Octane at altitude...
- Thread starter samsonic
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sx sonic
New member
Welcome to the forum Tbone1. Sharp looking car!
The sonic is marketed for 87oct because it is more marketable to the average buyer.
Generally if a car is tuned for a certain octane there will be no gain and possibly even a loss in power with running higher octane.
Higher octane for all intents and purposes will only help an engine if it encounters knock/detonation on a lower grade of fuel. This is because the ECM detects knock and temporarily retards spark timing to prevent it, this results in lower cylinder pressures and a loss in power.... And economy since that power could have been used to propel you down the road. Under the same conditions higher octane would prevent the knock and the ECM will not have to cut power (by retarding spark timing).
On some cars that are finely tuned there can be times when higher octane might help such as high ambient temps or sustained heavy loading, or poor fuel quality. Both of which are pro knock factors.
Now here's the weird bit. The 1.4t uses a unique ECM with a "dual map", one map is tuned to the ragged edge and uses more ideal spark and fuel timing/trims with less regard for potential knock (i'll call it the high tune). The other map is more conservative with acceptable but not ideal spark timing and as such will be less susceptible to knock (the low tune).
This allows the 1.4t to leave the factory more aggressively tuned to eek out the most economy and power per t drop of fuel. But should it detect any knock it will go to the low tune with its more conservativepark timing, this is a long term anti knock counter measure (I suspect it fights knock conventionally on the low tune. Ie, only as it happens.)
So GM gets to sell a car with the appeal of having great mpg AND running cheap gas, while running on the ragged edge of timing for the best mpg and drivability. But because of the low tune still be safe long term. (even thou the ECM can quickly kill detonation It's not something you'd want to be bumping into often)
How does the car know to run the High or Low tune? After every fillup it resets to the high tune, and will bump down to the low tune if it detects knock.
SO FINALLY TO AWNSER YOUR QUESTION.
This engine CAN benefit from higher octane gas....... If it knocks on 87oct, which it may or may not based on conditions, driving habits, fuel quality, etc.
Many people report better drivability and mpg (1-4mpg) when running 91/93oct.
Myself and several others that have done logging/testing have not noticed a measurable difference. My best and worst on each blend have been within 0.5mpg (favoring 93) since I don't drive in a laboratory I consider .5mpg a neglible difference.
Tl/dr- higher octane has potential to give better drivability and mpg. Log a few tanks of each and decide for yourself.
Oh and either fuel is safe long term
The sonic is marketed for 87oct because it is more marketable to the average buyer.
Generally if a car is tuned for a certain octane there will be no gain and possibly even a loss in power with running higher octane.
Higher octane for all intents and purposes will only help an engine if it encounters knock/detonation on a lower grade of fuel. This is because the ECM detects knock and temporarily retards spark timing to prevent it, this results in lower cylinder pressures and a loss in power.... And economy since that power could have been used to propel you down the road. Under the same conditions higher octane would prevent the knock and the ECM will not have to cut power (by retarding spark timing).
On some cars that are finely tuned there can be times when higher octane might help such as high ambient temps or sustained heavy loading, or poor fuel quality. Both of which are pro knock factors.
Now here's the weird bit. The 1.4t uses a unique ECM with a "dual map", one map is tuned to the ragged edge and uses more ideal spark and fuel timing/trims with less regard for potential knock (i'll call it the high tune). The other map is more conservative with acceptable but not ideal spark timing and as such will be less susceptible to knock (the low tune).
This allows the 1.4t to leave the factory more aggressively tuned to eek out the most economy and power per t drop of fuel. But should it detect any knock it will go to the low tune with its more conservativepark timing, this is a long term anti knock counter measure (I suspect it fights knock conventionally on the low tune. Ie, only as it happens.)
So GM gets to sell a car with the appeal of having great mpg AND running cheap gas, while running on the ragged edge of timing for the best mpg and drivability. But because of the low tune still be safe long term. (even thou the ECM can quickly kill detonation It's not something you'd want to be bumping into often)
How does the car know to run the High or Low tune? After every fillup it resets to the high tune, and will bump down to the low tune if it detects knock.
SO FINALLY TO AWNSER YOUR QUESTION.
This engine CAN benefit from higher octane gas....... If it knocks on 87oct, which it may or may not based on conditions, driving habits, fuel quality, etc.
Many people report better drivability and mpg (1-4mpg) when running 91/93oct.
Myself and several others that have done logging/testing have not noticed a measurable difference. My best and worst on each blend have been within 0.5mpg (favoring 93) since I don't drive in a laboratory I consider .5mpg a neglible difference.
Tl/dr- higher octane has potential to give better drivability and mpg. Log a few tanks of each and decide for yourself.
Oh and either fuel is safe long term
T-BONE
New member
Thank you for the complete explanation on the updated technology.
this makes sense to me and given what I have read I think I will tell my daughter (bought the car for her) to put in premium.
I have an 07 mini cooperS that if you put 87 in will bog down like a dog the timing gets retard so much.
my 04 spyder is NA and runs awesome on 87 all premium does is carbon up the intake and cylinders.
I know this is important long run and the mixes messages in the marketing and lack of dealer clarity have me flummoxed given this seems like a neat system to protect the car (been at few stations where they have been out of 91-93)
This seems like a great car and thank you again for having the time and pertinence to clarify. You must have had to do a fair amount of research to glean that info
this makes sense to me and given what I have read I think I will tell my daughter (bought the car for her) to put in premium.
I have an 07 mini cooperS that if you put 87 in will bog down like a dog the timing gets retard so much.
my 04 spyder is NA and runs awesome on 87 all premium does is carbon up the intake and cylinders.
I know this is important long run and the mixes messages in the marketing and lack of dealer clarity have me flummoxed given this seems like a neat system to protect the car (been at few stations where they have been out of 91-93)
This seems like a great car and thank you again for having the time and pertinence to clarify. You must have had to do a fair amount of research to glean that info
T-BONE
New member
Just thought I would share this link
Chevrolet Sonic - Engine - car safety information, failing parts, recalls, bulletins, complaints
not in hot humid climates 87 seems to yield stalling problems and difficult restarts.