ON TIME

Hi there, 100 %octane for $5.25. vs 91% octane for $2.25. why should i use 100 octane? How often should use 100% octane. Will the car run better? Can i mix them

sweanders

It depends on what your car is optimized for, you have no need for higher octane than what the manual says if it is stock.

Bruce SEA 993

Hey Kim,

The inside of the gas flap and the manual lists 93 octane. I usually run 93 to 94 in the car and the butt dyno definitely has the engine running smoother and quieter. The throttle response is also improved.

When I was driving in Montana where I could only get 92 I noticed a reduction in power and response. Perhaps my car is more sensitive to changes in octane or I notice it more. Although I could tell in my Audi V8 when I upped the octane...and I can feel the 94 octane when it hits the engine if I have been running 92 and the 94 works its way into the injectors.

ON TIME:

Try a ratio of 100 octane in your 91 to see if you feel a diference. I notice it within about 3/4 of a mile if I am going up a very slight incline with a VERY steady throttle. Overall the car is more responsive but you can feel it kick in.

Cheers!

ON TIME

Thank you for the info.

Bruce SEA 993

Kim,

I don't know if there is any measurable performance improvement as I have not dyno-ed the car with and without.

The anti-knock system in these cars is very sophisicated and the absense of know does not indicate that the engine management is supplying the maximum amount of advance to the engine. All is is doing is retarding the ignition so it does not knock. These cars "run fine" on lower octane however the absence of knock is not an indication of the engine running at its optimum.

Can't explain the lap times but there are more than a few parameters involved in lapping.

This has been kicked around a lot from time to time and I guess everybody should run what they feel comfortable with. I clearly notice a difference in the engine's response and feel of how it runs. If it does not increase my lap times...oh well...I like the way it runs.

Cheers

ScottMellor

Sniffff Sniff.
Our local 76 station just pulled the plug on the 100 octane. With a modified TT, it is pretty necessary if I want her to "be all she can be."
Someone once told me that on a hot day with 91 octane, we can lose 100 hp from a stock motor due to the ecu backin' off on the timing and boost. I can't recall who it was though.

Mark in Hermosa

I was always under the impression that higher octane does not mean performance gains. I believe it allows an engine to run more effeciently and a bit cooler. I think it was Steve Weiner that gave that info.

Bruce SEA 993

Maybe Mark has it plus "feeling better"!

FSAEracer03

Higher octance (which is not a percentage by the way) fuel allows for greater combustion pressures. The higher the octane rating, the more boost a turbo charged car can run. Similarly, a higher compression N/A motor, or any motor that runs hotter (like an air-cooled) needs higher octane fuel to reduce knock then a similar engine with a lower compression ratio or cooler operating temp.

If your car runs great on X octane gas, increasing the octane rating will only decrease your wallet rating

Steve Weiner-Rennsport Systems

Hi:

This is really a complex subject full of subtleties that do not encourage hard & fast rules of thumb for every case. In short; This is not a black & white issue.

One must understand that the octane requirements for naturally aspirated and turbocharged engines are very different as their cylinder pressures at all RPM's are not the same.

Next, detonation thresholds (thus octane requirements) in all engines, especially air-cooled ones, are dynamic and change with factors such as:

A) Outside air temperature and density

B) Cylinder head temperature

C) Oil temperature

D) Engine RPM

E) Engine load or throttle position.

To this mix add that every engine is slightly different due to variations in compression, leakdown, cam timing, and carbon buildup. Now, you can see that no two car's octane requirements are identical. As 993's tend to vary more than most, one person's car can run better with 94 or better, while another's feels no different with the "good stuff".
I would also strongly remind everyone that the Gluteous Maximus is not a calibrated instrument (at least in this regard) should never be relied on to make unofficial or crude assessments in acceleration or power. Using a proper chassis dyno or stop watch is more reliable,....

Turbocharged engines with active knock sensing and adaptive engine management (Motronic 5.2 or better) really respond to higher octane fuels, and modified ones even more so. I've seen 993 TT's on the dyno lose 60-70 HP using 92 octane fuel and watched it come right back with 100 octane unleaded. Its pretty dramatic to watch the Motronic do its thing by reducing boost and timing in real time with the PST-2.

Finally, I advise anyone with an air-cooled Porsche to use at least a mix of pump premium and unleaded race gas when participating in Driver Education events for getting maximum performance from these cars. Never rely on your ears and "back side" to determine whether the engine is pinging-knocking or not in cars that are noisy. For the CA folks, I'll say that 91 octane fuel is marginal at best and insufficient in hot weather and during track events.

I've barely touched on this subject and you can read a bit more about this at http://www.rennsportsystems.com/2a.html

ON TIME

TO ALL. THANK YOU FOR THE INFO

ON TIME

Thank you steve for your info. On time

Arjan B.

Hi,

Where I live in the Netherlands Shell sells since a few weeks V-power. This is a more powerfull and better quality fuel. This is for all cars, and you can get it at every SHell service station.

Problem is it's only 95 Ron [European]......
But..... when I hop over the border [10 minutes] I am in Germany where the V-power is 100 Octane [Ron]
Better run and more power of the engine because of your knock sensor adjusment. Your ignition will be set aerlier by your DME, so a better performance will be there. It's proven.

V-power is also in Germany aat every Shell station and will cost a bit more then the usual fuel, about 1,25 Euro per liter.

ON TIME

bump

slapshot

Thanks On Time for bringing this subject back! So, I guess the bottom line is . . . if you're running in a TT or go with Steve's recommendations (which I highly respect) you would definitely work with a blend. Down here in Cali we get 91 at best so for a 993 NA, does creating a higher blend or using Trick help in the carbon deposit department, cleaner burn, genuinley help with a little more HP? My car runs great at 91 but I am always willing to enhance performance and keep the engine as happy as possible.

Anyone else have any other thoughts specific for those of us with NA 993s? Randall G.?