Negative. It does burn a bit more, but I’m actually seeing about the same MPG on the new setup as I did with the old. Keep in mind the new setup is a 427 with a big cam, the old was a 348 with a mild cam. So in some ways it’s actually turned out to be more efficient for me. At WOT it’s using more fuel, sure. But it’s also making nearly 200 more RWHP than it did before, that’s a lot more energy so clearly it takes more fuel to produce that energy. But at cruise etc. it takes less throttle-position to do the same speed since the motor is making so much more power/torque so it ends up evening out pretty well.
And I couldn’t make the power I’m making on 91, so it’s not even reasonable to compare cost to 91. If you want to compare costs I’d have to compare to at least 100 octane unleaded which is NOT cheap around here.
There are a few local C6Z guys with similar heads/cam/intakes to mine (both stock and aftermarket short-blocks, but we’re all 427s) who are doing 580-590rwhp using 91 on the same dyno I put down 600 using E85. However, all of them have true 3" exhausts the whole way, I’m still running my stock Ti exhaust (with it’s multiple 180* turns in the flow-path, and ~2.25" pipe) and a 85mm stock C5Z MAF. We’re slapping a better exhaust on it and ditching the MAF this week (hopefully, if all works out) to see what it’ll do then it’s going to the strip Sunday. My builder is going to drive it because I’ll be back in Afghanistan by Saturday.
-TJ