What is Tuned Port Injection (TPI)? Tuned Port Injection is a type of fuel injection which GM first used in 1985. It was used by some Camaros and Firebirds from 1985 until 1992, and by Corvettes from 1985 until 1991. It provides excellent driveability, throttle response, and great fuel economy. It has a relatively flat powerband, and makes great bottom and midrange power. However, a TPI engine begins to suffer near 4500 RPM, as the intake does not flow well enough to feed the engine's needs. People often refer to other intakes such as the LT1 intake, the Holley Stealth Ram, or the Miniram as a version of TPI. This is not true. These other intakes are forms of port injection, but not forms of Tuned Port Injection. Tuned Port Injection is so named because of its long tube runner design. The air being drawn into the engine moves in pulses, and the runner length is such that air pulses arrive at the intake valve at convenient moments in the combustion cycle, and can force their way into the combustion chamber on their own. Back to Top
Why should I install TPI on my vehicle? Tuned Port Injection manifold is an excellent choice for a daily driver. It provides excellent driveability, throttle response, fuel economy, and power. It is often used for towing as well, as it has excellent bottom and midrange power. It has become one of the most popular fuel injection conversions for GM applications over the years. Intakes and parts are not difficult to find, and are relatively inexpensive. Back to Top
Is TPI difficult to install? No, it is not difficult if you have done the necessary research before a conversion. Although it may seem overwhelming, if you take your time and understand what you will be doing before you begin a project, everthing will go much smoother. This is a very well documented conversion, and help can be attained from a variety of sources. If you can perform your own vehicle repairs and maintenance, you should be able to complete a TPI conversion. If your mechanical abilities don't run far beyond an oil change, it might not be a good idea for you to attempt such a project. Back to Top
How much power can I make with TPI? This will depend on a variety of things such as engine size, engine modifications, and tuning. A stock TPI engine in good mechanical condition can have between 205 and 245 HP at the flywheel. A max effort TPI engine can get near 400 HP at the flywheel, but these are few and far between. You may find some machine shops that say they can build you a 450 HP TPI engine, but this is not realistic. They are basically assembling an engine that is capable of 450 HP with a carburetor. Such a combination would have a moderately aggressive cam, and will probably peak in the 5500 to 6500 RPM area. Tuned Port Injection does not work well in this area, and will be a restriction for the engine beyond 4500 RPM or so. Back to Top
Why is Fuel Injection in general so complicated? Fuel injection is not necessarily any more complicated than a carburetor. It may seem more complicated to a novice fuel injection enthusiast, but in reality, carburetors can be more complex. A typical Holley carburetor has over 120 possible adjustments. A stock TPI intake has only three items which can be adjusted, both of which are on the throttle body (throttle position sensor, idle air control valve, and minimum air screw). The reason why it is often viewed as complicated is due to a lack of understanding of how the system works, not necessarily because it is complex. Back to Top
What is better, MAF or Speed Density (MAP)? They each have their advantages and disadvantages over the other. Which one will suit your needs better depends on your specific application. Both have the potential to work equally well on stock engines, as well as on modified engines. However, MAP is much more sensitive to engine modifications (particularly cam and head changes). A heavily modified engine with a MAP system will not run well on a stock tune, but can run flawlessly with the proper tuning. A MAF setup on the other hand can run very well on a stock tune even with a heavily modified engine. There are gains with prom tuning, but it is not as critical as the MAP system. Parts are readily available for both, but there is a difference in cost for sensors between the two. A MAF sensor is significantly more expensive than a MAP sensor. Back to Top
Can I get rid of emissions if I install TPI on my vehicle? You will need to check your local laws to determine whether this is legal in your area or not, depending on the year of your vehicle. A TPI intake can be installed without running any emissions equipment. For more information regarding emissions equipment such as EGR, A.I.R, or canister purge, view our tech article regarding emissions. Back to Top
