TPI, or Tuned Port Injection, is a type of electronic fuel injection (EFI) system. Unlike Throttle Body Injection (TBI), which injects fuel into the intake manifold before the air reaches the intake ports, TPI injects fuel directly into the intake ports. This allows for more precise fuel delivery, leading to improved performance and efficiency. GM first introduced TPI in 1985 on its Corvette and Camaro lines, using it on their 5.0 and 5.7 Liter V-8 engines. The system uses a unique manifold design with tuned intake runners leading from a common plenum to each cylinder.
How TPI Works
TPI systems feature a fuel injector for each intake port, delivering fuel directly into the intake runner. This contrasts with TBI, which is described as a "glorified carburetor system" because it delivers fuel to the intake manifold in a less precise manner. The "tuned" aspect of TPI refers to the design of the intake manifold runners, which are carefully engineered to optimize airflow and fuel delivery at different engine speeds.
TPI Advantages and Disadvantages
- Advantages: Improved performance and efficiency compared to TBI, better throttle response and increased power, especially in the mid-range.
- Disadvantages: Can be more complex and expensive to maintain than TBI, the factory TPI intake itself can be a performance limitation at higher RPMs (above 3400 RPM), sometimes resulting in a "good low end torque" but underwhelming high-end performance.
TPI vs. Other Fuel Injection Systems
TPI is a type of EFI. All TPI systems are EFI, but not all EFI systems are TPI. Modern fuel injection systems, including those found in KTM's TPI two-stroke motorcycles, employ different technologies and approaches. KTM's TPI system, for instance, is a novel approach to fuel injection specifically for two-stroke engines.
Common Misconceptions
Some sources suggest that the factory TPI intake manifold is a performance bottleneck. While the system offers improved performance over TBI, upgrades and modifications are often undertaken to maximize its potential at higher RPM ranges.
