The turbo kit we are using for this story is the Hellion Heat system. It is designed to fi
Sometimes we have to wonder why anyone is trying to make N/A power anymore. We concede that there are a zillion racing rules to prevent power-adders from dominating, and turbos look kinda complicated. But you'll need to get over it. We realized this after getting hooked on watching those turbo small-block guys on YouTube beat the hell out of Vipers and any sportbike jockey willing to risk the road rash. Forget the big cam and loose converter; you won't need 'em. You don't even have to wonder how to stash a big-block under the hood or where to cut the blower hole. All you need is a turbo or two to make obscene power, and we're going to show you how to get one.
Big or small? On the pressure or cold side of the turbo system is the compressor. As spent air and fuel exits the exhaust port, it spins the exhaust turbine wheel which spins the turbo shaft that is connected to the compressor wheel. The size and pitch of the wheel and the shape of the housing determine where the combination of air flow and boost pressure is most efficient. The trick is to select the compressor size that delivers that efficiency in a usable rev range. A smaller compressor wheel will be more efficient lower in the rpm range but will create more heat at higher engine speeds. It will also restrict the flow at higher rpms. Too large a compressor will cause boost lag and possible compressor surge in the lower rpm range and be the most efficient at higher engine speeds. Since the compressor wheel predicts the horsepower needed from the turbine, it is very important to get the sizes correct. Too small a turbine spools fast but restricts at the top end. Too large a turbine can't deliver enough power to the compressor at the low end.
The key to the Hellion system is the Turbonetics Custom 60 turbo with a 61mm F1-65 compres
The pressure ratio and corrected mass airflow are the two numbers you need to evaluate the compressor on a map. Select the turbo with a compressor map that puts the two plotted points between 65 and 70 percent efficiency for a street application. To get the pressure ratio, simply add the amount of boost in psi to standard atmospheric pressure (14.7) and divide it by 14.7. We will use 10 psi because it is nearing the threshold of safety for a nonintercooled pump gas engine. The pressure ratio for a 302-inch engine at 6,000 rpm is 1.68.
Looking at a compressor map, it is possible to make the mistake of simply multiplying the total engine CFM by the pressure ratio to get the corrected mass airflow and connecting the dots. The truth is that the corrected mass airflow number is a result of several complex calculations involving air density, pressure ratio, engine CFM, and even air density at boost. If you do manage to get through the math, you'll note that the final piece of the puzzle is the efficiency of the compressor itself determined by a table.
The shortcut to all this is what Turbonetics engineer Dave Austin calls tribal knowledge. Look at what other guys are doing and see if it works or simply call a reputable turbo company to get some suggestions. Turbonetics, for example, has a matrix of its popular turbo categorized by engine size and horsepower based on years of trial and error. The entire grid is too large to print here but you can access the knowledge with a simple email or call to the tech line. Just be sure to know all the details about your car and your plans for its use.
The key to turbo longevity is cooling and lubricating the bearings. Oil that is not change
Picking a turbine involves choosing the wheel that is small enough to respond quickly and large enough to spin the compressor wheel fast enough to produce the desired boost pressure and minimize backpressure. The rule of thumb is to pick the smallest wheel diameter that still allows you to meet your horsepower goals without putting a kink in power. Modern turbos are ultimately tunable with replaceable and clockable turbine housings, so you can fine-tune the system if you miss the mark.
To help you choose a turbine housing to suit your needs, turbo manufacturers rely on a simplified tool called the A/R ratio. The A is for area and the R is for radius. The A/R ratio is the relationship between the center point of the cross-sectional area in the passageway and the radius from the center of the turbine wheel at the inlet to the volute. This is a simple division of A over R. As A gets smaller, air speed of the gas increases, as does its effect on the speed of the turbine wheel. If A gets too small, it will choke and not be able to deliver enough energy to the compressor, and the peak power will suffer. The backpressure on the engine will also get too high, causing back flow into the cylinder when the exhaust valve opens. As A gets larger, it will be able to deliver more energy to the turbine wheel at the expense of speed. The efficiency of the turbo and the design of the turbine wheel also have an effect, but usually it is the A/R and the turbine wheel size that determine the spooling, overall airflow, and pressure that are delivered. As a general rule, an A/R of 1.5 will deliver more power and an A/R of 0.5 will have better low-speed response. According to the matrix, engines between 5.0 and 6.0 liters will like between 0.68 and 0.81 A/R.
The Hellion system includes the engine oiling system hoses. Pressurized oil from the engin
Wastegastes And Bypass Valves
As you can probably imagine, since boost pressure is created by exhaust pressure and a spinning compressor wheel, it is possible to feed the engine more boost than the fuel's octane rating or even the engine itself can handle. This condition is called overboost, and it can be controlled by a valve called a wastegate that bypasses exhaust gases around the turbo and into the exhaust flow. Wastegates are boost-referenced to regulate the maximum amount of energy delivered to the turbine and therefore the amount of boost created by the compressor. The type, location, and size of the wastegate are the keys to an effective system.
Most factory turbos have an integral wastegate where the mechanism is built into the turbo housing and actuated by an arm that connects the compressor to the turbine. Although it is compact and functional for a low-boost single- or twin-turbo setup, it cannot be clocked for installation and puts the gate in the least desirable part of the system. External wastegates are sized according to the amount of power you wish to make and should be located where it can collect all of the exhaust pulses, such as the end of the header collector or manifold. Gases should be prevented from turning back on themselves or turning sharply to exit the turbine. Since the gas will take the path of least resistance, it is possible that at high rpm the turbine will continue to increase speed if the path to the exhaust is restricted or the wastegate is too small.
