1:1 Boost referenced adjustable FPR w/ return or Static FPR with return?

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
Question: 1:1 Boost referenced adjustable FPR w/ return or Static 72PSI(or other PSI) regulator with a return? Just curious from people's actual experiences with both. Pros/Cons etc. Please chime in.


This is my low pressure fuel system set up:
525 & 535 in stock bucket
BMP4 fuel pump controller
Driver's side top hat restrictions removed via PR top hat
Aftermarket FPR(adjustable or static TBD) w/ return to bucket located in engine bay
Aftermarket fuel filter
6x Bosch EV14 750 CC injectors
Stock 'V2' HPFP


The EV14 fuel injectors we use for PI are supposedly good up to 8bar fuel pressure or 116 PSI so says the internet. However, Black Market Parts claims they work up to 10 bar. I will assume 8bar as that is what I have seen most often as the max psi. As I probably don't want to run them at the limit, 100PSI should give 'enough' headroom in my opinion, almost 20%. With a Boost refenced 1:1 FPR targeting 72 PSI LP then add in + 30 PSI of boost = 102 low pressure fuel psi required for PI to inject at 72 PSI. Max would be 44 PSI of boost which would hit the EV14 limit of 116psi not that I want to touch that or get close. I can lower my fuel pressure below 72psi to keep the combined fuel pressure + boost below 100 PSI, this just eventually starts to limit the flow of the injectors which is not a problem, can always go 1000cc.


The internet tells me this:
Tested Static Flow Rates for the EV14 750cc fuel injectors:
750 cc/min at 3.0 BAR (43.5 psi)
818 cc/min at 3.5 BAR (50.8 psi)
885 cc/min at 4.0 BAR (58.0 psi)
970 cc/min at 5.0 BAR (72.5 psi)
Black Market Parts claims this:
750cc @ 3bar (43.5 PSI industry standard)
900cc @ 4bar (58.2 PSI)
1050cc @ 5bar (72.5 PSI)
The numbers don't match but they are close enough, I will use the lower numbers to be on the safe side.


The Walbro 285 pumps fall off flow wise around [email protected]. At 13.5Vdc and 100psi still plenty of flow for my needs(I have a 525 and 535 in my bucket and will have a return):
F90000285-Flow-Chart.jpg



For a static FPR I would likely be using one of these: https://precisionraceworks.com/products/in-line-micro-regulator?variant=42398655840449


So what would you use, target, and why?
 
Last edited:

wheela

Lieutenant
Jun 4, 2021
1,082
599
0
Twin Cities, MN
Ride
2015 e84 X1 35i Msport
Sorry this isn't actual experience, but it's an interesting question, and thought I'd chime in. Since n54 has low pressure fuel monitoring and PID for targeting its low pressure fuel target with the ekp, will that defeat the purpose of the 1:1 boost referenced pressure adder on the regulator? It seems like the oem lpfp system would drive the pumps to hit the programmed target and prevent you from hitting the increasing target from the 1:1 boost referenced external fpr?
 

nyt

Sergeant
Sep 15, 2019
331
1
289
0
Ride
2010 335xi
I'm running with a 1:1 rising rate regulator up to around 40psi of boost. I ran with it static at 72 for a bit, but I wasn't comfortable with such a large fuel to intake manifold pressure differential change. Using a pair of 535 pumps.
 
  • Informative
Reactions: Torgus

wheela

Lieutenant
Jun 4, 2021
1,082
599
0
Twin Cities, MN
Ride
2015 e84 X1 35i Msport
I'm running with a 1:1 rising rate regulator up to around 40psi of boost. I ran with it static at 72 for a bit, but I wasn't comfortable with such a large fuel to intake manifold pressure differential change. Using a pair of 535 pumps.
Are you seeing low pressure fuel pressure rise with boost in your logs since installing the 1:1 regulator? I'd have thought the stock system would slow the pumps down to keep on target🤷‍♂️
 

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
I'm running with a 1:1 rising rate regulator up to around 40psi of boost. I ran with it static at 72 for a bit, but I wasn't comfortable with such a large fuel to intake manifold pressure differential change. Using a pair of 535 pumps.

