Up here it's something like 10 to 12 cents per litre difference between 87 and 91...and with there being 3.78 litres to a US gallon, it's works out to around 45 cents a gallon/$7 a tank difference.

 

Modern EFI cars have sensors which will adjust tuning if a less-than-optimal octane rating is used. This avoids valve knock and damage to expensive engine parts chronic knocking will cause, but the power curve drops a little and you aren't getting the ponies you paid for when it's running in this "dumbed down for cheap gas" mode.

Don't lose any sleep over it if you've put 87 octane in a late-model car for which 91 is "recommended" but not required. No harm done--they're all made to cope with it since 91 simply isn't available in all parts of the country all the time.

 

I think in the long run gas milage wont be the same. They made the motor like that for a reason. I would think there is some reason why.

 

The reason is the 2.4 is a higher compression engine at 10.5 to 1. At higher compression ratios you are more likely to get pre ignition hence the higher octane fuel.

 

There was sarcasm in my post. Guess it wasnt noticed.

 

I obviously did not pick up on it. my bad

 

I didn't pick up on it either.

Then again, I haven't been able to correlate the reply with the quoted text

 

In the old days of leaded gas, you could go 1/2 tank leaded reg. and 1/2 tank of unleaded premium and the lead in the reg. would give a slight boost to the premium's octane.

 

And I am using 91 octne.....2.4 with less than 3000kms. Will try 87 (reg.) sometime after 1st oil change to see how it goes. It is the min. recommended in the manual. Best rating I've seen is 91 octane. I don't have a Shell stn. nearby so 93 is kinda hard to find.

Jim

 

I alternate between Preimium and Regular Unleaded. My observations are with just Premium, I get a little better gas mileage.