Diesel turbo's-turbo's in general

Diesel turbo's-turbo's in general

Postby Gary [OP] » January 24th 2011, 5:49am

Found this article and thought about the recent interest in diesel conversions and about turbo's in general.Warning-it is long,but you have to spent time to absorb it.Still a great read.

Diesel Turbocharging 101


The difference the turbocharger has made in producing power has really turned some heads, and whether it is on a gasoline or diesel engine the popularity of the turbo has increased.

By Bob McDonald


The turbo was used on road tractors for years but I guess it was never really appreciated until it was introduced on mid-size trucks in the late ’80s. Up until that point, most of us knew only diesel engines without the use of a turbo.

I recall the diesel engines used in small cars and trucks as well as mid-size trucks were really weak, so in 1989, when the Dodge Ram came out with the Cummins turbo diesel, the public started taking note. It was amazing what a turbo could do for something that used to be so weak. This was the start of change for the manufacturers of mid-size diesel trucks. Soon others would follow and now it is standard option for all mid-size trucks with a diesel.

How does the use of a turbo make more power? It all has to do with air density, which is the mass per volume of the earth’s atmosphere (Figure 1). An engine is dependent on air in order to make power. If more air can be introduced into the engine the more power it will produce. The turbo takes the available air and compresses it into the cylinders, raising the air’s density.

Along with the increased use of the turbo has been the necessity of the intercooler. When the turbo is working, the air being compressed becomes hot. The intercooler is like a radiator and cools the compressed air before it enters the engine. This, in turn, raises the air’s density further.

There are two common types of intercoolers: air-to-air and water-to-air. For road use applications the air-to-air is commonly used. Water-to-air is more for racing: even though it cools more efficiently, it takes more components to introduce cool water into the system.

The use of a turbo is thought of as free horsepower, because the exhaust system is doing the work to make the turbo function. And integration with the exhaust system is critical.

Let’s examine the parts of the turbo to explain how it works. A turbo has two housings: the exhaust and the intake. When the exhaust gasses leave the engine they enter the exhaust side of the turbo in what is known as the turbine housing. The turbine wheel consists of angled blades that are connected to a shaft.

On the other end of the shaft, in a separate housing, is another wheel with angled blades known as the compressor wheel. Just like the turbine housing in which the exhaust gas spins the wheel, the compressor housing has an opening to take in fresh air from the air filter as the compressor wheel spins from being connected to the turbine wheel. The fresh incoming air is compressed and forced out of an opening in the compressor wheel housing.

From there the compressed air travels into an intercooler (if equipped) and into the intake manifold. As engine speed increases, the turbine and compressor wheel speed also increases. This forces more compressed air into the intake manifold, which causes a pressure rise, what we refer to as “boost.”

In the aftermarket there are so many upgrades for turbos, especially on the mid-size diesel trucks. How do you determine which one is right for your application? One thing that is always a concern is boost, because people associate boost with power. While this may be true, determining the right turbo goes beyond how much boost you want to run. The first step is to find out how much horsepower you want to produce and make sure this is a realistic figure for the application.

In street applications a smaller turbo works best because of its excellent response time, while in racing applications a larger turbo is needed because response time is not as much of a concern. The main concern in racing is optimum power at optimum engine speed. For street applications you’re usually looking for the best all-around performance at various engine speeds.

When choosing to upgrade the turbo, we often leave this decision to the turbo manufacturer for our application. This is a good thing because the manufacturers have spent many hours and resources on developing their turbos, especially on production vehicles.

However, leaving the designs to the experts doesn’t mean you can’t learn more about what is going on inside the turbo and its effect in producing power (see Figure 2).

First, let’s consider the term “trim.” Trim refers to an area ratio between the turbine and compressor wheels. Since the blades of each wheel are spiral and fan shaped they have two diameters. These two diameters are known as the inducer and exducer. The inducer diameter is where the air enters the wheel, while the exducer diameter is where the air exits the wheel. However, pay attention because this is where it gets tricky!

On the exhaust side in the turbine housing, the inducer is the larger diameter of the turbine blade. This is where exhaust gas is entering the turbine housing. On the compressor wheel the inducer is the smaller diameter of the compressor blade, because this is where filtered outside air enters the compressor housing. On the turbine blade the smaller diameter is the exducer, where the exhaust exits the turbine housing into the exhaust pipe. On the compressor wheel the larger diameter of the blade is the exducer where compressed air exits into the compressor housing to the intake manifold.

Here’s an example: Lets say you have a compressor wheel with an inducer diameter of 55mm and an exducer diameter of 75mm, What is the trim of the compressor wheel?