Hey man, always liked your ride!

If a rising rate regulator is 1:1 boost referenced is there any difference from a normal FPR?

Any reason you went with a rising rate regulator?

What fuel psi do you target with your 1:1?

72psi + 40psi of boost is 112 which is still within the operating parameters of the injectors, granted right on the edge ;)



Are you seeing low pressure fuel pressure rise with boost in your logs since installing the 1:1 regulator? I'd have thought the stock system would slow the pumps down to keep on target🤷‍♂️

At WOT the fuel system is open loop I believe. Pumps just pump and dump and the regulator regulates is my understanding.
 
  • Like
Reactions: nyt and wheela

carabuser

Lieutenant
Oct 2, 2019
855
1
745
0
UK
Ride
Z4 35i & 335i
You could increase the DME LPFP setpoint, ideally it should be just under what the regulator is set to. That way your DME is trying to back the fuel pump off as you up the pressure.

The table references mg/stk of injected fuel and rpm:

1674684418278.png
 
  • Informative
  • Like
Reactions: wheela and Torgus

nyt

Sergeant
Sep 15, 2019
331
1
289
0
Ride
2010 335xi
Hey man, always liked your ride!

If a rising rate regulator is 1:1 boost referenced is there any difference from a normal FPR?

Any reason you went with a rising rate regulator?

What fuel psi do you target with your 1:1?

72psi + 40psi of boost is 112 which is still within the operating parameters of the injectors, granted right on the edge ;)

At WOT the fuel system is open loop I believe. Pumps just pump and dump and the regulator regulates is my understanding.

Hey, thanks. The car has a lot more in it :( The exhaust is limiting it to around 800whp now. I can throw boost at it, but power drops off. The current tune I run daily makes about 36psi at 4500 rpm and tapers down to 26 or so at 8000rpm. If my shop construction ever finishes, I'll likely work on redoing it with something that flows better but still keeps things quiet.

Normal FPR in these just holds 72psi static. Any FPR that has a boost/vac reference is rising rate.

I have plenty of pump, so I want to be able to get as much fuel in there as I can. More pressure, more fuel. I'm using 950cc secondary injectors with straight e85.

I don't remember what base pressure I'm targeting exactly. I can check next time I fire the car up.
 
  • Like
Reactions: Torgus

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
If anyone cares I am going boost referenced. I want my fuel pressure to be 70ish psi when the PI injects, after accounting for boost pressure other wise I would be injecting at 40psi which would limit the flow of the 750cc injectors. I should have plenty of low pressure fuel pump to get there with restrictions removed from the driver's side fuel top hat and running a return etc. The 750cc injectors at 70ish psi should be all the PI fueling I should need.

Assuming the online injector tool is correct 750 cc at 72psi should be worth of around 550whp on 100% e85 at 90% injector duty cycle. If the stock injectors are good, with a healthy HPFP, for roughly 450whp on 100% E85 this gives a total of approximately 1000whp potential with the 750cc injectors. Granted I think I would upgrade to larger PI injectors if I ever came close to that whp # just for headroom etc. And hopefully to reduce the stock injectors duty cycle down and less stress on the HPFP.

Part of me wonders if running the stock DI at stock levels and the rest via PI would make the injectors and HPFP live longer. I assume high duty cycle with the injectors reduces their life...but so does age.

I spent a bit on this fuel system but it should be 'done right' and I will never have to touch it again.

If anyone has any comments or suggestions please do not hesitate to post.
 
Last edited:

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
The regulator will go after the PI rail and then the return line will go back in my case to the driver's side tank.

