fuel pressure regulator?

U2SLO450 · Jul 20, 2007

Well im getting ready to do my hci swap and i was wondering if i needed to get one? I have gt40p heads, e-cam, cobra intake, and a 70mm throttle body. I plan on using my factory fuel injectors but im not sure if i need the fpr. Any help would be greatly appreciated.

bill302 · Jul 20, 2007

what you need is an adjustable fuel pressure regulator..

1992mustangLX · Jul 20, 2007

Holley makes a good one for around $60 and its not a bad idea, makes for better tuning. You want the adjustable fuel pressure regulator.

Turkey Sammich · Jul 21, 2007

I agree with the two statements made above. Get a good adjustable fuel pressure regulator.

millhouse · Jul 21, 2007

IMHO, AFPR's are quite often overused and not necessary. Really, because of the stock ECM's adaptive strategy...any changes to the fuel pressure will eventually be lost by due to the computer compensating. The stock fuel pressure regulator will work just fine. I'd save the cash for future upgrades.

vristang · Jul 21, 2007

If an AFPR is used to push the AFR away from stoich, then don't bother...

If you use the AFPR to push the AFR toward stoich, then it can be beneficial....

just my opinion though,
jason

U2SLO450 · Jul 21, 2007

bill302 said:
what you need is an adjustable fuel pressure regulator..

what is the point of having an adjustable fpr? im dont see why i shouldnt be able to use the factory one.

bill302 · Jul 21, 2007

the point of having the adjustable fuel pressure regulator was best described by 1992mustangLX

1992mustangLX said:
Holley makes a good one for around $60 and its not a bad idea, makes for better tuning. You want the adjustable fuel pressure regulator.

believe me when it comes to owning a mustang you get a fever for upgrades...but if you remain stock the factory regulator will do fine....i needed the adj regulator for my nitrous upgrade..also at the dyno an adjustable fuel pressure regulator on my stang with a few bolt ons running na gave me 10 more horses just by dropping the fuel pressure from 40 to 37 psi...get it now so you dont need it later.

millhouse · Jul 21, 2007

bill302 said:
the point of having the adjustable fuel pressure regulator was best described by 1992mustangLX believe me when it comes to owning a mustang you get a fever for upgrades...but if you remain stock the factory regulator will do fine....i needed the adj regulator for my nitrous upgrade..also at the dyno an adjustable fuel pressure regulator on my stang with a few bolt ons running na gave me 10 more horses just by dropping the fuel pressure from 40 to 37 psi...get it now so you dont need it later.

Most pro tuners prefer a non-adjustable oem fuel pressure regulator as they work perfectly fine and hold their integrity over time. Chances are...if you have an adjustable unit they will set it to the stock pressure to enable them to more easily tune the vehicle. As long as you have enough fuel pump and injectors, there is no use for a AFPR.

FYI, if you adjusted your FPR to go leaner from stoich at WOT...the ecu will eventually compensate the tune for closed loop conditions. This will make the fuel pressure change worthless...as the new closed loop settings will directly effect the open loop WOT tune.

bill302 · Jul 21, 2007

millhouse said:
Most pro tuners prefer a non-adjustable oem fuel pressure regulator as they work perfectly fine and hold their integrity over time. Chances are...if you have an adjustable unit they will set it to the stock pressure to enable them to more easily tune the vehicle. As long as you have enough fuel pump and injectors, there is no use for a AFPR.

FYI, if you adjusted your FPR to go leaner from stoich at WOT...the ecu will eventually compensate the tune for open loop conditions. This will make the fuel pressure change worthless...as the new open loop settings will directly effect the closed loop WOT tune.

my tuner recommended an adjustable fuel pressure regulator so he could adjust air fuel ratio and he did start the tune at 40 psi then adjusted accordingly for optimal performance...but i would like to learn more about what your saying about the ecu compensating making the fuel pressure change worthless if U2SLO450 dont mind discussing this in his thread. does the ecu compensate thru the maf????

vristang · Jul 21, 2007

The ecu compensates via the 'Adaptive Fuel Strategy'
Basically the O2's will read a non-stoich condition (either too rich or too lean).
When the O2's indicate that the mixture is not stoich for an extended time, the ecu will begin applying a multiplier to the calculated injector pulsewidths.
If the O2's are indicating rich, then a multiplier of less than one will be applied, thereby reducing the injector pulsewidth.
If the O2's are indicating lean, then a multiplier of greater than one will be applied, thereby increasing the injector pulsewidth.

The factory A9* ecu's have a range of +/- 12.5%.
In other words the ecu can increase the injector pulsewidth by 12.5%, or decrease the pulsewidth by 12.5%.
A total range of 25%.

When you change the fuel pressure in order to create a lean condition at WOT, you also change the AFR at part throttle Closed Loop operation.
Eventually the Adaptive Strategy will learn that the mixture is lean (as indicated by the O2's), and apply a multiplier of greater than 1 to the calculated injector pulsewidths.
This multiplier will push the AFR for both WOT and Part Throttle, back toward stoichiometric.

