Sylvie Willis
The stock boost levels of a Z31 turbo are not a big deal, but pushing more pressure can be dangerous. The maximum usable boost for a stock T-3 Turbo is 14.5 psi. Above this, the rise in inlet temperature and backpressure in the exhaust manifold can become catastrophic. The stock injectors are at 100% duty cycle at 14.0 psi, and above this, they will not be able to maintain a safe fuel/air ratio. The stock pump cannot feed enough fuel for much over 300 HP. Running over 15 psi without an intercooler is not recommended, as the fuel system becomes a problem.
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What You'll Learn
- The stock Z31 fuel system can handle up to 15 PSI
- Above 15 PSI, you will need to upgrade your fuel pump, lines, and injectors
- A BOV can help protect the turbo from compressor surge
- A straight pipe muffler design will improve exhaust flow
- Nitrous injection can increase power, but the stock fuel system may not be able to handle it
The stock Z31 fuel system can handle up to 15 PSI
The Z31's stock turbo injectors are already working at close to their maximum capacity at 15 PSI. As a result, they will not be able to maintain a safe fuel/air ratio beyond this point, leading to an excessively lean mixture. This, in turn, can cause detonation, which can result in significant damage to the engine, including melted spark plugs and pistons.
To safely run higher boost levels, an upgraded fuel delivery system is required. This includes a high-flow fuel pump, such as the one found in the Z32 twin turbo, as well as upgraded fuel lines and injectors. The stock Z31 injectors are too small to deliver the required fuel quantity at pressures above 15 PSI.
It is worth noting that, even with an upgraded fuel system, the stock Z31 engine may still have limitations in terms of boost pressure. The stock engine can handle more than 15 PSI, but other components, such as the turbocharger and intercooler, may become limiting factors. Therefore, it is important to carefully consider the capabilities of all components in the system when planning any modifications.
Additionally, it is recommended to use higher octane fuel when running higher boost pressures. Higher octane fuel has better detonation withstanding abilities, which can help prevent engine damage caused by premature fuel detonation. It is also crucial to monitor the engine's air/fuel ratios and make adjustments as necessary to ensure a safe and optimal mixture.
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Above 15 PSI, you will need to upgrade your fuel pump, lines, and injectors
Upgrading your fuel pump, lines, and injectors is essential when aiming for boost levels above 15 PSI in a Z31 fuel system. Here's a detailed breakdown of the upgrades:
Fuel Pump Upgrade:
Upgrading to a higher-flowing fuel pump is necessary to deliver the required fuel volume and pressure for increased boost levels. A larger fuel pump, such as Holley's twin fuel Dominator EFI fuel pump, can provide the necessary capacity to meet the demands of higher boost. However, it's important to ensure that the electrical system and factory wiring can handle the higher-flowing pump to avoid issues with the fuel regulator and potential overheating of the fuel pump module.
Fuel Line Upgrade:
When upgrading to higher boost levels, careful consideration must be given to the fuel line diameter and length. The relationship between fuel line size and fuel pressure is crucial for optimal fuel delivery. Excessively long fuel lines can result in significant pressure loss, inhibiting the proper function of the fuel system. Therefore, it's important to select the appropriate fuel line size to minimize pressure drop and ensure efficient fuel delivery.
Injector Upgrade:
Upgrading to larger fuel injectors is crucial when running boost levels above 15 PSI. The injectors must be sized appropriately to handle the higher pressures and deliver the required fuel flow rate. Sizing the injectors larger can provide advantages, especially in boosted engines. For example, a 15 PSI boost level can reduce fuel pressure in the fuel rail, so larger injectors can compensate for this pressure drop and ensure sufficient fuel delivery. Additionally, it's important to consider fuel pressure when sizing injectors, as higher pressure will increase the flow rate.
It's important to note that upgrading the fuel pump alone might not yield significant benefits without corresponding upgrades to the injectors and fuel lines. Ensuring that all components of the fuel delivery system are upgraded and optimized for higher boost levels will help achieve the desired performance enhancements.
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A BOV can help protect the turbo from compressor surge
Compressor surge can cause serious damage to a turbocharger. This phenomenon occurs when the turbocharger compressor wheel is creating more air mass than the engine can ingest. When this happens, the excess air has nowhere to go and is forced back through the compressor wheel. This can cause the turbo bearings to experience added thrust load, which can ruin a turbocharger. In some cases, compressor surge can even damage the compressor wheel itself.
