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Fuel Grade

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fuel grade
43K views 85 replies 31 participants last post by  smitty 
#1 ·
I've heard a lot of debate over what kind of fuel the 1.4L T should use (regular or premium) and hoping to get some opinions from you guys and gals. I've heard that premium causes less detonation (whatever the heck that means) and is easier on the engine, increasing service life. Also if I was to use premium gasoline which is more expensive, will the cost justify the means due to the fuel economy evening it out?
 
#3 ·
you dont need a dyno to know if the premium fuel will make any difference. it will. its been discussed here before. i have a lot of experience with turbo cars and turbochargers in general and ive used regular on them before. never had any good results. car ran like crap, excessive knocking in the motor, and ridiculous amount of power loss. i wouldnt suggest trying it as i have lost one motor already to detonation. heres a really good explanation of what detonation is.

Detonation of Motor Fuels definition of Detonation of Motor Fuels in the Free Online Encyclopedia.
 
#4 ·
I understand what detonation is and how higher octanes work. GM is recommending 87 octane on all cruze's. I understand higher octane might be better, but if you engine blows under 100k GM replaces it for free..


Here is an email response I've received from their engineers:
Dear Mr. Miller,

Thank you for contacting Chevrolet and for your interest in the 2011 Cruze! We appreciate the time you have taken to write us.

We are unable to provide exact measurements for the octane ratings you mentioned in your response email. The vehicle will run more efficiently with a higher octane level however this will not provide you with added power. A higher level of octane will last longer and is generally cleaner than your lower level octane. The Cruzes 1.4 ECOTEC turbo engine is equipped to run on 87 octane and we would not recommend anything higher than 91 octane. For further details please consult your local dealer for technical assistance.
 
#5 ·
let me explain their email. see how they say the cruze is "equipped" to run on 87 octane. they use the word equipped instead of recommend because the car has a knock sensor which will dial back the timing of the motor when it detects low grade fuel. you said they are recommending 87 octane which doesnt state that in the email they sent to you. most of the older cars actually go into limp mode when they detect low grade fuel which basically just gives you enough power from your engine to "limp" home. also running anything higher than 91 is pointless for such a small turbo. now if you upgrade your turbo to something like a t67 then using a higher octane will make a difference.

yes they will replace the motor but do you think its worth all the hassle and losing the car for whatever the amount of time it takes them to diagnose the problem and put in a new motor or fix your old one. imagine if you were merging into the highway and suddenly experience detonation and the motor retards the timing which slows down the car. that can be a fatal problem if there is a car catching up to you. not trying to be a know it all but i have years of experience with modifying and tuning cars.
 
#8 ·
don't have the cruze yet. probably going to get it next year when they try to clear out the old models. so i can pick it up cheap. i did find some first hand account from owners that they did notice better throttle response when they filled it up with 91 after they got it from the dealership.

Great posts. I think I'll try out the 89 or 91. I do have one more question that I don't think I've found on here yet... can you mix different fuel grades or should you run your tank to just about empty before filling it up with a different grade of fuel?
yes you can mix different fuel grades. try avoiding running the tank empty on the turbo motor. running out of fuel while accelerating on a turbo motor is 10x worse than using low grade fuel as you will have increased air pressure due to the boost but then no combustion because of the lack of fuel. also dont try testing 89 and 91 until you fully break in the motor. i would suggest driving it on 91 for the first 500-1000 miles than do the test.
 
#7 ·
Great posts. I think I'll try out the 89 or 91. I do have one more question that I don't think I've found on here yet... can you mix different fuel grades or should you run your tank to just about empty before filling it up with a different grade of fuel?
 
#9 ·
...interestingly, the USA manual states 87 octane, but, seemingly, some overseas models state 91 octane.

...anybody know *why* the difference--possibly, fuel grade or quality?
 
