Advice on fuel pumps, regulators, injectors
12-10-19, 01:09 PM
#1
Advice on fuel pumps, regulators, injectors
This post is really two related questions:
1. The capabilities of the stock FPR paired with various fuel pumps & wiring.
2. General advice regarding fueling, boost & power levels.
#1:
#2:
What I'm thinking is:
RP rail + 2200cc secondaries + stock primaries
Either re-wired OEM or re-wired supra pump
1. The capabilities of the stock FPR paired with various fuel pumps & wiring.
2. General advice regarding fueling, boost & power levels.
#1:
It sounds like most aftermarket fuel pumps will overwhelm the stock FPR. I've heard repeatedly that the Walbro 255 will, and in turn I would expect the RP pump to also. Some people say this only happens when combined with one of the various wiring mods.
I assume overwhelming the stock FPR is ill-advised? I would think an overwhelmed FPR would open door to unpredictable pressure variation from things like altitude and ambient temp.
Can anybody speak to how the stock FPR handles the supra pump with/without the wiring mod? Can it hang?
I assume overwhelming the stock FPR is ill-advised? I would think an overwhelmed FPR would open door to unpredictable pressure variation from things like altitude and ambient temp.
Can anybody speak to how the stock FPR handles the supra pump with/without the wiring mod? Can it hang?
#2:
I'm preparing my FD for a tune, planning for around 12-13psi on stock turbos. The car is a 93 with the usual bolt-ons:
DP + high flow cat + RB dual tip
Intake + Y-pipe + SMIC
Twin power
PFC
I've seen quite a few different recommendations on fueling. The common thread seems to indicate that a stock pump is probably getting close to the limit, but generally OK for ~350hp (so probably fine for 13psi). However, it sounds like stock injectors get pretty slammed at that level.
DP + high flow cat + RB dual tip
Intake + Y-pipe + SMIC
Twin power
PFC
I've seen quite a few different recommendations on fueling. The common thread seems to indicate that a stock pump is probably getting close to the limit, but generally OK for ~350hp (so probably fine for 13psi). However, it sounds like stock injectors get pretty slammed at that level.
What I'm thinking is:
RP rail + 2200cc secondaries + stock primaries
Either re-wired OEM or re-wired supra pump
Last edited by mkd; 12-10-19 at 01:18 PM. Reason: Formatting
12-10-19, 03:56 PM
#2
RX-7 Bad Ass
iTrader: (55)
I'm running a Walbro 255 rewired, 550cc primary/1300cc RC secondaries, making about 330-350 to the ground. Stock FPR.
Most times the stock FPR is replaced just due to plumbing reasons with aftermarket rails. That's one thing that's nice with the RP fuel rail is you can keep the stock FPR, much less packaging and headache than an aftermarket FPR.
If you're going for 12-13 PSI you will be running out of fuel for sure on a stock pump. If you haven't done so read Banzai Racing's thread where they modify a stock FD and step through each mod, why it's needed, and how much power they made with each mod.
https://www.rx7club.com/3rd-generati...added-1104322/
I would go with the Walbro fuel pump and a re-wire. There's no good reason IMHO to run the Denso/Supra pump. I've had my Walbro running for 10+ years, rock solid reliable and putting out plenty of fuel.
Dale
Most times the stock FPR is replaced just due to plumbing reasons with aftermarket rails. That's one thing that's nice with the RP fuel rail is you can keep the stock FPR, much less packaging and headache than an aftermarket FPR.
If you're going for 12-13 PSI you will be running out of fuel for sure on a stock pump. If you haven't done so read Banzai Racing's thread where they modify a stock FD and step through each mod, why it's needed, and how much power they made with each mod.
https://www.rx7club.com/3rd-generati...added-1104322/
I would go with the Walbro fuel pump and a re-wire. There's no good reason IMHO to run the Denso/Supra pump. I've had my Walbro running for 10+ years, rock solid reliable and putting out plenty of fuel.
Dale
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tomatoto (12-16-19)
12-10-19, 11:02 PM
#3
So what you're saying is, even if the FPR is allowing greater than 38 psi to the rail, it can still be tuned reliably? If you and others have been this reliably for long periods of time, that is re-assuring -- but man it still worries me. Where I live it regularly gets into the 90s in summer, and just 200 miles away where my family and many friends live it regularly gets into the 20s in winter. I just worry that without fuel pressure pinned to 38psi I will see variation that could be dangerous in certain conditions.
Anyway I HAVE an RP pump, maybe I will just throw that in with the wiring mod and call it a day.
As for stock primaries and 2200 secondaries -- should be no problems there, right?
Anyway I HAVE an RP pump, maybe I will just throw that in with the wiring mod and call it a day.
As for stock primaries and 2200 secondaries -- should be no problems there, right?
