FI fuel upgrade options

Jinxx

I have the 255 walboro with the 650cc injectors .... I'm not sure what you meant by using the boost pressure in the fuel line

When I said upgrade the pump I meant further than the 255..

Also will the 255 and 650cc injectors support 12lbs safety ?

TopgunZ

Lol. Im having this same discussion in my thread with Evohunter.

I honestly don't know. I know what my car does with my setup.

If it does, it will be pushing everything to extreme limits. Safely? I wouldn't use that word.

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Jayhovah

The fuel is at some pressure, for an example of a nice round number lets say 30psi. What that really means is 30psi MORE than atmospheric pressure.

When you are NOT in boost, the pressure in your intake manifold is atmospheric pressure (or a little less since the car is pulling air and creating a vacuum) so you get the full 30psi of fuel pressure.

When you are in boost, lets say 12 psi (that is 12 psi OVER atmospheric pressure in your intake manifold). So your fuel pressure is only at a pressure 18psi higher than the pressure in the intake manifold - your effective fuel pressure is only 18psi.

However, I think your fuel pressure is being measured against atmosphere and not manifold pressure - so that is not the cause of your fuel pressure problems.

Switching gears a little.....
There are a few variables here to consider for your fueling. The flow of the pump, the size and duty cycle of the injectors, and the fuel pressure. These can all be related.. i.e., if your pump doesn't flow enough for the size/duty cycle of the injectors, then you will lose fuel pressure. This is what is probably happening to you.

Depending on if your injectors are maxed out or not, your tuner may be able to account for the loss in pressure by increasing the duty cycle of the injectors.

So, to answer your question: You don't have enough information.

1) Find out what your injector max duty cycle is. If it is >90%, you need to go bigger. Because you are already losing fuel pressure (your injectors are starting to outflow your pump), you will need to upgrade the pump too.

2) If your injector duty cycle is <90%, and you are CLOSE to having a good A/F Ratio curve, your tuner may be able to adjust the duty cycle to get you in a good place.

3) If your injector duty cycle is <90%, and you are NOT CLOSE to having a good A/F Ratio curve, you likely just need to upgrade the pump.

4) If you are going for 550+ whp, you should upgrade to the return fuel system. This upgrade will ensure your fuel pressure is even between your cylinders.

Confused yet? =)

For reference, I am at 520whp using a 255lph pump and 600cc injectors.

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