AndyT

Does running 100 octane at the track on a non-chipped car have any benefits? Some say I am wasting money , others say that it's a good idea to run 100 unleaded ?

38D

Running 100 will give you more detonation insurance, especially on hot days. On a stock car, it will give absolutely zero performance benefit. Personally, I run a 50/50 mix of 93 and 100 in my 91 turbo.

Geoffrey

The 993 Turbo is designed to be run on 91 octane fuel. In stock form running premium (93 octane) is safe and sufficient. Running 100 octane does not buy you anything.

The 91 Turbo has an older CIS injection system and prvovided it has been set correctly and the engine is stock, running stock boost, the same applies.

AndyT

OK thanks guys !!

Steve Weiner-Rennsport Systems

Andy:

I'd offer some different experiences,..........

Temperature plays a BIG role in detonation thresholds (knock-sensor activity) with our 92 octane pump gas and I've observed significant power changes on a chassis dyno between 92 & 100 octane fuels on stock as well as modified TT's.

You can easily feel the difference on the track, especially on a warm day,...

pstoppani

I also use 50/50 mix for track duty, especially on hot days, to ensure heat soak is not reducing power and to prevent detonation.

AndyT

Steve long time no talky ! I've been pestering Reiser a bunch : ) I figured I'd give you a break : )My car is back in shape thanks to your advice and Joels handywork. So OK, the 100 octane issue. I do notice a difference. People are telling me I'd be better spending money on dinner than 200 bucks in fuel. We pay about 5.50 a gallon for Sunoco 100 out here in NJ. I think I hit 0.8 bar earlier and it holds too. Now on pump ka-ka I hit 0.8 bar at the fule cut off point. Andy

Kevin

If you are taking your 993TT to the track. I alway suggest 4 gallons of 100 unleaded in the tank to provide some additional headroom. These cars are sensitive to knock and temperature. If you add the 4-5 gallons in the tank your car will not feel sluggish as the laps run by..

Steve Weiner-Rennsport Systems

Hi Andy:

Indeed, its been awhile,..... I'm glad you are pestering 'ol Joel as he needs the "exercise",...LOL.

I cannot explain why others say that 100 octane fuels are a waste of money here; perhaps these kind folks do not own/drive these air-cooled turbocharged cars and have no idea how sensitive the 993 TT is to outside air temperatures, cylinder head temps, charge-air temps and oil temps.

sonny1

For track duty, there is no such thing as "too much octane", I always take my VP jugs with me, and those are filled with 117 octane gas., 106 octane Unleaded VP for catalized cars.,kind regards, Sonny.

Geoffrey

The reason that the 993TT has reduced power is not so much from heat soaking, but due to the ECU reducing timing as the intake air temp raises. The ECU is doing its job in accomodating the changing engine conditions to keep the engine safe. 93 octane in a 993TT is safe, even on a hot summer day. One only needs to plug in the Porsche System Tool and look for knock counts if you are in doubt. I have done this and has verified that the engine runs without detonation. Similarly, 993TT engines that I've done with MoTeC have also run on street 93 octane and 100 race fuel depending on customer needs and power output.

There actually is such a thing as too much octane. Higher octane fuels burn slower and timing timing needs to be set accrodingly. Additionally, there is much more to fuel than the octane rating which is the most abused number relating to fuel quality.

I realize I'm in the minority here, but I do have factual experience.

pstoppani

Geoffrey, I don't think your in the minority at all. For a stock TT, I think most are saying that improving the quality of the gas and a slight octane boost (especially for those of us that can only get 92/91 at the pump) is a good thing for track use.

I understand that there is more to fuel quality than octane, but for most of us, the only hope of improving quality is to toss in some 100 octane available at the track. I have no clue how else to get qood quality other than this; I have to assume that the race fuel at the track is about as good as it gets unless you start "home brewing"

The air temp effect on the ECU is something I hadn't considered before; I had always assumed the ECU used the knock sensors as the primary mechanism for reducing timing. I'd assume it is looking at intake manifold temps, after the intercooler; is that correct?

Thx

Geoffrey

The misconception is that the knock sensors are "the holy grail" of keeping engines safe and they are not. Just as lambda sensors aren't the holy grail for keeping air fuel ratios in line. The ECUs have tables that are programmed with values to keep the engine operating properly under all conditions. Why do you think Porsche, or any OEM for that matter spends 100,000 man hours developing the programming for these cars. They test them in the desert, they test them in extreme cold to ensure that they run properly. The knock sensor is only one minor sensor that the ECU uses.

I guarentee that Porsche tested the 993tt on 91 octane fuel on a race track under extreme temperature conditions as part of the ECU development program. Further Porsche tends to be conservative which is how companies like Protomotive can enhance the performance. Race fuel in a stock car is a waste of money.

I have over 25k track miles of data logging from my personal 911 Turbo spanning 8 years not to mention the number of turbos I've done. In fact, just this weekend I just finished up a stock 996TT GT2 engine with a MoTeC M600 ECU controlling the variable cams which will be run at the Road Atlanta club race. And believe it or not, it can be run on 93 octane fuel and made 460rwhp@.55bar of boost. HP was limited due to the stock bottom end.

Monique

I fuel with 100 whenever possible. The lower option is 98 but I note a lower power output when doing so.

My rear end Dyno says so....

Jean

Geoffrey,
I think you bring a wealth of experience in tuning EFI to this board, but I will humbly dispute some of your statements to which I do not agree.

The knock sensors are not overstated, they are THE major advantage of Motronic vs. any aftermarket EFI system out there including Motec.
In the 993, they are mainly for protection, but on the 996, they are used to push the limits of tuning to its thresholds, since they can provide you with excellent feedback, you can watch the timing that the ecu runs and recalibrate accordingly without damaging your engine.

Motec will give you better results than Motronic if you are not able to access the codes needed to have a proper calibration, however a good Motronic tuner will certainly maximize the engine's potential 10 out of 10 times better than Motec, specifically with the help of the knock sensors. Another reason why world leading teams in Porsche racing all use Motronic, not Motec, for anything other than datalogging.

Concerning the numbers you are getting on the 996GT2 engine, I have seen them written in a couple of places on the board. It makes me wonder...Todd Knighton of Protomotive who is a well respected builder, built what is arguably the fastest 996TT in the US (not to say on the planet) running 9s quartermiles with 3800lbs of weight all day, it took him about 18 months or so of programming, calibration and testing to reach the levels of performance that he did, used very efficient turbos, did massive work on heads etc..and reached only 538 FWHP at 0.63 Bar or so on race fuel on his engine dyno. How were you able to achieve better numbers with so little, 2 hours of tuning and stock internals? Something is wrong Geoffrey.
If you ask Todd, he will tell you knock sensors were fundamental in reaching these levels and safekeeping the engine.

Food for thought.