KC911

I'm thinking about purchasing a used Autothority MAF system and have a question for the more knowledgable folks here. Will this 'require' having my car dialed in using a dyno, etc., or is it likely that the supplied Autothority chip is a "one size fits all' chip that will suffice. I always run 93 octane, have a euro premuffler & sport muffler, so I'm curious as to whether the Autothority chip takes these factors into consideration (...I'm assuming it doesn't) or if some dyno tuning is in order. I've read through the archives, and would love to hear some of the pros (or anyone elses) opinions! Thanks!

Keith
'88 3.2 CE coupe

Peter Kelly

I have an Autothority MAF and my experience was that the chip that came with it was mapped very rich at WOT throughout the RPM range, and particularly from 5000 RPM on up. I was seeing 11:1 AF ratio above 4800 RPM or so!

I have fine tuned my fuel map considerably, and now have a 12.8:1 AF across the whole rpm band at WOT.

To answer your question, to get the most out of it you should plan on some dyno time with a dyno shop that has a wide band AF meter AND ability to hack motronic chips.

Chuck Harmon

I might suggest you check out
www.911chips.com

rbcsaver

I second Chuck's suggestion.
regards,
Steve

KC911

Thanks Peter! How did you accomplish the fine tuning of your A/F ratios (i.e. were you dialing it in via one session on the dyno (tweaking the chip between runs), or was it dyno'd on separate trips), and how difficult was it? Chuck and Steve, thank you also, and you can bet that I will see what Steve Wong has to add about this. BTW, I've been running one of Steve's chips for a few years and am a happy customer. All other feedback is still welcome...thanks guys!

Keith

Peter Kelly

I have a wide band AF meter and a full data acquisition system permanently installed in my car. (since I am in the Racing Data Acquisition business it was quite affordable to do!). I check/adjust/fine tune my map almost every session at the track.

KC911

Thanks Peter...but what about us weekend hacks ? Obviously, the analysis/tweaking you have done over time is a preferred method. How 'close' do you think someone could dial it in by simply looking at the A/F ratios from a single dyno session, or is the monitoring of the A/F before & after the chip tweaks essential to getting it 'right'?

Steve W

These setups as they come from Autothority are mapped extremely rich - typically 10:1 throughout the entire WOT range. The net result is you will loose 20-30 hp, although the increased low/mid part throttle response from the rich mix will make one think the car is quicker. It's as if the manufacturing specifications of the MAF changed some time years after the original chips were developed back in the early 90's, and the chips were never remapped.

The meters were purchased from and separately manufactured by Pro-M, and each was individually hand curved to a desired specification. Pro-M filed bankruptcy and is now out of business, but the hand curving is responsible for the wide variation in flow measurements from one meter to the next. I have measured 1 AFR differentials from one meter to the next on the same car, although the voltage vs. air flow data from Pro-M showed they were supposed to be identical. The only way these meters work properly is to custom remap the chips. This requires AFR logs from a dyno, or LM-1, and it can take at least a couple of iterations to get it right. I have done it quite a few times for different tuners and clients, but its something I try avoid doing because it's very time consuming.

The stock AFM is actually very good, and combined with good modified factory software, is very accurate, smooth, and refined. If you take a car with a fully optimized AFM chip custom tuned to the motor, and compare it to a fully optimized MAF setup and chip, the difference is actually very minor. If you really want to maximize power from your motor, it is better to provide your chip tuner an AFR log of your car and have the chip custom tweaked. 911 motors have huge variations in flow from one motor to the next, and I have see more unexplained inconsistencies when mapping these motors than I have seen consistencies. This I attribute to inherent tolerance variations between engines, and/or off tolerance Motronic sensors, flow meters, and DME boxes of these aging cars.

KC911

Thanks Steve! I didn't know that you would see this thread, but I'm glad you did as I was going to contact you anyways. Hmm...I'm very much a novice at this stuff, but I've been under the impression that a 'good' MAF system was superior to stock (...again, like many things, not a 'night & day' difference, but offering slightly better throttle response, etc). Steve, if you recall, I had my car on a Mustang dyno quite a while back (I was doing a chip comparison between your chip vs. stock), but we were not logging AFR that day, so that's no help. It sounds like maybe I need to obtain some AFR data in order to see where I stand now (while using your chip) if I want to pursue this. Thanks again for posting!

Keith Craver

84_Carrera

FYI, from readings on the web, the Pro-M employees are / have reopened under a new company, I have the link at home. Granatelli really put the screws to them, forcing them out. The Pro-M MAFs used to be REALLY good, especially since you could have them tweak them individually, but you could definitely end up with a MAF that was way out. I'm speaking from other-car experience here, BTW. I told Pro-M years ago that their SHO injector size data on their website was off (they had 27 lb-hr, and it's actually 24 lb-hr for the V6's), but they insisted I was wrong. Yeah, I've only owned ten of them, and work on these cars professionally every week buddy.

With ANY MAF change, I'd always recommend doing it on the dyno w/ a wideband O2 setup, unless you've got your car so-equipped already. There are piggy-back adjusters like the MAFterburner that you can use to adjust voltage signal on the fly, but I have no 911 experience with some of those voodoo calibration boxes (have seen them on Ford setups that come stock w/ MAFs - some worked as intended, some made it worse).

Peter Kelly

Steve:
Isn't it true that all of the voltage vs air flow variations in a Pro M are a moot point at WOT?

Steve W

Keith, no problem - if you ever obtain an AFR log, just email it to me for fine tuning.

Peter, as you may have noticed, the output voltage of the MAF is never ignored at WOT. The slightest variation in output voltage affects the afr not only at part throttle, but also at WOT quite a bit, and should not be ignored if tuning for maximum power.

Peter Kelly

[QUOTE
Peter, as you may have noticed, the output voltage of the MAF is never ignored at WOT. The slightest variation in output voltage affects the afr not only at part throttle, but also at WOT quite a bit, and should not be ignored if tuning for maximum power.[/QUOTE]

Now I am confused. Your web site states:

(http://www.911chips.com/fuelmaps.html)

"Full throttle is signaled to the DME by the activation of the full throttle microswitch at the throttle butterfly. At full throttle all input sensors are ignored, including the air flow meter and the O2 sensor."

Steve W

Good catch - that statement applies to the AFM sensor and probably should be qualified. The factory AFM sensor bottoms out by 5000 rpm at full throttle, earlier for larger displacement motors such as a 3.6, and outputs a max voltage then of 4.3 volts. By then, the AFM sensor is no longer a reliable source of airflow information, and the full throttle fuel maps are the primary source of reference for fuel quantities. However, with the MAF sensor, there really is no limitation like this, and as the air flow rises, so does the output voltage - all the way to redline, and the rising voltage continues to influence the full throttle fuel calculations. That is why you noticed an 11:1 AFR at WOT on your car - you can't change the MAF sensor curve specifications without influencing all your fuel maps

Peter Kelly

I simply change the fuel maps to get the A/F ratio I want. BTW, I have plots of WOT MAF voltage vs RPM from my car in case you are interested. They are pretty darn flat from 6000 RPM on up. (I run my motor to 6500 or so)