What kind of turbo should i get

And while tires and suspension tuning can add speed in the corners, at some point, more output is required to go faster. But is putting a turbo on a naturally-aspirated car really that simple? The difference is that the turbo gets spun up by the expelled exhaust gases. This lets it compress more fresh air into the combustion chamber. More air means a bigger boom which means more power.

For example, differently-sized turbos are better in different parts of the RPM range, Hot Rod explains. But turbocharging an engine requires more than just picking the kind of turbo you want. As the turbos start spinning, they heat up, especially on the exhaust side, Haynes explains. This heats up the incoming air, making it less dense and oxygen-rich, which cuts into power output. In addition, making more power requires not just more air, but extra fuel, too.

The T-6 heat treatment often used on performance pistons will increase strength by as much as 30 percent. However, nothing replaces the forged piston for ultimate strength in a high-boost engine. When in doubt, go for the forged pistons, but recognize that your cylinder wall clearances may be different than what the manufacturer recommends if your piston selection includes an alloy shift.

While heat-treated hypereutectic pistons should work well for the high-horsepower street machine, forgings should be used on all drag motors.

The main thing to remember is that the alloy used is a big determining factor when sizing your cylinder bore for proper pistonto- wall clearance. Be sure to ask the piston manufacturer for their piston- to-wall clearance recommendations, and ask a few successful racers running the same engine too. He also uses Lo-Ko coatings to coat the piston skirts for reduced friction and a ceramicmetallic coating for the crown to create a thermal barrier.

The thermal barrier helps keep energy in the cylinder where it can do more work, plus it keeps the piston and rings running cooler. There is a downside for this kind of piston coating. The tendency for detonation increases due to the higher heat in the combustion chamber. For this reason, it may not be wise to use coatings on street-driven engines because fuel octane will become a bigger problem.

One way of combating this condition is to pull timing out by retarding it a bit, but then you may have just moved away from your optimum tuning point, as well. The best plan is to keep the piston coatings on the strip, not the street. Lo-Ko Performance Coatings, Incorporated of Oak Lawn, Illinois, uses a poly-ceramic coating for the piston crown, and a special blend of four compounds including Teflon for the skirts that both reduces friction and improves heat transfer from the piston to the cylinder wall.

This formulation is superior over Teflon alone. Testing performed by Indy car race teams quantified about a 2 percent horsepower gain, partially from the heat kept in the combustion chamber, but also from the reduction of friction between the piston skirt and cylinder wall.

The JE piston used by DLS Engine Development on the left is finished and ready for build, as compared to a non-prepped piston on the right. Note the ceramic coating on the crown and the black low-friction coating on the skirt. Shown is a stock piston from a Buick 3. Note the thin piston crown thickness 1. This piston would not stand-up well to high boost. This piston section is from a 3. Note the more robust design, where the piston has a thicker crown 1 and heavier top 2.

Also note the dished top that lowers static compression ratio for the turbo boost 3. This is a sectioned JE competition piston used by Dan Strezo.

According to John Vander- Meulen, president of Lo-Ko Coatings, when you use this coating, he recommends increasing the pistonto- wall clearance by an additional 0. The coating bonded to the skirt is thicker than some factory coatings.

Lo-Ko adds about 0. John says that about 0. The remaining increase in diameter tightens up the fit, but this is offset by the fact the piston is now running cooler and will not expand as much. Compression ratio is a major concern when building a boosted motor. Again, your intended use and fuel selection will play an important role in this choice. Other variables will include cam grind, cam timing, combustion chamber design, ignition advance, fuel octane, vehicle weight, and others.

Since each engine design varies as to how sensitive it is to detonation, it would be wise to research your particular engine and find out what others have learned about optimum compression ratio for your particular boost pressure level. For the average street motor you should stay in the 8 to 8. If you have a fairly lightweight car you can probably get away with or a little more, but watch your boost and detonation threshold. There are some racers running upwards of , which is pretty high compression for a boosted engine, but they are typically running alcohol or very high-octane gasoline.

Never modify any type of domed piston by machining it down to lower the compression ratio. That will weaken the entire structure by making the crown thinner and narrowing the top ring to piston crown strength. Be cautious about building your engine based upon the compression ratio rating for your pistons when you purchased them. This is an approximate rating. Variations in production tolerances will allow combustion chambers to vary in size. You also have to consider the head gasket thickness, which may be a special consideration in a boosted engine due to the popularity of using thicker copper gaskets, along with the deck height of the block.

These things all go into determining the actual compression ratio for your engine. Blueprinting an engine is a commonly overused term and means much more than just making the combustion chambers equal volume and balancing the rotating and reciprocating parts.