Hope that made sense....
jason

vristang · Jul 21, 2007

I can't stand double posters...

93gtmustang · Jul 22, 2007

You know, the more threads I read on here, the more I realize that a lot of these aftermarket upgrades don't really help and sometimes are even less performance than the oem units.

For example, stock air box vs. aftermarket conical air intake. The stock air box is just fine for a mildly modified n/a set-up. I switched from an in engine bay conical to the stock air box with a K&N and what a difference in idle and overall driveability.

There are so many, so called claims of added horse power for sale in parts magazines. Here are some below and my opinion of them used with a mildy modified n/a set-up.
1- Intake Manifolds, Edelbrock claims up to 37 hp on Performer 5.0 / Good performance upgrade. I have one. Came with the car. I don't know about 37 hp.

2-Underdrive Pulleys, BBK claims 10-15 hp without hurting your charging or cooling performance / No, I wish I never put mine on, along with the electric fan.
Charging issues, then spend some more money on a heavy duty altenator.

3-Throttle Body, BBK claims 8-16 hp / I guess, 65mm or 70mm, anything larger does nothing.

4-Phelonic Spacer / ? I have one but I don't know if it does anything for performance gains!

5-Cold air intakes, BBK claims 8-12 hp / ? I have a C&L cold air pipe ( my car came with it) with the stock air box. That's a big gain for a CAI

6- Larger MAF, Granatelli claims 10-23hp. / ? I have a 76mm C&L (came with the car)

7-Smog pump delete / ? (Came on my car) I've read it does nothing.

8-Shorty headers, BBK claims 8-15 hp / ? ( came on my car) I'd go with full length headers.

9-Adjustable Fuel Pressure Regulator, BBK claims up 12hp. ? I have a Holley. After reading this post I may put my stock one back on!!! Not really

I can't think of anymore at the moment.

Oh I know, I almost forgot this one. A while ago, I guy at the track told me he went from 15 sec. et in the 1/4 mile to 13.7 with his custom made dual fog light ram air kit made with aluminum dryer ducting.
I have to get one of those!!!!!

bill302 · Jul 22, 2007

vristang or millhouse or anyone with some knowledge i found this info on the net. about an adjustable fuel pressure regulator is this info. accurate. can you add or take away from this article.

Q: Do I need an adjustable fuel pressure regulator?

A: If everything is calibrated right, the stock regulator works great and there is not a lot to be gained by changing it. Small power gains can be made by adjusting pressure while dyno tuning, but that is about it. For the most part I recommend keeping the stock regulator until you actually need an adjustable one. However there are 3 circumstances where an adjustable regulator can be very useful

1) The MAF calibration is not perfect.
Pro-M and C&L meters flow more air, and are necessary for high output cars, but it is unfortunately all too common for their calibration to be off a little. Adjusting fuel pressure on a dyno or with a wideband 02 is an effective way to compensate. The ECU can only correct so far by itself. If you've ever monitored the 02 voltages over long periods of time you will see that the fuel pressure will affect the 02 readings even after many driving cycles where the ECU theoretically should have been able to re-trim the fuel settings to correct the air/fuel ratio. The ECU correction is just not that precise and is also limited in range. An adjustable fuel pressure regulator will improve performance in these circumstances if tuned properly.

2) High output fuel pumps cause “pressure creep” at idle.
If you are running a 255 lph or larger pump and a stock regulator, you may have noticed that fuel pressure at idle is higher than when driving at part throttle. This is because the pump pumps more fuel than can free-flow through the regulator. Under load the engine uses some of the excess fuel, so the regulator functions normally. But at idle the fuel is not needed and has return to the tank through the regulator. Pressure climbs above normal because the fuel flow back to the tank is restricted by the regulator fittings. This causes a rich condition at idle, wasting fuel, increasing emissions, and shortening the life of the spark plugs. The fittings on the newer versions of the Kirban regulator have a larger internal diameter. This eliminates the restriction, allowing the un-needed fuel to free-flow back to the tank for better control of fuel pressure during light load conditions.

3) Speed density cars are easier to tune with an adjustable pressure regulator.
The ’86-89 Mustang and 93-95 Lightning use a speed-density (engine speed + air density) program to calculate the fuel needs of the engine. Unlike Mass-Air systems, the ECU has no meter to measure the mass of incoming air. When modifications are done to increase the volume of incoming air you can quickly exceed the ability of the ECU to compensate through 02 feedback alone. This is especially true of wide open throttle performance because the ECU ignores the 02 sensors at wide open throttle. An adjustable fuel pressure regulator is very useful for tuning these cars. In the late 1980s before Mass-Air was installed in the Mustang, and before computer chips were available, several racers were running low 11 second quarter mile times using only fuel pressure and a timing light to tune the car.

white99gt · Jul 22, 2007

1) a adfr is NOT needed.
2) as far as "creep" with a 255 with a good tune ,its NOT there.I know i ran a 255lph HIGH pressure and had no issues stock or moddied.
3)MAF- if the calibration is off which on the pro-m and c&l they always are.Get a REAL tune with a ford maf(80mm or 90mm lmaf).With the corect tuner/software the car will drive better than stock..

