PCA SDR

I was at Buttonwillow DE events yesterday and today in my '06 Boxster S. I filled my tank (completely) with 100 octane gas at the track and I really feel it made a power difference. Does anyone have any sound opinions as to whether it is harmful to the car (catalytic converter, etc?) to use 100 when at track?

Don Costello

As long as it was 100 octane unleaded fuel, it won't harm your car, just your wallet. You shouldn't use race fuel with lead additive in your Boxster, though--it is not good for cats or O2 sensors. As far as adding performance, you will only make more power if the fuel you were previously using was triggering the knock sensor and the engine timing was retarded as a result.

TT

I agree that Tom is right. Also the late cars seem to like about 93/94 fuel. Adding more + then nessary to prevent knock actually reduces total power. Might try mixing that with lower fuel to get you closer to my numbers for stock build car. Or just add a octane booster to your 92 fuel..

There is an informative discussion of fuel quality and octane ratings/boosters, as well as detonation and timing, written by Steve Weiner, a very well-respected Porsche tuner, on the Rennsport Systems site, including a table for mixing 91 pump gas with 100 race gas to achieve different octane levels in the blend. I don't know what the ideal octane level would be for the newer waterpumpers like your Boxster, but I would prefer mixing such a blend of race gas over using any of the octane boosters commonly available, as they seem to have limited effectiveness and possible unpleasant side effects. I can't imagine that your stock motor would need more than a 95.5 octane rating to achieve optimum performance for DE events, and that could be achieved with a 50/50 blend of 91 with 100 octane unleaded, saving you some $$$ over a straight 100 fill.

YMMV,
TT

Thanks for the info.

I have seen it mentioned in similar discussions here that the computer on P cars takes about a tank full to full to properly adjust to a higher octane So in order to see benifit you would need run 100 octane before arriving or at least fromn the time you arrived at the track on Saturday morn.

On the more modern cars, the engine management system will advance the timing when it senses the higher-octane gas. However, it seems to take a while. I don't think you need to burn a full tank to get a benefit, but you do need some driving time for it to adjust.

I occasionally add 100 octane (our local Mobil station in Rancho Santa Fe has it at the pump, as well as 95 octane). I find that after 50-100 miles of driving, the car seems to run smoother and have more pep. Theoretically, you might get an additional 2-3% HP from the higher octane.
I don't think you will get any immediate boost right after you fill it at the track, but if you are doing DE sessions, I would think it would be adjusted by the second session.

One thing I encountered - if you run all your 100 octane gas out of the tank and then refill with the 91 octane available at most stations, you *may* get your Check Engine light to come on. Just like it takes a little while for the engine to adjust to the higher octane, it takes a little while to adjust down, and meanwhile you might get some excess unburned gas going through, causing the light to come on. If that happens, it should reset within a day or so. Or, you can mix some 91 octane in while you still have some 100, and give the engine some time to adjust.

Al lot of computers go in to "learn mode quicker if you disconnect the battery for 10 plus mins before. I do not have first hand experience, but have read about it..

GT3 owners manual I looked at specified 93 R+M/2 octane,presumably required for full power rating of engine. I wonder how many late P cars show same in manual for car.

93 is also recommended for the Boxster, but where do you find anything higher than 91 (except for the 100 octane, which is a bit pricey to use every day)?
All the newer cars would *like* 93, but will adjust and run with 91, no doubt with some loss of power due to the retarded timing to avoid pinging.

Kim Crosser wrote:93 is also recommended for the Boxster, but where do you find anything higher than 91 (except for the 100 octane, which is a bit pricey to use every day)?

You would find it in Europe, I think. In CA, good luck! The best thing to do would be to mix 2 gal. of 100 octane with every 7 gal. of 91 you put in the car to make a blend of 93 octane in the tank. Quite a hassle for every fill-up, though it might be worth it around track weekends. Depends on if you really want that little extra horsepower...

TT

ttweed wrote:

Kim Crosser wrote:93 is also recommended for the Boxster, but where do you find anything higher than 91 (except for the 100 octane, which is a bit pricey to use every day)?

You would find it in Europe, I think. In CA, good luck! The best thing to do would be to mix 2 gal. of 100 octane with every 7 gal. of 91 you put in the car to make a blend of 93 octane in the tank. Quite a hassle for every fill-up, though it might be worth it around track weekends. Depends on if you really want that little extra horsepower...

TT

I thought that there are a lot of states that have 93 at the pump, a friend just returned from Michigan where it was at the pumps. Didn't you note that on your recent trip Tom?

The guy who bought my 911 Cup recently just sent me this email from NorCal:

"Finally I had a chance this last Saturday early morning I took the car out to warm it up and get some High Octane Fuel, at the pump I had a choice of 94, 96, 98 and 100, I got 94, do you recommend higher grade?"

So, not all bad in all of California.

Bob, that sounds like a track with that many high octane choices.
Most Pump Premium is 93 East of the Rockies. From Colorado throughout the SouthWest, most of the Pump Premium is 91. In Washington State, Premium is 92.
I believe in Colorado, it has something to do with the altitude and cars not needing the higher octane (Regular is 85).
Out here, it is mostly due to politics!

Actually Chuck it was a regular gas station in Sunol California just east of Fremont on the San Francisco Bay.

Those are all unleaded selections too.

Plug address into Google Map to see where.

Sunol Super Gasoline
3004 Andrade Rd
Sunol, CA 94586