Ok... the MAF sounds incredible, but I think that a Ford Escort could beat me off the line. I have some issues to present to all who have come before me.

After 2 days of tuning, I have it pretty well dialed in. 18psi, 43psi fuel (34 resting). Here are the issues.

1. I have seen many pics of all your ARC 2's and your ***** are all right around the 12 o'clock postion, give or take a few clicks. Mine... well... are ugly. Low is at 10 o'clock, Mid is maxed out at 4 o'clock, High just above minimum at 8 o'clock, and accel at 11 o'clock.

2. When I come off idle (under load, like leaving a light normally), I have a lean condition from 1000rpm to 1400rpm, then it jumps to stoich. If I hop on it a bit, it seems fine. If I mash it, it blows the tires off of it from 2800 to 4 grand. There is a mess of torque, but after 4 grand it richens up and falls on it's face, then at 5 grand it leans a little.

3. It is like I have too much fuel under minimal load, not enough under mid load, and too much at high load. (going off the poistions of the ARC 2 *****)

4. I have dropped back the fuel as much as 22 resting and 33 in boost. When I have done that, I go lean up top, and am pretty good in the mid, and still a bit rich down low, and still have the lean coming off idle. (I have a peak and hold feature on the gauge, cool stuff, VDO special order, get one!)

5. If I go to 50 psi, I am too rich up top and have minimal power from 4 grand on, and a good amount of carbon out the exhaust.

The car is very driveable as it is, under normal driving. But when you get after it, the high is so rich that it is no fun. It just don't go like it did.

Anyone that wants to lend a tuning tip.. especially fuel pressures, please do. I thank you very much for it! The mods are in my sig.

 

Hi Perry, welcome to the world of jury-rigging the stock computer! You didn't mention what kind of chips you're using. If they are anything that was programmed for the stock turbo, then that's your problem. The stock turbo & wastegate combo created a boost-curve that bleeds off in the higher-RPM ranges. In stock trim, it was 12psi max down to 10psi at redline. If you then upgrade to AutoThority Stg2, the curve looks like 15psi max@3500 down to 10psi at redline. So the Stg2 chips are programmed for this kind of boost-curve.

With your Stg2 Turbo and aftermarket wastegate, you can probably hold any set level of boost all the way to redline, BUT the chips are still programmed for a dropping boost curve. Since the stock computers completely ignore the air-flow signal, O2-sensor and temperature sensors at full-throttle above 3500rpm, the ARC2 won't give you any tuning options in this case; fuel-pressure is your only tool.

However, since you have a rich mid-range, increasing fuel-pressure to compensate for high-RPM leanness will only make your mid-range even richer (fuel-pressure moves air-fuel curve up and down evenly at all RPMs).

I recommend doing dyno-testing where they can give you a plot of your air-fuel curve across the RPM range. Take this plot to the numerous BMW tuners who can burn Motronic chips (Dinan, Confortti, etc.) and have them burn you a custom set of chips for your particular configuration.

 

Perry,
Danno's probably right, he ususally is. But I would call and talk to Derick first. (It is an HR MAF?)
He can probably get it close enough to make it driveable.

One thing. When I upgraded my stage I to stage III, I found a vaccum line off at the throttle body. Really made a big difference in my settings. Wouldn't hardly run until I tweeked it. Just a thought..

DanD
0-60 4.8 Wooo Hooo!

 

Whoops, sorry I didn't mention that the SteveR or Milledge chips are programmed for flow on cars with big turbos. Probably cheaper than dyno-runs and custom-chip burning. Although from the looks of Farzaan's great dyno-comparison website, the CupCar chips are the way to go:
Farzaan's Dyno Day

Perry, try these adjustments:

Dan, damn that's fast! Naught to 60 in 4.8 SEC? Wow, what kind of launch technique do you use? Hope to see you over Thanksgiving weekend!

 

I had a 5.15 second (average of 3 runs) 0-60 with chips, cat back exhaust, LBE, and heavy replica 993 wheels. This was also with a full tank of gas, a 170 pound passenger, 60 pounds of junk I normally didn't have in my car, and while it was close to 90 degrees outside. Maybe I should borrow my friend's g-tech again and see if solo runs in colder weather are any faster...

 

Autothority stage 2 chips... but I do not have my stock ones (PO kept them). Should I get a set of stock and go from there, or what?

