Fox Maf Questions

dreadnaught156 · Dec 9, 2014

Hey guys, new to the forum! I'm on the market for a Mustang to build, and I have a question about the '89-'93 MAFs. I've read and been told that an '89 or later Fox with the MAF is capable of tuning itself after the addition of some bolt-ons, not as good as a dyno tune, but enough to run smoothly and gain some power. But how true is this? With my budget, I'm looking at something like a 1990 LX or GT 5.0 and adding a trickflow top end kit (just H/C/I), long tube headers, and a new exhaust all the way back. A guy with a 400hp Fox told me I could get 300 rwhp from the stock MAF and injectors, self-tuned... sounds a little too good, and that guy has a carb. I feel like all those upgrades would be a little too much for a stock MAF to handle. So basically, what can I realistically get out of a stock MAF and injectors without going to the dyno? The last thing I want to do is drop almost half my budget on a top end kit just to find out I can't use it without upgrading the EFI system. Thanks!

jrichker · Dec 9, 2014

You'll need an aftermarket MAF calibrated for 24 lb. injectors and a set of 24 lb. injectors to use with the Trick Flow head kit. Once you have that, the engine will run well enough that you may not want a custom burned dyno tune chip. The custom chip will smooth out some things and pick up some extra HP.

Fuel injector sizing & injector photos

Revised 11-Dec-2011 to add larger injector sizes to injector table

Injector HP ratings: 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

Diagram courtesy of Tmoss & Stang&2birds

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.

My Comments:

A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off or pressurizes the fuel tank! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.

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

FoxMustangLvr · Dec 9, 2014

You will also need to upgrade to a 155lph'ish in tank fuel pump on top of the upgraded MAF and injectors IF you were to do a HCI. So factor those costs into your build plans.

dreadnaught156 · Dec 9, 2014

Wow, thanks for the thorough response! I figured there'd be more to it, but it's nice to know the MAF can get a better air/fuel ratio without a dyno tune though. Now let's say I upgraded my MAF, injectors, and pump and then waited on the trickflow. Will the car still run like stock with these additions, or will it change the performance of the vehicle even without the trickflow?

addermk2 · Dec 9, 2014

jrichker said:
You'll need an aftermarket MAF calibrated for 24 lb. injectors and a set of 24 lb. injectors to use with the Trick Flow head kit. Once you have that, the engine will run well enough that you may not want a custom burned dyno tune chip. The custom chip will smooth out some things and pick up some extra HP.

My Comments:

A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off or pressurizes the fuel tank! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.

This is actually rather poor tech information. His car does not NEED a calibrated maf. However it is the easiest and fastest way to make the car run.

My opinion on this matter is that you SHOULD get it tuned. Regardless of whether or not YOU think it runs ok. A tune will allow you to run literally any maf on the market, with any injector that is compatible with the pcm. A prime example of this is my car. I had trouble dialing in my fuel injector slopes, so I hooked up my stock maf and adjusted the slopes to their proper setting. Once that was done, I hooked my HPX maf back up, and tuned the MAF transfer function.

So yes, for about 3 days, i was running a stock F1VF 94-95 maf with my 900cc (83#) injectors.

As for the fuel boiling off due to having a large pump... I run a 416lph walbro in my tank. It runs 100% all the time, and is capable of supplying enough fuel for 900hp on pumo gas, or around 750 on E85. I logged my fuel temp in my return line. It was 12* warmer than ambient temp. Hardly something I would concern myself with.

FoxMustangLvr · Dec 9, 2014

addermk2 said:
This is actually rather poor tech information. His car does not NEED a calibrated maf. However it is the easiest and fastest way to make the car run.

My opinion on this matter is that you SHOULD get it tuned. Regardless of whether or not YOU think it runs ok. A tune will allow you to run literally any maf on the market, with any injector that is compatible with the pcm. A prime example of this is my car. I had trouble dialing in my fuel injector slopes, so I hooked up my stock maf and adjusted the slopes to their proper setting. Once that was done, I hooked my HPX maf back up, and tuned the MAF transfer function.

So yes, for about 3 days, i was running a stock F1VF 94-95 maf with my 900cc (83#) injectors.

As for the fuel boiling off due to having a large pump... I run a 416lph walbro in my tank. It runs 100% all the time, and is capable of supplying enough fuel for 900hp on pumo gas, or around 750 on E85. I logged my fuel temp in my return line. It was 12* warmer than ambient temp. Hardly something I would concern myself with.

Why you getting your panties in a bunch? Jrich said that the MAF and 24lb injectors would getting him up and running well and then followed that up with saying a tune would make it even better!!!

his words right here,
from jrichker:
Once you have that, the engine will run well enough that you may not want a custom burned dyno tune chip. The custom chip will smooth out some things and pick up some extra HP. <------so what makes you think he doesn't recommend a tune??????

addermk2 · Dec 9, 2014

FoxMustangLvr said:
Why you getting your panties in a bunch? Jrich said that the MAF and 24lb injectors would getting him up and running well and then followed that up with saying a tune would make it even better!!!

Because I like breaking misconceptions... You don't NEED a "calibrated maf" to run different size injectors.

GroverDill · Dec 9, 2014

Just like you don't NEED a custom tune

madspeed · Dec 9, 2014

I NEED a drink...

mikestang63 · Dec 9, 2014

addermk2 said:
Because I like breaking misconceptions... You don't NEED a "calibrated maf" to run different size injectors.

9 posts and you're telling people jrichker gives out bad tech? Serious?

Quit while you are behind dude.

