what octane do you use on your stock 2.4 engine? (and ethanol?)

If there has been a thread about this before - sorry - please reply with the link

if not --

those of you that have stock 2.4 liter engines: do you use "regular", "mid grade" or "premium"?

here in Colorado the posted octane numbers are 85, 87 and 91 respectively

I have always believed that if you can't hear pinging, you are OK

I ran 85 in my 73S for years and then a mechanic I trust said i should run 91

isn't it true that higher octane fuel is more difficult to "combust"?

could 91 cause a misfire in my car?

and the subject of ethanol: the nearest place to get 87 ethanol free is 23 miles from my house - do you folks seek it out or not worry about it?

higher octane slows the burn down, in theory some loss of power. If it doesn't ping use lower octane. In Oregon we can buy alcohol free gas but only in Premium, so that is what I run, loss of power or not. Gordon

On my two 72 S's it will depend on what I'm doing. If its just freeway driving/ touring, then I use 89 octane. When I'm autocrossing or time trialing then I'll use the 93 octane. I have even run them on 87 with no problem, but not when I'm flogging them.

Pulled this from a thread on using iridium spark plugs and what octane fuel should be used with the 2.4 and MFI.

Check Measure Adjust page 36 says
2.4 engines should use 87 octane fuel, engines operating on higher octane fuel will not run properly since the greater the anti knock capacity (octane number) of the fuel, the more difficult the fuel becomes to ignite.

Hope this helps

Lash

I use 87 regular, ethanol free. The station is about 20 miles away, but worth the drive. 93 ethanol free is close to home, but the engine runs well on 87

I use 87 octane ethanol free. We have Racetrac stations all over Florida. I spent thousands of dollars last year on fuel pumps and one rusted gas tank in my collection. I'm ethanol free now.

Richard Newton
Historic Racing Images

agree with the no "ethanol" if you can find it - regardless of octane go sans ethanol - but if 87 it's fine

thanks for the replies

higher octane = more ethanol, correct?

it is a cheap way to add octane - yes - not to mention a way to move farm production away from food

Most gasoline that has ethanol in it will contain up to 10% by volume. Here are some articles to help explain a bit..

How is octane level "created"...

http://chemistry.about.com/cs/howthi.../aa070401a.htm

Some concerns about use of ethanol in fuel...

http://www.fuel-testers.com/gasoline...hanol_E10.html

I burn premium ethanol...and add a couple ounces of Startron to every tank full.

Quote:

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Originally Posted by FL-Frank

I burn premium ethanol...and add a couple ounces of Strartron to every tank full.

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do you have the stock compression ratio?

If you live in Boulder, you can use regular, octane demand drops with altitude. At sea level and hot weather you need premium to be on the safe side. At least I do. As hot as it gets here in Texas, and here it can be 95 in December today and 35 the day after, I find it safer to stick to Premium. Probably overkill, but cheaper than a hole in the piston.
And I have 8.5 to 1