Can you turbocharge a stock engine

This can be achieved in one of three ways: preferably fitting of forged low compression pistons, machining the top of the standard pistons or the fitting of a thicker head gasket or spacer plate. The camshaft specification should also be checked to ensure that the duration and valve overlap is not too great for the application.

Ideally this would be a camshaft of mild duration and overlap. The ignition timing needs to be retarded as the boost pressure rises. To specify the correct turbocharger for the application we would require the following basic information:.

If you are determined to still go ahead with turbocharging your vehicle, you must first locate a conversion specialist and seek advice from them.

They are usable but far from optimum. As an example, let's take a Garrett T03 from the '85 to '86 T-bird turbo coupe. Using the map in the Junkyard Turbo sidebar, you can see that with a boost pressure ratio of 1. To improve the efficiency, you need to increase the boost to the ragged edge of boost safety. With a larger engine, it will get worse. It's workable; you'll just have to be careful what you are doing. There is a gap between the equipment of the '80s and the new, redesigned factory turbos that appeared largely on import cars in the '90s.

Simple advances such as the number of components, bearing design, wheel trims, and materials have all changed for the better. Let's take the Garrett GT turbos as an example. The number of moving parts has been reduced from its early T model from an average of 54 components to around This 45 percent reduction in parts cuts the risk of component failures. The GT also has a ball bearing cartridge that eliminates the journal bearings that are actually more like bushings and the famous weak-link thrust bearing.

Better bearings mean less oil running through the turbo and a decreased likelihood of leaks or that a failed bearing will destroy the turbo and contaminate your engine oil. You also get the advantage of a lighter, well-designed compressor and turbine wheels that create more power with less lag and heat. Aluminum compressor wheels can be removed from the steel shaft, so aftermarket companies can offer various trim options for exact performance specifications and mix and match compressors and turbine combinations.

The result is a responsive system that runs cool and makes power instead of something you won't be happy with. Junkyard Turbo Junkyard heroes claim you can slap on a set of Thunderbird turbos and go to town.

That may be true, but you will be giving up a lot in doing so. Aside from the improvements in bearing technology that add longevity and performance to the turbo, the compressor efficiency maps on newer compressors are much wider, allowing you to run more boost in a wider rpm range than the OE stuff. You can also get away with running a single turbo to achieve the same power levels.

Turbo Terms Boost: Any pressure above atmosphere measured in the intake manifold. Boost threshold: The lowest engine rpm where the turbo can produce usable boost. Compressor map: A grid of numbers used as a tool to evaluate the efficiency of a turbo in relation to an engine. Compressor surge: Air that backs up, causing the speed of the turbo to become unstable when the throttle is suddenly closed.

Lag: The delay between the change of throttle position and the production of usable boost. Surge line: The line that follows the far left of the efficiency island on a compressor map where the turbo becomes unstable. The Cometic gasket company also makes a triple-shim gasket that is slightly larger in the bore area. This area accommodates a nitrogen-filled O-ring. The O-ring is coated with silver for better sealing. Not all engines can use this design. If the cylinders are especially Siamesed, then there is insufficient room for the design to work.

However, if your engine will accept it this process works well and will save time and machine shop money relative to traditional O-ringing. Compression ratio is simply the total volume of the cylinder and combustion chamber when the piston is at bottom dead center BDC divided by the volume of the combustion chamber when the piston is at top dead center TDC. The time consuming part of this exercise is the measurement of a the elements required.

You should have the CCV value from when you adjusted the combustion chambers to equal volume. Your HGV is an easy issue; simply measure the thickness of a used head gasket of the type you intend to use. The compressed thickness may also be available from the manufacturer. Then apply the calculation to find the volume of a cylinder using your basic geometry because the head gasket is just a very short cylinder.

The DH deck height is simply bringing the piston up to TDC using a dial indicator and then measuring another very short cylinder, which is the distance from the deck down to the piston crown. Your dial indicator can do this job easily. Now that you have the height, you use your cylinder bore and calculate the volume using the same formula shown above. The PDV is perhaps the trickiest to obtain assuming you now know your head cc value.

