Tuning 2g mas on 1g car

[Talon96tsiAWD]

having some issues with tuning my 2g mas on my 1g car.

specs: 91 tsi awd

safc2
255pump
FIC 650cc injectors
fmic
pocketlogger
2g mas wired to a 1g car

Ok i am currently at about -12 through -11% correction on the afc throughout the rpm range. I am seeing knock when i rev at idle, knock when i go WOT, about 10 counts, then it slowly goes down to about 5-7, back up to like 12-13 then slowly goes down. I've tried adding more fuel, the car starts cutting out, and while it cuts out the knock goes waaay up. When i lean it out the knock goes higher, i'm afraid to lean it out too much in fear of melting a piston. I'm at around 19-20* of timing advance while its doing this. a/f gauge reads first light in the rich zone at WOT. Any suggestions?

 

[Attack Eagle]

so you don't have an a/f guage, you have a blinky stock o2 reader?

 

[titogs95]

I am having sort of the same problem with mine, but that is not the point.
What I wanted to say and I want a wiseman to confirm is:
Once you put a 2G Mas in a 1G car the car itself will run about 20% leaner? so I have to raise it up to +20% on the Safc? right?

Oviously you have it covered with the injectors. If you have 660's, usually around -18%so, my point is 20% leaner and 18 % reacher, you should be about 2% or 5% of fuel correction on the S-afc. Remember rich condition can develop knock.
But what is your FPR set to?

BTW Make sure all your fuel trims are about 100% and not at 139%

for info here: http://www.dsmtuner.com/forums/showthread.php?t=58403

 

[DSM90AWD]

My calcualtion:

1.) 2G MAS flows 33% more air than 1G MAS at same Karman Hz.
2.) 650 Injectors flow 44% more fuel than stock 450s.

Difference is 12% on the Rich side so your -12% corrections seem to be proper.

Couple that with a Walbro 255HP (I assume that's what you have ) and you could be seeing an ever greater over-rich condition as your stock FPR is being overrun.

As mentioned by titogs95, check your fuel trims and get them in order first.

Other things that could be at issue are intake/boost leaks, vented BOVs , and FPR overrun that I mention above

 

[titogs95]

My calcualtion:

1.) 2G MAS flows 33% more air than 1G MAS at same Karman Hz.
2.) 650 Injectors flow 44% more fuel than stock 450s.

Difference is 12% on the Rich side so your -12% corrections seem to be proper.

Couple that with a Walbro 255HP (I assume that's what you have ) and you could be seeing an ever greater over-rich condition as your stock FPR is being overrun.

As mentioned by titogs95, check your fuel trims and get them in order first.

Other things that could be at issue are intake/boost leaks, vented BOVs , and FPR overrun that I mention above

I retract what I said and he is correct!
I confirmed the math and match wit his!
Thanks for the info it really helped me a lot too.

BTW get a FPR urgently! and set it to 38 or 40psi (depending of you car and no Vacum line attached to it)

Edit:
I have noticed something: many people say it is 20%. why theorical and practical doesn't match?
http://www.dsmtuner.com/forums/showpost.php?p=1507578&postcount=4
http://www.dsmtuner.com/forums/showthread.php?t=190368&highlight=mas
http://my.prostreetonline.com/howto/showarticle.asp?articleid=31

 

[djpast]

everywhere i have read since like 98, the 2g MAF will run a 1g about 20-22% leaner.... Kyle (kpt4231), RRE, multitudes of other sources have said the same...

i dont think that just because its 33% bigger or able to flow 33% more air, means it need 33% more fuel...

 

[DSM90AWD]

everywhere i have read since like 98, the 2g MAF will run a 1g about 20-22% leaner.... Kyle (kpt4231), RRE, multitudes of other sources have said the same...

I got my info from Jeff Oberholtzer (whom posted the in the link above). He recently got this elusive data from Mitsubishi charts, so don't think you can argue fact from theory.

i dont think that just because its 33% bigger or able to flow 33% more air, means it need 33% more fuel...

It's not just that it's bigger, it's that a 1000hz signal from a 2G MAS will be at an airflow of 33% more than a 1G MAS. The ECU reads the 1000hz signal thinking it's from a 1G MAS converts it to "X" Airflow and injects "Y" fuel based on internal fuel maps, but is your engine is now running lean because it actually got 1.33 * "X" air.

 

[djpast]

true, you cant argue fact from theory. but that doesnt translate into real life necessarily, which is why 20-22% has worked for the majority of people.

on a side note... i run a 2g mas on a my 1g...

i have 450s with a N/T FPR.

stock 450s and a turbo FPR @37psi flow ~415cc.
stock 450s and a NT FPR @ 47psi flow ~468cc.

Thats roughly 12.7% above stock, we will just say for the sake of arguement that its 13% richer. now i factor in i am running a 2g MAF. i add about ~20% to that, that comes out to roughly i need to add about 7% more fuel then stock. which is what my AFC is currently set to. I run 17psi, no knock, and near PERFECT fuel trims. this is on basically a stock dsm running stock base timing, only with a 2g MAF. When i run at stock boost levels, my wideband tells me im running a 9.6:1 a/f ratio, which is right near stock.

same exact thing on my talon before it was stolen, used 20-22% for my corrections, almost always came out perfect. *shrug*.

 

[Talon96tsiAWD]

no intake or boost leaks, checked that.

i dont have a fpr, i think thats often an overrated piece. I am running my non turbo regulator on my car which flows slightly more than the turbo one.

I was driving late last night up a hill in 5th gear cruising, and the knock started to hit. It was like 20-25, logger was beeping, then the logger read 192 knock?? I downshifted to 4th and it went away, i went WOT and no knock. Do you actually think that the fpr is being overrun at mid throttle causing knock? I'm thinking about taking the car somewhere to be tuned so i can see what the wideband reads.

 

[DSM90AWD]

true, you cant argue fact from theory. but that doesnt translate into real life necessarily, which is why 20-22% has worked for the majority of people....same exact thing on my talon before it was stolen, used 20-22% for my corrections, almost always came out perfect. *shrug*.

Agreed. In practice you also have to account for the fact that our cars have 10+ year old sensors, lower compression, boost leaks..etc Trim adjustments allow for the "aging" of our cars. I'd bet you were not at 100% LTFTs when stock.

Also by boosting your S-AFC corrections you could put yourself on a more conservative timing map allowing more boost / leaner AFRs. This is why it's always better to make these corrections at the ECU level (DSMChips / DSMLink). With mine calibrated for my 660s, 43 Base FP and 2G MAS (by JeffO), my low trim compensation is ~ +1-2%.

FYI.. another THREAD in DSM-ECU that talks of the 30% difference in airflow at same Hz output.

Sorry to tangent a bit

 

[DSM90AWD]

i dont have a fpr, i think thats often an overrated piece. I am running my non turbo regulator on my car which flows slightly more than the turbo one

If you are running the 255HP it will be overrun.

I was driving late last night up a hill in 5th gear cruising, and the knock started to hit. It was like 20-25, logger was beeping, then the logger read 192 knock?? I downshifted to 4th and it went away, i went WOT and no knock. Do you actually think that the fpr is being overrun at mid throttle causing knock? I'm thinking about taking the car somewhere to be tuned so i can see what the wideband reads.

Maybe your knock sensor is picking up mechanical noise? Worn oil pump/internal bearings, exhaust hitting the frame, worn engine mounts, noise lifters all could be picked up as knock.