FoxMustangLvr · Dec 9, 2014

addermk2 said:
Because I like breaking misconceptions... You don't NEED a "calibrated maf" to run different size injectors.

You're not breaking any misconceptions. MOST people do what Jrichker suggested and they do it successfully. Disrespecting the smartest guy on Stangnet is not the way to go for you either.

addermk2 · Dec 9, 2014

Smartest guy on Stangnet eh? We'll see.

As for the 9 posts comment, maybe you should look at my join date, and how often I don't come here.

Seems pretty obvious that I had a reason to stay away before.

pats93stang · Dec 9, 2014

Hey guys new here , I am running a 306 stock block 1087 wolverine cam 548 lift/ 222 duration. Crane gold 1.6 roller rockers. 202/160 twisted wedge heads .Explor upper an lower intak, 70 mm bbk trottle body egr delete,1 inch spacer, under
drive pullies.Bbk shorty headers, X pipe, Built T-5,Alum driver shaft, 373 gear. Now with all that said I am needing to up grade my fuel system. I am wondering if i go with 24# is it going to feed it or should i step up to 30#. My car is runing but popping threw the intake at cold when it warms up it runs strong. Any help would be great. Thanks in advance.

FoxMustangLvr · Dec 10, 2014

pats93stang said:
Hey guys new here , I am running a 306 stock block 1087 wolverine cam 548 lift/ 222 duration. Crane gold 1.6 roller rockers. 202/160 twisted wedge heads .Explor upper an lower intak, 70 mm bbk trottle body egr delete,1 inch spacer, under
drive pullies.Bbk shorty headers, X pipe, Built T-5,Alum driver shaft, 373 gear. Now with all that said I am needing to up grade my fuel system. I am wondering if i go with 24# is it going to feed it or should i step up to 30#. My car is runing but popping threw the intake at cold when it warms up it runs strong. Any help would be great. Thanks in advance.

Is your fuel system and MAF stock with that setup? 24# will work and like previously stated a TUNE is always preferred to dial in your engine for the best performance.

My combo is a 306 cid, forged pistons with valve reliefs, .542"/.563" lift, 224 intake/232 exhaust duration, ported Edelbrock performer heads w/ 2.02in 1.6ex, Scorp 1.6 RR, performer RPM intake, BBK 70mm TB, no MAF, 30# injectors, 155lph fuel pump, will be tuned with Stinger PIMP Microsquirt ECU shortly. 24# injectors would've worked fine for my combo but I got a good deal on my 30# inj from a Stangnet member that didn't need them.

FoxMustangLvr · Dec 10, 2014

addermk2 said:
Smartest guy on Stangnet eh? We'll see.

As for the 9 posts comment, maybe you should look at my join date, and how often I don't come here.

Seems pretty obvious that I had a reason to stay away before.

Don't know the reason you were gone so long and I don't care. Welcome back to Stangnet but eat some humble pie.

pats93stang · Dec 10, 2014

FoxMustangLvr said:
Is your fuel system and MAF stock with that setup? 24# will work and like previously stated a TUNE is always preferred to dial in your engine for the best performance.

My combo is a 306 cid, forged pistons with valve reliefs, .542"/.563" lift, 224 intake/232 exhaust duration, ported Edelbrock performer heads w/ 2.02in 1.6ex, Scorp 1.6 RR, performer RPM intake, BBK 70mm TB, no MAF, 30# injectors, 155lph fuel pump, will be tuned with Stinger PIMP Microsquirt ECU shortly. 24# injectors would've worked fine for my combo but I got a good deal on my 30# inj from a Stangnet member that didn't need them.

th

pats93stang · Dec 10, 2014

yes the whole system is stock . Should i upgrade the pump also. I would love to have it tuned when all is set up but i have yet to find anyone in my area to do so. Do the rails really make much diff. or should i just worry about the pump injectors an maff an then tune ? Is the poping caused from runing to lean ? It only does it when it is cold. Srry for all the random ? Just nice to here answers from someone who knows.

FoxMustangLvr · Dec 10, 2014

You could always run codes and see what's going on to be sure. Your stock fuel rails I believe will support up to 500hp so no worries there. Yes you should do all 3, the pump, 24# injectors and a matching calibrated 75mm ProM MAF. That should get you up and running an in the ball park of running well without a tune. A tune would make it better when you can get to it. There are programmers out there that you can buy and you can tune yourself if you want to take on that task. Some places that dyno tune may need to you supply that anyway like the one that is near me told me. I figure I'll just learn to tune it myself with the Stinger PIMP and save myself the money.

addermk2 · Dec 10, 2014

That's a pretty hefty chunk of money right there. I've heard of a guy that does a Moates Quarterhorse rental program. Supposedly you rent the QH and software from him, and he remote tunes your car.

Sounds pretty sweet to me. Probably a lot cheaper then paying a dyno tuner, or dicking with a stand alone.

FoxMustangLvr · Dec 10, 2014

addermk2 said:
That's a pretty hefty chunk of money right there. I've heard of a guy that does a Moates Quarterhorse rental program. Supposedly you rent the QH and software from him, and he remote tunes your car.

Sounds pretty sweet to me. Probably a lot cheaper then paying a dyno tuner, or dicking with a stand alone.

I'd rather spend the $730 and learn to tune myself. Gaining knowledge and not having to wait for somebody else to tune your car for you for a fee every time sounds like money well spent to me. If my combo changes in the future I'll have the ability to re-tune my setup at no cost. Where I am the guy wanted about $800 for a dyno tune and I still had to buy the tuning device on top of that. The system I'm going to get has been around for a while and has excellent customer support from WesK.

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