cage, subframe connectors and aftermarket rear control arms.  Otherwise, after a few launches with slicks and 700hp your car will look like a pretzel and the doors won't close.  Not to mention that with that much power you should be near the 9's and you need a cage and a bunch of other things to be legal to race.
   Second is the fuel system.  The stock style fuel system is for about 500rwhp.  Above that you are rolling the dice because the factory lines and rails can't keep up with the demands of the engine, no matter how big your fuel pumps are.  At this point you need to upgrade the lines, rails, pumps, and possibly even add a sump to the stock tank.  I am not going to get into the specifics but you should probably use at least -6 and -8 fuel lines and aftermarket fuel rails. The turbomustangs.com project car features a complete X2C motorsports fuel system which was simple to bolt in and utilizes OEM style Bosch pumps which are not terribly noisy.  We have run this system down to empty and never experienced a single problem on the street.
   Next is the powerplant.  The production 302 block can handle about 500 rwhp, any point above that and it can crack at any moment.  Sure there are guys out there making more power using the stock block but they are the exception and they are a ticking time bomb and they know that.  The stock block has been known to crack at even lower levels than 500 so be careful.  So now you must decide on where to go from here.  The first step is the Ford Sportsman 302 block.  Nobody knows for sure if these are worth the money they cost about $1000 shipped and might not be any stronger than a stock block.  Next is the old A4 block which you can only find used now.  They run about $1200-1600 and they can handle 1200+ hp.  Now comes to two major players, the Ford R302 block and the Dart Block.  Each block will take well over 1200 hp and they will both cost you over $2000 after machining.   Now you must throw in some high quality internals.  The eagle 4340 forged H-beams and crank are rated at ~1150hp from Eagle if you opt for the rod bolt upgrade.   Standard Eagle H-beam rods are good for 750.  It is my opinion that if you plan on over 1000hp you need Billett parts.  Billet crank and rods will cost you over $2000 easily and they will handle any amount of horsepower. Next you need some forged pistons designed for a boosted application and a good set of rings.  Try to get about 8.5:1 compression.  Now choose the best flowing heads and intake and get a custom turbo cam.  There are many different heads and intakes out there suitable for this power level.
   Last is the power adder.  As I said above you can make this much hp with either a twin or single turbo it is up to you.  The incon 800hp twin turbo kit can make 650rwhp. A single turbo kit with a T72 or bigger can make the same power.  It is your choice.  There are also large race oriented twin turbo kits that make 1000+ hp (Cartech Dominator) or there are large single turbo kits that utilize 90-106mm turbos that make 900-1500 hp (John Urists).  So it is up to you to make the decision.

What are the main tuning problems when dealing with Turbos?

   The main thing you need to control with a turbo is the timing.  It helps a great deal to have an aftermarket tuning device that will allow you to pull some timing at the point in the power curve where you are making peak torque.  An eec-tuner, tweecer, PMS, Speedbrain, FAST, AEM or a chip will allow you to do this.  This will help ensure that you don't have detonation.  You can pull out timing at the torque peak and then add in timing from there to get some more power.  Other than that the same tuning issues apply to turbos that apply for all power adders:  make sure you have a fuel and ignition system that is up to the task.

Which cam should I run?

    The stock cam will support enough hp to crack the stock block in half and provide superb driveability.  There is really no reason to change cams unless you want to make big time power.

Which heads and intake work best for a turbo??

As long as they have good flow capability then they will work.  There is no magical answer for turbos.  Just choose the best set of heads that you can afford.  There are people running 9's and 10's with every type of head out there.  THERE IS NO MAGIC ANSWER, THERE IS NO SPECIAL SET OF HEADS DESIGNED FOR TURBOS.

Also keep in mind the AFR heads will not fit with the Cartech turbo header without trimming the header flange.

What type of exhaust should I run?

    The main item here is mufflers.  You do not want chambered style mufflers like flowmasters.  You want a flow through type muffler like the dynomax super turbo or any other straight through design muffler.  I have heard that running chambered style mufflers can cost you upwards of 30 hp.  You also want the biggest exhaust you can get.  If you are running a single exhaust 3" is the minimum, for dual exhaust 2.5" will be fine.  But it has been said that too big of an exhaust on a turbo car is just right.  There really is no overkill here.  For more on exhaust systems look down towards the bottom...

