Motor Vehicle Maintenance & Repair Stack Exchange
Motor Vehicle Maintenance & Repair Stack Exchange

Questions tagged [octane]

A number relating to the ignition temperature of gasoline in a combustion chamber.

Higher Octane numbers ignite at higher temperatures. Engines and fuel control systems are designed for a specific Octane number. These engine manufactures recommended Octane rating should be used.

Using fuel with a higher Octane number will not result in better power or fuel mileage in engines that were not designed for that Octane number.

42 questions
82
votes
10 answers

What are the benefits of premium (high octane) petrol?

Here in the UK it's common for petrol (gas) stations to offer both regular and "premium" unleaded petrol. The premium stuff is (naturally) more expensive, and I've often wondered what the actual difference is. Would I need to fill up with premium…
Simon Whitaker
  • 1,053
  • 2
  • 9
  • 9
29
votes
3 answers

Static vs. Effective compression: Why does higher effective compression not require higher octane gas?

Background I've been trying to do a lot of research on boost lately because I'm planning on running a moderate turbo setup on my daily/light-duty-autox car in the future. I'm trying to get into the physics of things so that when I do my build, I'm…
Annath
  • 643
  • 2
  • 6
  • 13
29
votes
9 answers

Will higher octane fuel improve gas mileage?

I've heard from some people that high octane fuel will increase gas mileage. Around here, we have the basic unleaded(87), mid-grade(89), and premium(93 or 91). I've been using the basic 87 unleaded forever because it was the cheapest. Also, in my…
Earlz
  • 927
  • 6
  • 11
  • 19
17
votes
5 answers

Can I use lower octane fuel at high elevation?

Here in Colorado, gas stations sell "regular" gasoline which is rated at 85 octane ((M+R)/2). In most of the rest of the US, 87 octane is the lowest grade available. (As noted previously, higher octane fuel can withstand higher compression without…
Nate Eldredge
  • 1,068
  • 2
  • 14
  • 26
16
votes
4 answers

Difference between high octane and low octane?

What is the difference between high octane and low octane fuel? I'm not asking if one is better than the other for my vehicle, specifically, but rather what occurs differently both scientifically and mechanically when either is used?
HaL
  • 263
  • 1
  • 2
  • 5
14
votes
6 answers

Should I use gasoline 87, 89 or 93 on 2016 RAV4 SE

I read many articles online and people have different opinions about this issue. Some say 89 is the best for acceleration. Others say 87 is just fine. I'm worried only about the health of my car. So I read my user manual. Here are the…
Emily
  • 297
  • 1
  • 2
  • 8
12
votes
3 answers

Wrong octane fuel

I have a 2014 Fiat Punto and have been using 92 octane gas. I have never read the manual, but am now told I should use 95. Should I use what is in the tank before filling with 95 or is it OK to mix them.
Judith hb
  • 121
  • 1
  • 3
7
votes
2 answers

How much can sub-optimal octane affect efficiency or power?

Suppose a production fuel-injected engine is tuned for 93 octane fuel. As I understand it, the engine can still run on lower-octane (i.e., less knock-resistant) fuel, but it will pull timing to avoid knocking. In effect, on lower octane gasoline…
feetwet
  • 1,199
  • 2
  • 19
  • 41
7
votes
1 answer

Gasoline grade manufacturer recommends vs what was used during testing

Toyota recommends to use regular(87) grade of gasoline, but tested cars with the gasoline grade 91(see user manual). Somebody know why they recommend to use grade 87 if they did not tested cars with this grade?
P0MAH
  • 71
  • 1
7
votes
2 answers

Switching to a higher octane

This may be a very noob question to ask. But I recently got this car and was used with 92 octane petrol. However, to my negligence I overlooked the user manual which states to include 95 octane petrol. My question is, will it cause a problem if I…
Hasitha Shan
  • 417
  • 1
  • 5
  • 15
6
votes
2 answers

Accidentally put regular gas in Infiniti G37

So my 2013 Infiniti G37 requires premium gas (91 octane) but I just got it so I didn’t know, and I accidentally put regular gas (87 octane) into the car. I filled my tank almost fully with regular gas. I have only done this once since I just got it,…
Kyle
  • 95
  • 2
  • 7
6
votes
4 answers

Is it feasible to Turbo a NA engine while maintaining 87 AKI octane fuel use?

I have a Honda Civic with a naturally-aspirated Honda D17A2 (9.9:1 compression ratio). Goal: I want a modest horsepower gain (say +38 hp) in the lower-mid-range powerband; I'm not after the maximum horsepower potential. My goal is better overall…
Luke
  • 61
  • 1
  • 3
5
votes
2 answers

How can my car run on 85 octane but be recommended to run on 91?

My manual recommends I use 91 octane, especially when at altitude or towing, but says I can get by on 85. To my understanding, the octane rating is a measurement of fuels tendency towards preignition, which is caused by compression heat. I doubt my…
Sidney
  • 1,090
  • 3
  • 13
  • 21
5
votes
2 answers

Will 93 octane fuel burn completely in an 87 octane engine?

This is a little more specific than the "wrong fuel" question: I'm looking for the long term impact of using a higher-octane fuel in an engine designed for lower octane fuel. Not quite diesel in a gas engine but tougher burning fuel... :) This is…
Shrout1
  • 403
  • 3
  • 7
  • 19
5
votes
2 answers

85 octane gas causing engine knocking and retarded CAM time?

I'm about to betray my ignorance of cars but here goes: I am a driver from Minnesota (where the lowest octane rating is 87) vacationing in Colorado and have noticed that after I put 85 octane gasoline in my tank I have been experiencing engine…
Isaac Toenies
  • 51
  • 2
1
2 3