Imola_Tip_Soul-Ja

14:6 @ IDLE. I'm feeling pretty good, but I bet I can get some more HP (and Torque) out of this fuel curve. Just need to find some more sweet spots (in my fuel curve) while doing my street version of a dyno run.

My 951 seems to like the changes that I've made so far. At least I haven't blown a head gasket (common problem on 951s running hot (lean)), crosses fingers. Probably need to check the ground on my wideband 02 sensor, it's getting kinda jumpy (blinking on/off) in this cold weather.

PSmalls::DoggieStyle

I agree wholeheartedly with you that more homebrew guys should at the very least have a wideband 02 sensor (I'm guilty of not having one, but that might change. Then again, I've been saying that for a long time).

I can see your point of view on RPM specific tweaking being benefitial as well, but Lemmi has proven to make very nice power. Maybe there is more left in it with RPM specific tweaks, but just not that important (to me personally, happy to get in the ballpark). I'm glad others are willing to further push the envelope, though. I'm, self-admittingly, a wusspod when it comes to going for insane power. I'm only willing to go so far and do so much. I live vicariously through those of you willing to get that extra mile.

Regarding your car, may I ask why you are *richer* (edited) in the lower RPMs and then leaned out a little up top? I'd expect it to be the other way around with ~13 down low and ~12-12.5 in the mid range/top end.

Imola_Tip_Soul-Ja

are good ones.

First, I decided to got to Stage 3+ on my Porsche (1986) 951 because it's my "project car", the S4 is my daily driver (or was until I blew my second set of K03s this past October). I bought the 951 in 1996 and kept it stock until about 3 yrs ago. I went to Stage 2 (chip, boost gauge, EBC) and then decided to go Stage 3 last winter. My Stage 3 project was finally completed this October (around the same time that I blew the passenger side turbo on my S4 - again!).

Anyway, I've been trolling RENNLIST for years (just like AW) and from reading the 951 forum, I noticed that MOST of the high HP guys who were still using stock internals (pistons, crank, cams, etc.) were using "piggy back" fueling computers and fairly sophisticated fuel management software (like MAFterburner). Use of wideband 02 sensors is pretty much universal in the 951 world, starting at Stage 2.

So, with the significant upgrading of my 951's turbo, IC, fuel rail (replaced stock), and the addition of a MAF set-up (stock 951 set-up uses a Vane Air Flow Meter - 1980s technology). The need for a wideband 02 sensor (AEM UEGO) and fuel management software/computer (MAFTerburner) was a no brainer. Since the MAF set-up flows more air than a AFM set-up, the need for sophisticated fuel management becomes more of an issue for Stage 3/3+ 951s than S4s, in my opinion.

Before purchasing MAFterburner, I had NO experience with the product, or ANY fuel management product. The vendor (Lindsey Racing) that sold me MAFterburner provided a base map (on its website) to get my 951 started, but from my experience, it's too LEAN. I contacted Lindsey (tech support is included) and they did develop a FATTER map (one of my previous posts contains the data points for this map), specifically for me.

Anyway, the new map was still to LEAN for my set-up, and I began to get enough REAL WORLD experience during my MAFterburner runs, that I took the plunge and started developing my OWN fuel curve (using the Lindsey's new map as a baseline).

From my research on RENNLIST, and other 951 boards, the best AFRs for 951s range from 11:5 thru 12:9. The lower the AFR (RICHER), the more TORQUE that is yielded from that specific point in the fuel curve. Conversely, the higher the AFR (LEANER), the more HP that's produced at that point in the fuel curve. So, I've tuned my fuel curve to produce greater torque at the lower and mid-range RPMs (lower MAF voltages), and greater HP at the upper RPMs (higher MAF voltages - closer to 5V).

While on boost, as long as my AFR stays @ 12:9 or below, I don't run this risk of blowing a head gasket. Some 951 guys would say that 12:9 might be pushing it, because many 951 guys look for an AFR of 12:7 - 12:8 when on boost. Any AFR above 13:0, you are asking for BIG trouble, even at 951 stock (12 PSI) boost levels.

I stumbled upon the significance of MAF voltages and their impact on fueling while trying to work through some of my tuning hiccups. Once I obtained a basic understanding of how important the MAF voltage is to Bosch motronic (ECM) fuel maps, I started playing around with MAFterburner's MAF calibration function (it manipulates MAF voltages between the MAF ssensor and the ECM).

By moving the slider bar negative (MAF voltages), I noticed that my fuel curve became LEANER, without me making any specific, or gross fueling changes. When I moved the slide bar positive, my fuel curve became RICHER, again without me making a any specific, or gross fueling changes.