This is the formula:


TRIM = [Inducer2] x 100
[Exducer2]
= 55mm x 55mm x 100
75mm x 75mm
= 3025 x 100
5625
TRIM= 54

Whether it is the compressor or turbine wheel, the trim can affect performance by shifting the airflow capacity. A higher trim wheel ratio will, in turn, flow more than a lower one, but other factors will influence this so bigger isn’t always better.

Next is the term known as A/R (Area/ Radius). You can actually see this sometimes stamped on the manufacturer’s compressor housing. This is the equation that makes up the geometric shape of the compressor and turbine housings: it is the inlet cross-sectional area divided by the radius from the turbo centerline to the center of that area. It sounds confusing, I know, but (Figure 3) explains it. Changing the A/R in the compressor housing really doesn’t affect turbo performance and most manufacturers don’t offer A/R options for the compressor housings, anyway.

The turbine housing, on the other hand, is a different story. This is used to adjust the flow capacity of the turbine, which is what drives the turbine wheel to spin. A turbo with a larger A/R will have a slower rise in boost and operate at higher engine speeds while a lower A/R will have quicker boost rise but suffer from increased backpressure and not operate efficiently at higher engine speeds. Looking at A/R numbers you can usually see what the intended purpose is. If you have a turbo on your diesel with an A/R of .7, you can see that it was meant for great quick boost and street driving compared to if you installed a turbo with an A/R of 1.1.

In today’s mid-size diesel trucks, you may see a technology known as VGT, variable geometric turbo. This design allows the angle of the blades to change with engine speed. Manufacturers take the oil pressure used to lubricate the turbo and divert it to a solenoid mounted on the side of the turbo. The solenoid is controlled by the PCM. As engine speed rises the PCM will command the solenoid to open at a desired rate to change the geometry of the compressor blades. This is used to operate from no boost at idle to full boost at WOT. Manufacturers use this to help eliminate turbo lag and be more efficient. This way the compressor wheel in the turbo is not a fixed unit, and can change as the demand for boost changes.

Whether it has been used in normal or in towing applications, drivers should remember to let the engine cool down a little before shutting it down. When a hot turbo is simply shut off, heat soak begins. The heat from the head and the exhaust housing migrates to the center of the turbo. This is where the bearings are and this is the reason the turbo is fed with pressurized engine oil. A hot shut down can result in oil coking which, in turn, will damage the bearings of the turbo and can result in severe engine damage.

Many people who own diesels don’t realize the effects of hot shut down, especially when compared to a gasoline engine. One thing that turbo manufacturers have done to combat this problem is to use coolant from the radiator. So not only do you have oil to cool the bearings but also coolant from the radiator. So the coolant circulates to also help take the heat away in case the person who owns the diesel does not let it cool down.

Some aftermarket companies offer what is called a “turbo timer” that allows a driver to the ignition off, remove the key and lock the doors. The “turbo timer” will continue to let the engine run until the desired exhaust temperature is reached. At this time the engine will shut down and everything will return to normal.

Robert McDonald is owner of Atlantic Engines in Granite Falls, NC, and specializes in high performance diesel and gasoline engines and cylinder heads for street, marine, dirt and drag racing. You can reach Bob at [email protected].
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Re: Diesel turbo's-turbo's in general

Postby cowboydan » January 25th 2011, 4:17pm

Gary wrote:Whether it has been used in normal or in towing applications, drivers should remember to let the engine cool down a little before shutting it down. When a hot turbo is simply shut off, heat soak begins. The heat from the head and the exhaust housing migrates to the center of the turbo. This is where the bearings are and this is the reason the turbo is fed with pressurized engine oil. A hot shut down can result in oil coking which, in turn, will damage the bearings of the turbo and can result in severe engine damage.

Many people who own diesels don’t realize the effects of hot shut down, especially when compared to a gasoline engine. One thing that turbo manufacturers have done to combat this problem is to use coolant from the radiator. So not only do you have oil to cool the bearings but also coolant from the radiator. So the coolant circulates to also help take the heat away in case the person who owns the diesel does not let it cool down.

Some aftermarket companies offer what is called a “turbo timer” that allows a driver to the ignition off, remove the key and lock the doors. The “turbo timer” will continue to let the engine run until the desired exhaust temperature is reached. At this time the engine will shut down and everything will return to normal.

