So I think I understand how the return fuel system works, (now that I need to buy one). The stock fpr and fuel pump dont have enough pressure to overcome the pressure in the cylinder at 7-9+psi, and im assuming that this is why technosquare could not get my 440cc injectors to run rich with my vortech kit after 5500rpm.

So heres my question:
Since the high pressure in the cylinder at full boost pushes back on the fuel system, what if I were to get low compression pistons INSTEAD of the return fuel system?

 

please research more just spend the 1k on a return system.. if you lower your cr with new pistons it will cost much more b/c of labor unless you own a machine / mechanic shop and if your opening the motor why only pistons when Vq's usually go due to rod failure? it sounds like you got some extra bux to play with so do the return and build your block what are you at HP wise now just passing 400 right? its 430 am here so i could be wrong

 

rods fail in engines primarily because of tune. not that i'm suggesting stick with a stock rod when building an engine, but i suppose his goals are important to keep in mind (which, btw, what ARE you goals?) - but keep in mind, lower compression = more fuel and boost required to get approx. the same power. remember the formula:

(atmos. pressure + boost) * compression ratio = cylinder pressure. (or, on an engine compression gauge, it's atmos. * CR + ambient)

so along those lines, if you decrease the compression ratio, the cylinder pressures are decreased, meaning you will have to turn up the boost for the same result (it's not a 1:1 ratio, however). accordingly your fuel requirements will increase.

the point of lowering compression is not to make more power or to "be able to run more boost" it's (theoretically) SAFER power, but i digress.

personally, i think it's dangerous to do projects like that a single piece at a time, you wouldn't do pistons one week and rod bearings another - if you are running out of fuel, i'd do BOTH the kit and bigger injectors - you don't want to have to accomplish your goal by drastically increasing fuel pressure. you might also want to add a bigger fuel pump... in fact, you REALLY should (at least, all of my research on my own FI project and experience from past projects would agree).

 

im just going to go with the return fuel system

 

Im still amazed that TN and AAM are still flashing the ECU for guys when they know they will not get enough fuel up top . They know where the ceiling is and thats some where around what the stock Vortech pulley makes .

 

What are you talking about? The TN kit comes with a warlboro fuel pump which is more than capable of delivering the extra fuel pressure required for the daily operation of the kit. A fuel return line isn't a magic tube that fixes all fuel problems on the car, despite what some on these forums might have you believe. Safe operation can be achieved by raising fuel pressure across all injectors. With larger injectors and an aftermarket fuel pump, this can absolutely be achieved at lower boost.

Take my car for instance, my AFR graph is drastically flatter and more on-target than 99% of the tuned cars out there.

 

I didnt say anything about raising fuel preasure . In fact , if I were sja177 - I would do exactly that

Ive been PMed by no less than 8 guys , saying TN or AAM flashed thier ECU to run thier Vortech instead of the SS box . And all said the same thing . They got lean in the upper rpm range . What Im amazed at , is they do it with out telling the customer that this could happen and if it does , they should tell them the salutions for it . ANd it should be done before hand so the customer can make his mind up before hand . And not be sent out the door with a incomplete tune and possibly hurting his motor . The guy goes in the door and expects to leave with a safe tune . But instead leaves with a unsafe tune and has to spend more money that he wasnt expecting to spend to make it safe .
People on this site and others have had it in thier head that the SS box isnt capable of providing a good tune . When in fact it can . It's the fuel system that isnt the best . It works and will work for a long time . It when you start changing pulleys , that the fuel preasure starts getting way higher than Vortech intended in the kit . The life of the injectors will be lessened even more .

 

I see... however, I don't believe Turbonetics will actually flash ECUs for anyone besides ST owners. It will be news for me if they did...

edit: You might be thinking of AAM.

 

How does TN raise the fuel preasure ? Can it be done with the stock FPR ? Or does the kit come with a after market FPR ?

Oh...I did make a typo....I said when TN and AAM flash...when I meant Technosquare and AAM

 

I think we are confusing TN and TS

On the Vortech if you run the smaller pulley you will need the bigger injectors and bigger walbro pump to be able to tune it or you run out of MAF signal to play with.

 

Yes I did make a typo

I believe that is what is happening . They are running out MAF adjustments or what ever . Can it be over come with raising fuel preasure ?

 

The easiest way is to change the pump to a walbro pump and then you should be rich enough to be able to tune and play with the MAF before running out of signal.

 

There are 2 ways of looking at pressure in this world. There is "absolute", and there is "relative". "Absolute" is what the pressure really is, relative is what the pressure is compared to another pressure (a pressure differential).

For example, the pressure of earths atmosphere is 14.7psi at sea level. So when you are driving a non-boosted car and you floor it, the gauge reads 0psi. That is 0psi "relative". The atmospheric pressure is being used as the base line. But when the boost gauge says 0psi, there is really 14.7psi because of atmospheric conditions. So relative is used to compare a pressure differential, not actual pressure. Absolute is actual pressure. Of course the atmospheric pressure is greater at lower altitude as the earths gravity is stronger and pulls the air down harder. Such is the opposite of high altitude. So what this all means is that a boost gauge is a relative-to-earths-atmosphere-pressure gauge. Its calibrated to read ZERO when the condition of the outside air is the same pressure as the air coming in the vacuum line to it.

