Basic idea of how mass air works - explain?

[hoopty5.0]

Hey guys,

It's been many years since I've messed with a MAF. The vehicle in question is my bronco, but still the same theory at work. My question is on the robustness of a MAF system, as in what's the upward limit on airflow changes you can make to a factory system before it's not going to work right?
I remember you can swap in a MAF sensor calibrated for 24# injectors and a set of injectors and it'll not really need a tune (obviously a tune is always a good idea to verify)
But I'm talking super mild - GT40 intake, TFS1 or similar cam, and some small aluminum heads. I feel like this has been done 10 million times but that area of my memory is foggy.

 

[Noobz347]

You should not need [any] changes to the MAF system for those mods.

If you end up going with a larger MAF and TB then choose one of the OEM units that are 19# injector compatible. You won't need 24s for those mods.

 

[hoopty5.0]

Even better!

We took the truck to the beach this weekend and it was just about 50 hp short of starting to be fun. A mild HCI to get to 300/300 would be ideal.

 

[Mustang5L5]

The swapping MAF trick is really outdated at this point. Basically you are tricking the ECU into thinking the engine is seeing less air by reducing the sample tube size, and as a result it fires the larger injectors for a shorter period. It's all tomfollery and the issues come when you get that ratio incorrect.

I'd stick to the stock MAF (maybe even an 94-95 SN95 70mm) and 19's with thiose mods. Any larger injector and i would do a tune vs the calibrated MAF

 

[hoopty5.0]

Perfect, thanks guys!

 

[hoopty5.0]

You should not need [any] changes to the MAF system for those mods.

If you end up going with a larger MAF and TB then choose one of the OEM units that are 19# injector compatible. You won't need 24s for those mods.

Forgot to mention, this is a 351, not a 302. Probably be at the upper limit of a 19# injector, no?

 

[Noobz347]

Forgot to mention, this is a 351, not a 302. Probably be at the upper limit of a 19# injector, no?

You could be getting close

If so, an adjustable AFPR and another 5lbs of fuel pressure should get you there.

 

[AeroCoupe]

351W with 302 parts will get you 302 power but it’s your build.

 

[hoopty5.0]

351W with 302 parts will get you 302 power but it’s your build.

Well its a bronco. More for torque than HP.

 

[FastDriver]

You can increase the fuel pressure, and the result is the injectors essentially become larger injectors, but the result is also that your computer, thinking they're just 19 lbs injectors, will command them as such, and at idle, it'll run rich. This too gets offset in closed loop, up to ~12.5% (if my old knowledge is still correct), but once that limit is reached, the computer can't tune itself out of running rich. Just a heads up, BTW, the effective increase in injector size is not linear. i.e. adding 50% more pressure does not make injectors 50% bigger.

I have always used the rule of thumb that you should have 1lbs of injector for every 10 rwhp. Came up with it because foxes make 190-200 and run 19s. 93 Cobras make about 230-240 rwhp and run 24s. '03 Cobras, despite being supercharged, run 39s. LS1s made around 300rwhp and ran 28s IIRC. Seems like the factories comes pretty close to this rule. If you stick to that, you'll be in pretty good shape.

As far as the limitations of a given MAF, I think that has to do with how much mass flows through the MAF when the sensor is reporting 5V, even still, you can play tricks with the tune, or 'recalibrate' the MAF sensor to impact the voltage or to change how much fuel is actually injected to offset the impact of running more mass than the sensor can read. But, as far as what the upper mass limit can be input into the MAF transfer function, I'll have to defer to someone who actually tunes the EEC IV. I hope to become far more familiar with it when I start using the Moates Quarter Horse in Black Jack.

 

[hoopty5.0]

You can increase the fuel pressure, and the result is the injectors essentially become larger injectors, but the result is also that your computer, thinking they're just 19 lbs injectors, will command them as such, and at idle, it'll run rich. This too gets offset in closed loop, up to ~12.5% (if my old knowledge is still correct), but once that limit is reached, the computer can't tune itself out of running rich. Just a heads up, BTW, the effective increase in injector size is not linear. i.e. adding 50% more pressure does not make injectors 50% bigger.

I have always used the rule of thumb that you should have 1lbs of injector for every 10 rwhp. Came up with it because foxes make 190-200 and run 19s. 93 Cobras make about 230-240 rwhp and run 24s. '03 Cobras, despite being supercharged, run 39s. LS1s made around 300rwhp and ran 28s IIRC. Seems like the factories comes pretty close to this rule. If you stick to that, you'll be in pretty good shape.

As far as the limitations of a given MAF, I think that has to do with how much mass flows through the MAF when the sensor is reporting 5V, even still, you can play tricks with the tune, or 'recalibrate' the MAF sensor to impact the voltage or to change how much fuel is actually injected to offset the impact of running more mass than the sensor can read. But, as far as what the upper mass limit can be input into the MAF transfer function, I'll have to defer to someone who actually tunes the EEC IV. I hope to become far more familiar with it when I start using the Moates Quarter Horse in Black Jack.

So, considering this is a truck we're talking about and likely will rarely, if ever rev past 5k and we are aiming for torque production vs HP, what's your play with the mildest of mild parts? No change to the fuel system at all? Raise FP? Switch to 24s?

 

[FastDriver]

Sorry, somehow I got carried away with the idea of what maxes out an MAF from a tuner's perspective, not what the safe limit of the stock system is.

"GT40 intake, TFS1 or similar cam, and some small aluminum heads" & 351...

