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warmonger
Hard-core CEG'er

Reged: 08/16/01
Posts: 5810
Loc: Ozark, AL
MAF/Injector sizing for your hybrids...must read!
#379094 - 08/16/03 05:21 PM

OK, this post is resulting from the many PM's I receive about these topics. I will include enough information here that will enable you to choose your general type of engine management and estimate the cost WITHOUT having to ask general or stupid (yes, they do exist ) questions. Once you know what you want then you can ask for specific advice.

Credits and Thanks: Myself (practical application, writing and more); DemonSVT (tuning advice and MAF transfer function interpretation +more); PA3LSVT (MAF/PCM knowledge +more); Bnoon (engine knowledge +more); +all other pioneers and people who know who they are that added to the mix

What happens when you change the engine size and need to adjust the idle and maximum throttle airflow values?

Bigger injectors, bigger MAF, larger block, so what's the story?

Lets use the example of a normal contour 2.5L with 17#/hour injectors that has been modified to accept a 3.0L block.
A hybrid 3.0, or a straight 3.0 swap will still require proper mods to the engine management.
The stock maf is generally fine for most hybrid 3L applications since it will be difficult to max out its flow potential with only 0.5L increase in engine displacement.
The fuel injectors on the other hand are too small and the engine will run lean at high rpms. 19# injectors are more than sufficient for any 3L swap we've seen up to about 225-235 wheel horsepower!
However, lets say you're starting with 17# injectors and need to run bigger so you might as well go with the 24# injectors from the 3L; and stock MAF is ok for now.
The first thing you find is that the PCM doesn't know you have 24# injectors so it still runs the same injector pulse-width as it did with the 17's; only problem is the 24's inject 41% more fuel at the same pulsewidth than the 17's!!!
Therefore, the pcm must know that you are using 24# injectors so it can adjust the pulse-width. The PCM cannot be controlled by tuning the MAF for larger injectors if there is a really LARGE change. 17's-24's is over 41% larger!!!
I would say that MAF trickery will only work well for injector changes of around 25% or less.
Let me define MAF trickery. This is when you use a MAF "calibrated" for a different injector size than the car originally came with; this is also using an SAFC, eManage or mafterburner to scale the MAF voltage before the PCM reads it and in effect does the same thing as the MAF alone but is more flexible; this is also the same as using a MAF optimizer which is the least effective next to just swapping the MAF itself.
The reason that you scale the MAF voltage down is to make the pcm think less air is coming in so it lowers the pulse-width in order to drop the fuel now that your injector is 41% larger. However, when you do this you loose some of the sampling resolution that was designed into the stock MAF sensor.
Think of it this way: The normal MAF voltage range is about 0.5 volts to 4.9 volts. 0.5v is about the lowest flow the maf will see and 4.9 is the maximum flow that the maf can handle. On a stock 95 tour, that 4.9 volts may correspond to 280 CFM or so. On a Cobra mustang that 4.9 volts might be 500 CFM of flow.
No matter what MAF you use, this example of the contour PCM will interpret 4.9 volts as 280 CFM. If you are running injectors half again as big, you need to drop the voltage down to about 3.5 volts to compensate. Well, this works fine to get the fuel right at Max throttle and rpm, but the computer only "sees" (for example) 200 CFM of flow at 3.5 volts we'll say. With less airflow being seen, the calculations are all going to be off in other areas and it now forces the pcm outside is "learnable" range. Consequently the car will not run right.

Now look at the bottom end:
If 0.5 is usually the lowest voltage the pcm will see, then the average idle voltage should be a little higher, say 0.6 volts. A 40% reduction from 0.6 volts is about 0.42 volts; this is 0.08 volts lower than the lowest voltage the pcm expects to see from the MAF.
Therefore it doesn't know what to do with a 0.42-0.50 volt signal and will treat it all pretty much the same. Hence the piss-poor idle quality and off-idle throttle response of the more highly modified 3L projects.
Now this is still simplified because the 3L will draw in more air over the 2.5L but the example still applies.

REMEMBER: The MAF is just a sensor that operates off of a 5 volt reference source from the pcm. That means it is unlikely that it will operate from a full 0 volts to a maximum of 5 volts. The operating range must be within the 0-5 volt range. My MAF used to put out 0.08 volts just with the key on and NO airflow going through it. You may as well approximate 0.1 volts minimum just to turn the electronics on, and figure aobut 4.9 volts at the top of the scale too.

