87 vs 91 octane in a 3.6

[Joe Bob]

I pulled into my fave gas station last week after a long drive. Was on fumes.

Put the nozzle in and tried to fill up. I get 10 cents and a shut off.....stoopid me, I try again. Same crap.

Go ask WTF to Habib. He looks at me like I'm an idjut (I am, but how would he know?) We allah outta 91.

Put a sign up ya putz......

Anyways, had to fill with 87. Checked mileage after I burned the tank. Same mpg and no knocking. I have a 93, 3.6 non vario-ram.

Whutup wid dat?

BTW, need a new cool collar and an E=Ram

[911s55]

87 has less additives so more pure fuel, more bang. What's your compression ratio?

[Joe Bob]

Dual plug, I'm guessing 9.5:1 or more.

[uwanna]

Originally Posted by Joe Bob

Dual plug, I'm guessing 9.5:1 or more.

au contrere mon ami, it's actually 11.3 to 1 compression. That's why it's twin plug and has a knock sensor system.

[RedCoupe]

The 964 originally was 11.3 compression ratio, I believe, but with dual plugs and active knock sensors the system seems to be able to handle lower than normal octane levels on occasion. I have had to run 89 octane a couple of times and couldn't tell any difference, but I wouldn't want to try to run it on the track or on the dyno with that fuel in it. BTW, my owners manual only specifies 90 US octane, so either 87 or 89 may be within the tolerance that system was designed to handle.

[TCracingCA]

A lot of high tune engines, if you are easy on the gas pedal and just cruising around easily and such, then you can get buy on a lot of cars with good engines on a lesser octane gas. If you are just steady cruising it should run most cars.

But if the state of tune and compression, horsepower etc are such that you are hearing detonation, or your temperatures are going askew, just from switching gas, then it is a very octane sensitive engine and don't do it again. Yes I did say keep an eye on the temps also, because Octane does help there also.

[Elombard]

Can he drop in a bottle of octane boost for this tank?

[NYNick]

I counted 9 colloquialisms.
7 too many.

[uwanna]

Originally Posted by RedCoupe

The 964 originally was 11.3 compression ratio, I believe, but with dual plugs and active knock sensors the system seems to be able to handle lower than normal octane levels on occasion. I have had to run 89 octane a couple of times and couldn't tell any difference, but I wouldn't want to try to run it on the track or on the dyno with that fuel in it. BTW, my owners manual only specifies 90 US octane, so either 87 or 89 may be within the tolerance that system was designed to handle.

yes the lower octane works ok because the ECU retards the ignition when it hears
knocking (ergo putting out less power). When GM came out with the Northstar motor, they specified Premium fuel for best performance, but my owners manual stated you could use Regular fuel, without any negative effects on the motor, but would not have optimum performance. I did some informal testing and found I got better gas mileage with premium.

[911SauCy]

Gotta love a stock '78 vintage US 3.0

8.5:1 ... 87 all day