The HPFP will see higher low pressure fuel at closer to 102 psi vs the stock pressue of 72psi. No idea of what that means for the HPFP. My guess is not much...
 
  • Like
Reactions: DirtKurt and houtan

Cruizinmax

Corporal
Jul 18, 2018
121
70
0
Ride
09 335i
One point to add is you only need to look at the differential pressure on your port fuel injectors. The injectors won't "see" 112 psi at 40 psi boost since there is boost pushing pack on the pintle of the injector.

I agree with your decision to go boost referenced. I feel like surely the spray pattern of the injector must be effected negatively if they are only injecting at an effective 32psi at 40 lb of boost.
 
  • Agree
  • Like
Reactions: houtan and Torgus

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
One point to add is you only need to look at the differential pressure on your port fuel injectors. The injectors won't "see" 112 psi at 40 psi boost since there is boost pushing pack on the pintle of the injector.

I agree with your decision to go boost referenced. I feel like surely the spray pattern of the injector must be effected negatively if they are only injecting at an effective 32psi at 40 lb of boost.

Thanks! After thinking about it a bit more it only makes sense for me to go boost referenced w/ return. It's small money given everything else invested and fixes a lot of 'issues' that could pop up or be limiting by injecting at such low a PSI when compensated for boost.

The injector will only output what is is rated at for cc flow when you do the calc fuel low pressure - boost. So in this 'theoretical' case 102psi - 30psi = 72psi. The injector will inject the cc/min as advertised as the fuel pressure has been compensated for the boost.

Doesn't the injector 'see' the full 102psi? EV14 fuel injectors we use for PI are supposedly good up to 8bar fuel pressure or 116 PSI so says the internet. The injector flows 72psi in terms of cc/min but doesn't the 'body or internals' of the injector still see the full fuel pressure of 102psi? It has to have 102 psi to be able to compensate for the 30 psi of boost to end up with 72psi cc/min of flow.

This is sort of the dilemma if you will. If I go to 40psi of boost I am now at 112psi still within the 116psi injector limit but within very close to it(4 psi). How much PSI headroom is built in to the injectors? I think most people run EV14s lower like LS engines at 58psi for fuel low pressure I believe? At least NA...

Anywho at some point it just makes sense to upgrade to 900CC injectors if you need more fuel to give you more flow headroom but when compensated for boost 750CC injectors should be fine for almost anyone with an N54 as long as you are still using the stock DI injectors/system. If using the stock FPR and you run out of injector at say 500 or 750CC it would make much more sense to to add in and run an adjustable 1:1 FPR w/ return vs upgrading to larger injectors. The larger injectors are just a bandaid for the piss poor low fuel pressure. Like you, I also believe super low pressure can't be atomizing the fuel well with the correct injector spray pattern etc.

In the chart above you can see the 'issues' you run in to when you increase the PSI, the gal/hr of flow drops off a cliff. Only way to fix this is adding in more pumps I believe. You will eventually run out of flow. But...on an N54 with two 525/535s etc. and a return that is still a ton of fuel at 110psi. Especially if you fix the driver's side hat restriction or bypass it all together.
 
Last edited:
  • Like
Reactions: wheela

wheela

Lieutenant
Jun 4, 2021
1,082
599
0
Twin Cities, MN
Ride
2015 e84 X1 35i Msport
Thanks! After thinking about it a bit more it only makes sense for me to go boost referenced w/ return. It's small money given everything else invested and fixes a lot of 'issues' that could pop up or be limiting by injecting at such low a PSI when compensated for boost.

The injector will only output what is is rated at for cc flow when you do the calc fuel low pressure - boost. So in this 'theoretical' case 102psi - 30psi = 72psi. The injector will inject the cc/min as advertised as the fuel pressure has been compensated for the boost.

