I know the 2g mas alters the karman signal about the same amount 550's are bigger than 450's. I'm wondering if the ecu can make up the difference, and if idle will suffer. I really don't want an afc to trick my ecu if I can avoid it. I know it will work, but I don't know how well. If you've done this mod (with or without an afc (if it's with, please tell me your fuel curve settings)) let me know how well it worked. Thanks.

The second you use anything but a stock mas you are "tricking" the ecu.

If you want to run anything but the stock injectors you are going to need a SAFC or some sort of fuel control. Deal with it.

Well, that was helpful. I know it can work, because I've heard of people doing it, and I didn't think their afc trims were off more than 5% anywhere. Anyone else who's actually done it?

And yes, I do realize it's still tricking my ecu, but without actively tricking my ecu (via afc), I was hoping to get away from having to be so exact in my fuel calculations, that each mod would make me retune. I know the ecu can compensate at least 10% either way.

You have assume too much. If you heard people doing it, try it and let us know. I know you will run rich without any kind of fuel control. In close loop, the ECU maybe able to compensate for it. However, once it go open loop, it's a different story.

Yes, you will probably be pretty close without an AFC... however sometimes close isnt close enough. If you try it you need to have all the methods in place to monitor for correct A/F ratio, etc... otherwise you will be taking a bit of a risk.

2g mas + 550 w/o afc= not a bright idea


Don't risk screwing up your car. Get the right tools for the job. Bigger injectors means you have to tune them. Get the S-AFC or something similar (Haltech, Motec, whatever) and do the job right the first time.

My AFC was stolen out my car a few months ago and I had to limp the car home with the 2G MAF/550's. It would hardly idle from being so rich and wouldn't rev beyond 3500 and wouldn't even do 60 MPH no matter what I did. The car ran like it had 2-3 cylinders. I think the problem is that the two curves are very different, hence the need for the SAFC.

As with any "shortcut," anything is possible if you have the time/knowledge but whether it's worth it for saving $250 for is up to you. I'll spend the $250 and be happy.

Mike C.

Based on what I know about open loop operation, I guess I need an afc, since the ecu won't be able to compensate at all :/ Oh well, guess I'll get one... are digital o2 gauges worth it? or can I get an autometer pos to tune?

Originally posted by mike9146
My AFC was stolen out my car a few months ago and I had to limp the car home with the 2G MAF/550's. It would hardly idle from being so rich and wouldn't rev beyond 3500 and wouldn't even do 60 MPH no matter what I did. The car ran like it had 2-3 cylinders. I think the problem is that the two curves are very different, hence the need for the SAFC.

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This is something different. The problem is that the ECU wasn't getting an airflow signal without the AFC because the AFC intercepts it.

Originally posted by BatmanGSX


This is something different. The problem is that the ECU wasn't getting an airflow signal without the AFC because the AFC intercepts it.

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You're right batman. So, I guess to ask once again, has anyone done this? 550's + 2gmas with or without afc, and their results/afc settings? Hopefully with unhacked mas? I was hoping to tune by hacking the MAS (put in restrictions to richen, take out restrictions to lean). Obviously with O2 and egt gauges. What can I say? I like the stock ECU... feel free to tell me I'm crazy.

Originally posted by Irks
feel free to tell me I'm crazy.

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You're crazy.

I ran the 2g mas + 550's before I upgraded to 660's. I wouldn't do it without an safc.

You sound like you're just looking for someone to tell you it's ok to do. You don't want to listen to why you shouldn't. So just do it already and see for yourself why those of us that have been there say you need a safc.

You obviously want to try it and seem to have a concept of ways to make it work... so try it already. If you are willing to invest the time you probably will be able to make it run fairly well. There are alot of things that can be manipulated to help dial in your A/F. Air temps,baro, as well as modifying airflow proportions through the MAS. I have put several cars into the 12's without the aid of an AFC, VPC, etc. You just have to know how and what to fudge. In the past I have put 550's in cars without any fuel management... and was able to get great results. Alot of people on this board think you need to buy a fancy part for just about everything. The truth is in the early days of DSMing there werent so many fancy parts available and guys had to find ways to make things work. You just need patience and the ability to think. Now days everyone has tons of fancy parts on their cars and yet the majority of them are still slower than the simple setups of past years. Its the "bolt-on" generation I quess

Yes the AFC will make tuning easier, but its still possible without it.

Just as the days of carburetors are over, we now enter the era of fuel injection. Things change as technology advance. You just have to accept that. You can definitely try many things to make it work. Like you said, playing with IAT and barometric pressure to dial in the A/F. There is also playing with fuel pressure to get it to work. It's just not ideal because you are changing things across the board and global. With the help of fancy tools, you have more control, you can tune at rpms you want to which make it smarter than the older method. For someone that need to ask, suggestions like this is not recommended.