Which gauges should I have for my turbocharged Mustang?

   Fuel Pressure, Exhaust Gas Temperature, Boost, and all Mustangs should have an aftermarket coolant temperature gauge because the stocks one SUCKS!  You can use the EGT gauge to help determine if you are running too lean based on the readings.  This can help you prevent a blown head gasket or worse...  The fuel pressure gauge should be mounted where you can view it easily while blasting down the road.  You want to make sure the fuel pressure doesn't start to drop at the higher RPM's, this is indicative of a fuel system that isn't up to par.

If money permits add a wideband O2 to the tuning array.  The EGT is more accurate than an O2 sensor gauge, but the wideband in irreplaceable. The EGT is a little slow to respond but it gives you real time cylinder data on 1 cylinder. The wideband responds in milliseconds and is super accurate. There is one kit on the market that is a few hundred bucks. But, if you are a high roller you can buy a MOTEC wideband or an Autronic both of which will set you back about $2000 they are great kits and are worth the money. The wideband is best tuning tool there is, and if you can afford the gauge then that is the way to go.

7-29-02:  Which header tube should I probe for my EGT gauge? (contributed by Shailesh Patel)

   Go with the shorter runner, that will give you a reading on the leanest cylinder...in theory. (The GT-40 lower's shortest runner is #5)  On a boosted motor the chamber and runner will be full of air once the motor is pressurized, so granted there is not fuel drop across the rail on any given cylinder the readings on all cylinders should be fairly unilateral. Under non boost conditions the shorter runner will usually tend to run the leanest. After combustion, there is a void of air in the chamber and the shortest runner usually has the most air volume to make up for the drop since the air has less distance to travel before it hits the chamber. Longer runners will fill the cylinder completely after combustion but not with the same velocity as a shorter runner. The shorter runner will absolutely fill the chamber, but will have less air velocity due to the distance the air has to travel before hitting the chamber. (this is theory as to why longer runners make torque, and shorter runners make horsepower)
   Mathematically, a short runner needs 'x' amount of air to fill itself entirely, lets say the longest runner holds 1.25X as much volume as the shortest runner. Thus, the longer runner will require 'x' X 1.25 to fill the runner. This can lead to less air in the chamber vs the short runner since the volume of the runner has to be filled with air before air completely fills the chamber. Some air will trickle into the chamber but in order for the chamber to be full the runner has to be full as well. 
   Remember under boost this is all moot since there is pressure behind every runner. The best way to know for sure which cylinder is the leanest is to read the plugs after driving around under non boosted condtions, but the shortest runner should be the leanest cylinder and that is what I would read from.

Will the crossover tube supplied in the single turbo kits work with aftermarket oil pans and bellhousings?

   No, you will need to take the pipe to a muffler shop and have it altered.  I will post pics as soon someone sends me some.
Also the supplied crossover pipe will not fit aftermarket bellhousings.  An exhaust shop should be able to make it fit for less than an hours labor.

What compression ratio should I run with my turbo engine?

   Anything up to 9.5:1 should be fine with lower boost levels, anything higher than that and you are asking for trouble on a street car because you will probably have to run race gas all the time.  A typical 5.0 engine with bolted on aftermarket heads is about 9.25:1  If you are building a boost specific engine then build it for 8.5:1 or even lower, depending on how much boost you want to run.

How much boost can I run on pump gas?

   Most cars should be ok up to 8-10 lbs of boost.  Bobby said that he has run 12 pounds of boost on the street on 93 octane with 10 degrees of base timing.  Always be on the lookout for detonation.  It also helps a lot to have an aftermarket computer that will allow you to take out some timing at the peak torque rpm.

Should I run a turbo timer?

    A turbo timer is not necessary.  Just let the car idle for a minute after you have been beating on the car.

What additional maintenance is required for the turbo?

