V8StickConv

I'm still getting 20 mpg overall, considerably better on the highway. Good gas and STP motor treatment help injectors to function much better. Interestingly, I tried 89 octane with no appreciable benefit in performance or gas mileage.

cruisin5268d

89 is just a slight bump over 87 so I'm not sure why you'd expect major improvements. Go with the 93.

jt14894

I run non-ethanol 87 octane in my 05 GT and average (50 City/50 Hwy) between 23 to 24 MPG. Strickly on the highway going 70MPH, it can get has high as 27.5 to 28 MPG. City wise, it can get as low as 22 MPG.

amptor

at 80mph I would expect the fuel economy to go down on any car even if it is a prius. I don't like 70mph zones because people abuse the speed limit and set their cruise on 80-85mph and bulldoze through the traffic with their cars.

If you keep your cruise on at 65-70mph you should be able to get more mpg.

EPA specs on vehicles sold at dealerships typically are for the weight of oil that is on your oil cap (or in your car's user manual) plus driving at the legal speed limit. So you are correct that you would probably have to be setting your cruise at 65 or something. It really depends what speed they tested and rated the vehicles at.

I had a V6 and expected more fuel economy because I wasn't aware that with the traffic this area has, you should be going by the "city" milage, not by the one in the middle or the highway milage.

If you are getting 20mpg at 70-80 that sounds reasonable to me. I read on these forums some time ago that if you do a CAI and tune for 91 octane you can get better fuel economy but then you will have to be spending extra on 91. I have one vehicle that I use 91 in all the time and probably does not require it but I don't prefer purchasing the highest cost fuel all the time although it really doesn't matter a whole lot. Prices on gas go sky high anyway. I remember when 92 octane was a whole $1 less than it is for regular today. I used to buy it all the time and it wasn't bad.

amptor

This is what I want to achieve. I haven't seen figures like that since the first 1000 miles when mine was new. I need to drive more conservatively I guess. Also I have found that different brands of fuel are definitely performing differently in my car. I want to switch brands but chevron is the cheapest gas you can buy (which makes no sense to me haha but that is how it is, I used to avoid chevron with my other cars because it was always the most expensive).

V8StickConv

I am getting 21.8 mpg city/highway over my last 2 tank fulls. I admit, when I get in a 70 mph zone, I go 80. The car is an incredible smooth cruise at 80 mph, 2400 rpm in 5th gear. I don't use cruise control either, because I hate having machines in control.

jpplaw

Even with all my mods and the occasional romp, I still get 17-18 mpg city and have gotten as much as 20-21 mpg highway.

ZGrand

First tankful through the (new to me) '06 GT convertible I got 19.9 MPG. I'm used to driving my truck, so 19.9 seemed pretty welcome!