RomRaider

Hi, I am new to this, and have been playing with the tools from here and from openecu.org. I do have some fundamental thoughts which I want to share to see whether I am thinking this through properly.

1) Fuel system: The fuel pump of the WRX is a 130lph unit, per the service manual. This means, 2.166 liters/min, which also means that regardless of fuel pressure, the maximum injector size the fuel system can accomodate on a 4 cyl MPI system like the WRX is a 541.6 cc/min unit.

So, my first conclusion is that I should never run out of fuel using the standard WRX injectors.

2) The turbo characteristics of the TD04-13G which seems to be the WRX turbo indicate that you can get to around 2.25bar (~18PSI) @ 280CFM and 77% compressor efficiency.

So, the second conclusion is that there is some room for safely spooling up the turbo, beyond the 13.59PSI maximum boost target of my map. APS suggests you can go even to 19PSI before hitting diminishing returns. See http://www.airpowersystems.com.au/wrx/aps_turbo_technical.htm

3) My observations however on logging my AF411 stock ECU show several things:

- I am getting peaks of 91% injector duty cycle when the engine reaches aproximately 5700 RPMs under WOT. Per the books I have read, any point beyond 80% could cause fibrilation or overheating in the injectors.

- My boost is getting to aprox. 14.5 thus exceeding the targets.

- Wastegate duty cycle is pretty high but does not worry me too much yet

So, overall I think that the stock ECU tune-up pretty much maxes out the stock injectors given the standard target boosts.

Anyway, in order to confirm I tried a couple of Higher wastegate/Boost target remaps only to convince myself that I could get 15.5PSI but I was simply saturating the system and possibly going into a lean condition anytime boost and RPM would keep going up and my injectors were long stuck at 100% duty cycle.

No wonder, the last row of the Wastegate duty cycle, the 6800 RPMs one, is all 0s, and the corresponding target boost line is low ( aprox 7PSI).

The preliminary conclusions that I get out of these little experiments are that without changing injectors there are only very limited things I can do to add power to the car:

Alt.1 - Lean out my fuel map -- This would allow me to have a lower injector duty cycle for the same RPM / Boost, and thus I could raise boost target through the RPM band. This is risky however and I will wait until I decide to buy a Wideband O2 to do it.

Alt. 2 - Use standard power recovery techniques, like making a more free flowing exhaust which does not work so much against the engine, or an underdrive pulley

Alt. 3 - Even if my car runs fine, maybe my car's injectors are clogged and I need to clean them? Anyone experienced the Injector duty cycles I am describing on a Bone stock ECU?

So, having reached this point, unless my system is clogged, I do not see how COBB could claim a safe ~30hp improvement with just an ECU reflash. I figure there may be variables I am missing.

Ideas anyone?

one quick correction. 2.25bar is wayyyy more than ~18psi

and also. the stock wrx injectors cant flow 541cc regardless of what the fuel pump is doing.

the other stuff..iono? haha sorry

The stock injectors, at the pressure our regulator provides, only flow at about 380cc/min. The stock ECU is very close to maxing this out.


There's been a lot of talk about this recently on NASIOC now that the compressor map has finally turned up. It shows that around 4500rpm, the compressor is still quite efficient at 22psi. At that point, the wheel is spinning around 180,000rpm though, so the turbo will not likely last a long time. See http://forums.nasioc.com/forums/showthread.php?t=988825


This isn't really all that accurate because in open loop fueling, without tuning the fuel table the ECU has no way to compensate for the higher boost. If you're talking about at high RPM (like 6000+), you can probably get enough fuel to get your AFRs where you want them (maybe not..) but the compressor will be inefficient and your intake temps are raising pretty quickly. The end result is the same though, that is too much boost at 6k.


The freeflowing exhaust is definately the best thing you can do. It'll free up a lot of power even without tuning. Then, you should also be able to run less timing since there will be less backpressure, and less fuel.


It couldn't hurt to run a bottle of injector cleaner with your next tank of gas, but high injector duty cycle is pretty common even on stock cars. Actually, a clogged injector wouldn't cause high IDCs, it'd cause you to go lean because the car has no system to monitor this and rather than dumping in more fuel (and giving you higher IDCs), it'll keep working the same and you'll just end up lean.


Honestly, IMO, 90% of that power comes from increased boost alone. Like you said, you can't increase boost toward redline very much, but you can a little, and you can raise it more at lower RPMs. Because we hit peak HP at a relatively low RPM, their claims are probably not ridiculous.

That's probably 2.25 bar absolute pressure

ah I just realized that right before I came back to this thread

"Honestly, IMO, 90% of that power comes from increased boost alone. Like you said, you can't increase boost toward redline very much, but you can a little, and you can raise it more at lower RPMs. Because we hit peak HP at a relatively low RPM, their claims are probably not ridiculous."

This is true but there is also a good deal of power to be made from leaning out the stock map (which runs pig rich), even cobbs tune is very conserative on the fuel IMO.

I'll hopefully be getting the wideband tonight so I should see what you're talking about.

Lucky you, looks like I will be spending my WB money on a stock sensor

Anyways let me know how it goes. When you done I'd like to take a look at your image if you don't mind shareing (I belive our cars are close on the mods, at least they were till you ported that td04)

Our club got together and we all pitched in to buy the wideband (I say we, but it was before I came around..). If it were me, I'd spend my wideband money on the stock sensor and then my beer money on a wideband.

Thats good point! Shouldn't take long that way

The stock injectors can flow around 530cc +/- 15cc if you were to raise fuel pressure up. Remember, stock FPR is a 1:1 ratio of boost pressure and fuel pressure.
Kingpin found that "crushing" or putting a deeper dimple in the fpr would raise the fuel pressure, but be careful as not to ruin it.
IIRC the Nismo FPR which comes stock on jdm silvias(240's) is adjustable with the turn of a knob but i'm not sure if it fits our engines correctly.

yeah any local nissan parts dealer can get that fpr for u. I don't remember the price from when I worked there. but I do remember being able to get it. its in their nismo catalog. along with extra long studs

Many people see high IDCs with the stock map, because it is extremely rich at high loads. If you were to go with the stage 1 Cobb map (I'm assuming your stock), your IDCs would probably drop. I haven't heard much of problem with people running over 90% IDCs in the WRX (I have heard problems with other cars), so maybe this has something to do with the design of the injector. If you are hitting over 99%, then yes, obviously, that is a problem.

Sounds like a trick from the DSM days

What I meant to say is that with the 380cc injectors of the WRX (or 420cc depending on your source of info), you would never be able to starve the stock fuel pump. Even if you upgrade to STI Pinks, which I think flow 550cc/min you should still be OK in most cases. It is interesting to note that the STI fuel pump is 140lph which feeds the pinks in 100% of cases and would be able to accomodate up to 583 cc/min. However, comparatively, the STI fuel system is closer to being maxed out.

Also, from my inspection of the system, there is no intermediate fuel buffer in the FPR, which possibly indicates that the FPR is a purely resistive device, a 3 steps one by looking at the logs.

In the same line of thinking, I figure that 8x or 12x raising pressure FPRs have some sort of container where they accumulate fuel, such that when needed they can pump from that container as the stock fuel pump would not be able to feed them properly. [For the record, I think that raising rate FPRs are a cheap and dangerous DSM era trick].