wret
15+ Year Contributor
- 2,931
- 81
- Jul 3, 2003
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Bel Air,
Maryland
What size injectors do I need for my horsepower goal?
Like other selections made in the build process, such as turbo and fuel pump, the flow rate of the injectors will determine the range of horsepower that is possible. Injectors are identified by their flow rate, typically in cubic centimeters per minute, but the rating is based on 100% flow. In actuality the injectors are never open 100% of the time. The length of time they are open while your engine is running is called injector duty cycle (IDC). When IDC exceeds a certain point, horsepower can actually drop as the internal valves of the injectors are asked to open and close faster than they can complete each event and are essentially floating in a partly open/partly closed position. The maximum IDC can vary by manufacturer and design but it is generally between 80% and 90%. Therefore, when upgrading injectors it should be planned that IDC will not exceed 80%. This generally leaves a little safety margin. The table below is based on the mathematics of a duty cycle of 80%. There are several interactive calculators on line. Just google "injector size calculator".
HP Goal – Min Injector Size (cc/min)*
250hp-....... 550cc
300hp-....... 650cc
350hp-....... 750cc
400hp-....... 850cc
450hp-....... 950cc
500hp-....... 1050cc
*Injectors are generally available sized in increments of 50, although some are sized at other increments such as 680 or 720. There are fewer size increments available between 1000 and 1600.
There are several ways to extend the horsepower expected with a given size injectors. One way is running a leaner mixture with race fuel and/or water-alcohol injection. Another is to increase regulated fuel pressure higher than the normal 43.5 psi.
What fuel control upgrades are required with larger injectors?
The greater the increase of the injector size over stock, the more advanced the fuel control system requirement. Mild upgrades can be handled with a piggyback system or MAFT. Injectors with rates up to 650 can be successfully controlled with an SAFCII. Injectors larger than 650 require some programming changes to the ECU to control them effectively.
Injector size - Minimum fuel control requirement
Up to 550-......... MAFT or piggyback
>550 to 650-..... SAFCII
>650-................ EPROM ECU with revised chip such Keydiver/SAFCII or DSMLink
I'm upgrading. Should I just get huge injectors and never have to upgrade again?
The extra capacity doesn't hurt and injector cost is not relative to volume so it might make economic sense to get larger injectors and never have to upgrade again. Just make sure you plan on proper fuel management (see above).
What is stock injector size?
1G turbo- M/T 450, A/T 390
2G turbo- 450 for M/T and A/T
What is the color code for Mitsubishi injectors?
Like other selections made in the build process, such as turbo and fuel pump, the flow rate of the injectors will determine the range of horsepower that is possible. Injectors are identified by their flow rate, typically in cubic centimeters per minute, but the rating is based on 100% flow. In actuality the injectors are never open 100% of the time. The length of time they are open while your engine is running is called injector duty cycle (IDC). When IDC exceeds a certain point, horsepower can actually drop as the internal valves of the injectors are asked to open and close faster than they can complete each event and are essentially floating in a partly open/partly closed position. The maximum IDC can vary by manufacturer and design but it is generally between 80% and 90%. Therefore, when upgrading injectors it should be planned that IDC will not exceed 80%. This generally leaves a little safety margin. The table below is based on the mathematics of a duty cycle of 80%. There are several interactive calculators on line. Just google "injector size calculator".
HP Goal – Min Injector Size (cc/min)*
250hp-....... 550cc
300hp-....... 650cc
350hp-....... 750cc
400hp-....... 850cc
450hp-....... 950cc
500hp-....... 1050cc
*Injectors are generally available sized in increments of 50, although some are sized at other increments such as 680 or 720. There are fewer size increments available between 1000 and 1600.
There are several ways to extend the horsepower expected with a given size injectors. One way is running a leaner mixture with race fuel and/or water-alcohol injection. Another is to increase regulated fuel pressure higher than the normal 43.5 psi.
What fuel control upgrades are required with larger injectors?
The greater the increase of the injector size over stock, the more advanced the fuel control system requirement. Mild upgrades can be handled with a piggyback system or MAFT. Injectors with rates up to 650 can be successfully controlled with an SAFCII. Injectors larger than 650 require some programming changes to the ECU to control them effectively.
Injector size - Minimum fuel control requirement
Up to 550-......... MAFT or piggyback
>550 to 650-..... SAFCII
>650-................ EPROM ECU with revised chip such Keydiver/SAFCII or DSMLink
I'm upgrading. Should I just get huge injectors and never have to upgrade again?
The extra capacity doesn't hurt and injector cost is not relative to volume so it might make economic sense to get larger injectors and never have to upgrade again. Just make sure you plan on proper fuel management (see above).
What is stock injector size?
1G turbo- M/T 450, A/T 390
2G turbo- 450 for M/T and A/T
What is the color code for Mitsubishi injectors?
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