Is It Time To Upgrade To 24lb Injectors?

BKM48198

15 Year Member
Jun 7, 2008
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Ypsilanti, Michigan
My motor came from a 96 Explorer, GT40 heads with a set of TFS valve springs installed, Explorer intake with 65mm throttle body, 70mm mass air from a 95 Mustang, BBK headers, I have a Mustang Cam in it now, when I put the motor together I went thru with all new bearings, oil pump, crank polished, etc but kept the stock pistons. I am still using the stock fuel pump and pressure regulator. Before I get the car out in the Spring I will be installing a higher stall torque convertor in the trans so it will be ready for a larger cam than the stock 5.0 HO cam from my old engine. I'm not sure if I should get larger injectors and the matching mass air meter or if an adjustable fuel pressure regulator would be all that is needed, or are the stock parts are good enough for now. I'm just worried about running lean and causing a problem.
 
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You should definitely get a larger pump, an adjustable regulator is not necessary. And changing the injectors is kinda your call.

Me personally? I would.

I'd also have it tuned.
 
You are on the edge of needing larger injectors, here's why.

Fuel injector sizing & injector photos

Revised 26-Dec-2014 to add statement about figures are for flywheel HP and not rear wheel HP

Injector HP ratings: this flywheel HP, not rear wheel HP.
Divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines at the flywheel.
Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See http://users.erols.com/srweiss/calcpchg.htm to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.

With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.

Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure



Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS


Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.




Diagram courtesy of Tmoss & Stang&2birds
Ford_Injector_Guide.jpg


Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS


Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif[/b]
 
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I have read all this before but don't fully grasp fuel injection and all the electronics involved. From what I have read I am assuming the engine is now at or above the 258hp for the 19lb injectors and I should get 24lb injectors along with a bigger fuel pump and mass air calibrated for the 24lb injectors. If I do that will it need a tune or can they just be installed and the computer still work properly and adjust the fuel mixture properly? I don't want to just buy parts and not know what will happen or what to expect. It is a daily driver that won't see any nitrous, turbo, or blower, I just want the car to run properly and last while making the most power it can with the engine as it is now.

You are on the edge of needing larger injectors, here's why.
 
In many cases, the aftermarket MAF like Pro-M calibrated to match the 24 lb. injectors will be sufficient to get the engine running good enough for most guys...

The engine should run reasonably well, but there will be some extra amount of performance and drivability that a custom tune would make available.


Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.

It's about $25-$50 from Borders.com see http://www.amazon.com/ . Select books and then select search. Use the ISBN number (without dashes or spaces) to do a search. Try searching using M-1832-Z1 instead of the ISBN number if you don’t get any positive results. You may only be able to find a used one, since the book is as old as the cars it covers. Or you order it from your Ford dealer as SVO part no. M-1832-Z1.


Use the ISBN number and your local library can get you a loaner copy for free. Only thing is you are limited to keeping the book for two weeks. It is very good, and I found it to be very helpful.
 
Thanks for the info on the book, I'll see if my local library has a copy. Next question I have is about the fuel pump, it seems like the stock pump is not big enough and I'll need 110-120LPH pump, does that sound right? I think stock is only about 88 and might not keep the engine rich enough to be safe.

Local library didn't have the book but another library about 100 miles away does and will send it down here for me. :)




In many cases, the aftermarket MAF like Pro-M calibrated to match the 24 lb. injectors will be sufficient to get the engine running good enough for most guys...
 
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I was just figuring in my head that I would need at least one around 110-120lph, but I will go for the 155 in case I do install a better set of heads and cam. Right now I'm just looking at what I will need before Spring gets here, so I can watch for things to go on sale and hopefully save a few dollars. Do you know of any vehicles that came with a 24lb mass air meter that would work with a Foxbody Mustang? If I could save money on a Junkyard meter I'd try it before spending $250 for a new one.
 
There is a difference in the real world and calculations on paper.
I've spent years seeing it all first hand.
Some have stretched 19's to about 300rwhp, should you? Probably not, but I wouldn't goto 24's until about 265rwhp maybe a little more.
There's guys that have run their TFS top end kits with 19's.