There is a debate about the use of split-exhaust housings being more efficient than a sing
The bypass valve is plumbed into the cold side of the system and is designed to prevent surge and compressor damage. In a high-rpm/high-boost situation, if you quickly lift off the throttle, there is no way for the pressure to get into the intake manifold. Because the turbine and compressor are still spinning, pressure stacks up against the throttle blades. This pressure can stall the compressor wheel or cause a surge as it reverses direction, creating a low-pressure area and raising and lowering the compressor's speed. The bypass valve simply vents the pressure to the atmosphere when the throttle is closed. It is also the source of the chirping noise you sometimes hear when turbo cars lift to shift gears.
Heat, Detonation, And Intercooling
Early factory turbo cars had no intercooler and therefore no protection from the additional heat built by the turbo's ability to rapidly compress and heat the incoming air. This, combined with pump gasoline, introduced detonation, which is still the number one way to destroy your engine. The solution ranged from terrible static compression ratios as low as 6.0:1 to the turbo Corvairs' Turbo Rocket Fluid that was really just a jug of water/methanol that was introduced to the intake air stream to cool the charge. It worked great until you forgot to fill it. Low-compression engines with large turbos made for sluggish, low-rpm street cars that would suddenly wake up for some snap oversteer and wild, smoky fishtails. Just ask anyone who owned an early '70s Porsche 930.
The idea of an efficient engine with a reasonable compression ratio that has good low-speed response and uses enough boost to create real power is possible with an intercooler. The intercooler is simply a heat exchanger that sits between the compressor and the intake to reduce the heat that was added in the process of compressing the air. On the surface, intercooling the air charge allows you to run more boost or run a smaller turbo on an oil-cooled engine. What it is really doing is stabilizing the intake air charge to prevent detonation and expanding the entire compressor map, which allows you to make more power with a smaller engine and less violence. We also recommend an MSD with an adjustable timing curve or a boost references timing control system to avoid rattling the engine.
To prevent exhaust leaks, the kit comes with ball-flange-type connectors everywhere. You c
The cold side of the turbo system from the compressor to the intake manifold uses T-bolt c
The hot side of the turbo system from the exducer housing to the exhaust system uses V-ban
Although we've seen PVC and hose clamps for the cold side, it's best to use silicone hoses
To make more power, you'll need more fuel. There are three types of installations: the blow-through and draw-through carbureted and the blow-through fuel-injected systems. The draw-through carbureted system has a number of faults, the worst being the presence of an air/fuel mixture passing through the compressor and the lack of an intercooler option. The blow-through system is slightly less arcane and works on the same principles as any centrifugal supercharger blow-through system. Therefore, blowthrough carbs that are built specifically for this purpose are already available. We've made good power using Quick Fuel and Carb Shop blow-through prepped carbs and 10 pounds of boost, including a 600hp run with an ATI ProCharger on a Ford 302.
If you have a fuel-injected engine and are running 5 to 6 pounds of boost, you can use an FMU (fuel management unit) that boosts the fuel pressure or adds enrichment fuel in some other manner or step up to an aftermarket controller to remap the fuel curve and run larger injectors. On a 5.0L Mustang, a 255 GPH in-tank pump and 42 lb/hr injectors can be tuned to 550 rwhp.
Carbureted cars need a boost-referenced fuel regulator that increases the fuel pressure along with the boost curve.
From the exducer, the system includes the connectors for a stock exhaust system on a '79 t
Sourcing A Turbo
Using the math, you can build a complete system on paper. Using the science of compressor maps and some idea of the size and rpm range of your engine, you can add virtually any turbo to any engine. The trick is the availability of the maps and the A/R ratios of the turbine housing and sizes of the turbine wheels. Small factory engines yield small turbos with internal wastegates that will need to be run in pairs on a V-8. They are also generally water-cooled on OE vehicles for longevity. 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. The automatic transmission coupe has a single turbo with an A/R ratio of 0.48, and the standard coupe has an A/R of 0.63 and the compressor efficiency map designed for a 2.3L four-cylinder engine. Using the map in the Junkyard Turbo sidebar, you can see that with a boost pressure ratio of 1.68 (14.7+10/14.7=1.68), it's easy to get the turbos down to around 65 to 68 percent efficiency. 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.
The lure of the $80 junkyard turbo is enticing, but before you buy, take a look at the guys who are really having fun and see what they are using. 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 29. 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. New turbos have modern compressor maps with a wider variety of A/R ratios and clockable turbine housings, a variety of wheel size options, and tech support to help with problems. 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.
Note the oxygen sensor port for factory EFI (arrow). The turbine outlet should always be l
The wastegate is bolted to the crossover pipe from the driver-side header. Ideally, it wou
The Hellion kit comes with a Mitsubishi bypass valve. Turbonetics offers an assortment of
Here is the complete system as we would set it up for a blow-through carburetor-type syste
Because the turbo is clockable, we also test-fit the system with the included air-to-air i
The upgrade for this system could be the Turbonetics GT-K. The machined slots are called m
For combos that make 500 hp or less, use the Evolution wastegate. Turbonetics also offers
This is an example of an internal wastegate often seen on OE vehicles. Note the size of th
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.
This is the map from the "good" '85 to '86 Ford Thunderbird. Note that the surge line narr
This is the 60-1 compressor map from Turbonetics. Note the agreeable shape of the surge li
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.
|Cool Books About Turbos |
|Title ||Source |
|Maximum Boost by Corky Bell ||Bentley Publishers |
|Turbocharging Performance Handbook by Jeff Hartman ||Motorbooks |
|Turbochargers by Hugh MacInnes ||Motorbooks |
|Turbo: Real-World High-Performance Turbocharger Systems by Jay K. Miller ||SA Design |
|Description ||PN ||Price |
|Hellion Heat System ||N/A ||$3,999 |