Moving on to the fuel system...

The stock fuel system in the 350z/G35 has a fuel line that goes directly from the fuel pump inside the tank, to the fuel rails. That is where it ends. Inside the tank right next to the fuel pump is a fuel pressure regulator that maintains 58 psi all the time. It regulates the pressure by constantly bleeding fuel out of the fuel line to whatever extent required to maintain this 58psi. This is 58 psi relative, but that doesnt matter right now. Consider that all quoted and claimed pressure in the world is pretty much always relative unless otherwise stated.

When your car is not boosted, and you floor it... you have 58psi fuel pressure, and 0psi in the intake manifold and intake ports. That means there is a pressure differential of 58 psi.

Now, dont change anything at all except the fuel pressure. Turn it up to 64 psi. You know have a differential of 64psi at full throttle. What happens? You know exactly what will happen. The car will run richer because the higher pressure differential will force more fuel thru the injector even with the same exact injector opening duration (called the pulse-width, the length of the "on" signal).

So now lets put the fuel pressure back to 58 psi. Lets puts a supercharger on the car. Now lets exagerate the situation just for the sake of explanation. Lets say that your supercharger runs 58 psi of boost. Now what??? You have a fuel pressure differential of 0 psi!! What will happen each time the injectors open? Hardly anything, the only fuel that is going to come thru the injectors is the fuel that gravity pulls down and drips. Now turn your boost up to 62 psi!! Now the intake has 4psi more pressure then the fuel system, and instead of fuel coming into the engine, air is going to enter the fuel lines!!!

So lets get back to the real world conditions now. Your at the stock 58psi of fuel pressure now, but your running 8psi of boost. Now your fuel pressure differential has fallen to 50psi by the time your at full boost. Your pressure differential is falling off as your boost increases. This reduces the horsepower capacity of your fuel system to be able to maintain the ratio of air vs. fuel that you are looking for.

As airflow in the engine goes up, you need the flow of fuel to follow it to maintain that air/fuel ratio. When your fuel pressure differential is falling off as your airflow goes up, that is exactly the opposite of what you want!

Heres where the return fuel system fights back!

With a return fuel system, you can take that factory 58 psi regulator, which is called a static pressure regulator, and throw it in the trash. The return fuel system will include a new regulator, and this regulator will have what is called a reference line. The reference line is a vacuum hose that you connect to the intake manifold so that the regulator can see how much boost or vacuum that you have. The new regulator will be adjustable, and as just discussed: referenced.

The adjustable part means that you set the pressure to what you want. This is called the base pressure on a referenced regulator. Or we can also call it the differential pressure setting. Because this regulator will use the reference line and always maintain a static differential. Meaning if we set it to 58 psi, it will make sure that the pressure in the fuel rails is always 58psi higher then the pressure in the intake manofold.

So at 10 psi of boost, your fuel pressure is at 68 psi. At -10psi vacuum, your fuel pressure is at 48psi. At 20 psi of boost, your fuel pressure is 78 psi. See whats happening, as your boost goes up, the fuel pressure follows its precisely. This helps your case in two fantastic ways:

1: It will increase the HP abilities of your current fuel injectors as you can not only raise the base pressure a little if needed, but the fuel pressure differential will not be falling off like it did with stock fuel system. Your overall capabilities are now significantly higher.

2: It will be easier/cleaner to idle larger then stock injectors because now the fuel pressure will drop under vacuum, making less computer tuning required to compensate for the larger injectors at idle.

 

I believe sja177 has the walbro and 440 injectors installed and is still running lean up top .

 

Phunk
I think he is looking for a lower cost salution . Can the stock FPR's preasure be raised alittle ? Or can a after market FPR be installed with the stock returnles system to raise preasure enough to get by with the TS falsh ?

 

Nice write up Charles.

I assumed he had the stock pump since he stated thet the stock fpr and pump were not enough.

Adding just the injectors is not enough as can be seen by phunks explanation you not increasing the fuel pressure even with the inline pump. We did one with 380cc injectors and walbro pump and had plenty of room in the MAF signal to tune it with the smaller pulley running around 10 psi.

 

Nice write up Charles.

I assumed he had the stock pump since he stated thet the stock fpr and pump were not enough.

Adding just the injectors is not enough as can be seen by phunks explanation you not increasing the fuel pressure even with the inline pump. We did one with 380cc injectors and walbro pump and had plenty of room in the MAF signal to tune it with the smaller pulley running around 10 psi.

 

Phunk
I think he is looking for a lower cost salution . Can the stock FPR's preasure be raised alittle ? Or can a after market FPR be installed with the stock returnles system to raise preasure enough to get by with the TS falsh ?

 

Phunk
I think he is looking for a lower cost salution . Can the stock FPR's preasure be raised alittle ? Or can a after market FPR be installed with the stock returnles system to raise preasure enough to get by with the TS falsh ?

 

Nice write up Charles.

I assumed he had the stock pump since he stated thet the stock fpr and pump were not enough.

Adding just the injectors is not enough as can be seen by phunks explanation you not increasing the fuel pressure even with the inline pump. We did one with 380cc injectors and walbro pump and had plenty of room in the MAF signal to tune it with the smaller pulley running around 10 psi.