In this case, enter it into the formula as expressed, but as a negative value. The easiest way is to call the manufacturer and ask them. Your cylinder volume is easy, all you need is your bore and stroke.

Fortunately, when adding a turbocharger to a street-driven engine, the stock camshaft will normally do nicely. This aspect, along with the stock compression ratios ranging 8. Certainly all of the various components you plan to use contribute to developing higher torque and horsepower.

However, to develop the torque and horsepower at a certain RPM range—the cam becomes critical. Understanding cams can become easier if you take the concept one step at a time. The cam is a very old mechanical concept that simply transforms rotary motion into linear motion. In other words, the cam turns around and creates linear motion to operate the valves.

The motion is transferred to the valve either through a pushrod- to-rocker valve actuation or directly onto the valve in the case of an overhead cam engine. Since the valve actuation is critically timed relative to piston position, cam specs that discuss duration, or the time the valve is actuated, are always expressed in terms of degrees of crankshaft rotation.

The valves are open for just fractions of a second at high speed. Maximizing volumetric efficiency is the primary design objective of any camshaft. Longer duration means the cam is opening the valve longer for a given RPM. Maximum lift, the linear distance the valve moves, is also dictated by the cam. When the piston is halfway down the bore, the crankpin is almost moving linearly, which creates the maximum speed of the piston. If the intake valve is wide open at that point, the valve opening opportunity will be maximized because the valve will be at its max opening when the piston is traveling the fastest.

However, once the piston is at or near BDC, it has slowed down considerably. Due to the inertia of the intake air, there are several degrees of crankshaft rotation, even after the crankshaft begins forcing the piston back up the bore, where having the valve open will aid in cylinder charging.

At slower engine speeds, the cylinder has more time to charge, and the intake air carries very little inertia. Consequently, the intake valve likes to close earlier before the pressure of the piston coming back up the bore forces intake air back out the intake valve.

This creates a smoother idle quality. In a high-RPM engine, closing the intake valve later maximizes the intake air inertia and additional cylinder charging is accomplished because this high-speed air will have a force that is greater than the force exerted by the piston on the air charge in the cylinder, to a point.

This is why performance cams will typically have an ideal RPM range where their duration is more compatible with higher engine speeds, yet cause an unstable and erratic idle quality. The dynamics are a bit different in a turbocharged engine.

Since the intake air charge is now forced in under pressure, the air charge pressure in the cylinder rises at a faster rate, so people usually want to close the valve a bit sooner. This is also why a stock camshaft works very well with a forced air induction system. But the basic principle of delaying the intake valve closing for higher RPM operation still holds true.

Remember that an intake valve is a time metering device. In an extreme engine, such as a Bonneville racer, the primary concerns are power development at sustained high speed obtained from maximizing VE.

Even though you have boost pressure present, the amount of time you have to charge the cylinder is a constant challenge to horsepower development. In road racing, torque development at lower speeds is critical for acceleration, and you want the engine to move up and down the RPM band freely. Valve overlap is another critical factor for turbo cams. Valve overlap is a situation where both the intake and exhaust valves are open at the same time. Usually, when the exhaust valve is almost closed, the intake valve begins to open.

The duration of crankshaft degrees rotation when both valves are off their seats is referred to as overlap. In a naturally aspirated engine operating at high speed, there is a bit of cylinder scavenging done during overlap where the force of the incoming air helps to fully exhaust the cylinder. In a turbocharged engine, this happens very quickly since the intake charge is boosted.

If the exhaust valve remains open too long, it will allow the cylinder to loose too much cylinder charge. For this reason, the lobe centerline angle is usually degrees or more to minimize the amount of valve overlap. The shape of the cam lobe is critical as it relates to the quality of the time-metered event of valve opening.

