Turbo info, read before you post.

Not open for further replies.


This post is to help answer a few questions that some of the newbie’s have about turbos. By all means this is no end all information on the subject but only general information, one should still do there own research before taking on such a project.

There are two questions one should ask them selves when doing a turbo project. One is how much horsepower they plan to make. This is different from superchargers because you are no longer fixed to a boost level; with the help of boost controller on a turbo you could change psi levels thus hp levels. Second question is to ask how much you want to spend; this will also determine your horsepower level.

Another myth that should be dispelled is that “psi” is not what makes power; it is the speed and the amount of air that the turbo huffs out into the engine. “Psi” is a measure of restriction. For example motor A has a turbo that puts out 15psi and makes 400hp but motor B has the same setup as motor A but B has ported and polished upper/lower intakes and heads. Motor B’s turbo puts out the same 15psi but it makes 450hp. This is because motor B has less restriction in the “air path” and allows more air to go into the cylinders. So the key is not to make more power with more boost but to make more power with less boost and lessening the engine’s restriction to hit your horse power goal. Doing it this way will help make things last longer too.

Let’s say you where going to make your own kit and do the fabbing yourself, if this is the case then you should make a list of all the parts needed. If you’re buying a kit well then this will give you an idea for what to look for in kit that suits your needs, because not everyone will have the same hp goal.

When turbo’ing a 3.8,
1) Make a list of all the parts you need to finish the project,
2) Make a list of thing that need to be done.
3) Make diagrams and drawings too, (like: exhaust routing, oil lines with fittings, etc, etc..)
Because when you do your own fabbing you are constantly thinking about what parts you have and which you will need to buy, so it’s a good idea to get things as organized as possible.

As far as fuel goes, you will need to upgrade the fuel pump. The pump that most people are using is the 300lph focus pump, I would peg this to be good for 380-400rwhp anything more you may want run a cobra dual pump fuel tank or other upgrades.

The injectors of choice seem to be the 42lbs’ers. I would also peg these to be good for 400rwhp. According to http://www.midnighttouring.com/fuelcon.htm 42’s at 80% duty cycle and .5 BSFC will support 400hp.

You will need a new MAF. The MAF’s job is to judge how much air is going into the engine. Based off those readings it will tell the ECU how much fuel the injectors should squirt. The stock MAF will peg, meaning it will not be able to judge accurately, because the turbo will push a lot more air then the stock MAF can handle. When installing a new MAF make sure you have a lot of straight pipe before and after the sensor. If there are any curves to close to the sensor it will get bad readings and it will be hard to tune. The smoother the intake pipe’s transition to the sensor the better it will be.

Turbo selection is big thing. You will have to pick a turbo to the type of power you like. There tons of turbos out there that will make different types of power. A small turbo will boost quickly but will run out of steam at high rpms, a big turbo will boost slowly but will make big power in the top end. There are also turbos in between to get what you’re looking for. I’m going to try to explain compressor maps with out too much math, just the basics. But to get the most out of the car not just highest hp but the most efficient set up possible it is necessary to do further research and to do the math.

In this pic find the displacement of your engine on the x-axis, and then draw vertical line. Every time it intersects one of those solid lines, it represents engine air flow on the y-axis at different RPMs at 10psi, obviously the dashed lines is the same but at 15psi.

So now you have a set of values of air flow requirements at different rpm levels for a fixed boost level, next you look at different compressor maps. A compressor map is like a topographical map of how efficient the turbo compressor is at different pressure levels and different air flow levels.

Example of compressor map:

The x-axis is the engine air flow requirements; the y-axis is the pressure ratio also called boost pressure. All compressors have a definite combination of airflow (x-axis) and boost pressure (y-axis) at which they intersect at a specific efficient range. On the map 2.0=15psi and 1.68=10psi. Take 10psi for example; draw a line horizontal line (red line) from 1.68 on the y-axis all the way across the compressor map. Then draw the vertical lines from the 5 different airflow values (blue line) from the x-axis to the drawn horizontal line. Now make sure that all the intersections fall under a 70% or higher island, 70% or higher are ideal for an efficient setup it will also gain quicker boost response. And try not to get it to the left of that dashed line, your turbo wont work there. Also as efficiency drops, the heat will build up, even if the boost stays the same. In a twin turbo setup, divide the total airflow requirement in half, and then select a map that satisfies those conditions. Also when engine displacement increase, a given turbo still blows the same amount of air, but a boost gauge pressure reading will be lower.

Picking a turbine is a little bit harder then picking a compressor, picking a turbine will help customize the turbo for your particular setup. Here are 2 pics to help you out, keep in mind that they are very general suggestions. Use these to help pick a turbo, not to justify buying the turbo.