A blow-off valve (BOV) can help to prevent compressor surge by releasing excess pressure on the intake side, allowing the turbocharger to spool faster. This is especially important when pushing more pressure, as it can help to protect the turbocharger from the damaging effects of compressor surge. While a minor amount of surge may not cause any issues, a properly sized and high-quality BOV should eliminate audible surge.
For those with a stock Z31 turbo, a BOV is generally considered unnecessary and a waste of money. The stock Z31 turbo has a factory boost setting of 6.8 PSI, and the engine can handle up to 9 PSI without an intercooler and 15 PSI with one. However, it is important to note that the fuel system may become a problem at higher boost levels, and upgrades to the fuel pump, lines, and injectors may be necessary.
It is also worth mentioning that the Z31 has a detonation sensor from the factory, but it is mostly useless as the ECU disregards the feedback when the engine is in boost. An intercooler can be added to help lower the temperature of the intake air, allowing the engine to run more boost and keep detonation at bay. Additionally, a well-designed exhaust system can help to slightly raise boost pressure, resulting in even more power gain.
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A straight pipe muffler design will improve exhaust flow
The stock T-3 Turbo for the Z31 has a maximum usable boost of 14.5 psi. Above this, the rise in inlet temperature and backpressure in the exhaust manifold can reach catastrophic levels.
A straight pipe muffler design can improve exhaust flow and is a recommended upgrade for the Z31. A straight pipe muffler is barely a restriction and will improve the sound of the car. It will be louder, but not annoyingly so, and will improve the acceleration of the car.
There are a few options for upgrading the exhaust system. Certified Muffler is a recommended vendor for the Z31, offering high-quality and low-cost options. However, their turnaround time is not the quickest. A custom exhaust can also be made, but shipping and customs taxes can be expensive. The diameter of the exhaust pipe is important to consider, with 2.5-inch piping recommended for a quieter setup, and 3-inch piping for those seeking improved performance.
The piping of the intercooler is also important. It should be mandrel bent with smooth bends and no kinks or ripples, and the number of bends should be minimised. The length should also be kept as short as possible. A good system will come with a compressor bypass valve to prevent backpressure from stalling the compressor blades.
Other recommended upgrades include a cold air intake, a cone air filter, and a boost controller.
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Nitrous injection can increase power, but the stock fuel system may not be able to handle it
Nitrous injection can significantly increase power, but it may not be compatible with the stock fuel system. The stock fuel system on a Z31 can handle up to 9 lbs of boost safely without an intercooler and 13PSI with 93 octane fuel. However, pushing beyond these limits will require upgrading the fuel system, including the fuel pump, lines, and injectors.
Nitrous oxide injection, or N2O, involves injecting a gas consisting of two nitrogen atoms and one oxygen atom into the engine. This gas has a higher oxygen concentration than the air, allowing more fuel to be burned and, therefore, generating more power. There are two main types of nitrous oxide systems: dry and wet.
Dry nitrous systems introduce the extra fuel required through the existing electronic fuel injectors. This type of system is generally recommended for stock or near-stock engines up to about the 150 hp level. However, as power levels increase, sophisticated ECU reprogramming is required, and achieving consistent power gains becomes more challenging.
On the other hand, wet nitrous systems meter nitrous and fuel through jets with different orifice sizes, making it easier to fine-tune the air/fuel ratio. Wet systems are more popular, as they supply their own fuel source and are compatible with most vehicles. Direct-port injection, a type of wet system, provides the biggest power gains and adjustability by injecting the nitrous and fuel mixture directly into each cylinder.
While nitrous injection can significantly enhance power, it is important to consider the limitations of the stock fuel system. Upgrades to the fuel system may be necessary to handle the increased power demands and avoid issues such as running too lean or rich, which can lead to detonation and engine damage. Therefore, when planning nitrous injection, it is crucial to assess the engine's specifications and make the necessary modifications to ensure safe and optimal performance.
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Frequently asked questions
A stock Z31 fuel system can handle 9 PSI without an intercooler and 15 PSI with an intercooler. However, some users have reported running up to 13 PSI without an intercooler when using 93 octane fuel. Going above 15 PSI without significant upgrades to the fuel delivery system is not recommended.
Running too much boost can cause detonation due to an excessively lean mixture (not enough fuel) or an extremely high intake manifold temperature. This can lead to cylinder head gasket failure and damage to the pistons.
To safely increase the amount of boost, upgrades to the fuel delivery system are necessary, including larger fuel injectors, a high-flow fuel pump, and upgraded fuel lines. Additionally, an intercooler can help manage the increased temperatures associated with higher boost levels.