Robert McDonald is owner of Atlantic Engines in Granite Falls, NC, and specializes in high performance diesel and gasoline engines and cylinder heads for street, marine, dirt and drag racing. You can reach Bob at [email protected].

good info gary. this is a big reason why turbo cars always have reliability issues. i personally prefer n2o from a heat standpoint (racing application). i like any power adder but my absolute favorite will always be n2o...lol. just don't get caught on the street with it...lol there are pros and cons to every power adder, excessive heat is a deadly con for turbo cars. the owner not taking proper care of his turbo vehicle is another...lol
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Re: Diesel turbo's-turbo's in general

Postby chevymaher » January 25th 2011, 4:21pm

.lol. just don't get caught on the street with it...Why you say that is it illegal where you are?
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Re: Diesel turbo's-turbo's in general

Postby cowboydan » January 25th 2011, 6:33pm

chevymaher wrote:.lol. just don't get caught on the street with it...Why you say that is it illegal where you are?

turbocharging isn't illegal, nitrous oxide is. i like n2o because it hits extremly hard and super cools the air charge as apposed to turbos generating an excessive amout of heat. but because n2o is an oxidizer, it is classed as a haserdous chemical and can not be transported without a permit. that's why it is illegal in the states and canada.
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Re: Diesel turbo's-turbo's in general

Postby chevymaher » January 25th 2011, 7:08pm

I was refering to nitrous oxide not turbo.I never knew it was illegal.Everybody around here got it and nobody ever said they had any problem.I will ask around but to my knowledge I dont think there been a single ticket for it here.Or trust me I in that loop I would have heard watch out.
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Re: Diesel turbo's-turbo's in general

Postby Gary [OP] » January 25th 2011, 11:39pm

You guys have to take into account with the heat issues of turbo there are inter-coolers that take care of that.

With nitrous,I think you are making payments with each refill on mods you should have done to get there without it.
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Re: Diesel turbo's-turbo's in general

Postby cowboydan » January 26th 2011, 2:24am

Gary wrote:You guys have to take into account with the heat issues of turbo there are inter-coolers that take care of that.

With nitrous,I think you are making payments with each refill on mods you should have done to get there without it.


i am aware of intercoolers. it is the heat under the hood and like you said before... having to let the engine idle cool before shutting down that bugs me about turbo engines.
as for using nitrous, you can run up to a 75 shot with a dry system having colder plugs (obd2) and up to 125 shot with a wet system with colder plugs (obd2). most stock engines (obd2) will hold up to 150 shot with only fuel mods. after that, the heads max out their flow. it may cost 100 bucks to fill the bottle but no other power adder hits as hard as nitrous. you can also add nitrous on top of any other power adder. you can also get a nitrous intercooler kit. it sprays over over the surface of the intercooler and can lower the intercooler temp by as much as 100deg. the reason these nitrous kits are used is so that your engine can remain smog legal.
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Re: Diesel turbo's-turbo's in general

Postby Gary [OP] » January 27th 2011, 11:20pm

Hey Dan.We used to sell at a swap meet in Boston Mass.The guys from NYC would come there and pay whatever you wanted for those kits.We where getting them at a auction in Indy cheap.I have not met one old owner of them that didn't regret buying them.The addition of pressing the button and the wear and tear it created often force the sale.Those kits do not include the limits of O.E.M. parts let along they are really not intended for use below 2,500 RPM and need the support systems to retard the timing on the top end.Even the smaller ones.

So let's say you buy a bottle at $100.00 a month.That is $1,200 a yr.That $1,200 would buy you a really sweet 355 short block that would out last any sprayed O.E.M engine and might out run them as well.

I am not big about power adders.In fact I think the money is better spent on builds that get you there naturally.But given the history of semi trucks use of turbos,it seems like a better solution than spraying and it does follow along with how I feel about building engines building and spending the money on the build that is apart of the build to stay at no extra costs along the way after it is done.

Lastly,I found something about the tech advances with the electronic controls changing the pitch on the turbos interesting.It is something I didn't know.The formulas in the article are also very informative as well as a description of the different parts of the turbo.I put this thread up for you guys,but honestly I had my old buddy Mr_Roboto in mind who is big into turbos.The late night chats I used to have with him about them is something I am very fond of and remember well. :banana:
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Re: Diesel turbo's-turbo's in general

Postby cowboydan » January 28th 2011, 2:38am

i have no regrets. i bought the zex kit and proceeded to blow up engines... one i blew up on the 1st test. the second, i found out that my fuel pump wasn't up for it...lol. i had a blast learning about nitrous on my own wallet. when i finally got it all right, i could smoke any other (on paper equal) car n20 vs turbo/sc/na. the last engine i had put in my car lasted 80,000 km with the bottle. i'm not saying that n2o is the best, but when it comes down to win or loose, i'll use the bottle. i never minded paying for the bottle fill. and i got time slips, so later i could still prove i was faster. anyone can build a fast car. but not every fast car is going to be reliable. mine however was reliable enough to travel to manitoba several times for racing and i made more on bets then i lost. some people call it an unfair advantage.... hp is hp. when i had the money, i had power. i sold my system cause my wife and i decided to have another kid. i personally regret selling my system. but lets face it, nobody would take you seriously showing up to race in a focus wagon...lol no matter how fast you were
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