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Turbocharger - Boost Basics
Turbocharging your vintage Ford
Back in the first muscle car era, Ford offered all manner of performance hardware. Powered by high-winding small-blocks, canted-valve Clevelands, and Boss 429s, Ford products were right in the thick of muscle car mania. Though things looked bleak during the dreaded smog era of the '70s, the '80s brought back factory Ford performance machinery. The introduction of electronic fuel injection brought with it a renewed interest in factory forced induction. In a quest to balance power and mileage, Ford employed both turbocharging and supercharging, offering the four-cylinder Turbo T-birds and six-cylinder Super Coupes. Sharing an even more powerful version of the turbocharged four-cylinder was the SVO Mustang. These force-fed Fords offered the power of a V-8 with the weight and economy of a V-6 or inline four-cylinder. These early factory efforts eventually paved the way for such great products as the supercharged, F-150-based Lightning, the legendary '03-'04 Cobra and most recently, the 5.4/5.8-liter Shelby GT500. This proliferation of factory forced induction powerplants, coupled with a strong aftermarket offering similar means of pressurizing the intake charge, makes it easy for current Ford owners (both modern and vintage) to utilize these technologies for both performance and for show.
Ford performance certainly predated the 5.0L Mustang, but owners of early carbureted small-blocks still owe a debt of gratitude to the late-model 5.0L, as Ford's injected wonder engine unleashed a tidal wave of performance products. Though some were exclusive to fuel injection, a great many carried over to the carbureted contingent. Thanks to an industry that now revolved around the 5.0L, early Ford fanatics could now enjoy all manner of aluminum cylinder heads, custom roller cam profiles and even forced induction. Though originally designed for the fuelie Fords, the current crop of aftermarket blower and turbo kits work equally well on carbureted engines. Just imagine popping the hood on your Blue Oval beast to reveal a turbo or supercharged small-block. Toss in the recent introduction of low-buck turbos from companies like CXRacing, and it's a good time to consider adding boost. For the ultimate in low buck, you can also source the majority of a usable system from the wrecking yard.
The main component in any turbo system is the turbo itself. A turbocharger, as it's widely known, is somewhat complex in design, but quite simple in operation. The turbocharger is made up of two distinct, but related sections. They are often referred to as the "Hot" and "Cold" sides, but are more technically the turbine and compressor sections. The turbine section is responsible for receiving all of the hot exhaust gases. In the case of a single-turbo V-8 application, the exhaust from each bank of the V-8 is channeled together into a common Y-pipe, then fed into the turbine section of the turbo. The heated exhaust gas energy is used to spin the impeller blades in the turbine section. The turbine is connected to a matching compressor wheel on the other side of the turbo via a common shaft. When the exhaust gas spins the turbine wheel, this causes the compressor wheel to spin at an identical speed. The spinning compressor wheel draws air into the compressor housing and force feeds the engine more air than it would be able to ingest on its own accord. The extra airflow forced into the engine builds in pressure, and is registered at boost or boost pressure.
There is a significant amount of knowledge and science that goes into selecting the proper turbo for a specific application, but in general, the turbo (or turbos) must be sized properly for the intended boost and power output. Small turbos offer improved boost response, while larger turbos maximize flow and power. The key is to select the turbo that offers the best compromise of both. Lucky for enthusiasts, the manufacturers have done most of the testing for you and will have a recommendation on turbo sizing for your application. The key is to be realistic about your power goals and usage. If you are looking to improve the power output of your 225hp 289 Ford by 50 percent, there is no need to order a turbo capable of supporting 1,000 hp. Both spool up and eventual power will be much less than if you had selected a turbo capable of supporting 500 hp (still 160 hp more than your motor will make). Another consideration is the fact that the 1,000hp turbo might cost $1,500-$2,000 (or more), while the 500hp unit can be purchased online for less than $500. Turbo sizing is one of the times when bigger is certainly not better.
