Base Fuel Pressure

[cheekychimp]

As many of you know I have been having ECU issues, compatibility ones I guess through trying to use DSMLink in a JDM car. Anyway I have been in touch with Jeff who has offered to set me up with a chip to get me on the road until I figure out some of the other stuff for now.

One thing Jeff needs is to know what Base Fuel Pressure I'll be running.

This is a 6 bolt, 9.0:1 compression 2.3 litre stroker. I have a Supra TT Denso pump in tank and a -6AN from tank to the fuel rail and 850cc injectors although I may swap in the 800cc SARD ones before I hve Jeff do a chip.

Any thoughts on what to go with on fuel pressure? I thought initially I'd go with the 2G stock setting but will that be enough/necessary?

 

[Kenny_Kline]

37 psi

 

[cheekychimp]

Thanks!

 

Quoting krkline2gdsm:
37 psi



^

 

[iLLeffeKt vr-4]

Most injectors are tested at 3 Bar (43.5psi) which is what 2g's run.
So your 850cc's injectors will flow 783cc's at 37psi and the 800cc will flow around 737cc's
I would run them at 37psi first and then go from there.

 

Paul, is the Supra pump rewired? A lot depends on whether the rest of the fuel system can keep up, and what your HP goals are. At 43.5psi those injectors can flow 192 liters/hour at 100% DC. According to Jeff Lucius's flow data, the Supra pump at 13.5 volts, which I would *assume* means rewired, will flow more than that up to ~73 psi, which would be almost 30 lbs of boost.
Denso Fuelpumps
But, the second question is, do you need that much fuel for your HP goal? At 37psi, those 800cc injectors would actually only flow 738cc. According to RC's site, that would make about 505 crank HP, assuming 90% duty cycle and a .50 BSFC. At the full 43.5 psi they could make ~545 crank HP.
RC Calculator
Personally, since you seem to have the proper fuel setup to support it, I would run 43.5psi. The chip makes both fuel pressures run identically, so its just a matter of what your goals are and if you have the right support mods.

 

[Kenny_Kline]

Jeff, according to that website and calculations, IM SCREWED! I plan to make around 350-400whp on EVO8 560cc injectors. I will probably be close to 100% DC. Either the calculations I did were off or I need bigger injectors. I am on a 16g (roughly 25psi), wally 255HP, Aero FPR, 560cc EVO8 injectors.

Do I need bigger? Like 650cc???

 

The EVO injectors actually flow 585cc or more. If you jack up the base fuel pressure to at least 47 psi, and run the injectors up to 100% DC, you *could* hit your goal, especially on racegas. Would I recommend it? /ubbthreads/images/graemlins/dunno.gif It would be much safer with 750's. Most "650/680cc" injectors only flow 640cc, so there's not much advantage to them over the EVO injectors.

 

[Kenny_Kline]

Yeah I have a wideband, EGT, and logger so we will see what happens higher up in the RPM band.. I will watch closely. I have chip from you that is set at 37psi. If I change it to say 44 or so psi, how would it affect the chip?

My next buy will be ECMlink so 1000cc injectors will be ordered but just seeing on what I have to work with now.

 

If you raise the base fuel pressure to 44 psi, how are you planning on removing the 9% more fuel? If you do it with an AFC it will throw you off slightly on the timing maps, since the ECU won't be seeing the real airflow/load. You may end up with 1-2 degrees extra timing advance.

 

[brisvr4]

Here is something on the Sard injectors for your own info Paul.
My Sard 800's actually flowed 840cc's @ 40psi.
According to an old Email I got from Jeff when I was talking to him about my new chip that equates to
876cc @ 43.5psi, quite a bit more than 800!
You might want to get yours flow tested to check them so you can compensate correctly for them.

 

[Dialcaliper]

^ what Jeff said.

Keep it down at 37 psi, the stock level. The only reason to raise base fuel pressure is if your injectors aren't large enough, or you're trying to fool with A/F ratios without proper electronic tuning (or trying to avoid messing up the timing curves as much as with an SAFC).

Lower base fuel pressure is better, especially with high boost. Injector flow may go up, but your fuel pump flow will go down, and the harder working pump will heat the fuel up more.

With the 1:1 rising rate FPR, the pressure drop across the injectors into the manifold will always be the base fuel pressure (since you're trying to push fuel into a pressurized intake), but the pump will be trying to flow against the base pressure *plus* boost pressure. (For example, with 37 base pressure and 25psi boost, your pump already trying to push against 62psi).

Stock FPR's are actually pretty sloppy - acceptable from the factory is anywhere from 36 to 38 psi. Nonturbos are even worse - 47 to 53 psi. An AFR is basically there to let you dial the fuel pressure in much more precisely to where you want it, and more importantly, what your ECU fuel tables were written for.

 

[cheekychimp]

Guys, thanks, I knew there was a reason I had been thinking to go with the 2G base fuel pressure but it has been so long I couldn't find it. The fuel pump is not currently rewired. I relocated the battery to the trunk so I figured on doing this later when I cleaned up the trunk wiring.

Tim, I do also remember the SARD injectors being one of few that overflowed 800cc albeit at a higher fuel pressure, I think Bazeng is running these.

I guess the logical route is to go and get the SARD injectors flow tested as suggested whilst they are off the car and take it from there.

One thing I didn't understand Jeff, was about the chip running both fuel pressures 'identically'. I assume I have to 'choose' a fuel pressure but I'm confused as to what you meant by that?

 

What I was saying is that the ECU and car don't really care what the base fuel pressure is, the driveability, mpg, idle, etc are all identical at either pressure. Its just a matter of what your HP goals are, and fuelpump capacity. Pick a base fuel pressure, and as long as the chip is burned for that pressure everything else falls in place. Another way you can do it, to avoid flow testing your injectors, is to simply watch the HIGH TRIM after you install them. You can then tune the base fuel pressure until the HIGH TRIM stays at 100, then the ECU and injectors should be well matched.