Fuel Injector upgrade question : new fuel pump needed? [Archive]

View Full Version : Fuel Injector upgrade question : new fuel pump needed?

jakester888

10-17-2011, 11:17 PM

riptide motorsport

10-17-2011, 11:48 PM

I'm not much of An efi guy but my understanding is that you won't gain any HP by increasing injector size, sort of like going to a bigger carb that isn't needed and too big for the aplication. The extra fuel in this case with the larger injectors willl just be wasted. You need extras to support the injectors, like cams and headers and computerupgrades.. uOthers will know better HTH. .. Steven

Mike N

10-18-2011, 05:39 AM

5.0L Engine from a '93 donor. Stock fuel injectors are 19 lbs/hr @ 39 psi. I am considering an upgrade to Bosch F1TE injectors at 24 lbs/hr @ 43.5 psi. The stock fuel pump is 110lph.

Question : Do I need to upgrade the stock fuel pump to achieve the higher psi required of the Bosch injectors? Or can I achieve the same result with an adjustable fuel regulator with stock fuel pump? Safer to upgrade all 3?

Goal - increase HP by increasing injector flow rate.

534353425341

My guess : upgrade all 3, pump, regulator & injectors.

As stated above you will not increase HP purely by changing injectors, it's air fuel ratio optimization that will increase power and that is controlled by the computer not the injector size. If you are thinking of injectors like carb jets that is only partly correct. A larger injector can flow more than a smaller one but it won't unless the computer commands it to do so.

If you change the injectors don't forget that you will have to change the MAF meter to one that has the same calibration.

The Ford EECIV uses the injector flow rate at 39 psi as its baseline, your 24 lb/hr @ 43.5 psi Bosch injector only flows 21.5 lb/hr at 39 psi so hardly worth the price and trouble. 19 lb/hr injectors will support around 260 HP, so if your engine is not modified then you won't benefit from the larger injectors anyway.

Good idea to upgrade the fuel pump first before you do anything else. Walbro pumps are flow rated at 40 psi and 13.5v when new. If your alternator is not producing 13.5v or you are running higher than 40 psi fuel pressure such as on a supercharged engine then the pump is not producing the flow that you think it is.

Jeff Kleiner

10-18-2011, 05:40 AM

Jake,
As I recall you have a Cobra intake with stock heads and cam, right? If that is the case your current 19# injectors with the OEM pump and regulator will be fine. If you change injector size you will also have to go with a matching MAF or different ECU. So why not just use the bigger injectors anyway?---Generally, using too large of an injector will sacrifice driveability and low speed response.

To actually answer your question: the stock pump can produce enough pressure for those injectors. The factory pressure regulator is not adjustable and is set to maintain ~30-32 psi with full manifold vacuum applied and raise to 38-39 psi when vacuum drops off (such as at WOT).

With all that said, if you think you might make future upgrades you will eventually exceed the stock 110 lph pump's flow capabilities. It's a whole lot easier to swap it now rather than when the car is finished. A 190 lph pump should handle just about anything you might do unless you get really wild or go with forced induction in which case you'd want a 255. Switching to a higher flow rate pump does not require any change to the regulator or injectors.

Cheers,
Jeff

EDIT: Looks like Mike and I were typing about the same thing at the same time :)

AC Bill

10-18-2011, 09:47 AM

It seems that simply changing to the larger injectors, wouldn't be a great advantage, without other changes as well. Cam, etc. Wouldn't you then also need to increase the size of the throttle body as well, if you were to change the injectors.? More fuel, more air.

Performance isn't cheap..:(

Mike N

10-18-2011, 11:34 AM

You're right Bill. You really need a plan or a good strategy so that you don't wind up with a bunch of mismatched pieces. A good place to start is to decide what power level you intend to wind up with and pick parts accordingly.

skullandbones

10-18-2011, 03:46 PM

Ford Racing Performance Parts catalog has one of the best three page references to help a new EFI guy figure out the correct component combination. It's under the EFI section: EFI System Do's and Don'ts. It goes into the basics but also has formulae and tables to help you cross reference each peice to fit your system. I started with a 75 mm throttle body because that was the largest that my intake supports. The article allows you to pick the other components that match by usually giving you a range of hp (but also direct calculations). My setup called for 24 lb injectors with a matching MAF. The fuel pump even has a reference. It looks like mine is on the bubble so I will have to change out the 110 liter one (good to about 315 hp) for a 155 liter one (good to 440 hp). Of course, we are talking about NA engines. If you start here, it will give you a good reference point. Good luck. WEK.

jakester888

10-19-2011, 12:24 AM

Great pointers as I've come to expect from you all.

So upgrading to 24lb is in my mind, since I also think about increasing airflow by adding a larger MAF. Didn't realize this woud also necessitate a new computer. Could I get by with one of those computer module plugins (not sure what they do but since the factory didn't offer them and someone else does, I suspect ingenuity & improvement).

What computer should I upgrade to over stock in combinationg with a 75mm MAF and 24lb injectors? Trying to at least get to 300hp with these changes.

Jeff Kleiner

10-19-2011, 05:18 AM

Well, if you insist...you can keep your computer and change to a mass airflow meter tuned to match the injectors:

Pro-M plastic bullet (http://www.promracing.com/mass-air-meters-c-2/75mm-plastic-bullet-un-flanged-p-1)

Also available in chrome if you are into the bling.

Chris (Pro-M) can also set you up with matching injectors:

24 lb/hr fuel injector set (http://www.promracing.com/-c-5/24-lb-hr-fuel-injector-set-of-8-p-21)

Additionally you will need a larger throttle body (I'd recommend 70MM)

300 HP? Sorry, I don't see it happening. With stock heads and cam that combo will probably top out at 260ish. With a set of Ford Racing X heads and an E cam or TFS Twisted Wedge heads along with Stage 1 cam you'll see 325-350.

Good luck,
Jeff

Mike N

10-19-2011, 07:10 AM

Jakester the Pro M MAF meter is in my opinion the best deal, my choice would be the 80mm http://www.promracing.com/mass-air-meters-c-2/pro80-p-5 . Plus if you ever want to upgrade to even larger injectors they will re calibrate your meter for $100.

So if you want to upgrade your fuel system I would recommend the Pro M 80mm meter, get Ford Racing 24 lb/hr injectors and a 190 lph or 255 lph fuel pump and you are in good shape, no need for new computer, adjustable fuel pressure regulator or anything else. Throttle body, EGR spacer, etc are independent of the fuel system.