Whenever talk turns to turbos, the subject of turbo lag always comes up. Turbo lag is a phrase that attempts to describe the time between when you step on the throttle and when the turbo is able to supply boost. Boost supplied by the turbo is a function of the relationship between the exhaust flow out of the engine and the turbo (primarily turbine) sizing. Properly sized, modern turbos can provide maximum (or full) boost as low as 1,500 rpm. The downside to having this rapid response can be excessive back pressure (pressure in the exhaust system) at higher engine speeds and/or boost levels. The best cure for turbo lag is a powerful normally aspirated engine and proper turbo sizing. Installation of a turbo on a 300hp, normally aspirated engine will result in greater turbo lag than on a 400hp engine. Smaller turbos will offer quicker response than larger turbos. The key is to optimize the combination to suit your particular needs. Of course, packaging might also determine turbo sizing, as it might be physically impossible to mount a given turbo size in the desired location.
Pricing for the actual turbocharger can vary from company to company, and also depends on the turbocharger size and options. Company's like Borg Warner, Garrett, Precision Turbo, and Turbonetics have been providing enthusiasts with quality turbochargers (or hairdryers as they are sometimes referred to in slang), however companies like CX Racing and Master Power now offer powerful, yet very affordable turbos in a variety of different sizes. We have combined a pair of CX's 76mm turbos to exceed 1,300 hp. CX Racing, as well as many of the other turbocharger companies, also offers numerous turbo components for the do-it-yourselfer, including intercoolers, polished aluminum tubing, oil lines and fittings, silicone couplers and clamps, and even complete kits.
Any discussion on turbocharging would be incomplete with touching on the subject of charge cooling, or intercooling as it's more commonly referred to. The one downside to adding boost to any motor is heat, more specifically, elevated charge temperatures. Heat is a natural byproduct of compression and any time you add boost to an engine, the intake charge temperature will increase. Running 6-7 psi of boost pressure can usually be accomplished without running an intercooler, but every turbo engine (regardless of the boost level) will benefit from intercooling. Since the heated air temperature increases the likelihood of harmful detonation, any effort made to reduce the charge temperature reduces the chance of engine damage. Every effort should be made to reduce the intake charge temperature including a dedicated cold air intake. It makes no sense to go to the trouble of installing an intercooler in the system if you allow the turbo to draw heated engine- compartment air from an open-element air filter under the hood.
When it comes to intercooling, the three most popular methods are air-to-air, air-to-water, and water/methanol injection. There is no ultimate form of intercooling, just the best form for a given application. From a maximum heat rejection standpoint, the air-to-water system will easily surpass the typical air-to-air. The increased potential comes from a combination of the density and temperature of the cooling medium. Water is considerably denser than air and as such, offers greater thermal transfer. This is combined with the ability to dramatically lower the charge temperature using ice water. It should be noted that air-to-air systems can be run with nitrous oxide (or CO2) as an additional cooling medium to further improve their effectiveness. Drag racers (and land speed record attempts) often employ ice water to keep the charge temperatures down on their turbocharged (high-boost) race engines. Road race (and most street) engines usually rely on air-to-air intercooling, as the weight (and transfer from sloshing water) associated with the air-to-water system are both difficult to package and detrimental to performance. Plus, road race cars usually have a steady stream of airflow since they are continually running at speed. For short spurts (like drag racing), or where weight isn't a major factor (like Bonneville), air-to-water seems to be the intercooler of choice. For most street and road-race applications, air-to-air is most common. The most important thing for any street/strip application is to have efficient intercooling, and not get caught up in which form is the ultimate.
Another form of intercooling is water/methanol injection. The injection system can be used to supply either water or methanol, but the most common is a combination of both. The introduction of water and/or methanol into the air stream to act as a cooling agent to suppress detonation has been around nearly since the introduction of the internal combustion engine. The most recent systems, like the Boost Cooler pictured from Snow Performance, are significantly more sophisticated than the simplistic windshield washer bottles and pumps employed not long ago. The Boost Cooler featured a pushbutton, digital variable mapping controller, an LCD screen, and ultra high-output discharge pump. The mixture supplied can be varied using different nozzles sizes combined with changes in the mapping provided by the pump settings. Tailoring the supply of water/methanol will suppress harmful detonation without killing power. In many cases, enthusiasts have relied on water/methanol in place of a traditional intercooler, while some have combined the two in an effort to maximize the amount of ignition timing and boost that can be run on 91-octane pump gas.
