help me understand calibrated maf sensors and injectors

[stackz]

this is going to sound like the age old stupid question...but...here goes....as it is still news to me.

so I am almost done putting together my top end budget build for my 95 vert. I am still saving separately for my turbo kit and pimpxshift ecu. in the mean time though...I am at the point that all I really need is pushrods for my heads and I'm good to go with setting the engine up as naturally aspirated.

so basically, a bone stock 95 mustang gt vert. I got EVERYTHING fixed on it and it is back to stock and now I am comfortable modifying it. plans are as follows (parts I already have):
flotek 180cc heads, summit e303+ cam, crane cams steel tip roller rockers 1.6, bassani equal length headers (94/95 specific with the egr bung), edelbrock performer rpm intake, I have two 80mm or whatever they are bbk throttle bodies and trick flow elbows that somehow just flopped in my lap.

plan was to toss all this on and just stick with stock injectors and maf for a while but everyone local to me says I will peg the injectors or maf out....ok. I dont want to tune yet as I would rather just deep dive with the pimpx shift.

earlier today I came across a guy selling a complete vortech supercharger setup with injectors and maf and NOTHING else for fueling. I did ask him if he had the stock ecu (yes) and if he had a chip (no). but he had 50lb injectors and a bone stock non-chipped ecu. it had an SCT maf on it.

so does this mean I can literally just get a matched set of injectors and maf and my ecu will be happy and I wont have issues? I am ok with this bandaid until I sell a couple things to finish saving for proper engine management as I want to get the engine up and running properly first before I take the next step. if that makes sense? I had plans to run the stock maf and injectors and just be gentle but then I see these listings:

Pardon Our Interruption...

 

[stackz]

and I guess along these lines, which maf should I stay away from? I'm guessing Pro-m and SCT are the go to guys these days and stay away from c&L and such?? and can I use an oem ford lightning maf or should I go with one of the custom tuned ones??? its so weird to me.

 

[Noobz347]

I did ask him if he had the stock ecu (yes) and if he had a chip (no). but he had 50lb injectors and a bone stock non-chipped ecu. it had an SCT maf on it.

I have done this before with a set of 42 lb injectors and a meter calibrated for an A9L and 42 lbs injectors.

It ran... "meh".

Yes, a "calibrated" MAF can accommodate the larger injector size but what it does [not] accommodate is the stock fuel tables in the EEC. What I mean is, even though the "calibrated" MAF lessens injector pulse to adapt to the larger injector, it can not adapt for the injector slopes, tip-in differences, etc., between the two injectors. Driveability suffers as a result. Low speed manners are horrible and the farther you get from the OEM size injectors, the more these issued are amplified.

Picture two fuel volume ramps in your head. One for a 19lb and one for a 50 lb. Both injectors can achieve a set fuel volume point. When directed to reach that point the 50 lb injector will obviously achieve it quicker just because of it's physical characteristics.

The other potential issue with "calibrated" mass air meters is that it 'lies' to the EEC about the amount of air mass it's measuring (reporting less air resulting in the larger injector firing slower than the stock 19). This is not an issue except that it [shrinks] the scale that the MAF has available to report to the EEC. This lessens the resolution available to the EEC and used by the MAF to report air mass. This makes it less accurate because it reporting from a reduced scale.

Tuning can take care of a lot these issue by making full use of the entire scale with a larger number of subdivisions across the available 5 volt range of the MAF and correcting the fuel ramps for a given size injector.

Hope that helps.

 

[AeroCoupe]

I see nothing in your planned setup that would make me run out and get larger injectors and a bigger MAF. Would it run better with some 24’s or 30’s and a bigger MAF? Properly tuned yes but being your plans are to install a turbo I would wait until that happens.

If it’s going to be awhile before you boost it and the plugs show signs of it running lean then get a calibrated MAF and some 30’s as you can sell it all later.

What are your plans fuel system wise?

