Kia Optima Forums banner
1 - 20 of 21 Posts

·
Registered
2015 Kia Optima
Joined
·
1,016 Posts
Discussion Starter · #1 ·
If the manufacture says to use 87 or higher, is 91 a waste of money?
As with cars that are tuned, higher octane can benefit them. But for a stock car, does the ecu recognise the higher octane and thus advance timing accordingly? Curious about the new 2.5T.
 

·
Registered
2013 Kia Optima
Joined
·
173 Posts
If the manufacture says to use 87 or higher, is 91 a waste of money?
As with cars that are tuned, higher octane can benefit them. But for a stock car, does the ecu recognise the higher octane and thus advance timing accordingly? Curious about the new 2.5T.
I've always used mid grade. Most cars or bikes i've used don't like regular and i can hear and tell the difference. Especially during winter when they put in additives.
 

·
Registered
Joined
·
63 Posts
Depends who you talk to. I've never noticed much difference besides my wallet being a bit lighter. In my opinion, the cost outweighs any small difference. The ethanol free gas is probably a better investment, if you can find it where you're located.
 

·
Registered
2015 Kia Optima
Joined
·
1,016 Posts
Discussion Starter · #4 ·
I use shell. The manual says 87 or higher.
Cost aside, trying to figure out if 91 will add to the performance of the engine or not.
 

·
Registered
2015 Kia Optima
Joined
·
1,016 Posts
Discussion Starter · #6 ·
I know it's been discussed many times over anf that hyundai engineers claim +10 hp on premium due to ecu advancing timing, want to know if its the case with the 1.6t and 2.5t.
2.5T is gdi and mpi... If it makes a difference.
 

·
Registered
2018 Kia Optima
Joined
·
1,146 Posts
One way to find out is if you are willing to buy some dyno time and test there.
 

·
Registered
2020 Kia Soul X-Line 2.0 MPI
Joined
·
102 Posts
Very tempted just to get to the bottom of this lol
You will need three consecutive tankfuls of 91-93 Premium, to judge the difference. Many owners try only one tankful and most times it takes a couple more tankfuls to feel the benefits.

Trying to find non-ethanol in 87 octane is almost impossible here in Michigan. Shell, BP, Mobil , Exxon.....etc.....etc.... all are 5-10% ethanol now.

The laws have changed here. No longer do the gas pumps have to read non-ethanol or up-to 10% ethanol. By law it's no longer a requirement to say one or the other on the gasoline pumps that house 87-93 octane..
 

·
Registered
2018 Kia Optima
Joined
·
1,146 Posts
Can't be much worse than pumping gas in a state that has either the highest or second-highest gas tax in the country, in addition to having either the highest or second-highest overall gas prices (per gallon) as well.
 

·
Registered
2015 Kia Optima
Joined
·
1,016 Posts
Discussion Starter · #12 ·
Let me put things in perspective for you.
Here in Quebec Canada we pay the equivalent of 4. 67 per gallon for regular and 5.35 for 91. I think your prices are great. Now, the amount of taxes we pay is a whole other story.
 

·
Registered
2016 Kia Optima
Joined
·
43 Posts
youre going to get a lot of anecdotal evidence. - i would suggest with going what the manual says but if you are open to it, you can investigate it yourself. some people will say theyve had best luck at 87 others with higher. all depends haha. also price can definitely be an issue as well.
 

·
Registered
2015 Kia Optima
Joined
·
1,016 Posts
Discussion Starter · #14 ·
New genesis has the same engine and uses 91 octane and is rated at 300hp. Could be the same for the 2.5T.
Been using shell 91 and so far I'm at 9.3L/100km
Improved from the 10.1L
 

·
Registered
2018 Optima EX Premium PHEV
Joined
·
14 Posts
If the manufacture says to use 87 or higher, is 91 a waste of money?
As with cars that are tuned, higher octane can benefit them. But for a stock car, does the ecu recognise the higher octane and thus advance timing accordingly? Curious about the new 2.5T.
On a naturally aspirated motor I'd say premium is a waste unless explicitly recommended... On a boosted motor (turbo charged) it's definitely worth it...Like someone else mentioned, it'll take a few tank fulls for the ECU to adjust timing to take advantage of the higher octane fuel, but I'd put money on it that you'd eventually notice a seat-of-the-pants difference in performance. 👍🏼
 

·
Registered
2012 Black SX Prem. & Tech.
Joined
·
2,181 Posts
On a naturally aspirated motor I'd say premium is a waste unless explicitly recommended... On a boosted motor (turbo charged) it's definitely worth it...Like someone else mentioned, it'll take a few tank fulls for the ECU to adjust timing to take advantage of the higher octane fuel, but I'd put money on it that you'd eventually notice a seat-of-the-pants difference in performance. 👍🏼
Even if you notice the improvement, I'd still suggest analyzing the actual dollar cost for that improvement.