The turbine’s job is to spin the compressor fast enough to produce the airflow requirements at the desired psi. Basically small turbines spins faster then larger ones, which will have little lag, but will have more backpressure which will restrict exhaust flow. However, a bigger turbine will make more power then smaller ones because the turbine wheel’s overall diameter and the turbine housing outlet’s inside diameter will determine the turbines ability to generate the “shaft power” needed to spin the compressor at the airflow rate required to create the boost level or power level. But the trade off is that it will have more turbo lag.

Next to look at is the A/R ratio. Which is area over radius; this basically determines where the turbo starts to spin. Take a look at pic below

The turbine looks like a snail shell, unwrap it and looks like a cone. The end of the cone is cut off leaving a hole, the cross sectional area of this hole is the A in A/R ratio. The hole size at the end determines the velocity at which the exhaust gases exit the turbine scroll and hits the turbine blades. Smaller the hole, the higher the velocity, but greater the restriction to exhaust gas flow. The R in A/R ratio is the distance from center of the cone’s cross sectional area to the center of the turbine shaft (see pic above). A smaller R means faster rotating speed of the gas to the turbine; a larger R will give the turbine shaft a greater torque to drive the compressor wheel, imagine like using a cheater bar at the end of a ratchet to loosen a nut off a bolt, longer the cheater bar the greater the torque.
Now we know what A/R means. A high A/R will be slow off the line but once it starts to accelerate it will be smooth and linear. A lower A/R will give a quicker response.

There are 2 basic options you could go here, air-to-air, air-to-water.
With air-to-air you have tube and fin and bar and plate. Tube and fin is cheaper generally then bar and plate, but the trade off is that you have more pressure loss in a tube and fin then a bar and plate. A bar and plate also flows better.

There is also a difference between cross flow and vertical flow and size too. Generally a cross flow that stretches across your bumper will cool the air more but will lose more flow and pressure since it spends more time in the intercool. The vertical flow like the ATI Procharger style will not cool the air as much as a cross flow but it will loose less flow and less of a pressure loss, since the air spends less time in the intercooler. But when picking an intercooler either way try to get one that looses less then 2.0psi across the core.

There is also that water squirting thing, but I rather have an intercooler that never runs out.

Wastegates are used to control the turbo, without it a turbo will spin out of control and will over boost a motor. Wastegate’s have a spring-loaded valve that is operated by a diaphragm assembly which is actuated by a boost signal. The valve releases excess exhaust pressure when a specific boost level is reached, thus controlling the turbine wheel’s speed and keeping boost under control.

There are internal and external wastegates, there really are no big differences they both do the same job. An internal wastegate are pretty easy to use, the external ones require more thinking. External wastegates come in different sizes that should be matched to how much power you’re putting out. Too big a wastegate and it may open early making it hard to reach the desired boost levels, and it could leak more pressure then you want, so when it closes again your turbo will have too spool up again. Too small a wastegate and the engine may over boost and it will hard to control.
Wastegate size for power level
32mm up to 400hp
38mm up to 500hp
42mm up to 900hp
51mm up to 1400hp

Mounting a wastegate is very important too. Can’t stress that enough. To the get the best performance form the wastegate the exhaust gases should not have to drastically change direction when headed towards the turbine in order to flow through the wastegate; this means a split Y configuration is BEST. A wastegate mounted at a right angle to the turbine inlet pipe is the WORST. Also the wastegate dump should connect back to the turbine outlet pipe at least 18 inches away from the turbo; this will help with performance of the wastegate.

Wastegates can bet set at fixed boost levels with a specific spring rate inside the wastegate. So a wastegate with a 6psi spring will open its valve only after the turbo has reached 6psi. This is not that great since the turbo has reached 6psi but the upper intake may see less then 6psi since there will be pressure loss in the intercooler.

Or you could get a boost controller. This tricks the wastegate to staying shut longer to raise boost pressure. But let’s say you have 6psi spring in the wastegate, with a boost controller you can raise the boost higher then 6psi, but you will not be able to lower the boost lower then 6psi.

It always a good idea to get a blowoff valve, not just because it makes a cool pshhh sound, but because it release pressure in the intake tube. When the throttle blade slams shut, there is pressure wave created that bounces off the shut throttle blade and goes back to the turbo which can damage the blades on the compressor. I believe the best place to mount this is before the intercooler, since that is the place where most of the pressure will be (also a louder psshhh). Try to pick a blow off valve by not which one sounds the best, but which works the best, I’m sure the best sound is not worth bent compressor fins.

Oil is big a thing, turbos don’t need that much oil, so you could run 3–an line to a turbo, and you could get oil restrictors to further restrict oil. It’s a good idea to use an oil restrictor, because you don’t need or want to put a lot of oil in there, sometimes it will bypass the seals and leak into the turbine and will cause a lot of blue smoke out the tail pipe, and it may cause draining problems.

