When to hack the MAS

[venom2097]

I've looked around the site and can't find a steady ans.
Most people seem to say only after bigger injectors.

What I want to know is can/should I hack mine? I have a bigger fuel pump, 16g, and a AFC. no injectors yet.
If I do hack it what can I expect to gain from doing so, and is it worth the trouble at this stage? If not why?

 

[L2RTSiAWD]

If you have a 2G there is no need to hack the MAS all it will do is cause problems. You are fine with a un-hacekd MAS. Just get the proper fuel mods(injectors,pump,and AFC).

Later,

 

[IPT]

You need to hack the MAF sensor to put off fuel cut. If you are not hitting fuel cut I don't know that I would worry about it. One other time to hack the MAF is when it starts to mis count the incoming air flow. IE high boost pressures or big turbo.

 

[venom2097]

How do I know if it is mis-counting the air flow?

also if I don't hack the MAS won't the ECU just counter-act the afc...
ie.. I lean it out, the ECU will then richen it, or I richen it and the ECU will lean it?

 

[L2RTSiAWD]

The MAS only starts to mis-count when you in the 500hp range. No it won't conteract becasue the AFC modifies the air-flow count before it hits the ECU.

Later,

 

[Quacylla]

"The MAS only starts to mis-count when you in the 500hp range. No it won't conteract becasue the AFC modifies the air-flow count before it hits the ECU. "

What part of your ass did you pull that from? And what are you talking about 2G MAFs for he has a 90 GSX?

If you have an AFC then you don't hack the MAF to avoid fuel cut. You can achieve the same thing by just reducing the airflow reading with the AFC.

You hack the MAF to push back MAF overrun. MAF overrun is where the volume of air going thru the metered section of the MAF is too great. What happens is the Karman Votex Street starts to break down and no longer properly reflects the volume of air entering. The MAF then starts giving an inaccurately low count to the ECU... and it's irratic. The ECU then only supplies enough fuel for this low count and so your a/f ratio falls off.

How do you look for it? Well it's easiest if you have a logger. You do some wot runs in at least 3rd all the way to redline. Look for a drop in the airflow curve that does not correspond to engine speed. You can also do this by graphing the airflow on your AFC. Watch for any small or large drop from the peak value before you let off the gas. The airflow should keep increasing as the engine speed does... if it doesn't then you've got MAF overrun.

MAF overrun hits pretty early on unhacked 1G MAFs and should be watched for as early as 250 hp. Then it's time to start hacking your MAF to make more of the total air go thru the unmetered section and less thru the metered section. This will postpone MAF overrn.

If this causes you to run too lean just up the airflow value at the AFC to compensate.

If you don't have an AFC then hacking the MAF can help you get around fuel cut, MAF overrun, pre-fuel cut and get you some power by leaning out the a/f ratio. I'm currently doing a web pag on this and will post it up when done.

MAF overrun is very dangerous and needs to be dealt with. Another good option is to upgrade to a 2G MAF as opposed to hacking. The 2G MAF flows 20% less air thru the metered section then the 1G and it has a higher overrun threashold.

 

[venom2097]

Here is a ruff drawing of what my AFC graph looks like through 2nd gear.

So is this a normal looking graph? why the vertical line before the shift?

 

[Boosted_TSi]

What boost level / turbo are you running on your '99? That dip at about 5900 rpm looks like it could be a miscount on your MAS, or it could be something else... Please post your other mods, as that will aid in diagnosing that lil dip. Also let us know what your settings on the S-AFC are, both hi and low. I think it may also be possible that there is a small problem in your settings...
Does anything noticable happen at that time? aka: a short stutter, sudden surge in power?

Eric McCabe

 

[venom2097]

Boost level is 17-18,16G,intake, 3in exhust,hks bov,xtrem mbc, walbro255,afc,A/F gauge. I think thats all the major parts.

The car will accelerate good up to ~4.5-5000rpm then the car studders or hisatates, the exhust note also changes to a farting type sound, at ~5800-6000 the car will start to run fine again. The studdering ALWAYS starts about 14-15psi of boost, rpm range unkown.
If exact #s are needed I can graph rpm vs karman and post.

I havent really tuned the afc yet, waiting on injectors+EGT.
current afc settings:
low left at 30% , 0 all the way
high set at 80%, -10 all the way(trying to counteract the fuel pump xtra pressure)
I've tried it at -1 through -15 trying to fix it, don't want to go to crazy with no EGT or logger.
It did this before adding the AFC also.

 

[Quacylla]

If you rpm was a smooth curve the airflow should be a smooth curve. Something is happening at 3 different points on that graph. It could be a number of things. I'd love to have a look at a datalog of airflow/rpm/throttle position/o2 sensor/o2 trim/timing/knock.

You certainly have the mods to be worried about MAF overrun. If you can't get your hands on a logger then give us a rpm vs airflwo chart with peak number values included.

 

[Enigma_Man]

Quacylla, the thing under the guy's name says he has a 1999 GSX, not a 1990.

 

[Quacylla]

My bad! My very bad! Somehow with the fonts I read 1990 GSX. I take it all back.

 

[hdswanny]

don't take anything back, all that info was good!!
it makes people like me understand a little more about tuning. Let us know when you have tha page up!