The only car that ran 24's was the 93 cobra, but it required a cobra computer.

Remember, injectors are a supporting mod, not a power adding modification.
If you are worried about being lean or rich pay $75 for a few dyno runs.

If the mustang cam you speak of is a stock cam, i'd be surprised if you cracked 250rwhp. And as far as i'm concerned, that's 19lb territory.
 
2000xp8 knows his stuff! you really don't need 24's at your current power level. Heck my HCI combo made 300rwhp and 315rwtq N/A using 19's. A/F ratio was perfect up to 6200rpm.
But if you just want bigger stuff, I did a quick search for a meter on the Corral for ya: http://forums.corral.net/forums/win...-cobra-valve-covers-1inch-tfs-spacer-c-l.html

It's a 73mm C&L at a pretty good price. Get's you in the game. You can find some good used parts on the Corral.
 
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Onefine, i'd try and avoid c&l meters in general, even more so when you are considering an injector that is a little over sized.
The sampling tube method is about an inaccurate as it gets.

I'd probably look for a 75mm pro m bullet calibrated for 19's if i was him.
 
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Onefine, i'd try and avoid c&l meters in general, even more so when you are considering an injector that is a little over sized.
The sampling tube method is about an inaccurate as it gets.

I'd probably look for a 75mm pro m bullet calibrated for 19's if i was him.
True they're not the best meters, but like I mentioned that used one will get him in the game at a cheap price. I ran a 73mm C&L cal'd 30's for years on my Saleen until I had to go bigger. Then I went with a ProM 80 for the 42's.
It always ran fine with the C&L though.
 
I already have a 70mm TB off a 95 Mustang on the car so 3mm isn't much different. I built the engine last year but stayed with the Mustang cam because I couldn't afford a higher stall torque convertor at the time, that is the 1st thing that will change this year. All the upgrade cams said to get the higher stall or lose a lot of low end and I didn't want that. I will probably get a different cam also this year but worry about running it too lean and causing damage. I've got a couple stretches of open highway on my way too and from work that I can't seem to keep my foot off the gas on, with 3.73's I'm over 4000rpm a lot and have had it up close to 6500rpms. At high rpms the car has plenty of power, will spin the tires when I drop a gear and floor it at 50mph and then chirp them again shifting up to 3rd gear. I have owned the car since it was new and it never did that before with the stock 5.0, not even with a 10 inch torque convertor.

2000xp8 knows his stuff! you really don't need 24's at your current power level.
 
Onefine, i'd try and avoid c&l meters in general, even more so when you are considering an injector that is a little over sized.
The sampling tube method is about an inaccurate as it gets.

I'd probably look for a 75mm pro m bullet calibrated for 19's if i was him.
A guy has a Pro Flow Technologies 75mm bullet for sale and I've been talking to him about it the last few days, same as a Pro-M but older model before they changed name or were bought out, I can get it for $50 calibrated for 24's. I'm really wanting to get the fuel system upgraded before I change heads, cam, or run too lean.......the car is 25 years old and still has the stock fuel pump in it which is only 88lph and if I can get the air and fuel done first when I do upgrade the cam/ heads it will be ready. I'm looking at about $200 for a 155lph fuel pump, meter and injectors which isn't bad when the meter itself brand new sells for $299. I plan on selling the GT40 heads and getting a set of aluminum heads as soon as I can afford them, hopefully my tax return will give me enough to get them.
 
Sounds like you have a progress path all mapped out, and from your description, it should work well together.
I'm thinking this is the time of year to start looking for parts while everyone has their cars put up for the winter. Just talked to the guy with the Pro-Flow meter and he said he will drop the price to $40 so I told him I'd take it, he also has injectors and I might get them also. I just want to get all the parts ready so once the weather starts getting nice I'll be ready.
 
Get the motor together and running, do a few base runs on a dyno and see what the A/F ratio and other variables look like. Using the stock cam, I doubt you are going to need larger injectors.
The stock cam is only in it because I couldn't afford a higher stall convertor last year after building the motor, I plan on getting the higher stall TC and a different cam before Spring, aluminum heads also if they fit in the budget, gotta see how much I get back in taxes first.