Building A Turbo Combination

They are the voodoo child of aftermarket power adders. Shrouded by secrecy and shunned by many racers and street enthusiasts, turbochargers have long been the most misunderstood, yet feared, power adders on the performance planet. According to Job Spetter, president of Turbo People, turbochargers have gone from laughing stock, to lucky strike, to unfair advantage over the last 25 years, but to him turbos are just another way to go fast.

Using the black art of recycling exhaust energy into intake efficiency, some would say turbos could turn your engine into a perpetual energy machine--if only you could understand how to set them up. After chatting with a few respected turbo tuners, we've learned the real secret about turbos.

Turbos really aren't the freak wallflower of the performance dance. In fact, turbos need the same things many of the more popular power adders need. When it comes to turbos, the usual piecing together of a combination and detail tuning make or break them just like any other method of unnatural aspiration.

The only real trick with turbos is you simply can't swap pulleys or jets to step up the performance, nor is it always simple to change turbos, as the exhaust system and turbo are critically linked. As such, it's exceedingly important to get the turbo system setup from the get-go. For street cars, going with a production turbo kit from one of the companies listed in "The Latest Power Craze" story on page 30 is the easiest way to go.

More aggressive, and well-heeled, street/strip and race turbo fans may wish to go with a custom turbo kit. This means going to an expert and doing it right the first time. "There are different turbos, which will satisfy different needs," Spetter says. "Anybody with some turbo background can do that for you. It's not terribly difficult. It's just like a blower or nitrous. You can't put a 500-shot on a stock motor." The choice depends on "how much fuel system they have, how much computer, how much injector, and so on," he adds.

Building The Host
What goes under all the turbo hardware is at least as important as the turbo system itself. Once you decide on your performance goals, think about the big picture. Turbo combinations tend to be easier on equipment, according to Bill Devine of Downs Ford Motorsport, who drives Jon Yates' 7-second turbocharged Pro 5.0 car and his own turbo Pro car, one of the first in the 7s. However, as Dennis Lugo, driver of Tom Moore's mid-8-second Street Outlaw and proprietor of Lugo Performance Automotive explains, a turbo loads the whole engine--not just the crankshaft, like a blower.

Because any power adder can be rough on the engine, you don't want to put a ton of boost or nitrous to your 200,000-mile short-block. That's not to say you can't do well putting streetable boost to a stock engine. However, if you want to step it up like most speed addicts, you'll likely be leaning on the equipment. "It's a smoother torque curve. I would think the load is probably easier on the engine when it's done correctly," Spetter said. "When it's not, it looks just like your worst nightmare' like somebody got in there with a plasma cutter."

As such, Spetter approaches the engine as a workhorse and the turbo as the thoroughbred. "The theory being the motor is the host and whatever you put on it needs to do the work, whether it's nitrous, a belt-driven supercharger, or a turbo," he says. "The host needs to be strong. Not overly fancy. Not crazy. And we let whatever we put on it do the work. When you have both of them doing a lot of work, it doesn't usually work out so well."

Though a turbo engine need be strong, it need not be complicated. Any good set of aftermarket cylinder heads should work just fine. Porting is better, especially on the exhaust side, but as Devine says, you reach the point of diminishing airflow returns because the turbo is forcing air through the engine. Any quality aftermarket intake should also be fine with a turbo, but they do lean toward intakes with more plenum volume--that's typical of superchargers, too.

The one area where turbos really stand out from the crowd is camming. While any naturally aspirated engine needs overlap between the closing of the intake valve and the opening of the exhaust valve to promote scavenging--where the evacuating exhaust actually helps fill the cylinder--racier supercharger applications also get away with a bit of overlap as any boost loss is usually overcome. Turbos, however, are reliant on exhaust flow for motivation, so the intake and exhaust events must be quite distinct.

This makes the camming different from most performance applications, as you actually want to run a "small" cam for better performance, which is a boon to those running turbos on the street. In fact, many installers of street turbo kits stick with the stock camshaft to provide great performance with impeccable driveability. Those wanting more are best suited to approach a turbo tuner for a proven cam grind.

Carrying the Load
As with any power adder, the ancillary systems like fuel and ignition are critical, but no more so with a turbo. "They need to be properly sized," Spetter reiterates. "If you set up a car to shoot 600 horse of nitrous or put a double X on it, and you don't have enough fuel system or a good enough computer to control it, you're going to break it. It's, again, a matter of sizing it properly."

According to Lugo, sizing a turbo fuel system properly means leaning toward more capacity. Because turbos provide such a long, flat torque curve, the engines are under load for a longer period of time than, say, a supercharger. Turbo engines simply make a lot of torque, which requires a lot of fuel. As for the ignition system, turbos need a high-output system, just like any forced-induction application, as the increased cylinder pressure means the mixture is more difficult to ignite.

The real trick with an aggressive turbo setup is the engine management. While you can get away with using the stock computer and 36-pound injectors, according to Devine, anything more means some kind of programmable engine management.

Of course this is right up Spetter's keyboard. "Power is power. No matter how you make it, the tuneup is everything. The right combination of parts, of course, and then the tuneup is everything. When you are off with that you could have the best of everything and it just doesn't work," he says. "Being able to choreograph it in the end and put it all together is what separates one from the other."

Naturally, you can use just about any electronic engine management to maximize your turbo application, but be sure to select one your tuner of choice is familiar with.

Getting it Right
In today's Mustang racing environment, there is a shift toward turbocharging because of their efficiency in producing power. The real trick is that thus far turbos have been a rarity in the drag-racing ranks, so there are few tuners familiar with their quirks. Even though a turbo runs quite well when set up correctly, you may have to pay for that setup at the hands of an expert. "The word is that turbos have this huge advantage and it's just not true. There are no free lunches," Spetter says. I've been doing this for 25 years and certainly have had my shed full of broken engines and camshafts that didn't work. Using a turbo doesn't buy immunity from any of the other things that break race cars."

Turbos are also making more 5.0 race cars fly, and we suspect many of you running street Mustangs may soon follow suit. So long as you follow some common-sense guidelines, the only problem you'll have is paying for all those new rear tires.

Horse Sense:
Twin turbos have the reputation for spooling up quicker and putting up less back pressure, but, on a 5.0, they also have only four cylinders to spin each turbo, so they have less energy on tap than a single turbo driven by all eight cylinders.