Finally found a gas station here in Chandler Arizona which dished out 101 Octane racing fuel (or so they called it).
It ran $3.99 per gallon and in the first 40 or so miles, I noticed the following:

Boost which was running at .7 almost all summer (in the heat here in the greater Phoenix area) hit a solid .8 and touched .9!

Not sure if it is worth the added expense of twice the fuel costs... but boy was it nice to see the boost gauge off of .7 bar.

Anyone else see such a drastic (in my mind) difference when going from 91 Octane to 101 Octane?

Joe West

 

Will be finding out soon - got my GIAC today and am scheduled to dyno stock and the 93 on tuesday then the 100 program on wednesday

 

I always run a 50/50 blend of 91 and 101.

FWIW, there's a gas station on Chandler Blvd, West of the 10 about 2 miles, right next to an autoparts store. Thought I'd mention that just in case it is NOT the one that you already know about. It always helps to have a few alternatives in case one place is sold out.

 

Would a blend of 91 & 101 be better than straight 101 for daily driving? Someone mentioned that straight 101 doesn't burn as quickly and can bog down the car...Humm???

 

Cool... Would like to see the results

 

Well, the 101 certainly would be less likely to preignite. But, I've never heard of it causing a bog.

I run the blend (actually 100/91) because my main EVO/GIAC program is for 94 octane. The blend gets me 95.5 octane, giving me a slight margin for error, which, if nothing else, gives me piece of mind, with the heat around here.

 

Joe -- sounds like you may have an inaccurate/optimistic boost sensor if you're seeing .9 bar consistently with a stock Turbo. It's my understanding that Porsche programmed the stock Turbo ECU to reach maximum boost of .75 bar -- typically down low at around 2500-2800 rpms and then it tapers off rather quickly to .6. That's why most people only see .6 at higher rpm's (when they glance down at the boost gauge at the end of their run) and the occasional .7 bar. Brief boost spikes showing more than .7 bar (usually as you let off the throttle) are possible, but the "best " gas in the world will not cause a car to produce more boost than is programmed into its ECU.

Just my 2 cents FWIW.

 

You can also get a flawed reading if you lift off the throttle abruptly. Is the .9 bar steady state as you keep the throttle nailed (and don't lift) until you shift at or near redline?

 

In my original post I said it touched .9 I guess I should have been more accurate. I get a solid .8 (up from a solid .7) and a blip at .9 which almost instantly goes back to .8

The factory manuals I have spec boost at .8 for a standard turbo, they unfortunately do not spec standard deviation around the .8 so I have no idea whether a momentary .9 is abnormal or not.

Keep in mind that we are dealing with 100+ temperatures here in Phoenix, and I am absolutely positive that ambient temperature plays a roll in how much of a difference you will see in boost performance as a function of octane.

At WOT, peak boost is appearing before redline and actually rolls off as I approach redline. I didn't note the numbers... just the trend.

Joe

 

The only way I know of for the Turbo engine to "know" what octane is in the cylinder is through the knock sensors, and it's when the octane is too low. If the knock sensors detect pinging the timing is set farther from top dead center. If no knock is dectected, the engine sets the timing closer to top dead center, to the timing where 93 octane is optimized.

The higher the octane the more retarded the gas is. To get the power out of higher octane gas the spark has to be delayed, relative to lower octane gas, to allow for more compression of the charge.

Octane shouldn't have anything to do with boost.

 

Joe -- I agree wholeheartedly that heat/high temperatures (as well as other factors) will affect a Turbo car's ability to produce its maximum programmed boost, and that higher octane gas will help our cars reach their programmed potential. Porsche programmed the Turbo to produce maximum power with a minimum octane of 93 (USA). Unfortunately, we both live in states with maximum 91 octane gas unless we go for the racing gas mix.

I've attached a photo of the boost curve graph (#1) for a stock Turbo -- thought you might find it interesting. Take note of the max. boost at 2500 rpm and the roll off as rpm's increase to a max. boost of barely more than .6 bar at redline. You can see that Porsche left a lot on the "boost table" with which after market chip tuners can play.