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Discussion Starter · #1 ·
I read over on D-Series in the infamous "Powerful Street NA D16y8/Z6" thread that 55psi is the optimal pressure for good atomisation with the OEM injectors. I've got an AEM FPR on the way, so I'm going to try it out. Anybody have any opinions/experiences with this (looking for the tuning guys here)? I'm feeling a little bad about leaving the rex alone from mods for a while, I want to get back into it and get this motor built.
 

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Discussion Starter · #2 ·
No replies eh?

Well... I was looking at fuel pressure gauges today. I was going to just go ahead and order the B&M unit, but I found that it's not liquid fillled. Summit makes one that is, but it doesn't come with the 90 degree bend like the B&M gauge. What is the piece I would need for that? I don't know anything about AN, NPT etc. I'm also thinking about drilling a hole in my Z6 fuel rail and tapping it to mount the gauge there, instead of on the fuel filter. It makes sense to me to have it closer to the FPR, and also I'm planning on running all stainless braided fuel lines with an inline filter, so it won't be able to go on the stock filter then anyway.
 

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If you are going to drill and tap your fuel rail, just be very sure that you clean it out very well after the machining is done.

I looked at the summit FPRs and it looks they are only low pressure, in the range of 4.5-9psi. I don't see any others from summit that operate in the range of 55psi.
 

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with my build i just used the stock GSR FPR. and im using the B&M guage. well i was, i dont even have the guage hooked up anyore, since the FPR is stock, really no need.

if you want a liquid filled guage but it doesnt come with the 90* bend you can pick one up from the hardware store. 99% of the guages out there will use a 1/8 NPT fitting, so you will need a male-female 90* 1/8 NPT adapter.
 

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jmart said:
If you are going to drill and tap your fuel rail, just be very sure that you clean it out very well after the machining is done.

I looked at the summit FPRs and it looks they are only low pressure, in the range of 4.5-9psi. I don't see any others from summit that operate in the range of 55psi.
What about these:

This one

Or this one

Here's the source page

Not cheap, but they'll do the job well.
 

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Woops, sorry Tom. Reread your post and it was the Summit gauges that you were talking about. Ya, just pick up an adapter at a hardware store. NPT is pipe thread. The threads actually increase in overall diameter as they get further from the end so that when you screw it in the treads actually make a seal. AN fittings have a tapered edge at the end of the threads that does teh sealing. i think there may be two differnt types with different taper angles. Then theres flare tubing and a couple of others types of tube fittings.
 

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Discussion Starter · #8 ·
I'm about to order the gauge, the FPR is sitting lonely in my tool box :( I have an extra borrowed fuel rail from Scott to work with, I just need to get the plumbing sorted out. Would I be better off drilling a hole and welding a fitting onto it, or tapping some threads for a fitting? Where would I get the appropriate bung or tap for this?
 

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SETI20 said:
Upping the pressure will do NOTHING for your AFR, except when at WOT in open loop. The ecu will compensate everything else out.
Unless you are me or tom with closed loop disabled. We have our widebands inputted to the ecu for logging purposes only.

Or if you cranked the FPR to some crazy level, then the car wouldnt be able to sort that out either.

So, for us, upping the fuel pressures almost linearly increases fuel output for us. If the injector performs better at around 4 bar instead of our stock 3 bar then why not. We use a 4 bar (@ atmosphere) regualtor on the audi with no adverse effects. It effectively turned his injectors into 970cc ones.

now, a related question I have if anyonge knows for certain. the AEM and Aeromotive FPRs are touted as being 1:1 boost reference, meaning in boost they continue to up the fuel pressure. I was under the impression the stock regulator does this as well, but 2 people have told me to the contrary. Does anyone here know for sure?

[email protected]
 

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I would get a wide band O2 and set my fuel pressure to what my O2 reading is, not what some peolpe posted on a board somewhere...
 

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ludesrv said:
I would get a wide band O2 and set my fuel pressure to what my O2 reading is, not what some peolpe posted on a board somewhere...
toms not talking abotu tuning his car by changing the fuel pressure, hes talking about changing the baseline fuel pressure for better atomization of the fuel, which is a concept Ive heard about, but never seen applied.