 

[stackz]

I see nothing in your planned setup that would make me run out and get larger injectors and a bigger MAF. Would it run better with some 24’s or 30’s and a bigger MAF? Properly tuned yes but being your plans are to install a turbo I would wait until that happens.

If it’s going to be awhile before you boost it and the plugs show signs of it running lean then get a calibrated MAF and some 30’s as you can sell it all later.

What are your plans fuel system wise?

gotcha. I was just second guessing myself that the stock 19s would be up to the task or not considering even just the 94/95 cobras use 24s factory and all they really have is a bit better cam and gt40 heads/intake as some of the locals were making me paranoid about running out of injector lol. as far as fuel goes, its just going to stay mainly stock aside from a walbro 255 pump. nothing special.

 

[General karthief]

The closer to stock the stuff, the easier it it to fix bugs.
Work the bugs out and then toss on the hair dryer and related parts/pieces.
Too many times I've seen people find deals while putting things together with thoughts of turbos and blower futures danced in their heads and then can't get the junk running right cause it's a jumble of 'I'm gonna put a turbo on it later' parts.

 

[KRUISR]

The concern of whether you will peg the 19s or not is more of a question of how do you plan to drive the car?

My current combo has 24s, but I ran 19s with it for 2 years before the switch. I have an Anderson PMS hooked up (mostly used for monitoring engine operation than tuning) and with the 19s the duty cycle of the injectors only became a concern when I was 5000+ rpm - which I didn't do every often - it would peek at about 95% at 5500 rpm (my shift point with my AOD at the time). I had both 73 and 76mm C&L MAFs with calibration tubes for 19s (I actually have my own calibration tube sizing - different than published). The only reason I switched to 24s was the high duty cycle and I had a set on the shelf, but I could have stayed with the 19s.

If you are not planning sustained high RPM runs, the 19s should be fine and car should run smoother (because the ECU was designed for that injector size).

 

[stackz]

The concern of whether you will peg the 19s or not is more of a question of how do you plan to drive the car?

My current combo has 24s, but I ran 19s with it for 2 years before the switch. I have an Anderson PMS hooked up (mostly used for monitoring engine operation than tuning) and with the 19s the duty cycle of the injectors only became a concern when I was 5000+ rpm - which I didn't do every often - it would peek at about 95% at 5500 rpm (my shift point with my AOD at the time). I had both 73 and 76mm C&L MAFs with calibration tubes for 19s (I actually have my own calibration tube sizing - different than published). The only reason I switched to 24s was the high duty cycle and I had a set on the shelf, but I could have stayed with the 19s.

If you are not planning sustained high RPM runs, the 19s should be fine and car should run smoother (because the ECU was designed for that injector size).

this makes so much sense to me. much more than I've been reading. I'm just going to stick with my stock injectors as long as I have the stock ecu...which is what I had originally planned to do but then started second guessing myself when people started feeding thoughts in my ears...

 

[2000xp8]

You should worry about making the car run right as is before messing with anything else.
Forget turbos and superchargers for now.
I'd run it with the 19's and stock meter first, because if you change too much without intimate knowledge of what is going to happen you could be chasing your tail forever.
Flotech heads which i think were formerly pro comps aren't exactly known for their quality control.
On a stock lower end i'd be surprised if they exceed 275rwhp, which 19's are fine for and my guess is that you aren't pegging the stock meter.

Also most intakes will only accept a 70mm throttle body, so i'm thinking you do not have any 80's.

 

[93gtmustang]

Check this link. some good info.
According to Ford Racing,
19 lb. injectors are good up to 275 flywheel hp
If it's 275 flywheel hp you're all set with the 19 lb. injectors.
If it's 275 rwhp = approx. 324 flywheel hp.
24 lb. injectors are good for up to 345 flywheel hp.
You may have to go with a larger fuel pump if you haven't already done that.

