[Shovelman]

Doesn't higher octane make an engine harder to start in cold weather? Not normally a problem but if the battery is low or if there are other problems, wouldn't 93 in a 91 engine be more likely to leave you cursing?

[nioh_lbbm2]

The gas is already blended for different seasons for mass public use. Stop worrying. If your battery is discharged the problem you have is that your battery is discharged.

It's a mass produced car sold worldwide

[overcoil]

I’d never read that high octane gas made an engine harder to start, is that true ?

I have read that high octane gas will be less likely to pre detonate on a high compression engine or an engine that is on the upper limits of efficiency/ performance ( high rpm, direct fuel injection, fuel pressure, brake mean effective pressure )

[RoundelM3]

93 octane gas will not make an engine harder to start - the octane level prevents detonation (pre-ignition) in high-compression/forced induction engines. Has zero to do with cold starting.

[B58togo]

E85 blends cause longer start times in colder weather. I run E40 and notice a slight increase in start time when it’s under 35 degrees or so, but not enough to concern me.

[KennyFSU]

The only downside is that it costs more.

[morphomeman]

If we are talking 91 vs. 93, there is no price difference, because most markets carry either one or the other. Here in New York, it is 93. I have sometimes toyed with the possibility of using 89, which is about halfway between 87 and 93, but have never done so.
Is OP suggesting that 89 would be better in the winter than 93?
That would be a great excuse for spending less money on fuel, though I drive so little these days . . .

[RoundelM3]

If you use lower-octane fuel, your engine will not produce full power due to the DME pulling back timing to reduce engine knock/detonation. It will NOT make your engine "start quicker" in cold weather and you run the risk of engine damage. Read your owner's manual where it clearly states that you should only use premium-grade fuel (91/93 octane).

[KennyFSU]

Originally Posted by morphomeman

If we are talking 91 vs. 93, there is no price difference, because most markets carry either one or the other. Here in New York, it is 93. I have sometimes toyed with the possibility of using 89, which is about halfway between 87 and 93, but have never done so.
Is OP suggesting that 89 would be better in the winter than 93?
That would be a great excuse for spending less money on fuel, though I drive so little these days . . .

In FL, there is a price difference between 87, 91, and 93.

[Shovelman]

It clearly states 89. My question is because resistance to detonation seems to mean resistance to firing, an event necessary to starting.

[nioh_lbbm2]

I don't think you understand how an ICE works.

Detonation in laymen terms is spontaneous combustion of the fuel before it reaches ignition from spark. It causes knock.

[3.0L]

Originally Posted by nioh_lbbm2

I don't think you understand how an ICE works.

Detonation in laymen terms is spontaneous combustion of the fuel before it reaches ignition from spark. It causes knock.

Detonation can be very destructive including dents and holes in the tops of the pistons, or worse.

[albertw]

Originally Posted by Shovelman

My question is because resistance to detonation seems to mean resistance to firing, an event necessary to starting.

I would like to rephrase the question.

The spark temperature is far higher than the spontaneous ignition temperature of the mixture or the temperature of the flame front once the mixture starts burning. Thus, firing is not the issue.

I have heard several backyard experts say that high octane burns a bit slower. If that is true, it sort of makes sense that on a cold startup when the fuel doesn't fully vaporize before ignition (making the gaseous portion of the mixture leaner than intended), the flame front might advance more slowly with higher octane. This might cause lower octane to start a bit better.

I have no opinion on this and I would like to have a better understanding of it.

[3.0L]

Originally Posted by albertw

I would like to rephrase the question.

The spark temperature is far higher than the spontaneous ignition temperature of the mixture or the temperature of the flame front once the mixture starts burning. Thus, firing is not the issue.

I have heard several backyard experts say that high octane burns a bit slower. If that is true, it sort of makes sense that on a cold startup when the fuel doesn't fully vaporize before ignition (making the gaseous portion of the mixture leaner than intended), the flame front might advance more slowly with higher octane. This might cause lower octane to start a bit better.

I have no opinion on this and I would like to have a better understanding of it.

Why not let the fantastic computer controlled fuel injection system in our cars figure it out.

[Maynard]

These engines use such a high pressure for direct ignition that 'don't fully vaporize' isn't really possible. FWIW I stick with 93 all year and never noticed any slow starting, but if the manual says 89 or better you could certainly use that to save a few bucks (if you aren't really horsing on it in the winter, you won't miss a few Hp). And I think the additive packages for cold weather make more difference for driveability than the octane ever would.

[Shovelman]

Thank you for your responses, they have helped me to understand and clarify my question.

I understand very well how an engine works and about detonation. What I am asking about is chemistry. Specifically, does higher octane have the side effect of resistance to ignition in the proper fashion?