#13 ·
the difference is not in the car nor the available fuel grade. its all about who they are selling the car too. they are trying to market this in north america as a really affordable sporty sedan. but they also know that recommending that consumers only use premium fuel in the cruze will deter a lot of people. remember the whole uproar about how the chevy volts were marketed to require premium fuel while everyone said they want it to use regular fuel. its the exact same scenario here. they dont want their high mpg and low budget sedan to look like a hypocrite by preaching savings but require more expensive fuel.

thankfully this way of thinking is not as widespread in other parts of the world. which is why on their manual its says the "right" fuel to use. ask anyone who has worked with turbochargers and superchargers. they will all tell you why you need to put premium fuel in your turbo car.

So after reading this discussion, I should put 91 in my cruze when I pick it up???
yes you should.
 
#74 ·
Where do you buy 91 octane fuel? Shell carries 87 89 and 93 same with BP and Speedway in Cincinnati. According to a google search, Sunoco carries 91. i think maybe back in the 80s they did along with 94 octaine. Now in Cinti they are 87 89 and 93 like everyone else.
 
#11 ·
...use the octane that your Owners Manual states.
 
#14 ·
...one has to wonder, however, *how* GM can warranty the engine on 89 octane, if, as you say, 91 octane is what *should* be used.

...sorry, I'm not buying it. Granted, using 91 octane might help you gain somewhat more HP when you're drag racing, pulling a heavy maximum capacity load, or climbing through mountains fully loaded, but it is probably not necessary for the 99.9% population who drive under "normal" conditions.

...if 91 octane was required, it would've been so stated in the Owners Manual, by the GM lawyers.
 
#16 ·
anyone who has enough experience with these kind of engines knows well enough that the need for a higher octane for daily driving is to prevent detonation under load. even if you dont floor the car detonation can still occur if the engine gets hot enough. like bpipe mentioned the knock sensor will retard the timing to compensate which should help protect the engine. but there will still be a few cars that the engine will go kaboom. for gm they are willing to take that hit since they will more likely lose more customers by them advertising that the cruze needs 91 octane compared to them just fixing premature engine failure when it does happen.

if you actually check one of the earlier post on this thread. there was a reply from a gm engineer and even the engineer said the same thing ive been saying. that you can use 87 octane but they recommend 91 octane.
 
#19 ·
...my personnal policy: 87 octane for all 'normal' driving and 91 octane if/when driving under 'loaded' conditions, ie: heavy/full weight load, or climbing through mountains, etc.
 
#21 ·
Octane requirement is effected by lots of things. Boost certainly plays a big part, but so does ambient temps, coolant temp, oil temp, humidity, compression ratio....ect.

Worst case scenario...lots of boost, extremely low humidity, high air temperature, heavily loaded, coolant temps near boiling. All these things increase octane requirements, you might need an octane of 110 or more in those conditions. Cold humid weather. lightly loaded.....you might only really need 80 octane if it were availible.

The car manufacturers err on the side of caution. It would be interesting to know what they have the peak boost set at.

MHF
 
#22 ·
...regarding "peak boost" -- there are people now who are attempting to learn if that info can be read-out over the OBD-II port using one of the aftermarket gauges (such as ScanGauge or UltraGauge, etc.).

...first, we have to know if such info is "GM_Proprietary" and as such wouldn't be made available to the general public (ie: a general code).

...then, because we *still* want to know, it becomes a 'detective' game of literally searching through all the available engine control unit (ECU) codes to see if the data is available, but unlisted.

...finally, using the programability function of a ScanGauge, one could code it to search for and read the illusive info...and display it on the gauge readout.

...nothing is impossible, just sometimes it's rather improbable (ha,ha).
 
#23 ·
Originally Posted by VinceTrifecta
Well, just got done doing some logging. There's most definitely room for improvement.
Here's some numbers from the stock tune:
Commanded AFR @ WOT (PE Mode): 10.3:1
Commanded Ignition Advance: 8*
Sustained boost: 15-16psi
Wastegate %: 74% of maximum potential
Engine Coolant Temp: 221*F
The thermostat is electronically controlled to be at 220degrees F all the time, which is terrible for performance.