I run a stock fp regulator ,80mmlmaf and a good tune car drives WAY better than stock.

AS far as conical air filters vs a stock air box.The conical MAY help with some issues but the problem is the under hood heat.Which in turn will hurt power output.AS far as effecting power output,the stock air box can support 300+rwhp with no issues(i know i still have the stock air box on mine).

vristang · Jul 22, 2007

I'm not really sure how to respond to this, so I have just made my comments in red.
This is only my opinion, I would expect others to chime in...

bill302 said:
vristang or millhouse or anyone with some knowledge i found this info on the net. about an adjustable fuel pressure regulator is this info. accurate. can you add or take away from this article.

Q: Do I need an adjustable fuel pressure regulator?

A: If everything is calibrated right, the stock regulator works great and there is not a lot to be gained by changing it. Small power gains can be made by adjusting pressure while dyno tuning, but that is about it. For the most part I recommend keeping the stock regulator until you actually need an adjustable one. However there are 3 circumstances where an adjustable regulator can be very useful
(Really the only time an AFPR is effective, is if the AFR is straying from stoich. Using an AFPR any other time, will simply invoke the Adaptive Fuel Strategy...)

1) The MAF calibration is not perfect.
Pro-M and C&L meters flow more air, and are necessary for high output cars, but it is unfortunately all too common for their calibration to be off a little (This error can account for about 50% of the Adaptive Strategy itself, even with 'good' meters). Adjusting fuel pressure on a dyno or with a wideband 02 is an effective way to compensate (if pushing the AFR back toward stoich). The ECU can only correct so far by itself (+/- 12.5%). If you've ever monitored the 02 voltages over long periods of time you will see that the fuel pressure will affect the 02 readings even after many driving cycles where the ECU theoretically should have been able to re-trim the fuel settings to correct the air/fuel ratio. The ECU correction is just not that precise and is also limited in range (The ecu can take quite a while to fully 'adapt'. Changes are only made to the Injector pulsewidths after the ecu sees a variation from stoich for a determined time frame). An adjustable fuel pressure regulator will improve performance in these circumstances if tuned properly.

2) High output fuel pumps cause “pressure creep” at idle.
If you are running a 255 lph or larger pump and a stock regulator, you may have noticed that fuel pressure at idle is higher than when driving at part throttle. This is because the pump pumps more fuel than can free-flow through the regulator. Under load the engine uses some of the excess fuel, so the regulator functions normally. But at idle the fuel is not needed and has return to the tank through the regulator. Pressure climbs above normal because the fuel flow back to the tank is restricted by the regulator fittings. This causes a rich condition at idle, wasting fuel, increasing emissions, and shortening the life of the spark plugs. The fittings on the newer versions of the Kirban regulator have a larger internal diameter. This eliminates the restriction, allowing the un-needed fuel to free-flow back to the tank for better control of fuel pressure during light load conditions.
(This is complete hogwash... For the 6 mo. before parking my 408w for the rebuild, I ran on a 255lph pump and factory regulator. As far as I know it was the original regulator. If you compare the fuel pressure during idle to part throttle cruise, you will see a fuel pressure difference. This is due to a variation in the manifold vac signal though)

3) Speed density cars are easier to tune with an adjustable pressure regulator.
The ’86-89 Mustang and 93-95 Lightning use a speed-density (engine speed + air density) program to calculate the fuel needs of the engine. Unlike Mass-Air systems, the ECU has no meter to measure the mass of incoming air. When modifications are done to increase the volume of incoming air you can quickly exceed the ability of the ECU to compensate through 02 feedback alone. This is especially true of wide open throttle performance because the ECU ignores the 02 sensors at wide open throttle. An adjustable fuel pressure regulator is very useful for tuning these cars. In the late 1980s before Mass-Air was installed in the Mustang, and before computer chips were available, several racers were running low 11 second quarter mile times using only fuel pressure and a timing light to tune the car. (This method of tuning is still not 'ideal' as it leaves room for error in the 'Load' calculation. Load is used to calculate Injector Pulsewidths and Ignition Timing. So, if the Load number is off, then so is the Ignition Timing and Injector Pulsewidth. I cannot say how much of an error this would create, or if it could be compensated for with base timing and fuel pressure. However, it is not 'ideal'...
The same error in the Load calculation is created when using a large fuel injector with a calibrated MAF meter. The larger the injector, the larger the error in the Load calculation.
Again, I'm not yet sure how much of a problem this may cause, as I have not been able to test anything lately...)

Well, those are my aimless ramblings...
BTW-
Where did you find this writeup?

jason

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