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

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25
votes
3answers
7k views

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 ...
3
votes
1answer
49 views

Is it fine to use higher octane gasoline than what is recommended on the fuel cap sticker

I've got a 2000 W202 Mercedes C240. It's got a V-shaped, six cylinder gasoline engine. On the fuel cap, it says RON 95 EN 228. And in the manual also it says "Use only Premium Unleaded petrol". I ...
12
votes
4answers
5k views

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 ...
1
vote
1answer
35 views

What grade of fuel should I use for my car? [duplicate]

I have a 2006 Volvo XC90. The manual says that the recommended fuel is 91 octane, and the minimum is 87. I found a forum thread with people recommending various things, but the consensus seems to be ...
3
votes
1answer
63 views

Premium vs. regular in medium compression engines

We probably all know that using premium grade gasoline in a low compression engine (less than 9.5:1) is nothing but a waste of money, but what about medium compression engines with a compression ratio ...
7
votes
1answer
50 views

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 ...
63
votes
9answers
26k views

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 ...
5
votes
2answers
2k views

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 ...
1
vote
1answer
47 views

How can I tell if I would benefit from higher octane fuel?

Given the number of variables involved in whether an engine will knock on a given fuel in a given environment: How can an end user determine whether the engine is retarding timing due to fuel octane? ...
2
votes
1answer
43 views

How often does my engine check fuel octane?

I have an Acura TL, which specifies "premium" fuel. However, I know that the engine has anti-knock sensors that retard timing to prevent detonation if somebody accidentally fills it with lower-octane ...
5
votes
2answers
87 views

Is it a good idea to top off the gasoline with higher octane fuel in a specific case?

When topping off the gasoline in a vehicle that is rarely driven (100 miles/month), is there any advantage in topping it off with a higher octane gasoline? I've heard stories that the octane of ...
8
votes
3answers
22k views

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 ...
4
votes
8answers
16k views

When given a choice between octane 89 and 93, which should I choose?

I just recently got a 2005 Volvo S40 with a turbo engine; I want to take good care of it, so naturally, when the instruction manual recommends 91 octane fuel but says it takes a minimum of 87, I have ...
23
votes
8answers
63k views

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 ...
0
votes
1answer
517 views

How much Octane Fuel does Honda CBR 250R (India Version) needs? 91 or 93?

Honda CBR250R STD 2013 Model's manual state that fuel(petrol) used should be 91 or more. Seems like they have defined the minimum threshold of RON than stating the optimum RON for the given bike. ...
2
votes
2answers
136 views

Toyota Sprinter does not specify octane rating

I have recently acquired a 1999 Toyota Sprinter (Japanese domestic import). I realised that the engine "ping" so someone recommend to use 90 Octane petrol. I went through the manual but it only says ...
4
votes
3answers
1k views

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

I initially thought there should be a way to bolt on a small aftermarket turbo onto my naturally-aspirated Honda D17A2 (9.9:1 compression ratio) engine in my EM2 Civic EX without having to switch from ...