This is from a company called Trifecta who played a huge part in Cobalt ECU tuning and will do the same for the Cruze hopefully (they just bought a LTZ and are using it as a test mule)
 
#29 ·
Car engines are built for a specific octane. Lower octane is more flamible (contrary to what most people think). Years ago, the reason people would use higher octane in an older car to prevent knocks is for this reason: build up (some times lead) in the cylinders causing a smaller compression space meaning the piston was firing too early before the spark, thus causing a knock. Higher octane is less flamible meaning it would allow the piston to fully compress and not explode prematurely. Using 91 in a brand new Cruze means you are putting less flamible gas in the engine for which its designed. There is no mechanical reason for a knock, nor a reason to supress a knock.

Quesion for those claiming 89 is causing less hessitation: Are you driving 1.4 or 1.8?
 
#33 ·
Well and thats the thing, I wrote to GM and they said the car CAN run 87, but do not run anything higher than 89. They would not give me a direct answer on what I SHOULD be running. It was very odd.

I'm no sure how European octanes differ from US but in Europe they recommend 89...
 
#34 ·
Honestly I don't know what they are thinking telling everyone to use 87 with this much boost. Maybe they wrote the instructions for the LS normally aspirated engine and forgot about the 1.4 turbo or something.

You know what would be great? An indicator that tells you when or how often the knock sensor goes off. Or tell us the timing advance setting so we can see what the engine is doing at different octane ratings, loads and weather conditions.
 
#37 ·
i had a long talk with vince from trifecta last week. very smart knowledgeable guy. really enjoyed our conversation.

here is the deal, chevy tuned the car to run on 87 for reason previously stated and its why its so **** slow for an FI car. so in its stock form without any sort of tune, 87 OCT is just fine to run. you might notice its runs better with 89 OCT since it is a FI car.

if you were to get some sort of tune like the one Vince from trifecta offers it will have to run on 91 OCT or it will knock regardless of knock sensors or anything else.

cruise control is right about running 91 in FI cars, but that's is for a car tuned to run on it. like with the hondas and aftermarket turbos which are tuned for big horsepower number and have very high air to fuel ratios so u have to run 91 to avoid knocking also known as detonation. that is not the case with the cruze in its stock form it was not tuned for performance not power. it was tuned for 36 mpg on the high way bottom line
 
#38 ·
i had a long talk with vince from trifecta last week. very smart knowledgeable guy. really enjoyed our conversation.

here is the deal, chevy tuned the car to run on 87 for reason previously stated and its why its so **** slow for an FI car. so in its stock form without any sort of tune, 87 OCT is just fine to run. you might notice its runs better with 89 OCT since it is a FI car.

if you were to get some sort of tune like the one Vince from trifecta offers it will have to run on 91 OCT or it will knock regardless of knock sensors or anything else.

cruise control is right about running 91 in FI cars, but that's is for a car tuned to run on it. like with the hondas and aftermarket turbos which are tuned for big horsepower number and have very high air to fuel ratios so u have to run 91 to avoid knocking also known as detonation. that is not the case with the cruze in its stock form it was not tuned for performance not power. it was tuned for 36 mpg on the high way bottom line

and this is exactly what we already speculated. Vince is a really smart guy too, glad you had a good talk with him :)
 
#40 ·
Maybe the tankful of fuel from the dealership was old fuel, or contaminated with condensation, because it hesitated a lot upon acceleration until I put a new tank of fuel in. And I put in 91. Next fill up I'll put in 87 and see if it goes back to hesitating again or not.

BTW it is "slow" for an FI car because of the small displacement. 1.4 liters is a small engine. It is designed to be fuel efficient not a hot rod. I understand it may be designed to run on 87 but keep in mind the engine thermostat is set to 220 deg. F. unlike other cars that are set to 195 deg. F. That might cause the fuel to ignite a bit faster.
 
#45 · (Edited)
just because the motor is a small displacement engine does not determine why its slow. look at the number that Vince pulled from just a tune and nothing else out of the little 1.4l. his numbers are whp, so they are more inline with a 2002-2005 wrx at the crank and that is a 2.5l. so how is displacement the reason for it being slow?

its slow because it was not tuned to be fast. my 1.8 integra is perfectly cable of making 250 whp on a totally stock engine with a simple stage one turbo kit, will it ever be a 500 ft lbs of torque without major engine overhaul? no of course not there is no replacement for displacement, however it is not fair to call it slow simply because of it displacement when it is indeed a FI car
 
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