Ignition, fuel system, exhaust, and electronic controls

Modern turbo cars have a complex ignition and fuel system controlled by computers. Making changes to any of those systems can change the way the other systems work as well. With that in mind, the old "change one thing at a time" rule may still lead to some unexpected results.

One very important rule that I always try to remind people of is that just because something works on a race car, doesn't mean it will work on your street car. It is very easy to spend money on these cars, but money doesn't always equal horsepower. You can buy equipment that can easily hurt the performance of your car instead of helping it.

You can't just throw a huge turbo on the car and take it out racing. Actually, you can, but it won't last long, or run terribly well. Many companies offer upgrade packages or "stages". These kits are usually a good place to start, but be prepared to spend more money than the kit alone, even if you do the work yourself.

Every racer knows that increasing horsepower exposes the next weak link in the car. If you have 25,000 miles on your current stock clutch and add 125 more horsepower in a performance package, chances are your stock clutch will be a memory in short order. Don't just build the engine, build the entire car.

I don't know how many times I have seen someone build a really nice engine, stick it in a Camaro, and run the same times or slower at the track. The reason is that he built an engine and forgot about the rest of the car. Things like Exhaust, suspension, tires, U joints, axles, transmission/clutch, all have to be considered. Subtle items like chassis flex eat gobs of horsepower, but go unnoticed by most. Front wheel drive cars can get almost undrivable because of torque steer under full throttle. It can be improved dramatically, but it takes building the rest of the car to match the engine.

Fuel system

When you add a bigger turbo to your car and crank up boost pressures, there are other things that you must do to make it all survive. A big turbo puts more air into the engine, but it doesn't add more fuel. Adding boost may tell the computer to add more fuel, but a bigger turbo has higher air flow. Turbos all have a CFM (Cubic Feet per Minute) rating attached to them. They are rated for air flow at a boost pressure of 15 PSI. This is so you can compare the efficiency of given models and makes of turbochargers.

Lets say you have a stock Mitsubishi TD05 12A turbo on your car, and you run it at 15 PSI boost. Now you go out and buy a TD05 16G turbo and stick it on at the same 15 PSI of boost. The car runs much harder, but now it's leaning out at high RPM (since you also have a air fuel monitor on it right?). The reason is pretty simple, the 12A turbo produces 320 CFM at 15 PSI of boost, but the 16G makes 505 CFM at the same 15 PSI boost. So the new turbo is feeding almost 65% more air to the engine at the same fuel rate. The stock computer has very limited means of keeping up with this increased air flow, so you run lean which leads to more heat, piston damage, and uncontrolled detonation.

Most computer systems have a limited ability to retard the timing as boost rises, or if it hears detonation in the engine (pinging). The problem is that most factory detonation sensors are not terribly good at picking out anything short of destructive detonation, and then the system reacts too slowly, or has to small a range to retard the timing. The answer is to avoid detonation instead of trusting the computer to save your investment.

That can be done in several ways. The easiest way is to install a rising rate fuel pressure regulator. These regulators increase fuel pressure as the boost pressure rises. That adds more fuel to the mixture over the same injector pulse width. At the same time, install a good Air fuel gauge. There are several out there, and most work well as rich or lean indicators. None that I have seen are accurate, or fast enough to give you a true idea of the real ratio. That's ok though, all you need is something to glance at to see if you are too lean at full throttle. The actual ratio isn't important at that point.

There are some things that have to be done at this point so that you can see what your setup is doing. As I said above, get an Air fuel monitor. Also get a good quality vacuum/boost gauge. I know, many say screw the vacuum gauge, but those are the ones that follow there cars around with a dust pan and a broom. A vacuum gauge can tell you a lot about the condition of your engine, especially the valve train/upper end. I like having a fuel pressure gauge as well, but it isn't required hardware. Make sure you have a tach that is accurate, and fast acting enough to keep up with the engine.

Ok, so now we have the gauges we need to see what is happening under the hood. Pay particular attention to the air fuel monitor until the fuel system is adjusted in. Since that is where the most damage can occur, we'll do that first.

