440cc Injectors are too much, options?

[All_talk]

So I finally decided to get off my ass and crank up the boost on the EJ20G in my ’91 SS. Background, ’04 WRX top mount IC, Helix 3” turbo back, TurboXS manual boost control, vgr3 FCD, stock EJ22T ECU.

First a note on the stock turbo, MBC is set at 15psi, full boost by 3000rpm and it will hold that tell about 4500, after that it slowly drops to about 9psi at redline (6500). Seems the factory picked the smallest turbo that would hold designed boost at redline, which means the quickest spool… well engineered.

With the stock 370 injectors I had an AFR of 13:1 from 0 to 4psi then jumped to about 12:1 with a slow drop in the last 2000rpm to about 11.5:1 at redline. I would really like to see the whole range shift down 1/2 to 1 point. So yesterday in go the 440s, now the 0-4psi is at 12:1 then that jump is to 10:1, dropping to about 9.8:1 at redline. I guess I shouldn't be surprised, this is just about what I calculated with a 20% increase in flow. On full boosting pulls I could feel a bit of bogging from the overfueling. The stock ECU trimmed the idle and cruise back to stroich quite well. This morning on the way into work it seemed the whole range of AFRs was up by about 1/2 a point, so maybe I’ll leave the 440s in for a few days and see what shakes out.

Question, can the stock ECU trim the whole fuel range? I assumed it would only trim in closed loop and leave the rest to the stock mapping. Can it use the trim required to adjust the CL to move the OL map?

If the 440s don’t trim back a bit more I think I’m going back to the 370s and I’ll up the fuel pressure a bit to get the 10% or so I’m looking for. I like to see about 12.5:1 in the transition and 11.5-11.0 under high load.

Once I finish my stroker build/V24 I’m sure I’ll need the 440s if not 550s, I figure at that point a piggyback is my only choice.

Comments, ides or suggestions?
Gary

P.S. the 15psi hits like a hammer in 1st & 2ed gear. My poor tranny.

[vrg3]

I believe it can use information learned during closed loop to actually trim fuel even in open loop, but it takes a while for it to start transferring that data around. I wouldn't rely on it to do what you need here.

It sounds like what you really want is stock injectors and a very low ratio rising rate fuel pressure regulator.

[BXSS]

I actually used an adjustable FPR to lower base fuel pressure a bit on my 440s.

Works good.

I think a FMU / stock injectors will work very well.

[All_talk]

Hmmm... back to the 370s and raise the pressure or keep the 440s and drop the pressure? I'm only looking for about 10% so thats like 4psi. Dropping with the 440s would put less load on the fuel pump, but would the lower pressure (should be about 32psi) cause issue with the injector spray pattern/atomization? I wouldn't think so, anybody have experience to share?

Gary

[BXSS]

I set my base pressure @ 31psi with the Vac. line disconnected & am having no problems.

The way I have this working on my car is - the 440s behave like 370s on low load since the base pressure is lowered, but once there is boost the injectors spray slightly more than the 370s would @ a given boost level.

Here are some estimates of flow under boost.

-------Pinks Greys (@ 31psi base fuel pressure)
Base 370cc 371cc
5psi 390cc 403cc
10psi 410cc 430cc
15psi 429cc 455cc
16psi 433cc 460cc
18psi 439cc 469cc

It is basically the same as running a Low ratio FMU (about 1.5:1) on the stock pinks, without the problem of very high fuel pressures as boost increases.

Pinks @ 10psi on a 1.5:1 FMU would be 429cc, the Greys @ 10psi are 430cc.

[vrg3]

I'm not sure I follow your logic, BXSS.

A standard FPR doesn't make injectors flow more under boost then at low load. The differential pressure remains the same. If you run the 440s at 31 psi instead of the rated 36.3 psi, you have the equivalent of 400 cc/min injectors. At all times.

[BXSS]

I'm not sure I follow your logic, BXSS.

A standard FPR doesn't make injectors flow more under boost then at low load. The differential pressure remains the same. If you run the 440s at 31 psi instead of the rated 36.3 psi, you have the equivalent of 400 cc/min injectors. At all times.