You should easily be in the 240-270 range (a lot more if those little aluminums are AFRs or something premium). So, I'd honestly aim at bigger injectors. I'd personally look for a matching set of injectors & MAF. You can find something like this for $200-300. I saw a Pro-M 75mm Bullett with matching 30lbs injectors for $220 on the marketplace, last week. It sold. I recommend either 24s or 30s, and while an actual tune is preferable, the used matching MAF & injectors is likely to be the most affordable route.

 

[Noobz347]

The intank pump needs the most attention as far a fuel components go.

If you start re-thinking in to bigger after-market cylinder heads then I might go 24s. Otherwise... Save your money for the next, next upgrade. Then you will know (because of blower, of course) how big of an injector you're [really] going to need.

I mean... It's a 351. If you're gonna keep it, eventually you're gonna boost it. Why wouldn't you?

 

[FastDriver]

Ok... So, I do think you can get away with 19s at, say 240 rwhp... and you can play tricks to get away with more... I think it was GrnTrunk on Corral that made over 300rwhp on 19s with a bazillion psi of fuel pressure. That said, if you factor a somewhat conservative .55 BSFC for an N/A combo with 19lbs injectors from the chart Noobz posted, it yields 276 hp. You NEVER run injectors static and the rule of thumb there is 85% at max... That's 234hp. The rule of thumb to convert hp to rwhp is also about 85% through a manual. 85% of 234 is 199 rwhp. Pretty well right in line with the previous rule of thumb I stated. Noobz is right... I'm right... this is a shades of grey situation.

I just personally would not be comfy with 19s making 240+ and I'm almost positive you'll be there.

If you're really interested, I'll break out some old injector math on this stuff. I can help you figure out what pressure to run to make your 19s flow like 24s. Off the top of my head, I think that's somewhere around 55psi, but keep in mind, you'll need an adequate fuel pump to keep up.

 

[Noobz347]

Note that the chart is Crank HP!

From a dyno... with LTs and little else.

 

[hoopty5.0]

Yeah, absolutely no boost on the bronco. The mustang is headache enough! Just looking for a hair more grunt than the factory 215hp E7 headed 351 offers now. Thanks for all the info!

 

[hoopty5.0]

Ok... So, I do think you can get away with 19s at, say 240 rwhp... and you can play tricks to get away with more... I think it was GrnTrunk on Corral that made over 300rwhp on 19s with a bazillion psi of fuel pressure. That said, if you factor a somewhat conservative .55 BSFC for an N/A combo with 19lbs injectors from the chart Noobz posted, it yields 276 hp. You NEVER run injectors static and the rule of thumb there is 85% at max... That's 234hp. The rule of thumb to convert hp to rwhp is also about 85% through a manual. 85% of 234 is 199 rwhp. Pretty well right in line with the previous rule of thumb I stated. Noobz is right... I'm right... this is a shades of grey situation.

I just personally would not be comfy with 19s making 240+ and I'm almost positive you'll be there.

If you're really interested, I'll break out some old injector math on this stuff. I can help you figure out what pressure to run to make your 19s flow like 24s. Off the top of my head, I think that's somewhere around 55psi, but keep in mind, you'll need an adequate fuel pump to keep up.

I appreciate the info, probably no need to break out the slide rule. I have a buddy with a MAF calibrated for 24s for cheep.

Ill need to tear into the motor soon to address a knock in the valve train. It knocks at 375 beats per minute when the motor idles at 750rpm which leads me to believe its a cam issue. Its got new lifters/push rods/rockers and the noise didnt go away so its time to keep digging!

 

[AeroCoupe]

You do not want to run an injector at 100% duty cycle as they cannot be controlled when they go static. Good thread on injector duty here:

H/C/I injector size??

OK well combo is in sig im just curious what injectors to run?? im on 19's and i think they are hurting me (well the stock maf is hurting me but if im gonna upgrade i might as well do injectors) so 24's or 30's?? I'm just gonna ballpark and say i have 350wheel hp. im gonna do a little summer...

stangnet.com

 

[Cheapskate207]

You seen this thread?

A bit of info for those looking to build 300+hp 5.0L/302s - Ford F150 Forum - Community of Ford Truck Fans

1987 - 1996 F150 - A bit of info for those looking to build 300+hp 5.0L/302s - The goal of this thread is to serve as a guide for those individuals looking to make upgrades. Some of this is fact, some of this is from experience and some of this is purely my opinion. This is in no way, the end...

www.f150forum.com

I know it’s for the 302 but lots of good info

 

[FastDriver]

Sooo... it's a good read/fountain of knowledge type of thread. He definitely has confidence in his opinions... These are his questionable statements in my view:

I do not care how hard a B303, E303, Z303 or any other Mustang camshaft pulls in a Mustang. It is not a TRUCK camshaft and has no place in a truck. A Mustang camshaft in a truck causes you to lose low end torque, which is what a truck needs

The main goal is to keep the intake runner size at about 170cc’s or less

What this means is that the truck intake is better than a 5.0 HO Intake, a 5.0 Cobra/GT40/Explorer Intake or any other 5.0 intake that Ford built

Would really like to know why he'd say that one... Hard to imagine a stock manifold outperforming a GT40/explorer... maybe torque at 2k RPM or something, but even there it's hard to imagine a seat of the pants difference.

for aluminum heads, they tell you to use Fel-Pro 1250, but I’m here to tell you that you are looking for trouble if you use it. It is (in my opinion) a race only gasket that will deteriorate over time.