The solution is to use a CHIP or Tweecer, or standalone engine management system. The stock maf is usually adequate for most swaps and the MAF curve won't need to be altered, just the injector sizing.
IF you are going to have an extremely large change in airflow and your maximum airflow requirements have exceeded the stock MAF range (i.e. 3L turbo) then you are going to need a MAF that is sized for larger flow. Now it becomes even more impossible to use MAF trickery ( BEEN there Done that!!!) so you need a chip yet again to go along with the bigger MAF. This time you use the chip to input a new injector size and a new airflow function.
The MAF transfer function is a data table that corresponds MAF voltage output to Airflow Volume.
1 volt might be 50 CFM and 4.5 volts might be 300 CFM.
If you need a biffer MAF, then you need access to this data. PRO-M supplies this data with their MAF's and is invaluable in programming the chip into the right "ballpark" the FIRST TIME. If you have this data then you minimize the risk of damage and the number of re-burns you must pay for. If you want a MAF from another car, then make sure the computer from the car that the maf is coming from is "Read" by the chip maker so they can copy the MAF transfer function from it and put it into your chip.

Last:
Using MAF trickery on top of a chip. It doesn't make sense to use it if you are tuned right except under certain cirumstances. With the eManage and the SAFC you can make small changes in fuel without doing any real harm to the calibration in order to fine tune without paying for a reburn. I run the eManage at that same time as my chip so I can fine tune AND use the datalogging to store data on my hardrive. Then I can reference it for better understanding of how my engine is performing.
In the long run it will save money if you can make small changes with the A/F computers so you don't have to constantly get your chips re-burned; assuming you have been tuned into the "ballpark" somewhat close.

~costs:
chip -- $300-$700 depending on source and tuning
Tweecer -- $400-$500 (correct me if I am wrong)
eManage -- $300 - $1000 (depending upon add-ons and options; full featured, highly flexible)
SAFC -- $300 (nice display w/good basic features...less expandability)
custom MAF -- $200 - $400 new
used MAF's -- $25 - $125
Injectors -- $5 - $300+ for a set depending upon size and new/used

Tom


--------------------
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black

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ScottK
Hard-core CEG'er

Reged: 03/26/02
Posts: 1325
Loc: San Diego
Re: MAF/Injector sizing for your hybrids...must read! new
#379101 (Re: warmonger) 08/16/03 05:44 PM

Originally posted by warmonger:
19# injectors are more than sufficient for any 3L swap we've seen up to about 225-235 wheel horsepower!
However, lets say you're starting with 17# injectors and need to run bigger so you might as well go with the 24# injectors from the 3L;




Why even go to 24 then?

There's been just one 3L that got to the power range that might need the extra fuel (DavidZ's) - and he was still using his stock 19's with no extra A/F management. Seems you could avoid cost, compleexity and tuning headacche by just sizing for what you need to begin with? IIRC people running 19# out of the box had much lesss trouble getting there 3L's to run right.

--------------------
97 Contour SE MTX
K&N 3530, UR UDP, 19# Injectors, mystery mod, FMS wires, Fordchip.com chip, SVT: TB, Flywheel, clutch, exhaust

04 Grand Caravan SXT

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svttour
Hard-core CEG'er

Reged: 08/13/01
Posts: 1089
Loc: land of the heat!!~both the team and the temp.
Re: MAF/Injector sizing for your hybrids...must read! new
#379211 (Re: ScottK) 08/16/03 10:56 PM

I suggest we pin this topic

--------------------
99 T-RED 3L SVT
Apillar Guages How-To

3L 98 CSVT SF/MB 4 SALE 7500 obo pm me

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mmarfan
Hard-core CEG'er

Reged: 09/21/01
Posts: 1516
Loc: Middletown, Oh
Re: MAF/Injector sizing for your hybrids...must read! new
#384653 (Re: svttour) 08/22/03 01:44 AM

What about going from 17# to 19#? How much must be adjusted there? Will the upgrade in engine size compensate for the 2# increase?