Go out on some lonely stretch of road with no traffic and cruise at about 40 in 3rd gear. I use 3rd because you have more time to watch gauges while under boost than 1st or 2nd. Now nail down the throttle and as the car pulls, glance at the air fuel monitor several times before you run out of RPM. It should be well into the rich side of the monitor. If it is near the middle or "ideal" area, lift off the throttle NOW! If it is a fully segmented monitor, it should read above 3/4 scale to be safe. You can run a bit leaner than that, but you start trusting that the computer will save the engine again. On the Intellitronix monitors, I like to see the first red light lit on the rich side the last yellow is a bit lean for my taste. Gas is cheaper than pistons.

Ok now you have a general idea of what is going on. So how do you change it if it's too lean? If you have a rising rate regulator, and your not too far to the lean side, you can increase fuel pressure. Be aware that this can kill a stock pump, so now is the time to think about getting that high flow Bosch pump. If you are too far into the lean side, you will need to get larger injectors, and that high flow Bosch pump.

Another option is to invest in an auxiliary fuel controller (AFC). These allow you to add from 1 to 4 injectors to the fuel system under control of the AFC system. The AFC activates the injectors as needed to enrich the fuel mixture. Most AFC systems are fully programmable to individual needs. They usually run from $350 to $550 new.

Some companies offer programmable modules for the stock computer so that you can use large injectors and adjust the pulse width under boost. This doesn't kill fuel mileage as badly as a performance replacement (remapped) computer. These setups can run upwards of $1000 though depending on the type of car. Unless you need the wide range of possibilities offered by such a system, I'd suggest sticking to tuning for your needs.

If you are going to make 350 hp or more, you'll need some kind of aftermarket fuel management system. At that point you'll want to invest in an exhaust temp gauge (EGT) to get an accurate idea of what the injection system is really doing. The EGT measures the exhaust temperature, which can tell you how rich or lean the car is running. The cooler the temp, the richer the mixture. At above 1450 degrees or so most engines will start having problems (too lean). Somewhere between 1380 and 1440 is average for most engines.

Exhaust

As soon as you decide to put that big turbo on the car, you first stop should be to the local speed shop, mail order warehouse, or muffler shop. Virtually all turbo cars can use a better exhaust than was provided stock. There are basically 2 types of bends that are made to pipes. Muffler shops use a standard pipe bender that crushes pipe as it bends. This in turn reduces the flow of the pipe, but it can still be used if the bends are not too sharp, and the pipe diameter is large enough. 3 inch pipe works well if a muffler shop can make slight bends to keep it from crushing down to stock size.

Mandrel bending produces smooth bends without crushing the pipe. This is certainly preferred, although more expensive than a muffler shop. The actual size of pipe used will depend upon which method you use. A muffler shop can do a good job on a performance exhaust using 3 inch pipe if they can build it without creating bottlenecks in the pipe. It all depends on the type of car, so see a couple of shops before having the work done. Mandrel bent systems can be bought from several sources in pre-made kits. You should stick to at least a 2 1/2 inch system.

You can also combine both methods above. Several companies offer sets of 180 degree pipe bends. These are mandrel bent, and can be cut and welded as needed by a muffler shop to get the correct pipe layout. This is generally between the two options mentioned above in price, but offers a fully custom system with the benefit of mandrel bent pipe.

A 3 inch system is pretty much overkill on most street cars unless it is shop bent. Even on a 2 1/2 inch system, I'd recommend using a 3 inch high flow converter for added flow. A good quality high flow muffler towards the back of the car is best. I like Flow Master, but there are several good brands out there. If you want to get more pricey there are full stainless steel systems available in mandrel bent as well.

Ignition

What can I say, don't skimp on the ignition system. On a turbo car, the ignition will have to deal with extreme pressures in the combustion chambers, high heat under the hood, and drastically changing driving conditions.

There are many good ignition systems available by MSD, Holley, Crane, Mallory, and others. These are multiple discharge systems that fire a spark plug several times per combustion stroke instead of just once. This produces better efficiency and more complete burning of the mixture. When combined with a high output coil, these systems are capable of handling of over 700 hp.

Because of the high temperatures under the hood, I like 8 mm plug wires. Several makers offer kits for most cars. I would stick to the spiral core type wires instead of solid core. Some computer systems don't get along well with solid core wires.

Be sure to go down in heat range on your spark plugs by a couple of steps. This will help engine cooling and to reduce detonation.