Regular or premium

time2roll wrote:
I would use the minimum recommended octane as specified by GM.
My 1970 Mustang required 98 Octane and best available was 94 then 92. Probably ran a lot better in 1970.

The R+M/2 rating system is what changed, current premium is about the same octane as before 1970. Of course the ethanol causes higher consumption and the lack of lead causes more valve and valve seat wear.

I would use the minimum recommended octane as specified by GM.
My 1970 Mustang required 98 Octane and best available was 94 then 92. Probably ran a lot better in 1970.

It depends a lot on the engine. Compression ratio, turbo or not. Most vehicles will make a small amount more power with Premium. If it is designed for Premium, it can make a noticeable difference. The only vehicle I've ever owned that cared, is my 2014 Cruze Eco MT with the 1.4 turbo motor. It calls for 87 octane, but in the summer it runs horrible on 87 octane. I can tell it runs the best on premium unless the temp's are below freezing. I run 93 octane most of the year, 89 octane in the late fall and early spring and 87 octane when the temps are below freezing. I can see how the 3.5 in the Fords with the turbos would behave in a similar fashion. It is only under certain circumstances, but it will really pull the timing and cut the boost to keep from pinging.

In the 6.2L, if you're not towing and in cooler weather, you might be able to get away with 87 octane. If not try 89 octane. If not happy with that under some conditions, run 91-93 octane. You'll just have to try it to see what works. Towing, you probably need premium to avoid issues, but you never know. Weather/temps does make a difference since it reduces the intake air temps and reduces the combustion chamber temps prior to detonation so it reduces the chance or pre-detonation when the temps outside are cooler.

Don't most Hemi's call for 89 octane? At least when towing?

It seems like in years past, it was 10 cents bump from 87 to 89 and then 10 more cents from 89 to 93 octane. Now days it is pretty much a 30 cent bump pre grade. 93 octane is pretty expensive.

Groover wrote:


At the current price here of $1.75/gal that narrows the price differential for the Ecoboost from $0.40/gal to $0.32/gal. I will stick with regular.

At the current price of $1.75/gal, you could pump 5 gallons into the parking lot while filling up and be money ahead still!

It's crazy how cheap gas is in some parts of the country! Cheaper than most recent decades in history! (accounting for inflation)

mkirsch wrote:
Used to be you only needed premium for these engines if you wanted the horsepower.
Going towing or drag racing? Fill up with premium.
Grocery shopping or a road trip? Regular was fine.

Must be things have changed.

We used to have an '84 Cadillac with that 4.1L aluminum V8 that would ping horribly unless you ran premium fuel. Back then premium was only a couple cents more so it wasn't a big deal.

They haven't, although it appears that "some" engines/tuning does not support or adjust timing as well for low octane.
What you're speaking of is old engines that aren't smart. And if they're built for premium, they'll tell you right away when they're not happy with the cheap booze!

Groover wrote:
At the current price here of $1.75/gal that narrows the price differential for the Ecoboost from $0.40/gal to $0.32/gal. I will stick with regular.

Anecdotal without any data, my 3.5L ecoboost seemed to pull a lot better on 91 pure gas.

ShinerBock wrote:
Here is a study AAA did several years back that actual has an Escalade with a 6.2L Ecotec in the test. The study tests the impact of regular and premium fuel on engines that require regular and premium. It shows short burst full load dynos and sustained dynos at 2,000 and 4,000 rpm which is where the difference between the two fuels is most noticeable in the real world especially when towing. There is also graphs on the amount of timing is advanced/pulled along with temps of the catalyst along with MAP/MAF sensor readings.

One major thing to note is the 7.1% fuel economy increase on the 6.2L with premium fuel under normal load. This was contributed to ability of the 6.2L to stay in 4 cylinder mode more often due to the significant timing advance at this load level creating more power per cylinder. The gen one 3.5L Ecoboost also had a considerable fuel economy bump of 5% with premium fuel.

AAA Premium Fuel Research

At the current price here of $1.75/gal that narrows the price differential for the Ecoboost from $0.40/gal to $0.32/gal. I will stick with regular.

mkirsch wrote:
Used to be you only needed premium for these engines if you wanted the horsepower.
Going towing or drag racing? Fill up with premium.
Grocery shopping or a road trip? Regular was fine.

Must be things have changed.

We used to have an '84 Cadillac with that 4.1L aluminum V8 that would ping horribly unless you ran premium fuel. Back then premium was only a couple cents more so it wasn't a big deal.

Things have changed in the hp/cubic inch department and in engine control systems.

Here is a study AAA did several years back that actual has an Escalade with a 6.2L Ecotec in the test. The study tests the impact of regular and premium fuel on engines that require regular and premium. It shows short burst full load dynos and sustained dynos at 2,000 and 4,000 rpm which is where the difference between the two fuels is most noticeable in the real world especially when towing. There is also graphs on the amount of timing is advanced/pulled along with temps of the catalyst along with MAP/MAF sensor readings.

One major thing to note is the 7.1% fuel economy increase on the 6.2L with premium fuel under normal load. This was contributed to ability of the 6.2L to stay in 4 cylinder mode more often due to the significant timing advance at this load level creating more power per cylinder. The gen one 3.5L Ecoboost also had a considerable fuel economy bump of 5% with premium fuel.

AAA Premium Fuel Research

Used to be you only needed premium for these engines if you wanted the horsepower.
Going towing or drag racing? Fill up with premium.
Grocery shopping or a road trip? Regular was fine.

Must be things have changed.

We used to have an '84 Cadillac with that 4.1L aluminum V8 that would ping horribly unless you ran premium fuel. Back then premium was only a couple cents more so it wasn't a big deal.