EFI MAF/Injector SIZE

[BroncoinAlaska]

Got my EFi up and running. Here is the breakdown of the engine as it sat in the Mustang befor I pluged it in to the Bronco. The Mustang also had a turbo setup. So I think the injectors are too big!
Ford Racing Crate 347 Roller Motor
Aluminum Heads Ford
Trick Flow Upper and Lower
70mm BBK TB
76mm C&L MAF
30# Injectors

I wanted to swap the injectors and MAF for a smaller size.
24# Ford Racing Injectors
SN95 Mustang 70mm MAF

I am thinking that would make the Bronco a little more streetable and not so tempermental. Just looking for your guys input.

 

[Viperwolf1]

The SN95 MAF was used with 19 lb injectors. It really all depends on how your ECU is tuned though.

 

[DRBRONCO69]

With your set-up, I would run a 24 LB/HR injector.

 

[BroncoinAlaska]

The SN95 MAF was used with 19 lb injectors. It really all depends on how your ECU is tuned though.

I was under the inmpression that the SN95 MAF was good for 19lb and 24lb injectors?

What would be the best MAF for 24# injectors?

 

[Viperwolf1]

I was under the inmpression that the SN95 MAF was good for 19lb and 24lb injectors?

What would be the best MAF for 24# injectors?

It's not that the MAF is matched to the injectors. The ECU tune is for a specific MAF output curve and for a specific injector set. Yes the 70mm MAF will flow plenty of air for a 347 but you'll need to tune the ECU for that MAF curve and for the injector set you use.

 

[fromme]

I would bet my last dollar that you will get the results you desire by swapping out that C&L mass air meter for a Pro-M or PMAS. That is one of the worst MAF meters ever made. Most people aren't lucky enough to get one to work properly. But yes, your injectors are a little too big also. With a proper meter and proper tuning it would run so much better and those 30s would be just fine.

 

[vintage bronco]

if its a C&L mass air meter you should be able to swap the sample tubes. just change out to a 24lb inj sample tube if thats what you want to use. but you should have a custom tune done for the ECU. i never had any problems with a C&L mass air meter.

 

[marty]

i had a mustang for years with cast iron gt-40 heads extensively ported with tubular gt-40 ported to match. i used a 65 mm throttle body with a large pro-m mass air meter with 24 lbs injectors and never touched the ecm. car ran all day in the heat low 12's at 111 mph. you should not have to do anything to the ecm to run that setup. your injectors need to match a mass air calibrated for the injector size you are using. and all those piggy back aftermarket chips and such are going to do nothing for you either so don't waste your money. oh also you need to run a larger fuel pump and a adjustable fuel pressure regulator to boost the fuel pressure a bit to support the larger injectors. good luck

 

[fromme]

How is it that in this day and age, people still think that mass air meters are calibrated to a certain injector size? I don't mean to be rude here, but that advice is way off the mark. If someone was to take some time and better educate himself on how this works he would understand why using something like a C&L meter with different size sampling tube is a poor design. It is also not ideal to just simply slap on a better meter like a Pro-M, although they will work better. Both the computer and the meter are not calibrated for any injector size. Viperwolf has it 100% correct:

It's not that the MAF is matched to the injectors. The ECU tune is for a specific MAF output curve and for a specific injector set. Yes the 70mm MAF will flow plenty of air for a 347 but you'll need to tune the ECU for that MAF curve and for the injector set you use.

You might get really lucky and that Pro-M or C&L meter will be dead on, but it's not likely. Even if the engine seems to run well, chances are it's still not ideal. The only way to get it right is tuning with a wideband and a custom tune. They are definitely worth the money when dealing with MAF curves and larger injectors.
The ones who have what they think is a good running engine with just a meter and injectors don't usually go any further and don't know any different. The OP obviously has some issues he doesn't like.

Oh, and you only need a bigger fuel pump if you find it's lacking. Just because there's larger injectors doesn't mean there's a need for a larger pump. And the factory FPR setting is the best pressure, don't waste the money on an adjustable FPR on an n/a motor.

 

[Broncobowsher]

How is it that in this day and age, people still think that mass air meters are calibrated to a certain injector size? I don't mean to be rude here, but that advice is way off the mark. If someone was to take some time and better educate himself on how this works he would understand why using something like a C&L meter with different size sampling tube is a poor design. It is also not ideal to just simply slap on a better meter like a Pro-M, although they will work better. Both the computer and the meter are not calibrated for any injector size. Viperwolf has it 100% correct:


You might get really lucky and that Pro-M or C&L meter will be dead on, but it's not likely. Even if the engine seems to run well, chances are it's still not ideal. The only way to get it right is tuning with a wideband and a custom tune. They are definitely worth the money when dealing with MAF curves and larger injectors.
The ones who have what they think is a good running engine with just a meter and injectors don't usually go any further and don't know any different. The OP obviously has some issues he doesn't like.

Oh, and you only need a bigger fuel pump if you find it's lacking. Just because there's larger injectors doesn't mean there's a need for a larger pump. And the factory FPR setting is the best pressure, don't waste the money on an adjustable FPR on an n/a motor.

Very good info. So I am not the only one to advance past the stone age of EFI tuning.

The MAF measures the mass of the air. Sample tube and housing bore are pretty much irrelivent. All it does is measure the air, look into the programming and then sends a matching voltage to the computer.

The computer is programmed with the wame profile as the MAF. So the computer looks up the voltage then knows the amount of air entering the engine. The computer does it's math and figures how much fuel to add.

Then the computer goes to another part of its brain and take that amount of fuel and looks at the injector programming and figures how long to turn that size injector on.

For years we didn't have access to programming the computer. The (often ill)tuned MAFs were a poor crutch around the lack or proper programming. Lie to the computer about how much air is going in to cripple the comuter into under injecting oversized injectors. It is about on par with taking a carb, installing too large of a jet then leaning it out with a vacuum leak.