On my drive in this moring, I tweaked a little more. I started over, and now have most of the ***** back in the 11-1 o'clock postions. I and limped it onto the highway and got the high setting where I wanted it. It is still very rich in the 4-5 grand range, but overall is is good to go. I have the low and mid where I like it was well, but it richens up too easy under normal accel to about 5lbs boost.

It runs well, but just strange that I have too much fuel low and high, and less in the mid. I will check back later today.

I will do some Dyno time at some point, but no since going if I know is it not close to right.

 

Turns out I'll be at a mariage weekend with my wifie. Will you guys be driving through Montery on the run?

My launch technique used to be rev to 3k and drop the clutch. All I did was spin or bog. My new launch is a touch under 4k let the clutch catch for a split sec and then let it all the way out. Results were very little tire spin and instant power.

I'm going to try to take it to Sac Raceway this weekend (tomorrow) and see if I can learn the tree again. It's been 25 years.
Anyone in the Sac area?

DanD

 

We'll probably stay on the northern end of the peninsula.

Hey post your timeslips! So I still don't quite understand your launch sequence:

1. bring revs up to 4K
2. let out clutch and pause to let it grab
3. release clutch completely and floor it simultaneously?

 

Perry,


One of the reasons for your problem is that every 951 I have seen has a bell shaped fuel curve.These engines are alot more effecient at higher rpms then lower rpms.Because of this they actually need less fuel towards redline then they would at the torque peak, regardless of boost pressure. Even if you have 18 psi at 3000 rpms and 18 psi at 6500 rpms you will still have a bell shaped fuel curve.There is no way aound it even with a cam, bored and stroked motor,mass-flow,exhaust,etc.....The only way to change the shape of the fuel curve would be to buy some other kind of car. With the ARC2 you have..... custom mapping a chip is pointless because you are going to still end up with the same bell shaped fuel curve that all of these cars have built into their chips(or aftermarket chips for that matter). You will just pay someone to dial this curve in for you when you can do it with the ARC2

Your ARC settings are way off.Think bell shaped not linear! What I mean is that your ARC2 should have less fuel at idle, more fuel in the midrange and less fuel on the top-end.For example, the low **** should be set at -2%, mid +6% and the high -8%. If you were to plot these points out on a graph the bell shaped curve would become evident.Actually these points are very close to what most of these cars will use after being tuned on the dyno.Once these settings are dialed in the only thing left is fuel pressure.You can raise it up or down till you get correct air/fuel ratios across the rpm range.

Do not use the ARM1 as a Horiba meter because it is not! It is a simple volt meter that reads the voltage from the 1 volt 02 sensor and gives you LEDs to represent the mixture. Not exactly rocket science but it can be effective to keep you in the ball park. Use the ARM1 to give you an approximation of where you are. Use a dyno to know for sure. Hope this helps. If you need any more help you can give use a call at 619-596-6721.

Tim
86 951 http://www.speedforceracing.com

 

Thamks Tim...

I spent the better part of the week working on it and could not get it right.

Yesterday I made 3 hour trip, so i had time to play. I just so happened to lower the fuel pressure before heading out, and got it close enough to get on the highway. I got the high setting just right -6% and set the rest form there on out.

I have low -3%, mid +6% and High -6% and it is dead on, and the car moves. It is kinda like a needle in a haystack. HArd to get to the "close enough" point, but when there, very easy to tune.

I do hope to get it on a dyno and see what power I can get out of it. I am still a bit rich from 4 grand on, but overall it is excellent. Is 18-20psi safe for daily driving? I will always have it a bit rich for the longevity of the motor, since it is a toy and a daily driver at the same time.

My hope is to dyno it, max it out, then back it off a bit. We shall see.


Thanks!

 

I'm not sure I understand it either after today. Drag day was a joke. The launch pad at the track killed me. It isn't anything like the street. All day, fiddling with the launch I just got bog after bog. The only good launch was at 4500 and then I lost a vacuum line ending up with about 3psi boost.

No, I'm not telling the times, I'm wiping this day out of my mind so I can go autocrossing tomorrow. At least there, I'll have fun even if I do lousy.

The way I remember my street launch, you have it about right. The pause is minuscule. Almost like a hiccup. Oh, I don't encourage anyone else to try this. I have 2 spare trans, engines and drivelines. So my risk is very small. ( I still have to buy a clutch, or use an old one...)

DanD
(John Force I'm not)