Low octane Performance Question
Thread Starter
Instructor
Joined: Jul 2005
Posts: 103
Likes: 1
Low octane Performance Question
My 97 C5 seems to lack the snap that other C5's have. It is a new purchase and the dealer filled it with low octane fuel. This car is in nice shape with 46000 miles.
I was told:
When using low octane fuel, the computer will drop the engine down to a low performance mode.
Is this true?
I was told:
When using low octane fuel, the computer will drop the engine down to a low performance mode.
Is this true?
Racer
Joined: Nov 2006
Posts: 264
Likes: 8
From: Centre, AL
The octane rating is a measure of the autoignition resistance of gasoline. It is a measure of anti-detonation of a gasoline or fuel, thats all it is. Nothing to do with the energy in the gas.
Modern vehicles use computerized engine management systems that can react to engine knock and retard ignition timing if low octane fuel is being used. My guess is only up to a point. Things like outside temp and barometric pressure will also affect knocking. Knocking will destroy your engine. If you want to use low octane gas, you can reflash the chip to only use 87. Other people in this forum might know better about things like that though....
Modern vehicles use computerized engine management systems that can react to engine knock and retard ignition timing if low octane fuel is being used. My guess is only up to a point. Things like outside temp and barometric pressure will also affect knocking. Knocking will destroy your engine. If you want to use low octane gas, you can reflash the chip to only use 87. Other people in this forum might know better about things like that though....
Race Director
Joined: Jul 2004
Posts: 16,794
Likes: 62
From: Lake Havasu City, AZ
The computer does retard the timing as octane drops but it does not drop it into a low performance mod.
The difference should not be enough to account for the "snap" you seem not to have.
Are the other Vettes stock or modified? What rear gears do they have versus yours?
There are many things that can be done to improve performance..
The difference should not be enough to account for the "snap" you seem not to have.
Are the other Vettes stock or modified? What rear gears do they have versus yours?
There are many things that can be done to improve performance..
Le Mans Master
Joined: Aug 2001
Posts: 8,145
Likes: 1
From: Bradenton FLORIDA
Detonation from running 87 could damage the pistons in a short time if run hard even with the knock sensors. It only takes a little to start to eat the pistons up & although it may still run, the power loss is very noticeable. Want to see some of the effects in person? Stop by the shop & we have some to show you.
Supporting Vendor
Joined: Jul 2003
Posts: 6,486
Likes: 2
From: http://www.mphparts.com 800-364-1975
Hi guys,
Our PCMs utilize two timing tables -- one for low octane, and one for high octane. When the PCM detects knock, depending on the severity of the knock, it blends timing between these two tables.
I once set my high octane table to the values from the low octane table just to see how it felt (so the car was always in low octane mode). The car was a SLUG! It felt like something was mechanically wrong with it.
So yes, using low octane gas can cause your car to run substantially slower *IF IT KNOCKS* as a result of using low octane gas.
There are also lots of other mechanical reasons a car might feel more sluggish than other C5s, but I would start with a decarb procedure and then only add 93 to the car and see if that helps (my reasoning for the decarb is because it's a relatively old C5 and may have carbon buildup, further contributing to pinging/pulling timing/feeling slugish).
Our PCMs utilize two timing tables -- one for low octane, and one for high octane. When the PCM detects knock, depending on the severity of the knock, it blends timing between these two tables.
I once set my high octane table to the values from the low octane table just to see how it felt (so the car was always in low octane mode). The car was a SLUG! It felt like something was mechanically wrong with it.
So yes, using low octane gas can cause your car to run substantially slower *IF IT KNOCKS* as a result of using low octane gas.
There are also lots of other mechanical reasons a car might feel more sluggish than other C5s, but I would start with a decarb procedure and then only add 93 to the car and see if that helps (my reasoning for the decarb is because it's a relatively old C5 and may have carbon buildup, further contributing to pinging/pulling timing/feeling slugish).
