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3.8 Fuel - Regular or better?

TinsleyC

Registered Member
406
146
43
Dallas, TX
Genesis Model Type
Genesis G80
I was please to see the 311 HP 3.8 takes regular fuel, but some have said the performance is better with higher octanes. In Dallas I can get 87, 89, or 93 octane.

I'm coming off an Infiniti G37 that "required" 91 octane, and although it runs fine on 87, I could really tell the difference when I used 91 or 93. Most people thought I was nuts, but I would mix 2 parts 93 octane with one part 87 to get the required 91 -- 87+93+93=273, and 273/3=91. 12 gallons of 93 topped with 6 gallons of 87. It saved me a few bucks per tank and only added 30 seconds to the fill-up.

So is anyone seeing any performance gain or MPG increase with running a higher octane?
 

EdP

Supporting Member
SUPPORTING MEMBER
SUSTAINING MEMBER
6,320
2,929
113
Parrish, FL
Genesis Model Type
Genesis G80

TinsleyC

Registered Member
406
146
43
Dallas, TX
Genesis Model Type
Genesis G80
With Top Tier gas being 40+ cents more per gallon between regular and premium, saving $7-8 per full up is attractive. It's not like the 3.8 is a performance car, but some cars do run noticeably better on premium fuel.
 
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danygenesis

Genesis owner
1,788
1,403
113
Miami, FL
Genesis Model Type
Genesis G70
Here is South Florida the difference is around 60 cents a gallon. Refueling once a week would be around $500 yearly toll.
______________________________
 

bubbaG80Sport

SUSTAINING MEMBER
440
225
43
Genesis Model Type
Genesis G80 Sport
This topic has been discussed in several threads in this forum. See "Regular or Premium" thread here for example. This topic starts a holy war. It's like talking about sex, politics, religion and gun control.

Short Answer: IMO there is no benefit (performance, MPG, engine life)) to running higher octane (+87) in the 3.8.

Long Answer:
IMO the only benefit to running higher octane gas in the 3.8 is possibly different/better additives in premium versus regular gas. I'd put in a tank of premium 91 octane in my 2011 Hyundai Genesis 3.8 and Techron Concentrate FI (the better Techron) cleaner every 5K miles otherwise she got 87 octane. Engine ran as smooth as a baby's butt until I traded her in at 100K miles. One potential downside to premium is less is sold. Premium sits in the filling stations tanks longer and thus more prone to water accumulation in the stations tank. Cars drink gas and don't like water.

Even in the 5.0 I see little benefit. The Hyundai/Genesis claims a minimal increase in HP (+2->5 I recall) running premium gas, but how often are you running at maximum HP (rarely and only for very short periods). Unless your dragging/tracking your 3.8 or 5.0 Genny there is minimal benefit to running premium.

The 3.3 (turbocharged) engine is a different beast. The Hyundai/Genesis makes no comment on running premium gas and manual says run a minimum of regular 87 octane. With the higher compression I've chosen to run "Top Tier" certified 91/92 octane premium in my 3.3. Based on my mileage per year (15K miles) it's costing me +$375 to run premium gas. 92-octane/10%-Ethanol versus 87-octane/10%-Ethanol price difference was $.050USD in March 2019.

I used to buy only Exxon, mostly out of habit/routine. Recently I've been switching between "Top Tier" brands. My hypothesis is different additives/cleaners betwixt the gas brands would be better for my engine.

We need empirical data to make this objective. If anyone has access to a dynamometer, run tests with 87 octane and 91/92 octane. Provide ethanol content, year and engine. and let us know maximum HP/torque results.

Summary:
For the 3.8 run regular 87 octane from a "Top Tier" certified manufacturer. Use the saved $ and take your Genny to a spa/detailer once a year.
 
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TinsleyC

Registered Member
406
146
43
Dallas, TX
Genesis Model Type
Genesis G80
Thanks Bubba, yeah certainly don't want to start a war here. I'll try the search feature next time. On other forums I participate in, the search doesn't work so well.

