You can type here any text you want

Fuel pump/Injector flow graphs

Welcome!

By registering with us, you'll be able to discuss, share and private message with other members of our community.

SignUp Now!

87GN_70GS

Active Member
Joined
May 28, 2001
Messages
1,593
In order for this not to be a duplicate post, I have included E85-specifc information on the attached chart (note the hp estimates based on E85 bsfc). This is a continuation of a discussion that 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.
 

Attachments

  • fuel4.jpg
    fuel4.jpg
    64.4 KB · Views: 702
Great post.

In regards to stock fuel lines I've always understood that 83s @ 100% DC is the limit of the stock fuel lines and would require the lines and rails to be upgraded if more fuel was required. I say it probably needs to happen before that so you can have some headroom as you have said in the past.

The HP at this level should be somewhere around 500 HP and is understood as the limit for E-85 in a stock fuel line and rail car.

Some have stated that by upgrading the fuel rail connections, ie welding new ones on would thus remove some of the factory restriction and give more headroom. I'm still under the impression that at this point in the upgrade process it would be better to go ahead and upgrade to a champion rail and new lines, etc.

We have this exact question asked many times here: At what point do I upgrade fuel lines? Are the above statements close?
 
Hard to say about stock fuel lines. The best way to figure that one out would be from empirical data (i.e. results from users in the field). You could rig up a test set-up to measure flow/pressure through a stock system and characterize it that way. That should give you the flow loss (and resulting hp loss). You could use the data to reconstruct the graph above which would generate a whole new set of general guidelines/recommendations.
 
Back
Top