I just installed a fuel pressure gauge on my 04 Z06 with Vortech V2 and it looks like my fuel pressure drops from 60 to 40lbs at higher rpm's under boost. The car was recently tuned and is making low 500's rwhp on a Mustang dyno with a little over 5 lbs of boost. My tuner says this is fairly normal and they would have tuned around it. My injectors are ~70lbs/hr. We did not record/monitor the fuel pressure when tuning. The car runs great and I am already putting an upgraded fuel system together for when I increase the boost. I am just wondering if anyone else has seen this. It is 2004 so it has the later fuel system which I hear is harder to modify.

 

Stock fuel pump?

 

I believe so

 

sounds like you could use a bigger pump or a boost-a-pump (which increases voltage to the pump as boost pressure increases).
just be careful of getting too big of a pump... then the stock fuel regulator won't be able to relieve the pressure enough. i ran into that putting a 450 on my car after the stock+booster still dropped pressure. the 450 was then pushing fuel to 70+psi, so i did a return conversion & adjustable regulator. now it's happy at 58psi.

 

I would finish putting that upgraded fuel system together ASAP, one of the most critical elements of a boosted set-up is proper and CONSISTANT fuel delivery, might also get a second tuner opinion...

 

It is not "normal", and they should not have tuned around it

They should have clearly stated you need to fix the problem, and when it is fixed, you will need retuned.

Even at 5psi boost, that's leaving only 35psi across the injector, this is lower than is ever recommended and will affect spray patterns and operation of the injector.

 

Thanks for the replies. Fuel system is in the works. I might change te fuel filter in the meantime.

 

Fuel pumps flow more maximum flow rate at the lowest possible pressure.

Get large enough injectors that you can run a low fuel pressure. I shoot for 34 to 38psi of base fuel pressure. With 30psi of boost that is 68psi total fuel pressure required. 1psi per psi of boost is regulation reference.
With large enough injectors the low fuel pressure has many benefits,
1. less likely to leak or blow a fitting, less stress on the fuel system
2. Longer fuel pump life, lower pump temperature
3. Reduce fuel heating
4. Easier to tune large injectors at low pulse widths
5. Most fuel pump flow rate potential at given voltage

I will never run a high performance forced induction application base fuel system pressure at 50 or 60psi. That is fine for tiny fuel systems on stock engines I guess but its unnecessary and unwanted for high performance applications with large lines and high flow rates, high demand, rapid changes.

there is no down side to doing this way.

 

"4. Easier to tune large injectors at low pulse widths": really?

 

Injectors flow less with reduced fuel pressure so the injector on-times will be higher allowing you to avoid non linear difficult portions of low injector ontime at low rpm with large injectors

some injectors open sporadically or partially at low on-times with large variability forcing owners to raise idle rpm or live with rich a/f ratios which foul plugs

 

he's full of ****, ignore most of what he says. Obviously with lower pressures, spray patterns turn to **** so clearly it is a very dumb notion.

 

not really full of ****, he sometimes makes a good point. but this doesnt make sense.

for some reason the corvette loses pressure. i havent seen this on other cars. even in stock configuration with a lingenfelter 225, 10mm line and a regulator up front its 10-15% on my car. the same pump supports over 15 psi of boost. i tune around it but 40 psi of course is too low.

 

No it won't, if working correctly with stock setup, within it's flow abilities, pressure will remain pretty constant. Not withstanding losses from the reg being at the back...but again this comes to flow demands and supply available.

40psi fuel rail pressure with 15psi of boost would be pure ****, leaving only 25psi across the injector to actually inject fuel. No sane person would deliberately do that

Injectors need a certain level to achieve good spray patterns and atomisation of the fuel. Low pressure is **** for this unless the injectors have been specifically designed to run at low pressure. Which pretty much no current EFI injector on a port injected car will be.

So a sensible pressure of 45-60psi or thereabouts across the injector is an ideal range. To suggest otherwise, is dumb ****. The absolute minimum would be 30psi delta, but very few systems if any these days aim for this lower pressure. 45-60 base is more common, for good reason.

 

Factory ECU for all vehicles sprays fuel to a closed intake valve where fuel pools and sits there, vaporizing as a puddle.


You simply do not understand how engines work I'm afraid.

Right now you fall classified as 'the bullshit epidemic'

http://injectordynamics.com/articles...****-epidemic/

 

You should use your own brain to decide what is right.
When I suggested 38psi of base pressure I assume of course that the system have some referenced fuel regulator for boost, i.e. 1psi per 1psi of boost rising rate.
I would never and have never in over 1,000 tuned forced induction vehicles tuned a forced induction car without a rising rate regulator. It does not make sense to run 30 or 40psi of boost on an engine with only 40psi of fuel pressure it would have zero psi of fuel pressure. Anybody who will make this mistake and assumption I question their logic.