Last edited by mkd; 12-10-19 at 11:35 PM. Reason: Spelling
12-11-19, 09:31 AM
#5
RX-7 Bad Ass
iTrader: (55)
38 psi is base pressure with 0 manifold vacuum. Under vacuum pressure will go down and under boost it will go up. This is to keep a consistent pressure differential. Think about it - if, for example, you had 38 psi of boost in the manifold and 38 psi of fuel pressure, no fuel would squirt out since the pressures are the same.
The FPR maintains that pressure. Big problem is the injectors can draw more fuel than the fuel pump can keep up with, resulting in a drop in pressure. Not the FPR's fault, it can only maintain pressure.
Read through the thread I linked, that will give you an idea horsepower-wise and mod-wise where the limits are.
With the RP fuel rail and a good drop-in pump IMHO you're set for whatever you want to do with the twins. Just need to have it tuned properly.
Dale
The FPR maintains that pressure. Big problem is the injectors can draw more fuel than the fuel pump can keep up with, resulting in a drop in pressure. Not the FPR's fault, it can only maintain pressure.
Read through the thread I linked, that will give you an idea horsepower-wise and mod-wise where the limits are.
With the RP fuel rail and a good drop-in pump IMHO you're set for whatever you want to do with the twins. Just need to have it tuned properly.
Dale
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tomatoto (12-16-19)
12-11-19, 02:02 PM
#6
I have read through the Banzai thread several times -- it's a great thread!
Just got off the phone with Chris @ RP (what a guy!) and long story short is, he says there is nothing to worry about with using the stock FPR with high-output pumps. He thinks the most important parts to the pump equation are the following (in order of importance):
1. Upgrade the last-mile ground. Connect a wire to chassis ground in the trunk area and splice it into the FP harness black wire as close to the plate as possible
2. Upgrade the actual internal PF wires to something like 16 gauge
3. Fix the low speed mode resister under the brake booster (they sell a plug-and-play kit)
4. Fix your ignition switch wiring
I certainly could be incorrect, but it sounds to me like the common types of FP wiring mods you see here equate to #1 and #4
Just got off the phone with Chris @ RP (what a guy!) and long story short is, he says there is nothing to worry about with using the stock FPR with high-output pumps. He thinks the most important parts to the pump equation are the following (in order of importance):
1. Upgrade the last-mile ground. Connect a wire to chassis ground in the trunk area and splice it into the FP harness black wire as close to the plate as possible
2. Upgrade the actual internal PF wires to something like 16 gauge
3. Fix the low speed mode resister under the brake booster (they sell a plug-and-play kit)
4. Fix your ignition switch wiring
I certainly could be incorrect, but it sounds to me like the common types of FP wiring mods you see here equate to #1 and #4
12-11-19, 02:35 PM
#7
The stock fuel pressure regulator can return approximately 4000cc/min at 3bar.
https://adaptronic.com.au/blogs/arti...f-a-difference
The stock fuel pump on stock wiring in my car can't maintain a 3 bar pressure differential over about 12psi. With the wiring modified to give full voltage at the pump it can maintain pressure to 15psi (haven't tested past that). At 15psi, my stock injectors are at 75% duty cycle on the primaries, 100% on the secondaries, ~11.5:1 AFR. Any fluctations in fuel pressure result in a fluctuation in AFR because the injectors can't deliver any more fuel.
https://adaptronic.com.au/blogs/arti...f-a-difference
The stock fuel pump on stock wiring in my car can't maintain a 3 bar pressure differential over about 12psi. With the wiring modified to give full voltage at the pump it can maintain pressure to 15psi (haven't tested past that). At 15psi, my stock injectors are at 75% duty cycle on the primaries, 100% on the secondaries, ~11.5:1 AFR. Any fluctations in fuel pressure result in a fluctuation in AFR because the injectors can't deliver any more fuel.
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i recall Higgi showed me a log with a stock 20B fuel system and the regulator clearly topped out (stopped increasing pressure) over 10psi, the FD regulator is better, but its still setup for a stock car...
item 2, is that if you keep the fuel pump speed wiring, the FD regulator seems to do just fine with a bigger pump, but if you give it 12V it won't, and car will run noticeably worse at idle.
item 3 is kind of a moot point, but we generally tune things richer in the USA, so we need more fuel pump and injector than the Japanese guys do. they also run colder plugs, and take steps to eliminate inductive crossfire and RFI problems from the ignition. would refer this; only deviation from stock fuel is the pump https://www.rx7club.com/3rd-generati...added-1104322/
item 2, is that if you keep the fuel pump speed wiring, the FD regulator seems to do just fine with a bigger pump, but if you give it 12V it won't, and car will run noticeably worse at idle.
item 3 is kind of a moot point, but we generally tune things richer in the USA, so we need more fuel pump and injector than the Japanese guys do. they also run colder plugs, and take steps to eliminate inductive crossfire and RFI problems from the ignition. would refer this; only deviation from stock fuel is the pump https://www.rx7club.com/3rd-generati...added-1104322/
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