Anyone use regular gas in their Si?

AUGM1

Senior Member
Joined
Apr 22, 2019
Threads
48
Messages
105
Reaction score
18
Location
US
Vehicle(s)
SI
Country flag
Just wonder how the performance and gas mileage are affected.
Sponsored

 

Masked

Senior Member
First Name
Jos
Joined
Jul 12, 2019
Threads
17
Messages
253
Reaction score
275
Location
Quebec, Canada
Vehicle(s)
'18 Civic Si Coupe
Country flag
Oof big no for me, I'm on 94 and nothing less. This platform performs super well on higher octane gas, don't go below 91.
 

REBELXSi

Señor Member
Joined
Aug 12, 2018
Threads
44
Messages
2,443
Reaction score
2,377
Location
215
Vehicle(s)
'18 Si coupe RIP, '20 CRV EX-L Hybrid
Country flag
Just wonder how the performance and gas mileage are affected.
I've done it over a full tank of highway miles and it was fine but I was just cruising the whole time. Didn't see a hit on mpg.

I wouldn't do it if I was going to drive in a... Spirited fashion.
 


Bluecoupe777

Member
First Name
Eric
Joined
Aug 3, 2019
Threads
3
Messages
22
Reaction score
12
Location
98275
Vehicle(s)
2018 Civic Si Coupe
Country flag
Just my two cents..Honda recommends premium in the turbocharged Si for a reason. I would never recommend putting regular in a car that is designed to run on premium fuel unless you want to risk some type of future repair work. Also, I'm pretty sure it says either premium fuel only/required or at the very minimum, recommended right inside the fuel door as a reminder. I'd also think this could potentially void the warranty on the engine should something go wrong from running 87.
 

tinyman392

Senior Member
First Name
Marcus
Joined
May 21, 2018
Threads
14
Messages
3,265
Reaction score
2,082
Location
Illinois
Vehicle(s)
'18 Civic Type R (RR)
Country flag
Just my two cents..Honda recommends premium in the turbocharged Si for a reason. I would never recommend putting regular in a car that is designed to run on premium fuel unless you want to risk some type of future repair work. Also, I'm pretty sure it says either premium fuel only/required or at the very minimum, recommended right inside the fuel door as a reminder. I'd also think this could potentially void the warranty on the engine should something go wrong from running 87.
Required fuel is regular unleaded with premium recommended. So using regular fuel won't void the warranty, but it'll pull timing and cut power to adjust for the different fuel. Basically with the Si (and Type R), the engine is designed to run on premium, but can run on regular as well with an ECU that will adjust timing for the fuel that is in it.
 

Gino27

Red Rocket
Joined
Dec 18, 2018
Threads
6
Messages
91
Reaction score
39
Location
Ohio
Vehicle(s)
2020 si coupe
Country flag
Sometimes I put 87 in it just by habit. The power doesn't feel as smooth as with 93, but a lot of people would be totally fun with just regular.
 

REBELXSi

Señor Member
Joined
Aug 12, 2018
Threads
44
Messages
2,443
Reaction score
2,377
Location
215
Vehicle(s)
'18 Si coupe RIP, '20 CRV EX-L Hybrid
Country flag
Just my two cents..Honda recommends premium in the turbocharged Si for a reason. I would never recommend putting regular in a car that is designed to run on premium fuel unless you want to risk some type of future repair work. Also, I'm pretty sure it says either premium fuel only/required or at the very minimum, recommended right inside the fuel door as a reminder. I'd also think this could potentially void the warranty on the engine should something go wrong from running 87.
They definitely won't void the warranty for using regular. It says premium recommended.

If you want the full potential of the engine, stick to premium.

You could probably go far on regular gas and Honda fluids but this is a forum of mostly enthusiasts so there's a lot of synthetic oil from boutique manufacturers and definitely no regular gas.
 

MattyNice

Senior Member
First Name
Matt
Joined
Jun 5, 2018
Threads
2
Messages
344
Reaction score
284
Location
Charlotte, NC
Vehicle(s)
2018 Honda Civic Si
Vehicle Showcase
1
Country flag
Yeah, it says “recommended” I believe for cars with sport mode. I just figure I bought the car for the performance so may as well use high Tess. I have thought about using 87 at times but even my cheap *** has yet to do it.
 


pinhead66

Senior Member
Joined
Jun 6, 2019
Threads
45
Messages
711
Reaction score
447
Location
Bay Area, CA
Vehicle(s)
2019 Civic Si Sedan, 2018 Odyssey EX-L
Country flag
My first tank from the dealer was 87. After that nothing but 91. If you drive it conservatively all the time im sure 87 would be more cost effective. But since the gas mileage is so great theres no reason to skimp.
 

LittleturboSi

Senior Member
Joined
Apr 4, 2019
Threads
15
Messages
69
Reaction score
56
Location
Canada
Vehicle(s)
2019 Civic Si
Country flag
Yes I did that on purpose few times to test. The performance is affected by using 87, but not by much as I thought relatively (vs 2015 Si). The mileage is about 6-8% worst for the same type of driving.

For my 2015 Si, I could tell the difference right away even between 89 and 91.
 

Monocacy

Senior Member
First Name
Bruce
Joined
Aug 12, 2017
Threads
2
Messages
111
Reaction score
110
Location
Maryland
Vehicle(s)
2017 Civic Si sedan
Vehicle Showcase
1
Country flag
Yes, that is about what I found. Modern engines have knock sensors so if your engine begins to knock under load the computer will adjust the timing, reducing knock but also reducing fuel efficiency. Increased fuel efficency for high-octane gas partially offsets the increased cost of high-octane fuel.

Also, knock sensors don't adjust timing until they hear knock. Over time knock increases wear and tear on your engine.

For me it does not make sense to buy a sporty car and then not give the engine the fuel needed to perform as designed.
 

ltrinh

Senior Member
First Name
Larry
Joined
May 20, 2018
Threads
3
Messages
167
Reaction score
70
Location
Temecula, CA, USA
Vehicle(s)
2018 Civic SI Coupe
Country flag
Since dealer had 87 in the tank, I used 87 for the first 1k miles, then 91 (there is no 93 in SoCal) for the next 1k miles, back to 87 for the next 1k miles. Obviously this was for testing. 87 performed slightly worse in MPG, but not by much, as expected.
91 is better for the engine, more fun, and MPG. Enough for me to stick to 91 ever since the first 3k miles testing.
 

maggs_10thgen

Senior Member
Joined
Aug 9, 2019
Threads
10
Messages
513
Reaction score
410
Location
New York
Vehicle(s)
2019 Civic Si Coupe Old whips: 2005 RSX Type S, 2015 Civic Si Coupe, 1998 Integra GSR Green, 1998 Integra GSR Red
Country flag
Premium fuel is very important in a turbo charged vehicle. You want to avoid detonation.
Sponsored

 


 


Top