Like I said I've done around one thousand cars this way, reliable daily drivers. The baseline pressure for Nissan/Toyota turbocharged vehicles is 44psi anyways. That is literally the stock pressure we used for 25 years at 500 to 1000hp builds using stock Nissan/Toyota engines like RB25/2jzgte. 44psi baseline I only removed about 4 to 5psi from that for my purposes of getting every last ounce of reliability out of those setups, it is well within the workable and feasible ranges for modern fuel injector operation.

 

I run 60 psi base pressure and make sure the fuel system flows enough at that pressure
I haven't seen lots of folks run lower pressures but yes the pumps flow less at higher pressures which you have to account for
running higher pressures increases the flow pretty substantially and lowers the duty cycle
I also just use 80 % as target duty cycle not 50%
works well for me, and most vette guys I know so I'll stick with that until folks prove me wrong and show me why

 

It is not wrong. Merely non-optimal.

I am an optimization connoisseur.
There is no down side to reducing fuel pressure with large enough injectors. There are many gains.

1. Improve fuel pump lifespan
2. Inject more fuel into Peak Piston velocity window requires reduced duty cycle and large injectors to gain benefits in torque
https://forum.hptuners.com/showthrea...l=1#post470921
https://www.speed-talk.com/forum/vie...374186#p899554


https://forum.hptuners.com/showthrea...l=1#post686907
So, just these alone (larger injectors and reduced fuel pressure) = longer fuel system lifespan and more mid-range torque and power

I could keep going but I think I made my point

 

I'm not an expert - but I do see two potential negatives to running LARGE injectors. The injector pulse width at idle are already small - so bigger injectors mean even smaller pulse widths at idle, so resolution wise, it may be harder to command the exact pulse width desired, and second - manufacturing tolerances in the injector components can cause variation in the instant fuel flow starts. That is utterly irrelevant at WOT, but at idle that Can cause A/F ratios to vary a bit cylinder to cylinder, and in closed loop - that mans some cylinders may be running leaner than others.

 

Used to be a problem in the 90's but not anymore with quality injectors. I've tuned 150lb/hr on 4-cylinder engines suitably, it helps to reduce fuel pressure.
It just takes a quality injector with known opening time vs voltage and sometimes pressure (OEM ecu is a 3D table while most aftermarket ECU may use 2D)


Even with stock injectors, some cylinders running leaner than others at idle it is typical with a performance camshaft profile no matter what fuel injectors or carb application because that is what happens when the engine lopes, VE changes per cylinder in an oscillatory fashion. You can listen to a direct injection lope to confirm that the fuel distribution is same making air the variable.

Not to mention running lean at idle is desirable. I always tune 14.8:1 to 16:1 air fuel ratio at idle. Most aftermarket stand-alone ECU recommends this for reduce carbon deposits and improve economy.

And as to closed loop. Modern stand-alone computers use wideband closed loop now. There is no more narrowband closed loop. So the target a/f values are often kept much leaner than 14.7:1 on purpose as I previously mentioned.

If the ECU is factory I never used narrowband closed loop in 20 years. 14.7:1 is an emissions ratio, not a performance or ideal air fuel ratio. Narrowbands are basically useless unless you need to give the car to somebody who does not know how to maintain the vehicle for many years properly and re-tune for changing environments like climbing elevation where the vehicle was not previously tuned.

Bottom line is a lean engine at idle is ideal. It is also ideal for cruising. The problem is RICH at idle and cruise, that is what adds carbon deposits, pollutes oil, wastes fuel. This should be avoided at all costs.

 

There's a reason talon is banned on most forums....his bullshit just never ends. Running a low pressure is idiotic. End of story, unless he wants a carb.

And his spouting about injection timing is about as relevant to the OP's pressure issues, as an elephant.

And for a powerful car, it is almost impossible to always inject against a closed valve as he seems to suggest is the be all end all, because there simply is not enough time to do so. You'd need to be running IDC's around 50-60% or lower at all times to stand any chance of achieving that. And not even OEM's do that
And direct injection would **** up that theory too....no closed valves to inject against.

Spray pattern does of course matter, that's why large injectors etc like 2000's are just **** at low running in terms of mixtures, stability, and even more so emissions for those that need to pass tests. It would take a full retard to suggest it does not matter. Because everyone knows this.