Exhaust/Headers, Limited Slip Differentials and Fuel Injectors

Exhaust: High
The vehicle’s stock exhaust can be very restrictive of the airflow. If you have not already, you should eliminate the catalytic converter and have a high flow exhaust installed using larger diameter exhaust piping. By doing this, you will allow greater exhaust flow and obtain performance gains. Bring your car to a well-respected exhaust shop and have them build a custom exhaust for your car. There are two different types of bends the exhaust shop can utilize when fabricating the exhaust. The first type, utilizing a “tube bender”, is most common and produces the least expensive exhaust system. It bends the straight tube around a die. The down side of press bending is that the outside diameter of the tube in the middle of the bend will crinkle and cause airflow to become restricted and disturbed. The engine now has to use more of its horsepower to push the exhaust gas through the pipes, thus sacrificing performance. The second method of pipe bending is called mandrel bending. This style of bending utilizes a series of retractable and snug fitting, lubricated steel balls inside that section of pipe while being bent. This design keeps the pipe from shrinking or crinkling during the bending process, due to the steel balls inside the bend, thus providing the highest possible air flow. When you are looking for an exhaust shop, verify that they will be using mandrel bends. The cost of a custom exhaust varies, but for a very good quality exhaust, anticipate paying approximately $500.

Air Intake System: High
If the car has a stock air intake system, and especially if you have completed other exhaust work, this will be a worthwhile modification. If you can’t get air into the engine fast enough, it really does not matter nearly as much how quickly it can exit. The typical cost is $170 – 200.

Limited Slip Differential: Medium
To better understand how a limited slip differential (LSD) can be advantageous, let’s first look at how a standard differential works. When a vehicle using a standard differential has one wheel without contact to the ground and is powered by the engine (FWD vs. RWD), the contacting wheel will remain stationary, and the non-contacting wheel will rotate at twice its intended velocity. The result of this is no power being applied to the wheel on the ground. As in this example, the differential will supply the power to the wheel that is loaded with the least amount of resistance. In normal everyday driving, the likelihood of this situation occurring is very rare, or at least should be, except in slippery conditions. Even if it does briefly occur, losing ¼ second won’t cause you to be late for work or be a safety concern. During a race, when cars are cornering close to their limits and drivers are looking to shave lap times down as much as possible, experiencing this issue costs valuable time. So how does a LSD solve this problem? This type of differential allows some difference in wheel rotation velocity, but does not allow the difference to increase beyond a pre-set amount. What the LSD essentially does is sense which wheel has the better grip and biases the power to that wheel without completely removing power from the other wheel. This translates into the car having more power to the ground in extreme cornering situations. Even if your vehicle comes stock equipped with a LSD, there are typically differences between units built for a sports car versus a racing application. Your vehicle and the tracks that you race on will impact how much of a benefit the LSD will yield.

There are two different types of mechanical LSDs available. One type is a geared torque-sensing version that uses planetary gears to sense the torque on the drive shafts. The geared torque LSDs typically won’t wear like a clutch type could, but it is believed that the torque distribution characteristics can be less than ideal for racing purposes. The other type of LSD that I just referenced is the clutch type LSD. With this type of differential, clutch packs are installed which have varying degrees of force applied depending upon the differential wheel velocity. (Phantom Grip is a company that sells an LSD that somewhat emulates the clutch type using a spring block, but does not have clutches. I am not very partial to the Phantom Grip units for racing, but they do have a place outside of racing applications.)

Once you have determined which LSD you want to purchase, you also need to determine how it will be installed. Attempting to install an LSD would be very difficult for someone other than an experienced mechanic. My suggestion is to have the company where you purchased the LSD also install it if they offer that service.

Assuming the shop is not within easy driving distance from you, ship your transmission to them. It is an easier process than one might think. The first step is to get two boxes that the transmission will fit into. Trim one of the boxes down in size so it will fit into the other box. Completely drain the fluid out of the gearbox, then put a label on it identifying the model of the car and your name. All you need to do now is put a plastic bag around the transmission, put it into the box, and stuff the remainder of the box with newspapers or shipping Styrofoam peanuts. It is now ready to begin its journey. How can you ship the tranny? This surprised me a bit, but shipping companies such as UPS, FedEx Ground, DHL, and United States Postal Service will ship it at a reasonable cost. Shop around to determine which company offers the best price and service

The other option would be to bring the LSD and stock transmission to a reputable transmission shop and have them complete the installation. One benefit of having the company which supplies the LSD unit complete the installation is that if there are any issues, they can’t say it is because you had it installed incorrectly. In addition to having a company install the LSD, I recommend that you also have them rebuild your transmission.

Prices for the LSD range from $600 – $1,500 depending on the type of LSD and company you choose to purchase it from. For just the clutch type unit that I purchased, it cost me $700 for the LSD alone. When I had my LSD installed and tranny rebuilt, it cost me an additional $300 plus parts, for a total of $375 for the rebuild and installation. If your tranny is not in good shape, the cost to rebuild it will obviously be more but it is much better to know and take care of this now. Since you have the tranny off the car, now would be an opportune time to replace the clutch if that has not been done recently. A good quality racing clutch kit typically costs $300 – $375.

Race Exhaust Header: Medium
Although the header is a part of the exhaust system, this is considered to be a separate component. There are many different types of headers available from off-the-shelf units to dyno-tuned racing headers. For a decent header, anticipate paying approximately $400 – $600.

Blueprint Stock Fuel Injectors: Medium
People are often led to believe that it is necessary to purchase higher flow fuel injectors, but that is often not the case. In many cases, you can use your stock fuel injectors, but it might be worth having them “cleaned.” When using your stock fuel injectors, especially in higher mileage cars, the injectors may not flow optimally anymore. By having a company blueprint your stock injectors, any contaminants that may impede fuel flow or degrade the fuel spray pattern will be removed. The approximate cost for this service is $30 per fuel injector.