FI fuel upgrade options
 

After running car on the Dyno it seems to be losing fuel pressure in the upper rpms...I have talked to several reputable tuners I got some mixed answers ....some say I can tune it richer ...some say use larger injectors ...some recommended the return system .....now I would assume the return system would be the best route to take .

Some of my questions are... If I'm losing fuel pressure could I use a larger fuel pump to maintain the pressure ...I'm assuming there is a reason for this not to be a options....also ...im not sure if tunning is a option with pressure dropping how far has others run 650cc injectors on a return less setup

And my last question would be if I upgrade to the return system will it maintain the same fuel pressure as before with just the ability to hold the pressure in the upper end or will the lower rpm pressure be higher with return system .

I feel like I'm on the borderline of having to upgrade and just looking at all options that would fit best. Boost is at 12lbs and I dont want to try to increase any further ..just want to make a safe afr all the way through the the rpm range.

If its fuel pressure dropping off then a pump would help. A return would too because then you have a pressure regulator. You can also hook a boost line up to the FPR to compensate boost pressure against your injectors.

The only way I would be looking for injectors is if your duty cycle is 90% or higher

I'm not sure what the FPR is .....and if the pump is upgraded ...what is the problems with the returnless system .....

FPR = Fuel Pressure Regulator.

So you don't know if you have a stock pump or not? Get an aeromotive 340 in there if its stock.

The only problem with a return system is they cost a lot more money than a pump. But its best to have one regardless.

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 ?

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.

Looks like I'll be adding the return system then lol

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.

That's a lot of good info ... I posted the Dyno run and it is at 12.9 at 7200 rpm ... I think I'm close ... I'll have to find out the duty cycle / fuel pressure and see if maybe just in the tune


Also I am running the walboro 255 pump with 650cc injectors ...stage 2 supercharger 12lbs boost

So why does he need a return system? For 500-700 HP, it is kinda silly to unnecessarily heat your fuel. Why not setup a boost reference for the FPR and then diagnose whether or not larger pump and/or injectors are necessary. I feel the injectors are small, personally, but it isn't my build.

Sent from my SM-N920T using Tapatalk

I would highly suggest getting up with Charles-CJM. He is the man when it comes to fuel systems!!!

http://cj-motorsports.com/products/c...system-vq37vhr

That is a good question! I suppose that bit it just something that I have read over and over on here and taken as gospel. Perhaps not? Are there folks running boost referenced FPR's without return system?

Cosmo's advice is best, talk to CJM! Then report back here what he says so that future users can find the information in this thread =)

Call CJMotorsports(SN on here: Phunk). Charles has the best of the best fuel upgrades to resolve these issues.

I found the stock fuel line is too small (7 mm ~ 1/4") and only can deliver so much fuel.
There are other things going on when the fuel pressure drops and none of it is good.

Supply a true 12 volts with wire upgrades and relay Install a 3/8" (10 mm) supply line
and watch things improve.

Buy a S1 or S2 fuel kit from CJM and watch things get so much better.

I couldn't agree more with the wire upgrade.. Switching to a bigger pump and not upgrading the wires will eventually fail due to heat and not allow the pump work at a consistent rate...

You are right that the return system is the strongest solution to pressure drop. Tuning around a pressure drop can be reasonable if the pressure drop is extremely mild and consistent, but these are rare qualities of pressure drop. Once a piece of the system has reached the edge of its capacity, it will generally be pretty inconsistent as many day-to-day variables can shift the limits up and down.

A stronger fuel pump can sometimes alleviate the issue, but the nature of a returnless system really taxes the fuel pump output. No matter how hard your fuel pump works, the best it can do is hold 52psi inside the fuel pump module. When the flow restrictions through the fuel system begin to show as fuel is in high demand, the fuel pump's hands are tied, as it is allowed to output no more than 52 psi and anything extra will simply bleed out the regulator that resides right next to it. The pressure drop through the system will continue to grow as fuel demands grow.

A return system allows the pump to work harder for you by placing the regulator after most of the flow restrictions in the system, and blocking off the factory regulator port in the fuel pump module. Now the fuel pump is no longer regulated directly at it's output, and it will operate at a higher immediate pressure allowing it to push "harder" through the fuel system.

You can set the regulator to the factory fuel pressure setting and it will run the same pressure profile until where fuel pressure used to fall off, it will no longer fall (until much higher fuel demands).

There is no boost referencing the factory fuel system or regulator.

The factory fuel pressure settting is ~52psi. At 12 psi boost, the effective/relative/differential fuel pressure is about 40psi. There is 40psi more fuel pressure than there is intake manifold pressure, assuming no pressure drop in the system.

40psi with 650cc injectors isnt exactly a ton of fuel. If the pressure is dropping in the system, its even less. To resolve a case of pressure drop might extend the 650s into your required output. But if there is currently little-to-no drop occurring, than you just need larger injectors.

To investigate the minimalist remedy for your car, you would need to acquire some data. Is fuel pressure dropping below 52psi at the fuel pump module? This means the fuel pump is out of steam. Is fuel pressure holding steady at the pump module, but falling at the rails? This means you need upgraded plumbing or a return system. Is fuel pressure holding everywhere but the injector duty cycle is topped off? This means you just need injectors.

Most often, customers rather spend their money upgrading all of it in one shot rather than investing in detailed diagnostics to precisely locate the problem.

That's exactly what I'm doing with my build.:tup:

Now if I'm following this right ..... I know I need info for the duty cycle and fuel pressure to pinpoint the issue .... However from the nature of the stock fuel system is maintain 52lbs of pressure but at 12lbs of boost there would really be 40 lbs of pressure which to feed the motor and therefore leaning out as the boost increases from 0-12 .... So the real weak link is the stock system ... Switching to the return system gives the ability to increase the fuel pressure to the injectors to maintain 52lbs or greater if needed as boost increases .... Wouldn't changing the pump or injectors at this point be useless ?... The stock system would still regulate 52lbs and still starve injectors .... And changing injectors at this time would still only have 40lbs of fuel pressure to use and as result causing richer condition on the lower rpm side that would have to be tuned out .... Am I correct on this way of thinking ?

yup & yup.