    You should look at the wastegate signal line frequently.  If it falls off, you could get all the boost the turbo can make :O.  It is a good idea to use clamps on the lines to add a little protection.  Also, keep an eye on the intercooler hose clamps, they tend  to loosen up over time, so they should be tightened up occasionally. Or you could get the "good" clamps from a big truck store that should never loosen up. I think they lock somehow. Also, if a turbo car stops making boost, look for either an exhaust leak or possibly an intake leak.
    You should always be listening for detonation and check the plugs if you suspect something.  Also keep an eye on all the wires under the hood to make sure nothing is melting.

My car seems to be falling on its face at peak boost, what is wrong?

   Most likely the boost is blowing out the spark.  Try running a tighter spark plug gap.  Bobby runs .025-.028 on his T76, anything wider than that and he experiences problems.  You also might need to upgrade your ignition system if the car continues to blow the spark out.  Something like a 7AL should cure all your woes. (keep in mind this is for the people running 18+ psi, not the average street car.  The average street car will not need the 7AL.)  For a typical street car .032-.035 should be the right plug gap.
Remember to keep up on regular tune up items.

    Also, always keep an eye on your fuel pressure gauge at peak boost.  If the fuel pressure starts coming down then you need more fuel or a bigger fuel system.

How do I launch my Turbo Mustang?

   You may want to get a 2 step to launch a manual tranny turbo car. It's not necessary(Mike Ward's car went a 1.56 60 ft on dr's launching at about 3500-4000 w/ a T5 and no boost on the line), but the 2 step WILL help the motor build boost at the starting line.  I was also told if you're racing, a trick to get better spool up is to take timing out at rpms below your launch rpm, of course you will need a custom computer or chip to do this. 

More updated stuff: 2-1-02: Cartech Street Sleeper Kit

   Because I have decided to order a Cartech Street Sleeper kit, I have been learning a lot about them.  I will post everything that I know here:

What type of exhaust setup should I run??

   Well, since you will now only have one path of exhaust gasses, there is no reason to use an h-pipe or an x-pipe.  So here is what I am going to do:  Run a 3" pipe from the downpipe almost back to the mufflers.  From there I will "Y" it out to the existing cat back system.  This way I can retain the stock dual exhaust look and I won't have to bother messing with a 3-3.5" single pipe.  The Cartech kit comes with a y-pipe that you but it is only 2.25".  If you plan on doing a custom exhaust then have Cartech delete the Y-pipe from your order.  I plan on paying a muffler shop to help me out with this setup.

How loud is a single turbo with a wide open downpipe?

   The reason I asked this question is because I wanted to know if I could drive my car around with no exhaust for a while, until I can get to the muffler shop.  The answer can be found on the multimedia page.  Look at the videos and sound files of turbonotchback's car.  He runs a wide-open downpipe and it isn't loud at all.  In isn't any louder than a Mustang with 1 chamber flowmasters!  There is another video in the multimedia section a 5.0L mustang idling with a wide-open downpipe, check it out!

What is the point of the bypass valve (BOV) upgrade that Cartech offers?

   The stock BOV supplied in the Cartech SS (street sleeper) kit is a Bosch unit.  It can effectively operate only up to 12-13psi.  So if you plan to run more than that I suggest the upgrade.  The larger BOV requires a different fitting welded onto your piping.

Which fuel pump is supplied in the SS kit?

   Cartech supplies the Walbro GSS340 255lph in tank pump in their kits.  This pump is well known for being great.

Does Cartech recommend a blow through or a draw through MAF setup?

   Cartech recommends that you use a draw through MAF meter which will be mounted in front of the turbo inside the fender.

What are the dimensions of the intercooler?

   They only offer the vertical mount intercooler now.  It is a 3 core 27" long and 3" thick.

How large can I go with the Cartech Street Sleeper kit?

   If you start out with a 4 bolt flange turbo, like the T64e that Cartech offers as an upgrade then from there you can go all the way to a T76 by simply changing the turbos!!  Of course I think that you will have to trim the fender a bit to get that monster to fit.  :-)

Which wastegate comes in the street sleeper kit?

Cartech uses the Deltagate, which should work up to 550hp.  However, the deltagate is well known in the turbo world as being unreliable.  I would suggest getting a Tial gate if you plan on making a lot of horsepower.