Well I wanted to post this in the thread that originally generated this discussion but i was told the E85 section wasn't the most appropiate so I'll post it here. Anyway, the discussion evolved into what injectors were suitable for which fuel pump and/or which pump could support what injectors. The general outline for this procedure has been posted on the gnttype site for a while, but the specifics were left out. I thought it would be helpful to present them here.
The attached chart shows performance curves of a few popular fuel pumps as well as some injectors. The fuel pump data is readily available on the web. The injector data is from the rated point (yy gph @ xx psi) and the other points on the curve from the square root equation. Injectors are assumed to run static (100% DC) and dc is a big determining factor. Boost is noted, and is usually 20 or 25 psi, others can be added, but it's already busy enough.
Where the injector curve lies inside (to the left) of the pump curve, there will be adequate pump capacity for that combination (supply will exceed demand). If a particular setup tries to establish an operating point to the right (outside) of a pump curve, pressure and volume will fall to where the pump-injector lines intersect (demand exceeds supply).
For example, if you have 50 lb injectors, running 100% dc, with 20 psi boost and 45 psi base fp (65 psi total rail pressure), and a hotwired walbro 307 pump, your setup will be ok. You will be at just over 50 gph total fuel flow. But you will only be able to increase fuel pressure by 3 psi or so.
Another example, with 65# injectors, 100% dc, 25 psi boost, 50 psi base, hotwired 340, you will be out of pump. In trying to run 75 psi, the 65# demand curve lies outside of the supply. A 340 will only give about 62 psi and 60 gph in this example. A supra denso will help but only with about 65 psi and 62 gph.
In the above example, you would need to either reduce base fp, reduce dc, or get a bigger pump or all 3. If you could be able to reduce dc to say 85%, reduce base fp to 45 and still have a safe AFR, that would be equivalent to a 55# fuel demand and the operating point would lie within the pump's capacity, resulting in 70 psi and 56 gph. But margin would be 0 with a 340 and 2 psi with the denso.
Obviously less % dc helps any situation, I presented worst case (100) for sizing purposes.
Credits: The pump data was taken from the manufacturer for the Walbro units (10 randomly pulled from production and averaged), the stock one is from richard Clark's (A2000rich) tests, the Supra denso from the stealth316 web page, the Apexi from maxcooper.com test, bosch from various, and pierburg from the manufacturer.
Losses from fuel lines/rails have not been taken into account.
Tuning hint: As rail pressures rise, pump output falls off as can be seen in the chart. You can actually increase fuel flow by dropping base fp and increasing pulsewidth (dc), up to reasonable imits. Example: you have a 340 w/ 60#'s and 20 psi boost, 52 base fp, and currently at 83% dc (= 54 gph), and your AFR is still lean. There is no margin to raise base fp. By increasing dc to 92% and dropping base fp to 49, the fuel delivered has increased by 7% (to 58 gph). I realize the base fp is kinda high, but it's only for illustration.
The attached chart shows performance curves of a few popular fuel pumps as well as some injectors. The fuel pump data is readily available on the web. The injector data is from the rated point (yy gph @ xx psi) and the other points on the curve from the square root equation. Injectors are assumed to run static (100% DC) and dc is a big determining factor. Boost is noted, and is usually 20 or 25 psi, others can be added, but it's already busy enough.
Where the injector curve lies inside (to the left) of the pump curve, there will be adequate pump capacity for that combination (supply will exceed demand). If a particular setup tries to establish an operating point to the right (outside) of a pump curve, pressure and volume will fall to where the pump-injector lines intersect (demand exceeds supply).
For example, if you have 50 lb injectors, running 100% dc, with 20 psi boost and 45 psi base fp (65 psi total rail pressure), and a hotwired walbro 307 pump, your setup will be ok. You will be at just over 50 gph total fuel flow. But you will only be able to increase fuel pressure by 3 psi or so.
Another example, with 65# injectors, 100% dc, 25 psi boost, 50 psi base, hotwired 340, you will be out of pump. In trying to run 75 psi, the 65# demand curve lies outside of the supply. A 340 will only give about 62 psi and 60 gph in this example. A supra denso will help but only with about 65 psi and 62 gph.
In the above example, you would need to either reduce base fp, reduce dc, or get a bigger pump or all 3. If you could be able to reduce dc to say 85%, reduce base fp to 45 and still have a safe AFR, that would be equivalent to a 55# fuel demand and the operating point would lie within the pump's capacity, resulting in 70 psi and 56 gph. But margin would be 0 with a 340 and 2 psi with the denso.
Obviously less % dc helps any situation, I presented worst case (100) for sizing purposes.
Credits: The pump data was taken from the manufacturer for the Walbro units (10 randomly pulled from production and averaged), the stock one is from richard Clark's (A2000rich) tests, the Supra denso from the stealth316 web page, the Apexi from maxcooper.com test, bosch from various, and pierburg from the manufacturer.
Losses from fuel lines/rails have not been taken into account.
Tuning hint: As rail pressures rise, pump output falls off as can be seen in the chart. You can actually increase fuel flow by dropping base fp and increasing pulsewidth (dc), up to reasonable imits. Example: you have a 340 w/ 60#'s and 20 psi boost, 52 base fp, and currently at 83% dc (= 54 gph), and your AFR is still lean. There is no margin to raise base fp. By increasing dc to 92% and dropping base fp to 49, the fuel delivered has increased by 7% (to 58 gph). I realize the base fp is kinda high, but it's only for illustration.
