Well, last I heard mos cars get best mileage between 40mph and 60mph. Sports cars tend towards the upper end of that range, while slow SUVs tend towards the bottom end. I get 2-3 mpg more going 70mph than I do going 80-85mph. It's all a balance between power spent running the engine and power spent fighting drag. SUV = high drag, small engine (compared to the car), sports car = opposite. Drag starts out as hardly anything at lower speeds, then grows fast at higher speeds, while power used to drive the engine is pretty linear. So adding on another 5mph at high speeds can hurt, but dropping 5mph at low speeds doesn't really help. So you might as well drive at least 70mph, and probably more than that. I balanced my real-world recorded mpg and time spent and 85mph turned out to be best for me. As for safety & speed, as long as you aren't in the top 15% then you are driving plenty safe (there's a study on this, but I don't have the link at the moment). On an interstate you can safely go 90mph no prob, as long as there aren't slower cars in your way. Frequent passing increases the chance of an accident. In fact, going slower than others on an interstate (even if you're above the speed limit) can increase the chance of an accident, especially if you make it hard for people to pass you.

 

I usually do 55 MPH, and not only because of the speed limit, but because I seem to get the best fuel mileage there. From what I read, most cars get their best gas mileage around 45 MPH. I noticed that when I do 70 MPH, I'll average around 25 MPG than my usual 30 MPG at 55. Anything passed 70 I seem to get even less. Around 80 MPH I usually get around 20 it seems like.

 

I try to drive less than 3200RPM, so maybe I'll get some better mileage.

 

That's strange. I get 24-25 @ 85mph and 26-27 @ 70mph. I don't think my mileage improves beyond 27 at 55mph, but it's been a long time since I've checked. My car has no significant mods. But I've noticed my mpg has gone up 1-2 mpg since I've got it (I track very carefully, and use cruise control). Maybe it's the maintenance items, maybe the redlining is cleaning things up, maybe it's seasonal. I dunno.

 

I was watching my wideband 02 meter today and I noticed at 65mph I was at 10.85:1 and at around 72mph I was more around 11.50:1. The engine is running more effeciently at 70-75 but is turning more revs.

 

What kind of ecu are you running, who tuned it?

 

If you are asking me... stock ecu, 2.75" exhuast I got 18mpg city/highway driving

 

uhh... i have an 88 TII and only gets about 150 miles per full tank fillup driving mainly city with a little highway using premium.....

 

You know, I see these threads once in a while, and ask myself: Why would I want to drive an Accord which gets 30mpg, when I could be driving a 600WHP supra that get's 29 off boost?

For an N/A, such things as a racing beat full exaust and header, streetport, and tuning the fuel mixture to lean it out with an SAFC will actualy increase milage from what I know and reaserched, because you get more efficient airflow, and the N/A 13B actualy runs quite rich with the stock ECU.

PS: Another thing one can do to increase milage, is to get realy light wheels/tires, and keep em at the correct tire pressure. A LOT of times, people get bad mialage just from having tires with like 5pounds of air in em!

 

it's not running more efficiently. it sounds like your car is just not tuned well.

 

During "Ultimate Street Car Challenge" hosted by SCC magazine, they had quite a few cars that were calculated to get... surprisingly... very good milage per gallon.

 

What do you have done to your GXL to get 30 MPG?

 

My car is "tuned" to the factory specs since it is all factory minus the exhuast system. I just have the wideband to watch the engine. I have a new fuel pump, fuel filter, plugs, plugwires, cleaned flowed tested injectors and the engine grounds have been cleaned and regrounded. Oh yeah the engine has 2000 miles on the rebuild. I am pretty sure it is in tip top shape...

My conclusion is that these cars run very rich from the factory, I plan on taking out alot of fuel with an AFC for highway speeds. This should pay for itself after a month or so.

 

highway cruise tuning is what i implied. if you are getting those AFRs cruising that is too rich. you can tune into the 15s/16s on cruise, basically go as lean as you can until EGTs start getting too high or the car starts bucking...

 

[QUOTE=coldfire;7384693]highway cruise tuning is what i implied. if you are getting those AFRs cruising that is too rich. you can tune into the 15s/16s on cruise, basically go as lean as you can until EGTs start getting too high or the car starts bucking...[/QUOTE

Well on a stock car there is nothing to tune