I assumed the base fuel pressure was 3 bar (43.5psi) so my #'s are based around that fuel pressure base.
Folks said they had Greytops flowed @ 440cc's & unless they specified a different fuel pressure all the injector cleaning flowing companys (RC eng, Deutch-werks, Marren fuel injection...)I know will test @ 43.5psi.

The FPR I have has a 1:1 rise with boost so if you set a base fuel pressure & run 5psi of boost the fuel pressure while your boosting is base+5psi.

I just plugged the #'s (base or base+(x)psi of boost) into the RC Eng. flow equation & came up with the values I listed above.

[vrg3]

A 1:1 rise doesn't increase flow with boost! It just keeps up with manifold pressure so that fuel flow stays constant. This has been covered several times (by me) on this board.

[BXSS]

I sort-of understand what you are saying about maintaining the pressure differential on boost, but when you say the flow out of the injector remains the same regardless of boost level on a FPR that has a boost referenced rise you lost me....
It just make no sense to me.

I'm saying

If you freeze the fuel pressure @ 15psi of boost, injector output should not be the same as it was with 0psi.
If you have a 1:1 fuel rise, it should be base pressure (lets say 35psi) +15psi.

If you plug that # (50psi) into the Flow calculator the injector should be flowing fuel more than the base value (35psi) was flowing.

I got a pretty chart that I could easily duplicate from Deutcsh-Werks based on this fact (it showed injector flow vs fuel pressure).

Flow out of the injector is a function of the fuel pressure going into it & your saying that regardless of the pressure going into the injector the flow is remaining the same @ idle vs. under boost on a regulator with a boost referenced fuel pressure rise.

[vrg3]

Pressure doesn't "go into" things.

Flow through the injector is a function of the pressure difference between the inlet of the injector and the outlet of the injector. Pressure difference. Absolute pressure doesn't matter in the least. The inlet of the injector is the fuel rail, and the outlet is the intake manifold.

So if the fuel rail is at 26 psi and the intake manifold is at -10 psi, you'd get the exact same amount of flow through the injector openings as if the fuel rail were at 46 psi and the intake manifold is at 10 psi.

And that's exactly what a 1:1 rise ratio regulator does. In fact, the numbers in the above paragraph reflect what the stock 1:1 FPR does.

[BXSS]

I thought a 1:1 rise regulator (referenced by your intake manifold) maintained the pressure differential of fuel pressure vs. manifold pressure (air).

Ex.
@ 0psi Intake Manifold pressure = 35psi fuel pressure - difference is 35psi between manifold & fuel pressure.

@15psi Intake Manifold pressure = 50psi fuel pressure on a (1:1) boost rise - difference is still 35psi between the manifold & fuel pressures.

Which makes sense to me - pressure differential is maintained.

[vrg3]

Yes.

[BXSS]

You are not getting the same flow out of the injector when the above happens.

You are getting the same ratio of fuel pressure to manifold air pressure.


Based on the above post

A LSS pink injector flows 370cc @ 36.3psi base fuel pressure.
That same injector will flow 418cc @ 46.3psi fuel pressure which is the same as base fuel pressure + 10psi of boost on a 1:1 rise fuel pressure regulator.

My bootleg chart's numbers above are based on a 3bar (43.5psi) fuel pressure base so they are slightly off.

[vrg3]

The pressure in your charts is the differential pressure between rail and manifold.

Just stop and think about this in terms of the laws of physics.

[BXSS]

I just added values to the scenario you "yes'd".

[vrg3]

Okay... I don't remember what you had there before, but it's still correct.

Let me explain a little better than just saying "think about it."

So. Rather than talk about pressure and flow, let's simplify and talk about force and acceleration.

You and I both stand at either end of a Legacy with the handbrake off and in neutral, on level ground. You're the fuel pressure in the rail, and I'm the air pressure in the manifold.

If you push with 36 pounds of force, and I push with 0 pounds of force, the car will accelerate in my direction.

Now. If you push with 36+10=46 pounds of force, and I push with 10 pounds of force, the car will move in my direction again, right? Will it accelerate towards me faster or slower than the first scenario? I hope it's clear that it would be the same.

So if you always match each pound of force from me with a pound of force from you, you will never actually increase the car's rate of acceleration. In order to increase the acceleration, you would have to respond to a 1-pound increase from me with more than 1 pound from you.

Does that make it any clearer?

[BXSS]

I see what you are saying.