The impact of making changes in MAF voltage is similar to Lemmi in concept, but I am NOT making any % changes to my fuel curve, I'm only manipulating the MAF voltage that the ECM interprets. The ECM interprets MAF voltage as the EQUIVALENT of AIRFLOW measurement.

Note, MAFterburner does have the ability to make gross % changes to the fuel curve (just like Lemmi) in increments of 5% (richer or leaner). I prefer to make my changes at SPECIFIC points in the fuel curve (which generally are at 400 RPM increments).

That's the beauty of MAFterburner, I can manipulate MAF voltage, monitor AFR @ specific points in the fuel curve, tweak fueling at specific points in the fuel curve, or make gross % changes to the fuel curve in 5% increments. It also gives you the capability to do data logging of AFR at specific RPMs.

After the experience with my 951, I'm sold on MAFterburner, and plan to use a non-951 version of the software on my S4 after my new (K03/K04) turbos are installed. I will then tweak the GIAC-X fuel curve. From my readings of the FAQs on MAFterburner's website, it should be compatible with the S4's Bosch motronic ECM and MAF.

PSmalls::DoggieStyle

This part interests me:

"The lower the AFR (RICHER), the more TORQUE that is yielded from that specific point in the fuel curve. Conversely, the higher the AFR (LEANER), the more HP that's produced at that point in the fuel curve. So, I've tuned my fuel curve to produce greater torque at the lower and mid-range RPMs (lower MAF voltages), and greater HP at the upper RPMs (higher MAF voltages - closer to 5V). "

I've always been under the impression that you wanted a leaner mixture down low to decrease spool time. I've never heard that part about richer mixtures resulting in torque and vice versa. Every S4 I've logged or seen logs from was much leaner in the low RPMs where spool-up takes place. Interesting to say the least.

lemieux@curbside

richer down low=better timing for less air going through=more tq maybe ..

Imola_Tip_Soul-Ja

My AFR at idle is pretty close to stoich (14.4 - 14.7). The median on MAFterburner's fuel curve is zero (0), and at idle (MAF voltage range 0.10 - 0.50),I'm pulling back fuel in the range of -24 (in MAF voltage range 0.40 - 0.50) through -30 (in MAF voltage range 0.10- 0.20) to achieve a (near) stoich AFR.

As my car accelerates (and MAF voltages increase), I add fuel to specific MAF voltage ranges (which equate to specifc RPM points). After stoich, the next fuel cell (MAF voltage range 0.50 - 0.70) equals zero ( neither rich or lean) on my fuel curve in MAFterburner.

This gets me an AFR of approximately 12:4 until I shift (to second), then my mixture goes LEANER (13:5 - 13:7). I have NO spool-up problems between first, second, and third gear. The car pulls like a freight train, because the mixture is RICH, but not TOO RICH (which would be an AFR of 11:0, or lower), thus giving me more TORQUE in that part of the fuel curve.

Believe me, you can tell when your fuel curve is TOO RICH, the car is SLUGGISH as HELL. Been there, done that, when I first tried developing my own fuel curve in MAFterburner. That's where tech (fuel tuning) assistance from the vendor, and trolling posts on RENNLIST came in handy.

Once my 951 is in second gear, I get an AFR of approximately 12:3 - 12:7. I'm trying to raise the lower number to approximately 12:4, or 12:5, to yield more HP in this part of the fuel curve. Thus, I'd like to have a tighter AFR in second gear, somewhere between 12:5 - 12:7 (giving up some TORQUE, but gaining some HP).

Currently, I'm tweaking the fuel cells in MAFterburner (via MAF voltages) that equate to the RPM range for second gear to get a tighter AFR. I'm also doing the same thing for third gear. In third gear, I'm trying to get an AFR of approximately 12:6 - 12:9 for maximum HP when I go on boost.

Anything above an AFR of 13:0 is waaay too hot for a 951 when it goes on boost, the end result is usually a BLOWN head gasket.

I'm basically doing the same thing that you would do on a dyno, but I'm using MAFterburner and a wideband 02 sensor, then doing street runs (like we all do with VAG-COM).

From my REAL WORLD experience, a lower AFR (but not too low) in the mid range (first/second gear) of the fuel curve yields greater TORQUE (car pulls harder). If you lean out the curve in the mid range, the pull is not as hard, been there - done that.

Now, keep in mind, my S4 (Tip) might behave differently than my 951, that's why I can't wait to see what happens when I install MAFterburner on my S4. Since both cars use BOSCH motronic programming, I expect the results to be similar.

MAFteburner will work on any car that uses BOSCH motronic (or Ford ECM) programming. The key is too have a MAF sensor that produces voltages between 0-5V, which the Bosch S4 MAF sensor does (I'm guessing that the Hitachi and RS4 MAF sensors also produce voltages in the range of 0-5V).

Hope this makes things a little clearer.