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Only if you have a very high compression ratio or are running ALOT of timing (or maybe a combo of both). The C5 has a set maximum timing amount and cannot go past that point. If the motor is picking up knock, then it may help, but you would only need a little more octane than what you are currently running (not as high as 103). Using more than 93-94 will not help.
Higher mileage motors with carbon build up can experience more knock than a new one, but it can be corrected with higher octane or a decarbonization process used by quite a few members on the forum.
Welcome to the CF board (98redvert). What Mike said is true, I added 1gallon of sunnoco 104 unleaded to my car while at the track and I lost 1.4 mph & 1tenth through the 1/4mi.
If I use 103 octane fuel will I notice a difference?
My car was on the opposite side of this. Vortech C5 did a data run on my car and noticed that I was getting knock retard of 5-7 degrees at the top of 3rd and 4th gear. I put in 5 gallons of 103 Sunoco and ran the car last weekend at the drag strip and picked up .6 seconds. Bottom line is if your car is getting knock retard the higher octane will help the power if your car is running perfect it wont help any and can actually slow you down. The higher the octane the slower the burn.
From: IF YOUR BIG DOLLAR PROJECT DOESN'T RUN 9'S OR BETTER ....BURN IT ! SHUT YOUR MOUTH AND GRAB A LANE ! CHICAGO IL. -------- HOME OF THE FASTEST STREETCARS BARNONE !
Re: 103 Octane worth it? (Yano)
Hi octane will benefit a Poweradder (nitrous ,sc) Especially if You don't want to lean out ,and as in Yano's Case his Vortech . I have to agree with Mike and I also say anything over 94 Octane will not be beneficial on a Untouched stockmotor. :seeya
Noting that all the previous posts are true, I can add that a modified '99 with a Lingenfelter motor shows a very noticable improvement running the higher octane achieved using Nulon's octane booster...which should put the 91 octane "poopie" that I have to buy somewhere between 95 - 97 octane. You're lucky to have the option to buy 103...if I lived there, I'd mod the engine JUST to take advantage of that gas!