We tune for AFR in the ECU using Innovate LC1s and Crome Pro.
 

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Fuel pressure and 02 reading are not per-se connected.
Higher pressure, does not AT ALL yield a higher capacity, only a higher flow.

Like I said, while -some- increase in pressure can be helpful, the preferred method is a longer duration for a more effective pattern.
Only if the duration is giving you issues, should you increase the pressure.

Besides, by the time you have reached the peak duration, you should have upgraded to higher capacity injectors to begin with.
Not at all the best basis for tuning if you ask me.
 

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I have to say IME Fuel pressure and AFR are directly related. If you are opening the injector for 100ms @ say 30 psi and 100ms @ say 40 psi, you are going to flow more fuel at 40 psi for sure (unless you hit the ceiling of the injector, whatvere that may be)

Toms not running out of duration capacity, thats not the point of increasing the fuel pressure, hes talking about increasing the pressure to a new baseline, then decreasing the duration of the injector back down.

The problem is, I dont know how youd test this theory of better atomization, personally Id leave the pressure at stock. But in the end, it wont have any adverse effects that I can see.

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I understand what you're saying. But you said it yourself.
You add pressure, decrease duration, so decrease AFR again.

And running open loop all the time, is not my preferred method of base lining.
In closed loop, upping the pressure would not give consistent results. Flooding the curve under WOT.

Oour injectors are not suited for these pressures. The usual write ups use peak/hold injectors as examples.
Most hond ainjectors are saturated.
 

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So yeah we are pretty much agreeing hten haha.

I just have no hard evidence one way or another that usiing a higher fuel pressure increases atomization, or how youd even test that in real world conditions.

You say our injectors arent suited to that pressure, where did you get that information? It seems like the info Tom got is contradictory (not to say whos right or wrong, just trying to figure it out.) The manufacturer of the injectors we put in the Audi rated their flow at 3 bar, to be standard, but told us that running them at 4 bar would be no problem.

Anyway, I love running open loop all the time. Ive never gotten better fuel mileage and performance. I was able to lean my car way out at part throttle, which I wouldnt have been able to do closed loop. Part throttle tuning almost requires the use of open loop, if not at least narrowing the closed loop operation to idle and very light throttle, and at that point I dont see the reason to have it around anyway.

Do you know the answer to my boost reference question? like the stock fuel pressure goes from just above 2 bar at idle up to 3 bar at WOT, does it keep going higher in boost?

[email protected]
 

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Well nobody answered this yet, and here's a CRX manual sitting next to my terminal so ...

The fuel pressure regulator maintains a constant fuel pressure to the injectors. When the difference between the fuel pressure and manifold pressure exceeds 2.55 kg/cm^2 (36 psi), the diaphragm is pushed upward and the excess fuel is fed back into the fuel tank through the return line.
The regulation pressure is based on manifold pressure not atmospheric. The manifold pressure assists the spring that seats the check ball that allows fuel to flow back to the tank. In theory if you boost the manifold above atmospheric, fuel pressure will rise higher up to the limit of the supply pressure from the pump and what can flow through the stock regulator. Somebody must have data on how far the stock regulator can be pushed somewhere, but I'm too lazy to google for it...

[edit] Actually now that I think about it the supply pressure from the pump is really the only issue. As manifold pressure rises the check ball moves closed to reduce the amount of fuel flow back to the tank. The max flow through the regulator is actually at idle when manifold pressure is lower than atmospheric ... pressure in the rail might only be 21 or 22 psi relative to atmospheric if your motor draws a good vacuum at idle.
 

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Saturated small capacity injectors will not atomize properly at high pressures and flow velocities.
They will just squirt out a jet of fuel instead.

Tests have shown that this will lead in fair amounts of unburnt fuel.
I still say, save your money. Get a set of DSM 450 peak/hold injectors for under a hundred bucks instead.
 

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Ok, tahts the type of info I was looking for.

He still doesnt need biggerinjectors though, that wasnt the original point. The oringal point was that someone told him that the fuel injectors would work better at a slightly higher pressure. If thats incorrect, thats fine, but he still doesnt need bigger injectors.

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