91 octane?

the98stang

Active Member
Aug 12, 2005
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Clovis, CA
Hey guys I was just wondering if 91 octane gives our 4.6L engines more power? (assuming the car is naturally aspirated, with no tuner). I always thought our engines would LOSE power if we didn't run 87? Someone please explain the science behind this. Sorry if this is a stupid question, I just never really understood octane.
 
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Simply put, the higher the octane rating, the more resistance to detonation.. the more compression it takes before the contents of the combustion chamber will spontaneously combust. So running higher octane on a stock engine does you nothing besides empty your wallet more quickly, unless you have problems with detonation.

Running higher octane allows you to do things like advance timing, run higher compression, etc.. won't help you with the stuff you've got.
 
sgarlic said:
Simply put, the higher the octane rating, the more resistance to detonation.. the more compression it takes before the contents of the combustion chamber will spontaneously combust. So running higher octane on a stock engine does you nothing besides empty your wallet more quickly, unless you have problems with detonation.

Running higher octane allows you to do things like advance timing, run higher compression, etc.. won't help you with the stuff you've got.

Thanks for clearing that up :)
 
My wallet is draining from high octane as we speak. Just as I was going to trial some 93 octane to see if it gets rid of my rattling noise, the prices jumped 30cents! One tank in, still rattles. So anyways, like he said...stick with the 87, gas itself won't give you a power increase. Unless there's a hot gal at the pump next to you, then you could impress her by pumping the good stuff...and spray a little 93 all over the parking lot just to show her you've got money to blow.
 
I run amaco ultimate 93 they claim it "cleans your motor"...but I have to run it because of my blower....if I could run 87 I would...with gas prices in this country those oil tycons dont need any extra money from me
 
jstreet0204 said:
If your car isn't set up to run higher octane, you may be doing more harm than good. Higher octane fuel burns slower. If your engine isn't burning it all off it can leave more carbon build up.

Yes!! And you will actually lose the slightest bit amount of HP and gas mileage on the stock tuning.

However my SCT mail order tune can barely run on 93.