--------------------
Mazda 6S, V6, Speed Yellow
5 Speed, Sport package
Bose audio
Painted 'stash and HIDs!
w/Injen 1/4 14.750 @ 94.94

Former car:
99 Contour SE Sport Black MTX V6
SVT plastic...
1/4 - 15.012 @ 90.58

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warmonger
Hard-core CEG'er

Reged: 08/16/01
Posts: 5810
Loc: Ozark, AL
Re: MAF/Injector sizing for your hybrids...must read! new
#385053 (Re: mmarfan) 08/22/03 01:03 PM

You have to think in percentage of increase because that is the only way to get correct perspective.
The 3L is 20% larger than the 2.5L
The 19# injectors are 11% larger than the 17# injectors and on average will flow ~10% more fuel if swapped out. So just by doing this you have increased fuel flow by 10% but remember you may not need the full 10% increase at idle.
19#'s will work and can probably by compensated for by an eManage or SAFC if you just add about 8-10% fuel AFTER you install the injectors (again, Idle is a different story).
This won't be perfect, but it will work until you get to a dyno with A/F to tune it.
However, this brings another problem up. The top end of your airflow through the stock MAF will be maxed out at about 4.5 volts. This is because the emanage will add 0.45 volts on top of the 4.5 volts from the MAF to compensate for the additional 10% fuel you are asking for. The output voltage of the emanage going to your PCM will then be 4.95 volts even though the MAF is still only putting out 4.5v.
All you have to do now is figure out what airflow voltage the 4.5 volts is equivalent to and then see if that is enough peak airflow for the new 3.0L at max RPM.

Figure out your max airflow at max RPM = 7000:
3L has an 89mm bore x 79.5mm stroke.

44.5^2*PI= 6221 mm^2
6221x79.5 = 494580 mm^3 per cylinder
Convert from cubic mm to cubic feet:

494580 / 25.4^3 (in^3/mm^3) = 30.18 in^3
30.18 per cylinder x 6 cylinders = 181.1 cubic inches and is the way you calculate engine displacement.

30.18 / 12^3 (ft^3/in^3) = 1.747x10^-2 ft^3 of air per cylinder.
0.1048 ft^3 is the engine displacement in ft^3.

How many cylinders draw air at any given rpm:
7000 rpm / 2 = 3500 (because two revolutions per firing cycle)

# cylinders x vol. per cylinder:
3500 intake cycles/minute x 0.1048 ft^3/intake cycle = 366.8 CFM (cubic feet/minute)

OK. ~367 CFM at 7000 rpm. This can help you size your MAF correctly or see if your current MAF can actually go this high. Honestly this is right around the top range of the SVT MAF calibration so I don't know if your stock duratech MAF goes this high. However if you find out that it's close then you will be able to use it because you are almost never at 100% volumetric efficiency...which is what this math calculation assumes to be true. More likely at 7000 rpm you are 80% of that.

80% of 367 = 293 CFM
Now, does the 4.5 volts on your stock MAF correspond to 300 CFM or more? If it is more than say 10% less (i.e. 270 cfm) then you will not be able to safely use your stock MAF even with the 19# injectors, and DEFINITELY not with 24# injectors.

If you change the MAF then you are now in the other category where you must get a chip because you have changed TWO VARIABLES from the engine mangagement system (MAF and INJ) and now you cannot control it very easily with a simple MAF scaling device. It is possible with lots of tuning time to use something like the emanage with rpm and throttle position and 256 data points to get a close approximation, but it is never perfect. The best I ever got was with the stock MAF and 24# injectors. When I tried a non-stock maf and 24# injectors I had CEL's popping on at random engine speeds during cruise. Not the best way.

Tom



--------------------
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black

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svttour
Hard-core CEG'er

Reged: 08/13/01
Posts: 1089
Loc: land of the heat!!~both the team and the temp.
Re: MAF/Injector sizing for your hybrids...must read! new
#385708 (Re: warmonger) 08/23/03 01:26 AM

Tom ur mad smart yo... but this is on hybrids give me your input on straight 3L with SVT cams and SVT uim and lim .. should this go from 19# to 24# or no... and if u say 19# are sufficient in most cases why are 24#ers favored amongst the 3L population.

--------------------
99 T-RED 3L SVT
Apillar Guages How-To

3L 98 CSVT SF/MB 4 SALE 7500 obo pm me

Edited by svttour (08/23/03 01:28 AM)

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mmarfan
Hard-core CEG'er

Reged: 09/21/01
Posts: 1516
Loc: Middletown, Oh
Re: MAF/Injector sizing for your hybrids...must read! new
#386048 (Re: warmonger) 08/23/03 02:42 PM

This should also be addressed here:

How can you convert a returning to a returnless fuel system? Can you keep the returning injectors? Will they slide right into the returnless injector holes?