Nobody ever said it was ideal. Please dont think that what an AFC does is ideal either. Its all just a way to fudge the right values to get the ECU to do what we want.

If Irks wants to try it then more power to him. In fact he may actually learn something in the process. He already stated that he has the proper monitoring equipment in place.

I am not denying that the AFC is an excellant tuning tool. However people have been modifying mustangs, etc for many more years than DSM's and they did not use AFCs or anything of the sort. Bigger injectors and recalibrated MAS's. In essence the same thing as a 2G MAS and 550's.

Sorry if I have more respect for people who are willing to dive into things a little deeper than the average joe.

Oh, nobody is saying it's more ideal than said comparing to a Haltech standalone. No matter what you do with an AFC, you are still at the mercy of the ECU. But comparing to using pots, its defintely more ideal

In fact I think a standalone will be better if you really want to learn something. You have so much control you have to read/understand how the events work together to get it working. You have to *think* like the ECU and you can dive more into things by testing with different setting.

There is actually not much to test if you are just playing with pots and a few other things mentioned. It's just plain time consuming and by the time you know why you do that, you'll want the fancy tools

Originally posted by jw
...by the time you know why you do that, you'll want the fancy tools

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I agree with you 100% on this one. This is why several years ago I sold my VPC, tore out my ECU and installed a Haltech E6K. It all comes down to your individual goals.

get a fuel pump
get the 550's. and get an fpr
you do not need the afc to tune it. use the fpr and a data logger to get it dialed in.

also, anytime you change injectors you do NOT need an afc to "dial" them in

my car runs a hell of a lot better on 510's then it ever did on 450's
idles smoother. repsonds better. so the theory of "you changed injectors you need to control them" goes out the window.

im going to be going to a 2g mas here shortly due to "over run"

just remember, facny devices do not always make it better or faster.

Originally posted by Silent2g
get a fuel pump
get the 550's. and get an fpr
you do not need the afc to tune it. use the fpr and a data logger to get it dialed in.

also, anytime you change injectors you do NOT need an afc to "dial" them in

my car runs a hell of a lot better on 510's then it ever did on 450's
idles smoother. repsonds better. so the theory of "you changed injectors you need to control them" goes out the window.

im going to be going to a 2g mas here shortly due to "over run"

just remember, facny devices do not always make it better or faster.

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Tell me how you can add 13% at low throttle and idle, where no matter how many mods you do you won't be getting 13% more air in? Cars that run a bit rich often seem "smooth" as you have described it.

You will never get a good running car at idle, low throttle and high throttle without some sort of way to get the larger injectors opening for a shorter amount of time.

Wes, I agree with your theory, I got my friend's car to run beautifully at WOT with 550s and MAS hacking with no AFC. But it runs like crap at idle and low throttle. Most of the racecars from the good old days would run big injectors and high fuel pressures but they only needed to go fast and run good at WOT, low throttle and idle wasn't a concern. For the average guy it is.


But do whatever, nobody can stop you and it probably won't hurt anything, you may indeed learn something as well. I don't think you will be happy with it in the longrun.

I bought a 5 knob SAFC, the 550's,the 2G MAS, ported small 16G for 92 Tsi. Putting it all on this weekend. I could sure use some base SAFC settings to get me started. I searched, only one post found: -1, 15, 16,16,16. Also have a Spoolinup FP regulator, but I dont think I will be trying to "dial in" with that. I bought it due to the Walbro overrunning my stock reg. Any help would be appreciated.

Originally posted by BatmanGSX




Tell me how you can add 13% at low throttle and idle, where no matter how many mods you do you won't be getting 13% more air in? Cars that run a bit rich often seem "smooth" as you have described it.

You will never get a good running car at idle, low throttle and high throttle without some sort of way to get the larger injectors opening for a shorter amount of time.

Wes, I agree with your theory, I got my friend's car to run beautifully at WOT with 550s and MAS hacking with no AFC. But it runs like crap at idle and low throttle. Most of the racecars from the good old days would run big injectors and high fuel pressures but they only needed to go fast and run good at WOT, low throttle and idle wasn't a concern. For the average guy it is.


But do whatever, nobody can stop you and it probably won't hurt anything, you may indeed learn something as well. I don't think you will be happy with it in the longrun.

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The ecu can compensate for 13% more fuel by lowering the fuel trims. Mine changes it up 17-20% easily. takes it about 5 mins to learn the idle and about 2 mins of driving to get the part throttle settled in after resetting the ecu. otherwise it does just fine.