Originally Posted By: sciphi
Originally Posted By: dave5358
Originally Posted By: Finz
JHRZ2... How is this determined by a DIY'r?
JHRZ2 may jump back in with more specific information. Try to find a website / forum that pertains to your specific vehicle model or engine - someone there might know from experience.
Or, look in your owner's manual/ask a dealer technician for recommended fuels. If they say 93 octane fuel, then the advance curve will accommodate that advance. If it's only 87 octane, then probably not.
The problem sometimes arises when a person has a vehicle clearly designed for regular gas (87 or 89 octane). The manufacturer doesn't bother to include an advance curve for anything beyond that, so if you run a tank of 93 octane fuel, the extra energy is pretty much wasted. It runs okay, but not much benefit.
For the turbocharged Cruze at least, this is incorrect. It's pretty heavily detuned to run acceptably on 87. Exhibit A: a Trifecta or Vermont tune picks up 25-27 hp and 45-50 ft/lbs on 93 octane with no other changes made to the engine/intake/exhaust. Those tunes are fairly conservative to account for slight production and regional fuel differences. But when 18% more horsepower and 30% more torque can be gained on a 138 hp/148 ft/lb engine just by a reflash, that says that there's a lot left on the table in the stock tune.
The owner's manual may say 87 octane. Being turbocharged, it will run better on 91+ octane. Less knock means it can run less enrichment to prevent knock.
The surprising part of that is that your manual says 87 octane for a turbo car. My turbo Forester manual say 93 octane. It will run on 87. It just doesn't run as well, but the ECU can handle it.
If I fill my wife's Corolla with 93 octane gas, it runs well enough, but there's no real benefit - there's no 93 octane map in the ECU - the advance curve doesn't go there.
Originally Posted By: dave5358
Originally Posted By: Finz
JHRZ2... How is this determined by a DIY'r?
JHRZ2 may jump back in with more specific information. Try to find a website / forum that pertains to your specific vehicle model or engine - someone there might know from experience.
Or, look in your owner's manual/ask a dealer technician for recommended fuels. If they say 93 octane fuel, then the advance curve will accommodate that advance. If it's only 87 octane, then probably not.
The problem sometimes arises when a person has a vehicle clearly designed for regular gas (87 or 89 octane). The manufacturer doesn't bother to include an advance curve for anything beyond that, so if you run a tank of 93 octane fuel, the extra energy is pretty much wasted. It runs okay, but not much benefit.
For the turbocharged Cruze at least, this is incorrect. It's pretty heavily detuned to run acceptably on 87. Exhibit A: a Trifecta or Vermont tune picks up 25-27 hp and 45-50 ft/lbs on 93 octane with no other changes made to the engine/intake/exhaust. Those tunes are fairly conservative to account for slight production and regional fuel differences. But when 18% more horsepower and 30% more torque can be gained on a 138 hp/148 ft/lb engine just by a reflash, that says that there's a lot left on the table in the stock tune.
The owner's manual may say 87 octane. Being turbocharged, it will run better on 91+ octane. Less knock means it can run less enrichment to prevent knock.
The surprising part of that is that your manual says 87 octane for a turbo car. My turbo Forester manual say 93 octane. It will run on 87. It just doesn't run as well, but the ECU can handle it.
If I fill my wife's Corolla with 93 octane gas, it runs well enough, but there's no real benefit - there's no 93 octane map in the ECU - the advance curve doesn't go there.