Two cam lobes with the same lift and duration could have completely different mechanical profiles. A given cam could open and close the valves much faster, thus lengthening the time the valve is at max lift. This maximizes total average opening size of the timemetered event. This also means the valve will be traveling at a much faster rate. This is partly why different cams that have nearly the same specs can perform differently in your engine. Cams have to have entrance ramps and closing ramps.

These are the gradual inclines at each end of the cam lobe that allow the valvetrain to load and unload without too much shock to the entire system. The ramps allow the smooth engagement of the valvetrain and the exit ramp keeps from slamming the valve closed. Without these features, the cam would hammer the valvetrain apart. There is minimal flow below a certain level of lift, so the industry now uses 0. Aggressive cams will have very steep flanks, or ramps, where the valve is accelerated to the full open position to maximize the amount of duration at peek valve lift, thereby increasing the average valve opening as a function of time.

Older flat-tappet cams are somewhat limited in this area because a very aggressive cam lobe with fast flanks can virtually dig into the side of the lifter. This is the reason most modern engines use roller-tappet cams. Cams are typically thought of in terms of lift and duration, as these elements focus on how long the valves are open. The exhaust valve will typically begin to open before the piston reaches BDC.

Holding the valve closed longer allows more total combustion pressure to be applied to the piston, raising the mean effective pressure, which translates directly into horsepower. However, opening the exhaust valve too late causes the piston to do more of the work to push the expanded gases out of the cylinder and thereby gives up more energy to pumping losses. In the case of a turbocharged engine, the burn lasts a bit longer due to the increase in massflow.

If the exhaust valve opens too early it will blow-down the cylinder and allow the engine to lose BMEP brake mean effective pressure. Two cams can have the same lift and duration as shown, but they will perform very differently. The blue lobe obviously has the same total duration as the red, but you can see more duration in the blue lobe at full lift.

This is a graphical representation of the two cam lobes illustrated in the picture to the left. Using a dial indicator and a degree wheel and placing the cam between centers will allow you to obtain the data necessary to make this type of graph for your camshaft.

By taking dial indicator lift readings every 5 to 10 degrees of rotation, you will be able to plot your cam on a graph. Most cams are ground in a symmetrical manner, meaning that the profile of each lobe looks the same either side of the cam centerline. In a conversation I was having with Gale Banks, I taunted him with a question intentionally filled with conventional wisdom.

In extreme classes of professional motorsports, like drag racing or Bonneville type cars, the conventional wisdom goes right out the window. In these situations, testing cams with progressively longer and longer duration would likely pay dividends. If your engine was calculated to run at say 9, rpm and you were testing a long intake valve duration that closed the intake very late, you could possibly see this using a pressure transducer.

You would be looking for a 75Hz signal that would tell you the valve is closing too late. If at the speed range you intend to run, the signal does not reach this level, you can change cams and test progressively later and later valve closure to maximize the time the valve is open. Figuring the frequency you are looking for would be:. The hardest part may be to find a cam grinder who will make your custom grinds.

One interesting item to note is that the Banks Sidewinder Duramax diesel will produce a pressure wave that you can feel with your hand 12 inches in front of the turbo air inlet when the engine is at idle. If you liked this article you will LOVE the full book.

Click the button below and we will send you an exclusive deal on this book. At first I was inclined to say that most seasoned enthusiasts and professional builders are beyond the scope of this book. Check out this article if you want to learn more on installing turbo on a stock engine. I am a car enthusiast and a passionate rider who loves to discover new places.

Since the pandemic, I can't go to places and I started to blog and share information that I learned. I'm not easily distracted, I just OMG, do I hear a Supra? This site is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon. Hit enter to search or ESC to close. By Chai WJ. One Comment. Data in the ECU memory. Horsepower Gain From Turbo Without Tuning Installing a new larger turbo without tuning will not provide you with any horsepower.

Aftermarket baby. Why should I tell you? Things To Know Sometimes, tuning is not always perfect. Does It Add HP? Read Article. Chai WJ. Before They Run Out. Share Tweet Share Pin.

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