brucec59

I am curious about how much power our cars loose (or cannot access) in places like CA and other states where "super" is 91 octane. Is there any way to know how often and how much the knock sensors retard the timing? And can we translate that info to something meaningful, like HP and torque figures? Thanks.

ilko

The ECU is optimized for 91 Octane since that's the highest grade you can find in certain parts of the country so technically you're not losing anything.

There are too many variables to really get the correct answer other than doing dyno runs in identical conditions in the same car with the only difference being the fuel grade. But generally you can expect to see small peak hp and tq difference between 91 and 93 octane. And bear in mind to be really consistent you would want the two different octane grades to be from the same gas station.

Jon93

Here in australia, my fuel cap says use 96 octane.
In fact out fuels here nowadays are either 91, 95, or 98.
Does it matter which one i choose? I currently go for 98, because i beleive it may be better for engine. Is that nonsense??

NineMeister

Here's the difference between a 9m Motec converted 993 engine on UK 95 & 98 octane fuel. You are looking at a 5% loss in torque right across the rpm range.

IXLR8

That is of course under load, but if someone is driving one as a daily driver, how would those numbers change? I'd think there is more energy in lower octane fuel.

Steve Weiner-Rennsport Systems

The numbers do not change much on these Motronic engines since the EMS system is continually trying to provide maximum ignition timing, based on inputs from air temp sensor, knock sensors, cylinder head temp sensor, oil temp sensor, and throttle position.

When knock counts go up due to cylinder head temps, less-than-optimal fuel, air temperatures, and high oil temps, the ECU pulls out timing, 3 degrees at a time until the knock counts return to a background value. When this happens, power & torque are reduced and its quite noticeable.

These engines made max power at the factory using 98 RON fuel, but will accommodate up to 95 RON before performance suffers, under normal temperatures. Higher temps require higher octane fuels to maintain performance and conversely, low air temps reduce the need for octane.

Lower octane fuels contain the same energy as high octane fuels and we see this on the engine dyno. The difference is that higher octane gas simply contains more anti-knock compounds that resist spontaneous combustion at high pressures. Race gas, OTOH, contains compounds designed to "light off" quicker without detonation and this provides better throttle response.

911Dave

Also note that the need for octane is reduced as you gain altitude. 91 in Denver (5200 feet) is like 93 at sea level.

Van1

For our overseas freinds, keep in mind that your fuel octane is measured as RON (Research Octane Number) and our fuels octane is measured as the average of RON + MON (Motor Octane Number). 96 octane European gas is equilvelant to our 91 octane gas.

propeople

Hello, im on fu$@#$ brasil, here i just have 87 IAD (95 RON) oct fuel for my cayenne turbo 2012,car runs great but i ask any ideas of hp loss ???

My jetta 2.0 tfsi gets 240 hp and no knock......with this brasillian fuel 95ron+27% ethano

pp000830

• With 27% ethanol doesn't the lower BTU of the fuel come into play in relative engine output as compared to non-ethanol fuels?
• In theory, would engines running on this benefit from a different fuel system from that in the US, one that can push larger volumes of fuel into the engine to make up for the lower BTU content?

Anyone's thoughts on this?

Cupcar

My 993 owners manual claims R+M/2 = 93 Octane for best performance.

It will run on 91 but with timing dialed back and I suspect the torque loss on 91 is similar to loss that 9M posted.