Understanding The P7100: Fuel Pressure Requirements Explained

The Bosch P7100 is a symbol of diesel performance, representing easy horsepower for those who are handy with a wrench and huge horsepower for those willing to spend. The P7100 is a complex piece of mechanical engineering, with many moving parts inside. The P7100's fuel plate, for example, controls the maximum fuel output, and removing it can result in more rack travel and considerable power gains. The P7100 is also capable of flowing a maximum of 550 cc's of fuel, and increasing the diameter of the plungers and barrels can lead to even greater fueling potential. So, how much fuel pressure does a P7100 need?

The P7100 is designed for 35 PSI

The P7100 is a complex piece of engineering, with many moving parts inside. It is essentially a mini inline-six-cylinder engine bolted to the side of your inline-six-cylinder engine. The P7100 can be modified in various ways to improve its performance and increase horsepower.

One way to increase horsepower is to adjust the air fuel control (AFC) assembly. This can be done by sliding the AFC housing forward and backing out the pre-boost screw, which will bring in fueling at a lower rpm and adjust the rack forward. Combined with a star wheel adjustment, this can result in a peak horsepower increase of up to 60 horsepower.

Another modification is to install a "Mack rack plug", which increases rack travel from 19 mm to 21 mm. This simple and inexpensive modification can increase horsepower by 10 to 35.

Removing the fuel plate is another way to increase horsepower. The fuel plate controls the maximum fuel output of the P7100, and removing it will increase rack travel and result in power gains of 35 to 40 hp.

For those seeking even more horsepower, aftermarket delivery valve holders and delivery valves can be installed, allowing more fuel to flow through the pump. Governor spring kits can also be added to provide full fueling up to higher rpm, and the camshaft can be swapped out for one with a more radical profile to inject more fuel at a quicker rate.

It is important to note that increasing fuel pressure may not always result in power gains. Some users have reported no power gain above 45 PSI, and one user even reported no gain from 50 to 100 PSI. Additionally, fuel pressure above 50 PSI can run the risk of hydrostatically locking the rack, causing a run-away condition.

Some users report running their P7100 at 40-45 PSI

The P7100 is designed for 35 PSI, but some users have reported running their P7100 at 40-45 PSI without any issues. In fact, some have found that there is no power gain above 45 PSI. At higher engine speeds, there is less time to fill the plunger, and higher pressure should fill it faster.

One user reported that they had their P7100 at 40-45 PSI on their new Air Dog and that their truck was strong at this setting. They took it for a ride and, when they put their foot down, the fuel pressure gauge only moved by a pound or two, staying around 40 PSI.

Another user reported that they had seen as high as 50 PSI at wide-open throttle with a belt drive and that they had experienced no problems with their setup.

However, it is important to note that running the P7100 at higher pressures may come with risks. One user cautioned that over 50 PSI can run the risk of hydrostatically locking the rack, causing a run-away condition. Additionally, there may be concerns about cavitation and erosion on the inside of the pump with anything over 50 PSI.

Seals will live a long time at over 50 PSI

The P7100 is a pump that can be used to inject fuel into engines. The amount of fuel pressure it needs depends on the engine's specifications and desired performance. Some sources suggest that a fuel pressure of 35-45 psi is sufficient for the P7100, while others recommend a higher pressure of around 50 psi or more for maximum performance.

Now, regarding the statement, "Seals will live a long time at over 50 PSI", this is specifically referring to the internal seals within the P7100 pump and their ability to withstand high fuel pressure. Indeed, the seals within the P7100 pump are designed to withstand fuel pressures well over 50 PSI. One user reports that their P7100 pump has been running at 50 PSI for three months without any issues.

It is important to note that while the seals can withstand high fuel pressure, there are other considerations when operating the P7100 at such pressures. For example, one user cautions that fuel pressure above 50 PSI can cause cavitation and erosion inside the pump. Additionally, another user mentions that maintaining consistent fuel pressure under load is crucial.

In summary, the P7100 pump's seals are designed to withstand fuel pressures well above 50 PSI, but it is important to be mindful of other potential issues that may arise when operating at such high pressures. It is always recommended to refer to the manufacturer's guidelines and seek advice from experts when making adjustments to fuel pressure or any other engine modifications.

40-45 PSI is plenty of pressure

There are several reasons why 40-45 PSI is plenty of pressure for a P7100. Firstly, the pump doesn't have to work as hard to make injection pressure, and there will be a slightly higher pressure at the injector. This is particularly beneficial at higher engine speeds, where there is less time to fill the plunger, and more pressure will help it fill faster.

However, it is important to note that there is no power gain above 45 PSI. Jim Fulmer and others have proven that there is no benefit to increasing the pressure further. This is because, theoretically, the barrel is already full at port closing, so increasing the pressure will not help or hurt performance.

Additionally, maintaining pressure under load is crucial. While 40-45 PSI is plenty, it needs to be maintained at this level under load. This will ensure that there is no drop in horsepower.

Finally, going over 50 PSI can lead to issues. There is a risk of hydrostatically locking the rack and causing a run-away condition. Therefore, it is recommended to keep the pressure at or below 45 PSI to avoid any potential problems.

18 PSI is needed at idle

The P7100 fuel pump is a powerful component, capable of producing high horsepower and torque. However, it is essential to ensure optimal fuel pressure for the best performance and to prevent any damage to the pump.

The recommended fuel pressure for a P7100 pump is 18 PSI at idle. This ensures that the pump receives an adequate fuel supply to function effectively. Maintaining this fuel pressure is crucial for the pump's performance and longevity.

While some sources suggest that higher fuel pressure can lead to increased horsepower, it is generally recommended to stay within the optimal range of 18 PSI at idle. Excessive fuel pressure can put unnecessary strain on the pump and increase the risk of seal damage or other internal issues.

It is worth noting that the P7100 pump is designed to handle fuel pressure of up to 35 PSI, and some users have reported running their pumps at 40-45 PSI without issues. However, staying within the recommended range ensures a balance between performance and longevity.

Maintaining the correct fuel pressure can be achieved through regular maintenance and adjustments. This may include checking the overflow valve, fuel regulator, and fuel filter for any restrictions or issues. Making small adjustments to the fuel pressure can help optimize the pump's performance and ensure it operates within a safe range.

Frequently asked questions