View Full Version : big time fuel problems

10-07-2009, 12:15 PM
Keep in mind that this is on a supercharged V8, with 8 injectors lol

Ok, guys heres the skinny.

Im out of fuel.
I replaced my fuel pump with a brand spanking new walbro 255hp. The car doesnt drop fuel pressure anymore and doesnt go crazy lean anymore but i am officially out of injector.
Data logs show
at 5800rpm 87% injector duty cycle and 12.3 afr wot
and by only 6600rpm
99% duty cycle 12.1 afr wot.
Clearly im out of injector, now heres some ideas
Band-aid idea
i can run the injectors @ 4br 59psi rail pressure and give me a new flow of about 430cc per minute, and i should see 88-90 percent duty cycles by redline. Only problem is that with that rail pressure the walbro 255 will only flow enough fuel to support 440cc injectors. So ill be maxing out the pump yet again!!!! My only solution to this is to run either a second walbro intank, or an external pump such as an aeromotive.
The right idea.
Grab some deatscworks 550cc injectors and run them around 74 percent duty cycle by redline, but once again not enough for the walbro as at standard rail pressure it will only flow enough for 480cc. So im in the same boat. My main problem is $$$ i have officially run the project fund dry here, i cant afford to do both the pump and the injectors, so do you guys think that runnning the stock injectors at 4 bar and 88-90% duty cyclle is a bad idea? Obviously i would imagine that 99 percent is much worse, but im really concerned about the 12.1 afr as i would like it to be a tad lower in the 11.7-8 range.

10-07-2009, 03:22 PM
I am in a similar predicament. I was wondering if the stock lines will flow enough fuel for that setup and how are you going to do dual intank on an s14? Are you just going to y the 2 pumps intank to the stock outlet?
I would say if the stock lines will handle that much fuel why not up the fuel pressure and run dual walbros, that seems like the easiest idea. Plus I hear external fuel pumps are extremely loud.

10-07-2009, 08:59 PM
Put a Bosch 044 external pump inline of the Walbro and the rail. Titan Motorsports has the best price from what i remember seeing.

Then do whatever injector upgrade you have to or bump up the pressure.

10-08-2009, 11:23 AM
Keep it as is, throw some ID725's or ID1000's and you should be good.

10-21-2009, 12:11 AM
If you think you are maxing the pump then installing larger injectors wont do anything- likewise raising the pressure also reduces pump output so you are losing fuel from reduced pump volume while trying to get more into the cylinder with small injectors-

You did not mention power but if you have 36lb/hr Injectors at or near 80%DC you should be around 500~ horsepower, which is time to install an additional walbro as you rightfully proposed... Walbro is cheaper than injectors, also... usually

Most of the time, if I hit a 450+ spot where I need more fuel but I dont want to stress the fuel system, I add another pump and install heavier gauge wiring for everything. Sometimes I can get away with 500 on a single walbro... but also sometimes you can not. In fact the accuracy of the gauges and brake specific- like a V8 will be cool with 13.5:1 air fuels around 450 horsepower because of the lower compression (requires less octane- less activation energy offset) basically and so the walbro is just a 65% instead of 90% capacity like a SR20 needs every drop

hello jerry

10-22-2009, 02:26 AM
At your power level, twin walbros would do the trick, or add an additional (Bosch 044 or an inline 255HP for example) pump inline with your current setup and do injectors...it's the only right thing to do.

Running a single huge external is not necessarily a bad idea, but I never really liked that idea on 240's, namely due to how our tanks are, and how it's all ran. Keeping the walbro you have intake as a pusher in combination with a large external though is a fantastic idea.

Running stock injectors at an additional bar of fuel pressure is just ASKING for trouble. The coiling inside simply is not designed to withstand being run like that (which is coincidentally an issue with redrilled injectors as well)...they will eventually (literally) burn themslves up, leading to failure, something I'm sure you'd like to avoid.

Again, if your project funds are low/empty, shortcutting (to me) only forces you to spend twice to make it work right...once on the shortcut 'for now, and again on the right stuff 'for later.

10-22-2009, 02:30 AM
FWIW: I run an internal 255HP and an external 255 HP on my car, both rewired, JUST to be sure. Overkill? Yes. Safe? Yes.

10-22-2009, 09:27 AM
well this is the tentative plan, the car is running fine right now. This weekend im picking up a surge tank from mazworx.
I will be running the following setup.

walbro 255 feeding the surge tank
aeromotive a1000 fed from the surge tank
upgrading fuel line to -8
dual feed the fuel rails
750cc injectors x 8
aeromotive fuel pressure regulator
-6 return line

Then more boost maybe 8-10 psi, should get me to around 500 whp.

The 750cc should be enough fuel for 840 crank hp so ill have plenty of head room, and maybe more boost later on when im feeling frisky, after all i do have a 14lb pulley and belt sitting here in the garage.

10-31-2009, 02:40 PM
Surge tank is a great idea in your situation. A1000's are a great pump as well...we run one on the turbo mustang and have nothing bad to say about it...but on that car we sumped the tank and use it as the primary one...runs great!

-8 fuel line is another good idea for your level. I never thought about suggesting that, but it's an obvious soltuion...and as you say, the 750's are going to be plenty of fuel...hell we run 83 lbers on the TurboStang and they're barely being used...compared to the 50lbers that were at 90% at all times lol! If you really wanna save cash with the lines though, just go to like, a local parker hydraulic shop, and get some big hydro hose and push lock fittings...cheap and kick ass.