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Go with the 3.625" if you have 93 octane. With 91, I would stay with 3.75".
3.625" then
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Stallion Kings
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- Daniel
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- Whippled 2015 Mustang GT Premium PP
Whipple, can you explain why the recommendation? I normally mix my crappy 91 oct gas with 100 oct to make 93 but I have the 3.75". Just curious
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He was trying to achieve max power as he had LT's, another .125" smaller will achieve 20-30rwhp more when the octane is high enough (93-94). So mixing the fuel like you do for the 3.75" will still net a power gain, but if you want more you can go to the 3.625". But I would only recommend with the mixed fuel as 91 is just not good by itself. Many do it but it's closer to the edge then I like.
One thing to note, fuel from different stations vary drastically. There is Tier 1 and Tier 2 fuel types. Tier 1 is the big names like Shell, Chevron, Unocal, etc and Tier 2 is Coscto, Von's, Arco, etc. ones from Tier 2 are typically rejected fuel or fuel that didn't pass the test from Tier 1 companies. This fuel knocks more than others. That's why it's so cheap in comparison to Tier 1. We tested a few weeks ago Costco gas (customer had it filled up), motor knocked on the dyno. Drained fuel, put Chevron 91 and it didn't knock. Net difference 42rwhp due to timing change. We have come across a lot since we test so many vehicles over the past 28 years but it's more pronounced on the Fords with the added/subtractor knock system.
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