Where I live, the difference in cost between 87 and the higher octanes can be a dollar per gallon! So that's like $20 extra per fill up. For me, I'd rather keep the $20 and I'm plenty happy with the 87 octane performance in my turbo.

PLEASE NOTE If you have a turbo, maybe you were like me, where the turbo (electronic wastegate voltage setting) was not properly adjusted, so you had lower boost and lower performance. Adjusting the wastegate linkage was very simple and restored the lost performance, which was very noticeable difference compared to before the adjustment.

Bottom line, if you have poor performance, you might want to check your turbo before spending extra money on premium gas. Also, in the past, Hyundai engineers said the engine will adjust timing to take advantage of premium, and you'd get about 10 extra HP at the crank, which would translate to a few HP at the wheels. This is equivalent to going on a diet and losing some weight so your car would accelerate faster.
 

·
Registered
2018 Optima EX Premium PHEV
Joined
·
14 Posts
Even if you notice the improvement, I'd still suggest analyzing the actual dollar cost for that improvement.

Where I live, the difference in cost between 87 and the higher octanes can be a dollar per gallon! So that's like $20 extra per fill up. For me, I'd rather keep the $20 and I'm plenty happy with the 87 octane performance in my turbo.

PLEASE NOTE If you have a turbo, maybe you were like me, where the turbo (electronic wastegate voltage setting) was not properly adjusted, so you had lower boost and lower performance. Adjusting the wastegate linkage was very simple and restored the lost performance, which was very noticeable difference compared to before the adjustment.

Bottom line, if you have poor performance, you might want to check your turbo before spending extra money on premium gas. Also, in the past, Hyundai engineers said the engine will adjust timing to take advantage of premium, and you'd get about 10 extra HP at the crank, which would translate to a few HP at the wheels. This is equivalent to going on a diet and losing some weight so your car would accelerate faster.
I'm a PHEV owner coming from a twin turbo BMW and I'd argue that if you're driving a boosted vehicle, more times than not, the best fuel economy isn't your ultimate goal; performance is... Lol. Chasing hp #s can be addicting. Thank you for your valuable wastegate feedback.
 

·
Registered
2015 Kia Optima
Joined
·
257 Posts
Since there doesn't seem to be much in the way of empirical data here yet, I will share what I found on my older 2.0T. This may not directly translate to the newer 2.5T, but I have found these results to be somewhat similar in other performance cars. It seems that in performance applications, many ECM's have a base timing table that is somewhat aggressive, then one or multiple alternate timing tables that are reverted to if knock is found to be present consistently (use of lower octane fuels would do this).

On my 2015 SX-T with the 2.0T engine, I found a peak gain of 10hp between 87 octane and 91 octane. The dyno runs were done in the same gear, on the same dyno, about a week apart, and the car was driven 245 miles between the runs, about 150 miles on the tank of 91 after the tank of 87. The OBDII data showed as little as 1* more timing, and as much as 2.5* more timing throughout the run. The run with 91 octane always had more timing than the run with 87 octane. Coolant temps were within 7* at the start of the run (187* vs 193*) and the same at the end of the run (196*). Intake air temp was also within 7* between the two runs.

250279
 

·
Registered
2018 Optima EX Premium PHEV
Joined
·
14 Posts
Since there doesn't seem to be much in the way of empirical data here yet, I will share what I found on my older 2.0T. This may not directly translate to the newer 2.5T, but I have found these results to be somewhat similar in other performance cars. It seems that in performance applications, many ECM's have a base timing table that is somewhat aggressive, then one or multiple alternate timing tables that are reverted to if knock is found to be present consistently (use of lower octane fuels would do this).

On my 2015 SX-T with the 2.0T engine, I found a peak gain of 10hp between 87 octane and 91 octane. The dyno runs were done in the same gear, on the same dyno, about a week apart, and the car was driven 245 miles between the runs, about 150 miles on the tank of 91 after the tank of 87. The OBDII data showed as little as 1* more timing, and as much as 2.5* more timing throughout the run. The run with 91 octane always had more timing than the run with 87 octane. Coolant temps were within 7* at the start of the run (187* vs 193*) and the same at the end of the run (196*). Intake air temp was also within 7* between the two runs.

View attachment 250279
That's a decent amount just for better gas... In the crowd I come from that's a win! Thanks for that value added info! Btw @WS6_Keith what year was your Gen 4 TA? I had a 2001 with the Hurst and 3:23 rear. Cheers!
 

·
Registered
2012 Black SX Prem. & Tech.
Joined
·
2,181 Posts
Interesting in the chart how the max power and max torque came at different RPMs between the different octanes
 
1 - 20 of 21 Posts
Top