--------------------
Mazda 6S, V6, Speed Yellow
5 Speed, Sport package
Bose audio
Painted 'stash and HIDs!
w/Injen 1/4 14.750 @ 94.94

Former car:
99 Contour SE Sport Black MTX V6
SVT plastic...
1/4 - 15.012 @ 90.58

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warmonger
Hard-core CEG'er

Reged: 08/16/01
Posts: 5810
Loc: Ozark, AL
Re: MAF/Injector sizing for your hybrids...must read! new
#386095 (Re: svttour) 08/23/03 03:55 PM

Originally posted by svttour:
...but this is on hybrids give me your input on straight 3L with SVT cams and SVT uim and lim .. should this go from 19# to 24# or no... and if u say 19# are sufficient in most cases why are 24#ers favored amongst the 3L population.




A 3L is a 3L in so far as injector sizing is concerned. The 24# injectors are the correct size for the engine...Ford has already determined it.
People use the 24's so much because the 3L motors come with them and they don't have to pay more for them.
Then you have to figure that they are bigger and there is more room for improvement with things like nitrous.
19's are sufficient because of the high stock fuel pressure that the contours use. If I made another 3L swap or hybrid, I'd most-likely just use stock 19# injectors if it was an SVT unless I had bigger plans like a large nitrous shot.

Then again you have people that have stock duratechs with 17# injectors and a 3L. They don't have 19# injectors handy but they need something bigger than 17's.

It is no problem to throw 24's into an SVT and use an SAFC or eManage or probably a tuned MAF to control them. The 24#'rs are about 20% larger than the 19's that come with the SVT motors so that isn't too much of a stretch if you use an SAFC or tuned MAF or eManage.
It is just with the 17-24# transition that things get really fugged up.
IF you have a normal duratech and want to go with a 3L(hybrid or regular) You need to follow the same precautions!

IF YOU HAVE THE MONEY, the best way to insure that your 3L runs ok is to:

1. Send your pcm in to the chip maker to have them read the code.

2. Purchase a MAF where you KNOW the transfer function. Don't worry about tuning it to injector sizes, just ask for one that has the flow range you need!!! Don't get one that flows 700 CFM when you only need one that Flows 350-400 CFM and conversely if you are running a turbo you need a bigger one. Pro-M supplies all of this information with their MAF's so I recommend shelling the money for one of those since they work so well and give you a complete flow-sheet with it. Photocopy the flow-sheet and send a copy in with your pcm when they go to make your chip.

3. Have them input the correct injector size AND convert the MAF data from the sheet in order to put it into the new chip.

4. get your pcm and chip back and stick it in.

5. Of course don't forget to put the injectors in!



--------------------
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black

Post Extras: Print Post Remind Me! Notify Moderator
warmonger
Hard-core CEG'er

Reged: 08/16/01
Posts: 5810
Loc: Ozark, AL
Re: MAF/Injector sizing for your hybrids...must read! new
#386098 (Re: mmarfan) 08/23/03 03:56 PM

Originally posted by mmarfan:
This should also be addressed here:

How can you convert a returning to a returnless fuel system? Can you keep the returning injectors? Will they slide right into the returnless injector holes?




I do not know the answer to this question so I will wait for someone who does to come and answer it.



--------------------
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black

Post Extras: Print Post Remind Me! Notify Moderator
svttour
Hard-core CEG'er

Reged: 08/13/01
Posts: 1089
Loc: land of the heat!!~both the team and the temp.
Re: MAF/Injector sizing for your hybrids...must read! new
#386392 (Re: warmonger) 08/24/03 12:47 AM

Originally posted by warmonger:
Originally posted by mmarfan:
This should also be addressed here:

How can you convert a returning to a returnless fuel system? Can you keep the returning injectors? Will they slide right into the returnless injector holes?




I do not know the answer to this question so I will wait for someone who does to come and answer it.






i bet your hitting the books as we speak .

--------------------
99 T-RED 3L SVT
Apillar Guages How-To

3L 98 CSVT SF/MB 4 SALE 7500 obo pm me

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