 

[gkomo]

Check this link. some good info.
According to Ford Racing,
19 lb. injectors are good up to 275 flywheel hp
If it's 275 flywheel hp you're all set with the 19 lb. injectors.
If it's 275 rwhp = approx. 324 flywheel hp.
24 lb. injectors are good for up to 345 flywheel hp.
You may have to go with a larger fuel pump if you haven't already done that.

Thats a great .pdf. Sets you up for injector sizes, fuel pump cabapility and MAF sizing based on horsepower limits.

 

[2000xp8]

Those numbers are closer to rear wheel horsepower in the real world.
You can stretch 19's close to 300rwhp, should you? Probably not, but it's been done with the Trickflow kit.
And if you were to go by that chart anyone with 300rwhp would need 30's which is definitely not true.

 

[Noobz347]

...and if you discover that you're right at the top of the duty cycle, it's nothing that a 5 lb bump in fuel pressure won't fix so long as the pump can handle the volume.

Anybody that's interested can go to the [Resource] section and download, "Fuel Flow Forensics" to get a better idea of the relationship between pressure and volume.

 

[AeroCoupe]

This is all in a perfect world. I ran out of injector at 289 rwhp on 24’s. This was on a Mustang dyno running a wide band. Injectors were maxed out and had been recently tested and cleaned. The only thing that was done was swap the 24’s for 42’s and it picked up to 315ish rwhp and the drivability was spot on.

I think it’s car to car dependent due to all the different variables like pump size, voltage at the pump, how clean the injectors are, accuracy of the pressure regulator, etc.

 

[Noobz347]

This is all in a perfect world.

Very true.

I ran out of injector at 289 rwhp on 24’s.

I made over 400 FWHP on 19s at 70 psi with a 255L High Pressure fuel pump running at 14.2V, an FMU, and stock rails.

 

[General karthief]

All I've managed to do is run outta gas

 

[AeroCoupe]

You know that boosted applications are entirely different that NA setups.

 

[Willybill32]

This is all in a perfect world. I ran out of injector at 289 rwhp on 24’s. This was on a Mustang dyno running a wide band. Injectors were maxed out and had been recently tested and cleaned. The only thing that was done was swap the 24’s for 42’s and it picked up to 315ish rwhp and the drivability was spot on.

I think it’s car to car dependent due to all the different variables like pump size, voltage at the pump, how clean the injectors are, accuracy of the pressure regulator, etc.

A new comment on an older post…

My ‘86 did 314 RWHP on a Mustang dyno running new 24lb injectors and BBK MAF calibrated for the 24lb injectors, so it’s interesting that you ran out at 289 RWHP.

Bill

 

[General karthief]

A new comment on an older post…

My ‘86 did 314 RWHP on a Mustang dyno running new 24lb injectors and BBK MAF calibrated for the 24lb injectors, so it’s interesting that you ran out at 289 RWHP.

Bill

fuel pressure or supply issue could be the reason.
just say'n

 

[AeroCoupe]

I think the General was on to something for sure. Car ran out of fuel with the 331 on the dyno with the 42's and the tuner and I both were scratching our heads. He turned the pressure up from 39 psi to 46 psi and it "solved" the problem. Fast forward a few years I reworked the fuel system to an 6AN feed and return and had the injectors cleaned. I got the injectors from a buddy and they came off his 2001 Lighting. I just put them in the car and never thought about it. The guy that cleaned and flowed them said their average output before the cleaning was around 38 lb/hr and after it was 43 lb/hr. Also said the spray patterns sucked.

I also found an issue with the cold air kit which was my doing form years and years ago. I used a Procharger adapter to the 2000 GT MAF which necked down to about 2-1/2". It wasn't an issue with the 306 but the tuner was telling me I needed more air when the 331 was tuned. That is what got me looking so I got rid of everything except the part that bolts to the inner fender and the air filter mounts to. Its all 3-1/2" now and I transitioned the lip of the MAF to match the adapter that I bolted to it to reduce turbulence.

So there were issues from my ignorance that have since been corrected.