This also includes making sure that all combustion chambers are exactly the same size for balanced power production and to ensure that you know the compression ratio in all cylinders.

The process of actually calculating your compression ratio appears later in this chapter. Piston rings are an extremely important consideration as well. Consider the fact that all the trouble you go through to build an engine and pack more air in to the cylinders to match with your proper fuel flow rate comes down to whether you can hold it altogether and keep it inside the combustion chamber. Piston rings have three major design considerations. They must be able to seal the piston in the bore, they need to dissipate heat from the piston to the watercooled cylinder wall, and they must have the proper tensile strength to withstand the loads the engine will see including some percent of detonation.

In a boosted engine, those traits are all the same, except more severe. For this reason there are several types of materials used for success in engines that have extreme demands in these areas. Some production engines have gone to thinner and lower tension rings for improved fuel economy. If a piston ring fails to do one of its jobs, like transfer heat from the piston, failure can occur. Older ring designs were cast iron and they worked well because the cast iron was soft and seated in the bore rather quickly.

They are brittle and have a melt temperature of approximately 2, degrees F. Chrome-plated iron rings are stronger and their melt point is about 3, degrees F. Nodular-iron rings coated with Molybdenum, or Moly rings, are commonly used in competition engines. The Molybdenum has a melt temperature of over 4, degrees F. The double Moly ring sets use a Moly top and second compression ring combination. High-boost, high-horsepower strip engines will also use a stainless top ring and a Moly second ring combination.

Extremely high-boost applications will typically need the top ring end gap set a little wider to allow for greater expansion at peak horsepower. Most high-performance ring sets will come larger than what you want so that you can adjust the end gap for your particular build.

This is another important area where it pays to ask the right people what works best for your engine and application. The best policy when determining what variable, like ring end-gap or piston clearances, to use in an engine build is to get three sources of data.

The reason for three sources is really quite simple. If you asked one you have no basis for comparison, unless you really know your source well. Asking a third source is seeking consistency. If two of the three agree, you know which one to toss out. Sometimes just knowing what questions to ask, and to whom they should be asked, is half the battle.

Connecting Rods. The connecting rod has a tough job. It must have high compression strength, high tensile or pulling strength, and be able to carry high shear forces by its mechanical design. All these features are also packed into a component that needs to be as light as possible. There are many good name brand rods on the market. It is a good idea to Zyglo or Magnaflux your rods, even new aftermarket rods, right out of the box.

Then shot peen them to remove surface stress that can migrate internally to cause total failure. As with every part of the bottom end of a turbocharged engine, think strength. Regardless of your engine type, your rods will look surprisingly similar though the dimensions will vary greatly! This is a close-up of the Crower I-beam connecting rod. This rod has proven to work very well in high-boost, high-horsepower engines.

You could certainly do a lot worse. The Giannone rod end and cap uses a series of interlocking labyrinths to precisely align the rod and cap together on both the X and Y axis, which helps speed up engine build while insuring a perfect fit. It also allows an even thrust surface between rods sharing the same main bearing journal. With that said, the vast majority of turbo engine builds require forged aftermarket rods.

For mild to moderately boosted engines, a good set of forged rods is a must. As with pistons, they are the ultimate in strength. The first step up is the forged H-beam design, available from many manufacturers.

Some manufacturers also offer forged I-beam rods for even more strength. A little research into your particular engine will probably reveal which rods can handle which power levels. Rod bolts are commonly the weak link in connecting rods. Companies like ARP offer oversize rod bolts. Many engine builders always replace rod bolts at every engine build, while still others will magnaflux all rod bolts new or used as a form of insurance and quality in their build.

Not true! What is true is that a turbocharged engine can achieve higher volumetric efficiency with stock ports and combustion chambers than a naturally aspirated engine with gazillion-dollar heads.

A turbocharged engine is boosted to achieve over percent volumetric efficiency, and head work will take that further. Simply stated, VE is the measure of how close the actual volumetric airflow rate is to the theoretical flow rate. Few naturally aspirated engines get past about 90 percent, and most fall below that. The turbocharged engine will exceed percent VE since the turbo is cheating the formula by forcing the air into the cylinder under pressure.

These heads have been professionally prepared and are extremely expensive. This level of investment is not for everyone. But there are several modifications that you can do. The valve guide castings have been completely ground away then new valve guides pressed into place. The intake and exhaust valve openings are Siamesed and are as large as the head design will allow. The turbocharged engine actually has static pressure sitting on the manifold side of the intake valve such that as soon as the valve opens it fills the cylinder.

