champignon

Hi Chris,

Here are my 91 Octane Excel Logs. Please note that I did not have a co-pilot in the car so I had to activate the logging from the side of the freeway onramp, and then had to drive a bit until I could get off the road to end the logging. There is a lot of extraneous data, but you can probably isolate out the actual pulls. There may be a run in this set where I did not succeed in getting up to 6000+ rpm, due to other traffic getting in the way. I'll post the 93 logs in the next post.

Thanks,

ken

91_1.xls

91_2.xls

91_3.xls

91_4.xls

91_5.xls

91_6.xls

champignon

Here are the 93 Octane Logs. This is using 91 gas and adding enough Torco Accelerator, according to label directions, to get to 93 Octane. All runs were done on the same couple of stretches of Interstate 84 just slightly East of Boise, Idaho, at an elevation of around 2500 feet, and more or less level. It was hot, very hot, and I had the A/C on, which may not have been the best testing circumstances.

Thanks for any comments you may have. I did look pretty closely at the data, such as it is, and I couldn't find any associations on any of the parameters that held up consistently between the 91 and 93 Octane runs.

93_1.xls

93_2.xls

93_3.xls

93_4.xls

xmaciek82x

Any of those logs done at WOT? I don't see a TPS column.

If you are just cruising around then your car is in closed loop and your o2 sensors do majority of the a/f calculations.

Being in open loop and having a 93 octane tune with 91 octane tune is when you should be somewhat concerned.

Why not spend the $600-$900 and get a 91 octane tune so you can enjoy the car without worrying about it?

I never tuned a 996tt myself but did tune many Evos in the past and I would not run a 93 tune on 91 octane.

champignon

I certainly floored it during the brief runs from ~2000 to 6000+ RPMs, but you'd need to scan through a bunch of garbage beforehand, unfortunately. I did make some edited PDFs with the files but the headings didn't print out so posting them would make them hard to interpret.

Of course, there are degrees of "flooring it," in that I'm not keen on having an accident just to get a Durametric log done. So I probably could have done more of a WOT type run had I not cared about the risks of other vehicles getting in the way.

As to getting a new 91 tune, I could do that, or I could spend a small fraction of the same amount every year (for how much I will drive this car, which is only one of a number in my little collection) on the Torco additive. If I was going to put lots of miles on the car as in using it as a DD, then I would really be considering either going back to stock or buying a new tune, but this car is going to sit all winter long basically unused, and in the summer will have weeks on end where it sits on a float charger and isn't being used at all, when I am driving other cars.

Thanks.

911mhawk

Logging with the Durametric and a Surface/tablet is better than a big laptop but still PITA and you get a crappy sample rate anyway. If you're not going to drive the car much, but plan to keep it, spend the $1k on a tune, you'll sleep better, can move on to something more interesting and won't have to mess with stinky cans of additive.

If you don't plan to keep it long term, the next buyer will be happy to get one with a fresh tune from a vendor that uses log files to ensure your car is running right.

If the plugs and coils haven't been done, I'd do them, install a new MAF and pre-cat o2 sensors, pressure test the system then pull some log files.

Or, just Torco it up once in a while and don't worry about it...

champignon

The plugs were done 2X, and coils, 1X, in the last 12,000 miles. The last time was at least plugs, 2,000 miles and 8 months ago.

I've been driving the car a lot the last few weeks, and just put it up on a lift at my house. Time to drive something else. Today I drove my 1M, 175, mostly highway, miles, and it was a pleasure. I have a couple of other neglected cars that need a bit of use before I'll drive the 996TT again, likely two to four weeks from now.

It's a hard life, but someone has to live it :-)

Thanks for your comments.

T10Chris

Thanks for posting. Once filtering out the excess, it is pretty clear to me, but take this with a grain of salt, please- we don't have enough data points for me to get a complete picture so there are some assumptions being made and therefore this should be taken as my opinion vs fact. I'll give you the evidence and my methodology first:

Without having throttle position and speed readout I can't confirm a couple of things, but I am assuming these runs to be 100% constant throttle on the pulls that went north of 6K rpm and as you said, same stretch of road so I'm assuming none were done ascending or descending a noticeable grade, or if so that at least is a consistent grade since it is the same place. If there were steep hills, different gears, or throttle modulation done mid-pull, this invalidates some of my assumptions.

First, I tried to find graphs that have similar engine load at a particular RPM point. Engine load is a rough calculation of the volumetric efficiency of the engine and can give a general idea of the power output/torque curve. The thing that is very telling is your 93 octane pulls typically have a higher engine load, and a broader range of high engine load. The 91 oct pulls are lower and more peaky when plotted vs rpm.

Second, I am looking at what the MAF is seeing. The MAF is consistently seeing higher numbers, indicating more airflow past the sensor, on your 93 oct tunes. More air = more power.

Your injector duty cycles are higher on the 93 oct tunes. This is an indication of higher fuel consumption, which correlates with the higher air flow readings by the MAF.

Lambda readings (air:fuel ratio) are in line with what is expected. You're actually running slightly richer on the 93 oct.. and the ratio is also more consistent through the duration of the pulls. Inconsistent A:F ratio is a sign of the car compensating for something and needing to adjust.

Finally, your target boost pressure. Your car is commanding a higher boost pressure, and achieving higher boost pressure, on the 93 oct pulls. The computer is seeing something different between the 91 and 93 oct that is telling the logic in it that it is ok to ask for more boost without hurting the engine. The higher boost pressure and request boost pressure would be why the MAF is seeing higher airflow readings.

My opinion? Your car runs better on the 93. Im sure this isn't a shock to anyone, of course car runs better on higher octane. I imagine if you had speed plotted with the time, the acceleration would be quicker. From what I am seeing, it is certainly running safer on the 93 oct.

Is the car hurting itself on 91 oct? I cannot say. The computer in these cars is robust and can compensate for a lot of variables to protect the engine. It is doing less compensating, and allowing more consistency, airflow, and power with the 93.

Here's what I would recommend if I was a tuner- I would stick with your 91+Torco blend, or get a few 5 gal drums of MS109 and blend in with tank to get 93ish.. Whatever you are more comfortable with/cheaper. The MS109 probably be healthier in the long run because it isn't leaving manganese deposits. If you are in a bind and have to run 91, I wouldn't fill up on it and I wouldn't push the car on it. The performance vs cost of a retune to 91 seems kind of dumb to me when there are cheap and effective alternatives to boost the octane to the acceptable range. Why spend hundreds of dollars to make the car perform worse when you can spend $20-30 per tank and have it run like a champ?

Hope this helps, and again, just my opinion, your mileage may vary, follow my advice at your own risk, etc etc

Chris.