I'll plan on running a Top Tier 87 octane, likely Shell or Mobil. Thanks again.
 

Rodney Dangerfield

Registered Member
114
22
18
Texas panhandle
Genesis Model Type
1G Genesis Sedan (2009-2014)
Thanks Bubba, yeah certainly don't want to start a war here. I'll try the search feature next time. On other forums I participate in, the search doesn't work so well.

I'll plan on running a Top Tier 87 octane, likely Shell or Mobil. Thanks again.
The YouTube channel Engineering Explained goes into octane ratings and explains it very well and why you need to use one grade over the other as well as if using higher octanes in engines which don't specifically require it will benefit you in any way. I have a Gen 1 4.6 which states you can use either. The difference is about 10hp, which is about impossible to notice the difference.
 

MorrisGray

Hasn't posted much yet...
112
19
18
Rock Spring, GA
I would try both and my understanding is that unless you hear engine knock running regular 87 octane then you do not need premium grade gas. The reason I would try both would be to see for myself if there was a difference in feel, sound and/or fuel mileage. One other option that I have found that seems best is running 100% pure gas, no ethanol. That is my pick but not always easy to find. And keep checking your tire pressures regularly as they have a big determination on fuel mileage if running them under inflated.
______________________________
 

Alfer

Registered Member
619
242
43
USA
Genesis Model Type
2G Genesis Sedan (2015-2016)
Stick to Top Tier branded fuel and the octane noted in the owners manual. Period.
 

bubbaG80Sport

SUSTAINING MEMBER
440
225
43
Genesis Model Type
Genesis G80 Sport
I considered non/lower ethanol fuel when assessing what to give my G80 3.3T to drink.

1) 0% ethanol gas is generally same octane as regular 10% ethanol gasoline in the U.S (87). Ethanol is used as an octane booster, replacing lead (tetraethyl lead) in the U.S in the 1970's.

2) Ethanol has less energy density than pure gasoline. Gas mixed with ethanol will produce less power then pure gas in the same engine. The power decrease is not noticeable in most mass produced production vehicles. Only a single data point, but I ran 1 tank of 0%-E/87-O and got +0.5MPG over my long term average MPG. I did not "feel" any better performance from the engine/car.

3) The cost of 0% ethanol gas generally falls between mid grade and premium. In my "hood" costs (USD) per gallon March 2019 were.
Regular 10%-E 87-O $2.399
Mid 10%-E 89-O $2.649
Pure gas 0%-E 87-O $2.799
Premium 10%-E 92-O $2.899

4) There is no harm in using ethanol in today's cars. Early on there were issues with ethanol in cars (corroding/eating fuel system components). Materials have changed in "modern" cars that addressed this issue. Don't run ethanol in your classic/antique car!

5) 0% ethanol gas is not as readily available and becoming increasingly hard to find.

6) Ethanol is a renewable resource (made from corn). It helps provide a market for corn growers (along with government subsidies). This can/will drives up the cost of corn on the cob (the law of supply and demand) ;)

I chose to go with higher octane premium fuel because I was more concerned with knocking/pre-detonation in the 3.3 turbo versus getting maximum performance with 0% ethanol gas.
 
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Alfer

Registered Member
619
242
43
USA
Genesis Model Type
2G Genesis Sedan (2015-2016)
5) 0% ethanol gas is not as readily available and becoming increasingly hard to find.


Where I live, "pure" gas availability has become more and more abundant. QT convenience stores have added pure gas to many of their stations. So has Sinclair. I can now find pure gas very easily. It wasn't like that 5+ years ago.
______________________________
 

TinsleyC

Registered Member
406
146
43
Dallas, TX
Genesis Model Type
Genesis G80
Bubba, in your numbers, the mid-grade 10% ethanol gas cost less than regular-grade 10% ethanol. Is that correct, or a typo?