One final form of liquid intercooling comes from, of all places, the carburetor. Used either in blow-through or draw-through applications, the atomized fuel supplied by the carburetor has a dramatic charge cooling effect on the pressurized inlet air. Testing on typical blow-through carbureted applications has shown a drop in charge temperature of more than 100 degrees. This is one area where carburetors actually out perform electronic fuel injection, as the position of the injectors down near the intake valve (either in the head or intake manifold) limit the time for charge cooling. In many cases, the carburetor functions as an intercooler on low-boost, street/strip application. For the ultimate in charge cooling on carbureted applications, cooling from the vaporized fuel can be combined with traditional intercooling (air-to-air or air-to-water) or even water/methanol. We have even employed nitrous oxide as chemical intercooling, though the gains offered by the additional oxygen molecules are considerably more significant than those offered through charge cooling.
The Hot and Cold Sides
Thanks to the 5.0L Mustang, turbo kits abound for small-block and Windsor Ford V-8s. Though designed for injected engines, the majority of the components can be used on a carbureted powerplant, especially the intake and exhaust tubing. For the do-it-yourselfer out there, a simple turbo system can be produced for significantly less than $1,000. Forget everything you have read about equal-length, mandrel-bent tubing, and concentrate on getting all of the exhaust to the turbo. You can build a very effective turbo kit using factory cast-iron exhaust manifolds or opt for inexpensive shorty headers. From there, you (or a local muffler shop) can route the exhaust system to suit the turbo placement. Simply merge the exhaust from each manifold into a common Y-pipe and weld on a T3 or T4 turbo flange. The larger T4 is probably preferred for a single-turbo, V-8 application, but don't concern yourself with the size of, or crimps in the tubing, especially for a street application. Make sure the turbo position provides adequate room to run a suitable down pipe (the part that runs from the exhaust side of the turbo to your actual exhaust system) of sufficient size--we've run 850 hp through a single 3.0-inch exhaust). From the compressor, route boost from the discharge (pressure) side of the turbo to the carburetor bonnet or (alternately) through the intercooler and bonnet. All that is left is to provide pressurized oil to the turbo and drill a hole in the pan to serve as an oil drain back.
One area that needs to be addressed with any turbo system is heat management. Heat energy is used to spin the turbo, but the radiant heat from the hot side of the turbo must be taken into account when positioning the turbo. You'll want to keep the exhaust (turbine) side of the turbo and associated plumbing (including running the crossunder pipe) away from components or paint that may be damaged by the heat. It's also possible to insulate the hot side with thermal barrier coatings, header wrap, or turbo shields, but that actually diminishes the life of exhaust tubing. Heat management is another reason why individuals choose two turbos over singles. Sometimes it's easier to package a pair of small turbos than one large(r) turbo. For some, having twin turbochargers improves the visual statement by offering better symmetry. There is an argument in favor of running two small turbos (over a single larger unit) to improve boost response, but bear in mind that only half of the exhaust energy is provided to each small turbo in the twin set up. In reality, both the single and twin set can offer identical boost response and power with proper sizing.
Turbocharging Your Vintage Ford
By now you've probably figured out that turbocharging your automobile has tremendous benefits. Doing so can double or triple your power output without changing your driveability--once you experience the power of boost, it is hard to go back to a normally aspirated combination. A turbocharger system would also provide the basis for some interesting bench racing at the next cruise-in or car show, where everyone else will be sporting the standard single four-barrel or the occasional EFI engine.
While there currently doesn't seem to be any aftermarket turbo systems available for vintage muscle cars, many of the Fox-body Mustang systems can be adapted to fit with minimal modifications. There's also the custom route, and you'll find that there are numerous shops that specialize in building custom turbocharger systems. Then there is the DIY enthusiast who just sits down with a reciprocating saw and a welder and builds his/her own. On websites like www.theturboforums.com and www.turboford.org, you'll find numerous turbo systems being crafted in the garage, and plenty of like-minded enthusiasts looking to share information on the subject.