Without an ignition system...
Without an ignition system that can provide a hotter spark, a situation can arise in which the spark plug has its spark blown out by the increased pressure prevalent in the combustion chamber. Here, FFW competitor Chris Little uses an MSD-type ignition system to light the fire. You can also see the adjustable fuel regulator sitting on top of the manifold (arrow). The rule of thumb when utilizing a turbo is to increase fuel pressure 1 pound per every 1 pound increase in boost.
So, if twin-turbos will spool up and produce boost quicker than a single turbo, other than cost, why don't more street enthusiasts utilize a twin-turbo setup? It all comes down to application and driving style.
"A twin-turbo setup is more complicated in terms of fitment and fabrication," Head says. "For a street car, it's probably not necessary. A single turbo would probably be the best way to go." As Head explains, when installing a twin-turbo system, the fitment of the turbos, wastegates, and plumbing makes it tougher for some cars as opposed to others.
Is a twin-turbo system too extreme for a car that does have enough underhood space to install one? "If you are looking for big horsepower, then twins are the way to go," Horne says. "With twins, you get more boost at lower rpm as opposed to what you would get with a single, large turbo."
If you look at as many Mustangs as we do, you will see both single and twin-turbo setups on street-driven cars, showing that more and more, twin-turbos aren't just for race cars anymore. "It was not long ago that only race engines used twin systems," Napier says. "Now, many street systems utilize twins for benefits."
Fuel, Spark, and Internals
As you have read, there is much more to turbocharging than just bolting on a turbo and letting 'er rip. Now it's time to cover the other major aspects of running your engine success-fully with a turbo
It's common knowledge that an engine needs air, fuel, and a spark to run. With the turbo forcibly shoving a larger-than-normal volume of air through the intake and into the cylinders, the corresponding amount of fuel is needed to mix with the extra atmosphere to maintain the desired air/fuel ratio. By upgrading the induction system, an upgraded fuel system is a must as well. This includes fuel injectors, fuel pumps, fuel lines, and more.
"Having a fuel system that regulates fuel pressure based on manifold pressure and/or vacuum is ideal," Squires says. "Additionally, air/fuel ratios are richer on a forced induction application versus a naturally aspirated tune. We typically run our systems in the low-to-mid 11:1 range to stay on the safe side of tuning.
"According to Horne, there is a general guide-line for increasing fuel pressure when related to an increase in boost. "We set the fuel pressure at 43 pounds normally," he says, "and then raise the fuel pressure 1 pound for every 1 pound increase in boost."
The more power you make with the turbo, the more fuel you need to supply, starting with the fuel pump and a rising-rate regulator all the way to the injectors. According to Head, however, there is one item in the fuel system that is sometimes overlooked.
"Both the feed line and return line sizes are very important," he says. "They need to be large enough to support the fuel level but not be too large and cut down on flow velocity.
"Power is made when the ignition system lights the plugs and fires off the air/fuel mixture. In a forced-induction application, an upgraded ignition system and reduced spark-plug gap is often needed to properly induce combustion. "Above 10 pounds of boost, if you do not have a strong enough ignition, the spark plugs won't be able to jump the gap," Horne says. This can lead to a misfire or poor running condition.
"Ignition systems typically need to be upgraded to handle the additional cylinder pressure," Page says. "In addition to an ignition amplifier, the spark plugs need to have a smaller gap to allow the spark to jump the distance between the electrode and the ground strap in the high pressure atmosphere without said pressure blowing it out."
Most of those we interviewed for this article stated that a CD-ignition system like an MSD is the way to go. "A good ignition box, like an MSD 6AL or 7AL, would work," Head says. Along with the upgraded ignition components, which can include the MSD box and a high-output coil, the computer must be tuned as well. "Most modern ignition systems are computer controlled," Napier says, "so an aftermarket chip or flash tuner will also be a likely requirement to help the factory engine-management system adapt to the changes turbocharging requires."