93 Octane vs 91 Octane

[roddy]

This time of year, I don't notice much of a difference between 91 and the 94 we have here. In the heat and humidity of summer, the car runs noticeably different on the 94. So much so, that I put up with the crickets to run it. I wouldn't describe it so much as more power, it just runs better... Throttle response is better, there is less hesitation on initial tip-in, and an occasional ping that I get when rev matching is less apparent on the 94. My elevation (~300 feet) on the shores of Lake Ontario may play into that a bit.

[protpibe]

Will petro or husky 94 in canada be more beneficial on a turbo setup over shell 91 with no ethanol?

[Suberman]

Originally Posted by protpibe

Will petro or husky 94 in canada be more beneficial on a turbo setup over shell 91 with no ethanol?

Ethanol is high octane. There's no reason to avoid using it other than fuel economy suffers a bit since ethanol has less energy per litre.

Pretty much all North American gas has ethanol in it, more in winter, except for Shell V Power which uses a different (and supposedly secret) octane booster.

The stories about ethanol being a bad thing are just stories, not based on any fact.

Octane rating is a performance rating. 93 is higher octane rating than 91, regardless of what is put in the fuel to achieve the rating. 91 is European regular gas.

[wparsons]

^^ European octane ratings are also calculated differently... european 91 octane is the same effective octane as north american 87 octane. RON vs AKI (RON + MON / 2).

http://forums.rennlist.com/rennforum...explained.html

Octane is also not a performance rating, it's a rating of knock resistance. A side effect is that it lets you run more c/r and/or timing for better volumetric efficiency (and power).

Higher octane fuels actually burn a bit slower, so unless your engine is designed/tuned for higher octane you actually get worse performance from incomplete combustion. If you're not getting knock or timing pulled on 91 octane, running 93 or 94 octane isn't going to generate more power without a new tune.

[Suberman]

Originally Posted by wparsons

^^ European octane ratings are also calculated differently... european 91 octane is the same effective octane as north american 87 octane. RON vs AKI (RON + MON / 2).

http://forums.rennlist.com/rennforum...explained.html

Octane is also not a performance rating, it's a rating of knock resistance. A side effect is that it lets you run more c/r and/or timing for better volumetric efficiency (and power).

Higher octane fuels actually burn a bit slower, so unless your engine is designed/tuned for higher octane you actually get worse performance from incomplete combustion. If you're not getting knock or timing pulled on 91 octane, running 93 or 94 octane isn't going to generate more power without a new tune.

I've not seen 91 in Europe. They don't sell it as far as I know, at least not in Western Europe.

I don't know where you got your strange idea about high octane gas burning slower. The reason you get slightly less power if you use higher octane fuel in an engine that doesn't need it is it contains less fuel per litre. That's because it has more anti knock additives.

[Clipdat]

It does "burn" slower in the sense that it doesn't explode prematurely before the full stroke of the piston has been reached. 91 is "harder" to combust versus 87. That's the reason why if you put 87 in a twin the ECU has to pull back the timing and not be so aggressive.

Originally Posted by Suberman

I don't know where you got your strange idea about high octane gas burning slower. The reason you get slightly less power if you use higher octane fuel in an engine that doesn't need it is it contains less fuel per litre. That's because it has more anti knock additives.

[Fizz]

In Australia our Shell V-Power is rated as 98RON, but IIRC it's comparable to 93 is the US....is that correct?

Edit: Just found something interesting here. So it appears that 98RON is Australia is comparable to 93 in the US since American stations use PON rather than RON.
http://honda-tech.com/showthread.php?t=284380

[Mikeez]

The real difference between both of those is that 91 contains more lead. Therefore, lead is a metal and takes longer to burn. Since it's a fine metal, however it will not affect much since 93 do contain traces. What you can do is when you travel outside your area. Add better gas, you can use whichever you want.

[JB86'd]

Originally Posted by Mikeez

The real difference between both of those is that 91 contains more lead. Therefore, lead is a metal and takes longer to burn. Since it's a fine metal, however it will not affect much since 93 do contain traces. What you can do is when you travel outside your area. Add better gas, you can use whichever you want.

Seems legit.

[wparsons]

Originally Posted by Suberman

I don't know where you got your strange idea about high octane gas burning slower. The reason you get slightly less power if you use higher octane fuel in an engine that doesn't need it is it contains less fuel per litre. That's because it has more anti knock additives.

Science and facts, not sure where you get your magical ideas from. Talk to people that tune engines for a living and see what they say about 87 vs 91 octane or 91 vs 94 octane.

The power potential with a new tune is higher with higher octane, but just running higher octane than the tune is built for will do exactly what I said. That alone disproves your theory about the anti knock additives.

You won't harm an engine running it on higher octane, but you're just throwing away money unless it's tuned for the higher octane. That said, I only run 94 for autox and lapping because I get some tip in knock on 91 and 94 is cheap insurance for harsher driving, but daily I run only 91 through mine. I haven't dynoed it with both fuels, but the butt dyno says there is little or no difference in output. Once I get my OFT I'll log some pulls and throw them into virtual dyno to show the differences if there are any.

[Future]

We did the test at QuebecFRS.com... Difference between 87, 91 and 94 octane on an FR-S...

Results: 87: 155hp, 91: 160hp, 94: 166hp

Source (french) : http://www.quebecfrs.com/forums/index.php?topic=2222.0

[wparsons]

^^ I'm not going to go off on that article again, but without doing multiple runs for consistency and comparing logs of what was happening I don't trust the numbers. You could easily do two runs back to back with nothing changed and get a 5hp difference.

The only way you're getting more power form 94 is if the ecu is pulling timing on 91 because of knock.

[Mad1723]

Originally Posted by wparsons

^^ I'm not going to go off on that article again, but without doing multiple runs for consistency and comparing logs of what was happening I don't trust the numbers. You could easily do two runs back to back with nothing changed and get a 5hp difference.

The only way you're getting more power form 94 is if the ecu is pulling timing on 91 because of knock.

No one is more blind than the one who does not want to see.

Sent from my Nexus 7 using Tapatalk

[Suberman]

Originally Posted by Fizz

In Australia our Shell V-Power is rated as 98RON, but IIRC it's comparable to 93 is the US....is that correct?

Edit: Just found something interesting here. So it appears that 98RON is Australia is comparable to 93 in the US since American stations use PON rather than RON.
http://honda-tech.com/showthread.php?t=284380

94 PON (AKI to some).