When you squeeze open the spray nozzle all the way then let it close again you get a displacement of water much like the cylinder filling process. What it comes down to in part, is time. That aspect is an important component of basic cam design to be discussed later in this chapter. The other restrictions to flow are the obstacles in the path of that flow, as well as the orifice size.

The air sees obstacles and they slow down the flow. In the cylinder head, everything is an obstacle, the valve, the valve guide casting, even the port wall itself. Opening up those paths and smoothing their way for less drag on the boundary layer will create an easier flow path for the air, turbocharged or not. Head modifications are time consuming but important to overall airflow. The head, port size and shape, and valve orifice are major controlling factors to cylinder filling.

You may say your valves are as large as they can be, what else can you do? You can still open your port orifice through some manipulation of the valve edge and seat. It also dramatically increases the psi on the valve and weak valves may not stand up to the pressure. This modification is not extremely difficult, but it must be done carefully. The dotted lines illustrate how the seat is to be narrowed.

This illustrates how the same size valves can still allow for a larger orifice through modifications that will allow more airflow. You can reduce the valve diameter by mounting the valve in a grinder and removing the desired amount of material.

The outer edge should be rounded off using a fine emery cloth to create a nice smooth radius, but the valve should not be reduced in thickness since the radius is used to merge the narrowed seat into the valve body. The combustion chambers need to be measured and matched for calculating final compression ratio. To match the combustion chambers, all you really need is a small air compressor, a pneumatic hand grinder with emery rolls and arbor, a calibrated burette that has about a cc capacity, and a round piece of Plexiglas about 6 inches in diameter with a small hole in the center.

Install the modified valves with springs that have enough tension to make the valves seal. Secure the cylinder head on a bench, gasket side up so, that its mounting surface is perfectly level. To get the correct inlet condition, it is now necessary to estimate the air filter or other restrictions.

In the Pressure Ratio discussion earlier we said that a typical value might be 1 psi, so that is what will be used in this calculation. Also, we are going to assume that we are at sea level, so we are going to use an ambient pressure of We will need to subtract the 1 psi pressure loss from the ambient pressure to determine the Compressor Inlet Pressure P1. With this, we can calculate Pressure Ratio using the equation.

For the 2. We now have enough information to plot these operating points on the compressor map. First we will try a GTR. This turbo has an 88mm tip diameter 52 trim compressor wheel with a As you can see, this point falls nicely on the map with some additional room for increased boost and mass flow if the horsepower target climbs. For this reason, the GT37R turbo family is applied on many of the Garrett Powermax turbo kits that are sized for this horsepower range. This category is for daily driven vehicles that have up to horsepower over stock or wheel horsepower.

Looking at the previous map, the compressor does not flow enough to support this requirement, so we must look at the next larger size compressor. Another option that could also be considered is the GTR which has a slightly larger inducer compressor and the next larger frame size turbine wheel. This category is for real hot rod vehicles that have up to horsepower over stock and owners that are willing to give up some of the daily utility in order to achieve higher power gains.

For this flow and pressure ratio, the GTR is appropriate and is shown below. Since this is approaching a pressure ratio of 4-to-1, we are about at the limit of a single turbo on an engine of this size. The final case is the Competition category. Since this is a special case and there are so many ways to go about an ultimate power diesel application, it is not possible to cover it adequately in this article.

There are, however, some general guidelines. At this power level, as stated above, it is a good idea to consider a series turbo application. This is a situation where one turbo feeds another turbo, sharing the work of compressing the air across both compressors. The low-pressure compressor feeds the high-pressure compressor which then feeds the intake.

On the turbine-side the exhaust first passes through the high-pressure turbine and then on to the low-pressure turbine before being routed out through the tailpipe. We can still calculate the required mass flow, but the pressure ratio is more involved and questions should be discussed with your local Garrett Powermax distributor. To calculate the required mass flow, we use the normal equation.

This time the power target will be wheel horsepower over stock, for a total of wheel horsepower. This air flow rate will apply only to the low-pressure compressor as the high-pressure compressor will be smaller because it is further pressurizing already compressed air. In most cases, the high-pressure turbo tends to be about two frame sizes smaller than the low pressure stage.

Generally speaking, the proper turbine housing is the largest one that will give acceptable boost response on the low end while allowing for more optimal top end performance. This information should be used as a starting point for making decisions on proper turbo sizing. Of course, for more specific information on your engine, consult a Garrett Powermax distributor. Sign up to receive exclusive communications about offerings, events and news, surveys, special offers, and related topics via telephone, email, and other forms of electronic communication e.

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