Thanks
 

bubbaG80Sport

SUSTAINING MEMBER
440
225
43
Genesis Model Type
Genesis G80 Sport
Here's my full spreadsheet showing gasoline incremental cost increase going to higher octane/lower ethanol content.

16-Mar-19​
RegularMid-GradeRegularPremium
10% Ethanol10% Ethanol0% Ethanol10% Ethanol
87 Octane89 Octane87 Octane92 Octane
$ 2.399$ 2.649+$ vs $ 2.799+$ vs +$ vs $ 2.899+$ vs +$ vs +$ vs
$ 0.25010% Ethanol$ 0.40010% Ethanol10% Ethanol$ 0.50010% Ethanol10% Ethanol0% Ethanol
Mile/YrMPG$/ Year$/ Year87 Octane$/ Year87 Octane89 Octane$/ Year87 Octane89 Octane87 Octane
12000​
20​
$1,439.40​
$1,589.40​
$150.00​
$1,679.40​
$240.00​
$90.00​
$1,739.40​
$300.00​
$150.00​
$60.00​
12500​
20​
$1,499.38​
$1,655.63​
$156.25​
$1,749.38​
$250.00​
$93.75​
$1,811.88​
$312.50​
$156.25​
$62.50​
13000​
20​
$1,559.35​
$1,721.85​
$162.50​
$1,819.35​
$260.00​
$97.50​
$1,884.35​
$325.00​
$162.50​
$65.00​
13500​
20​
$1,619.33​
$1,788.08​
$168.75​
$1,889.33​
$270.00​
$101.25​
$1,956.83​
$337.50​
$168.75​
$67.50​
14000​
20​
$1,679.30​
$1,854.30​
$175.00​
$1,959.30​
$280.00​
$105.00​
$2,029.30​
$350.00​
$175.00​
$70.00​
14500​
20​
$1,739.28​
$1,920.53​
$181.25​
$2,029.28​
$290.00​
$108.75​
$2,101.78​
$362.50​
$181.25​
$72.50​
15000​
20​
$1,799.25​
$1,986.75​
$187.50​
$2,099.25​
$300.00​
$112.50​
$2,174.25​
$375.00​
$187.50​
$75.00​
15500​
20​
$1,859.23​
$2,052.98​
$193.75​
$2,169.23​
$310.00​
$116.25​
$2,246.73​
$387.50​
$193.75​
$77.50​
16000​
20​
$1,919.20​
$2,119.20​
$200.00​
$2,239.20​
$320.00​
$120.00​
$2,319.20​
$400.00​
$200.00​
$80.00​
16500​
20​
$1,979.18​
$2,185.43​
$206.25​
$2,309.18​
$330.00​
$123.75​
$2,391.68​
$412.50​
$206.25​
$82.50​
 

TinsleyC

Registered Member
406
146
43
Dallas, TX
Genesis Model Type
Genesis G80
Here's the wording straight from the 2019 G80 manual.

3.3/3.8 engine
Your new vehicle is designed to use
only unleaded fuel having an octane
number ((R+M)/2) of 87 (Research
Octane Number 91) or higher. (Do not
use methanol blended fuels.)
______________________________
 

Rodney Dangerfield

Registered Member
114
22
18
Texas panhandle
Genesis Model Type
1G Genesis Sedan (2009-2014)
We used to only have one station that sold non EtOH gasoline until last year when two more started offering it. It’s also a good idea to not use EtOH gasoline in small engines like lawn equipment.
 

Kraig Wilkinson

SUSTAINING MEMBER
624
145
43
New Jersey now live in South Dakota
Genesis Model Type
2G Genesis Sedan (2015-2016)
We used to only have one station that sold non EtOH gasoline until last year when two more started offering it. It’s also a good idea to not use EtOH gasoline in small engines like lawn equipment.
I run non ethanol in everything I own, I believe my Genny runs better on it. I average 28mpg with 5.0 sometimes it goes up to 34mpg believe it or not! Of course that is no red lights or stop signs. Love my Genny!!
 
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