Also use ½ id hose lines for oil drain, I would personally use nothing less then 5/8 id hose for drain. If the drain is too small the oil will build up in the center cartridge and leak to the turbine and/or the compressor.

Also if you want a really cool sound from the turbo, mount your filter right on the turbo, with no pipe at all; it makes a cool whistle/sucking noise, sounds like a plane taking off when under full boost.

Also a good tip to remember is that for the turbine to work well, you want pressure before the turbo and no pressure after the turbo.

There are 2 different ways you can set up your MAF, a suck through or blow through. This will also dictate if you’re going to have a blow off valve a bypass valve.
a. blow off valve will relive the compressed air in the atmosphere
b. bypass valve will relive the compressed air back into the compressor

in the pics
1) turbo compressor
2) air filter
3.a) blow off valve
3.b) bypass valve
4) intercooler
5) MAF
6) throttle body


That is the Blow through system, because air is being blown through the MAF. As you can see air enters the air filter, gets compressed by the turbo then the air gets blown past the BOV (blow off valve), through the intercooler, through the MAF, then finally past the throttle body. When the throttle body is shut, it will cause a vacuum in the upper intake manifold. A rubber hose is connected from the upper to the back of the BOV; the BOV will sense this vacuum. Inside the BOV is a spring and valve, on one side of the valve is boost pressure, and on the other side is vacuum. Once the valve senses high pressure on one side and vacuum on the other side, the spring will compress and the valve opens releasing pressure. Once the valve is open it will release the compressed air into the atmosphere. Then when the pressure difference tends towards equilibrium the valve will shut. The BOV works the same as a bypass valve or BPV.

In this blow thru system, the BOV has to be mounted before the MAF. This is because the BOV vents to the atmosphere, if it was mounted after the MAF, the BOV would release air that has been metered, if it vents metered air, then it will throw off the fuel and will make things rich, since the air that should be there isn’t there.


This is a suck through system, because air is being sucked in through the MAF by the turbo. Which one of the differences from a blow thru system.

In a suck thru system the MAF is put in front of the compressor. But the BOV still as to be mounted on the pressure side of the intake pipes, for it to do its job, which now has to be converted to a BPV with the help of that “green” pipe. The BPV can not vent into the atmosphere otherwise it will vent metered air. So it has to vent back into an intake pipe before the turbo and I believe after the MAF because you don’t want to meter air twice.

As far as which setup is better, I hope someone with more tuning insight can answer that. Because I’m sure it will come down to which is more easily tuned. But I like the blow thru system its easier to fab up and the louder “psshh” is a plus too.


Twin Six

Blow Through 302
062stang said:
how do i go about making this into a sticky? or does the moderators to it?

ima do some reseach on turbo spec cams too.

Turbo cams are very simple.

More exhaust timing, you want less overlap. Sort of similar to a nitrous cam except without the overlap.

Stock cams work quite well on turbocharged applications so really its not the place you really need to look to make more power. Also it requires more complicated work then most people would/are capable of.

Also this is really good, as long as a newby reads this sticky the really dumb questions may be avoided.

And I can't stress enough the "Turbochargers" book by Hugh Macaines (sp). Its made by HP books so its probably in every auto store you go to. Worth reading and it goes into much greater details on the calculations and theory.


**** winter
Thanks for the info I'm a newbie to turbos.

The book "Maximum Boost" by Corky Bell is a really good book to read if anyone wants info on turbocharging. It can be found in most bookstores in the automotive section. Its a little outdated but there is still some really good info on designing turbo systems.


Twin Turbo'd Fury
For the airflow chart that assumed 100% Volumetric Efficiency and gave charts for boost at 10 and 15psi, the vertical green line is in the wrong spot.

For our engines, move the green line (in your mind, you can't move it for real) to "3.8L" or 232 Cubic inches. I've found a piece of paper held to the screen to help keep the line perfectly vertical works well.

Then, find the 6,000RPM intersection point (top two lines). Follow them over to the left hand side of the chart, where you'll find #/min airflow requirement.

Then, go to the compressor map, and find the #/min on the x-axis (bottom). You'll draw another vertical line at that point, all the way through the chart. Then you have to find your pressure ratio. Pressure ratio = (desired boost psi + 14.7)/14.7 This is already done reasonably - 45#/min is roughly what I came up with when I did the calculations. I think I assumed 80%Volumetric Efficiency, which would take the number down to 36-40, depending on mods :)

Anyways, using our formula, a 1.0 Pressure ratio is no boost, just 0psi at the manifold. 2.0 Pressure ratio is 14.7psi. 1.5 would be...you guessed it, 7.35psi!

