2007 3.5 SXT Magnum w/U7136 - Bad Gas Mileage

[fokkerpilot]

Quick question:
Since I've installed the Predator canned tunes of either 91 or 93 octane (using Sunoco 91 & 93) I have notice a decrease of gas mileage to 11 mpg. K&N CAI and Dynomax true dual exhaust only mods. Also noticed fair amount of carbon on tailpipe tips. Currently trying the Modified Factory Tune for HP to see how things go, but there is a degradation of performance versus the 91 and 93 canned tunes. Any thoughts??

[09SuperBee]

something is not right here... I get 17-24 depending on how I'm driving, and I have the 6.1. Post a log so we can see what's up.

[Mike_Levy]

Gas mileage? Whats that? Seriously though, the 3.5 needs to work pretty hard to move the 4000lb boats, so I wouldn't expect good economy out of them. Definetly worse then the V8s.

That said, I get about 9.9-10mpg out of my 6.1, so 11 isn't that bad. You're probably putting your foot into it to try and move the car and higher throttle positions burn more gas.

[09SuperBee]

makes sense to me. I get great milage in my 6.1 when I drive normal, but when I get into that throttle it drops pretty quick. If I wanted a car that gets great milage I would have bought a Honda...

[daronthompson]

I have an 07 3.5L, K&N cold air, Flowmaster 50 true duals, I get between 23-27 on the highway, depending how I drive it. Just got the predator and running the 93 tune. Really woke her up, but I haven't done the mpg yet

[fokkerpilot]

Thanks Mike and Superbee. Didn't give it much thought on the weight issue and true, I had been putting the foot into it more than I normally did - but that was to get around the cell phone driving SUV idiots we have here. My drive to work is only about 6 miles round trip, stop and go, so that isn't helping. I do know that I have put a couple 180 mile drives on it with 29.8 for interstate mileage using the 91 canned tune - and that is no joke. I have noted that using the Modified Stock tune, for just running back and forth to work has, given me an increase in mileage. I'm just trying to milk the best possible mileage for the best increase in hp.

One thing I did notice lately. When using the 91/93 tunes, the stainless exhausts seem to carbon up rather fast. Using the Modified Stock tune, I haven't seen that appear yet. Without jumpin' me, what would cause that? I'm still learning about this stuff - not condeming it - and just looking for some input on the causes.

Not a ricer fan whatsoever. I'll work up a log on it.

**K&N CAI, Dynomax Cat-back Duals w/ Super Turbo Flow mufflers, Diablo Predator.

[Chargeron24s]

The carbon build up on the tips is most likely because your car is running too rich with the tunes..........its burning through fuel more then it needs to be by running too rich which in return is causing your bad gas mileage.......I had the exact same thing happen on my 5.7 Daytona charger.........using the 93 tune, the car would get terrible mileage and the tips would be black as hell after a half of day of driving...........using the 91 tune with 93 gas and playing with the WOT fuel it got better, but still ran rich.......put the stock tune back on there and the gas mileage went back up some, and the tips stayed much cleaner...........you would have to datalog and see where your car is at

[fokkerpilot]

Thats what I figured. I had the carbon issue with the 91 and the 93. No problem with the Modify Stock Tune. I still would like to use the 91 tune though. I'll need to do a data on the 91 and post it. Any suggestions on any specific parameters to log? I saw someone else had a data log about a mile long with too much info. I'd rather keep it brief. Anyone from Diablo want to chinme in on this one? Thanks