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Old 07-24-2013, 03:25 PM
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Join Date: Apr 2010
Location: Macomb, Illinois
Age: 52
Posts: 798
Gender: Male
Vehicle: 2004 Quad Cab diesel
Trim Level: SLT
Color: Silver
Engine: 2005-20?? 359ci (5.9L) Cummins ISB 610 24-Valve Diesel I6 325hp 610 lb/ft
Rep Power: 5
Rep:221
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I have a Challenger that I have a Diablo Predator on it. I had a guy custom tune it on a dyno where they can see the air fuel ratio and tune the car to it. A custom tune doesn't really mean much, he just bumped the timing up a couple of degrees from a stock tune and leaned it out a little bit.

With a Diablo you can record data to a laptop and look back and see different parameters. Two of them that you can log are short term and long term knock. I was getting some short term knock with my tune running 91 octane fuel. I'm sure if I was running 93 octane I would have gotten less or none. I was only getting the knock at the high rpms right before the shift into 4 gear. Short term knock isn't all that bad, I think mine was only pulling about 3 degrees of timing at the most. The problem is if you get a lot of knock, it dumps that into the long term knock which means its pulling timing all the time.

So to answer your question, depending the the tune and the tuner, 93 octane might or might not be needed.
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2004 3/4 ton Quad Cab, 24 valve 5.9 Cummins
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