At that point, find the intersection of the airflow requirements and pressure ratio. You want that as close to the middle "circle" as possible. Prefereably, actually, you want it slightly biased to the right, so that the compressor is in it's "sweet spot" for longer while you're boosting.

The only problem with that is that if you up the boost, you have to scale up the pressure ratio and re-read the chart! Ooops! now you're always out of the 70% zone! If that happens, you goofed and got the wrong size turbo :)

In the picture given, at the pressure level set by the original lines, you can see that that turbo is a little too large for the motor AT THE PRESSURE DEMANDED! If you upped the pressure ratio to 2.0 (14.7psi), then you'd be just about maxing out the turbo! Look what a little boost difference can make!

That's why it's important to know your goals, know your limits, and build accordingly, with your checkbook/cashflow in mind.

I've found, after much studying and examination of charts, the T3 Super 60 (.48 exhaust wheel and .60 compressor wheel) is the preferred choice for twin turbos for MOST people. If you're going for the biggest HP of all time, you'd need something different. I'll try and dig up the numbers and/or charts for that turbo, since it directly pertains to our motors :)



Twin Turbo'd Fury
Here's the map for the PAIR of turbos I'm using. Since it's twins, you have to divide the airflow requirements by HALF. 45#/min turns into 22.5#/min, since I don't believe our engines ever meet 100%VE, I assumed 20#/min at redline (which at the time I used 5,500, I'd have to go back and look/re-do for 6,000).

Trace to the right, find 20#/min, then trace upwards to find 10psi, or around 1.6 Pressure Ratio.


Now, why did I put the max flow point at the bottom of the compressor map max efficiency point? Honestly, it was the best choice available. Seriously, it gives me a helluva lot of room to grow! I'm planning on going to a 4.2L in the next year or so, and also upping the boost to around 15psi on the built motor, so I'll need that extra "headroom" of pressure ratio - to go to up to 2.0 on.



Twin Turbo'd Fury
keepingitbaker said:
if you had something in here for engine management
and how exactly the oil lines worked and hooked up

For Engine Management, there are a few basic solutions.

1) A Chip. SCT makes a damn fine product, as do several other companies. You can get them tuned at a local SCT dealer (they're all over the place, check out www.sctflash.com to find one near you).

2) Standalone. There are a ton of them out there, I have no ideas which ones work and which dont - though I've heard that several people have installed and gotten Megasquirt to run - apparently with excellent results. Downside to standalone is that it will NOT pass ODB2 emissions tests.

For Oil feed, that's really simple.

The oil supply comes off the side of the fixture where the oil filter screws on (on the 3.8L motors anyways). There's a plug in there that has a hex spot in it if I'm not mistaken, and you can take that out, and screw in an adapter that Justin carries (Velocity Mustang Performance, he's on the site!). It converts that size (whatever it is :crazy: ) to a 1/4" Female NPT fitting, to which you attach a 90* 1/4" NPT male-male fitting, and then the adapters to use the Hose fittings you need.

Anything bigger than #4-AN hose is overkill for an oil feed line - most kits use a #3 or #4. If you've got a T3 turbo that doesn't use a standard oil-fitting on the top, you can buy a T3 oil inlet adapter from www.atpturbo.com and a few gaskets, and they'll bolt up no problem. The inlet adapter again has a 1/4" NPT female threads - so you can get whatever fittings you need and make them work. Summit or Jegs or any of those places stocks a huge assortment and you can piece together whatever you need.

For oil drain, you can get the same type of adapter as I mentioned for the oil inlet, but in a much larger size - again, I think www.atpturbo.com has them. Only difference is the threads on this are 1/2" female NPT, so you get to use a MUCH bigger line for oil drain. When routing the drain, make sure you keep the line downward or flat - NEVER UPWARDS! If you have any traps or up-turns in the oil drain lines, your turbos will smoke. A lot. (Personal experience!). A good place to tap the oil pan for the oil return is on each side, right near the front of the pan, where it makes the 45* angle back - on that flat surface is a great place. If you want a good example of how to do it right, check out J's kit - I think he's on this site, but I know he's definately on v6power.net

Hope this helps!


Huge Member
keepingitbaker said:
but how does the oil go to the turbo, does it suck it in itself?
newb question maybe? lol

Electric pump. At least thats the way I remember someone doing it. I'm pretty sure Justin used a pump.


Twin Turbo'd Fury
The oil from the port I specified is pressurized from the motor - the oil pump (mechanical, inside the motor) provides the pressure to get the oil to the turbos, then it's gravity drained back to the pan (usually). You can have an electric pump to help scavenge the turbos of oil, but it's usually not necessary unless they're located very low in the car.

Not open for further replies.