Doesn't the injector 'see' the full 102psi? EV14 fuel injectors we use for PI are supposedly good up to 8bar fuel pressure or 116 PSI so says the internet. The injector flows 72psi in terms of cc/min but doesn't the 'body or internals' of the injector still see the full fuel pressure of 102psi? It has to have 102 psi to be able to compensate for the 30 psi of boost to end up with 72psi cc/min of flow.

This is sort of the dilemma if you will. If I go to 40psi of boost I am now at 112psi still within the 116psi injector limit but within very close to it(4 psi). How much PSI headroom is built in to the injectors? I think most people run EV14s lower like LS engines at 58psi for fuel low pressure I believe? At least NA...

Anywho at some point it just makes sense to upgrade to 900CC injectors if you need more fuel to give you more flow headroom but when compensated for boost 750CC injectors should be fine for almost anyone with an N54 as long as you are still using the stock DI injectors/system. If using the stock FPR and you run out of injector at say 500 or 750CC it would make much more sense to to add in and run an adjustable 1:1 FPR w/ return vs upgrading to larger injectors. The larger injectors are just a bandaid for the piss poor low fuel pressure. Like you, I also believe super low pressure can't be atomizing the fuel well with the correct injector spray pattern etc.

In the chart above you can see the 'issues' you run in to when you increase the PSI, the gal/hr of flow drops off a cliff. Only way to fix this is adding in more pumps I believe. You will eventually run out of flow. But...on an N54 with two 525/535s etc. and a return that is still a ton of fuel at 110psi. Especially if you fix the driver's side hat restriction or bypass it all together.
Yes, it will still be exposed to the full 102 psi, but the delta P across the injector is still 72psi because of the 30psi in the intake, so it will flow as it should at 72psi.

As far as the 116psi rating, I don't know the answer, but the mfg should know if they're talking about delta P pressure or just upstream fuel pressure. I suspect it's delta P.
 
  • Like
Reactions: houtan and Torgus

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
Yes, it will still be exposed to the full 102 psi, but the delta P across the injector is still 72psi because of the 30psi in the intake, so it will flow as it should at 72psi.

As far as the 116psi rating, I don't know the answer, but the mfg should know if they're talking about delta P pressure or just upstream fuel pressure. I suspect it's delta P.


Hmmmm

System pressure Max. 5 bar (8 bar for motorsport use) <--does not really clarify.

It would be interesting to know...either way I am fine for my application.
 
  • Like
Reactions: wheela

Torgus

Brigadier General
Nov 6, 2016
2,671
2,193
0
Boston
Ride
ACF 6466 E92 + METH
@Torgus Why Not use the PR Top hat with the built in regulator?

I am using it but having the regulator after the PI rail and then running a return back.

They both 'basically' do the same thing. There are just a few different ways to skin a cat they all end up being 'basically' the same albeit with some small caveats. The PR driver's side hat with the FPR built in means no return line, you use the stock return line that is built into the tank. You do need to run a vac line from IM back to driver's side hat so the FPR can do it's job as it needs a boost reference which you get from your intake manifold.

PR also has 4 BAR, 5 BAR, 6 BAR Static Micro Regulators which moves the fuel pressure regulation to the engine bay.

Finally PR has the Adjustable 1-to-1 Boost Reference Regulator which is what I am going to use and run the return back into the driver's side tank which then go into the stock venturi/return. Most people on this platform run the return into the passenger top hot. The PR system is just more modular and all plug and play.
 
  • Like
Reactions: Gaijin909

Gaijin909

New Member
May 31, 2023
4
8
0
bimmersport.co.nz
Ride
240zg, TA22, Golf R, 1m clone,
I'll be doing similar as you've mentioned Torgus, 535 and 450 lpfps, remove filter and intake reg bypassing them via a mod'd oem reg hat. Dual lpfp feeds out of the tank, reducing intake hose pressure losses, 10 micron filtered, then joined to a 10an single line up to the PI rail. Boost ref regulated after PI rail with the fuel returned to the lpfp tank tophat.
 
  • Like
Reactions: Torgus