wow your IS350s are crazy! my IS250 manual gets about 22-24 mpg, i drive mainly only streets. ive been shifting at low rpms recently to save a lil bit of gas

 

Based on the responses here, I don't think you can really make that conclusion. If I drive conservatively, I can maintain 21-22 on mostly city streets. I suspect that the remaining difference could easily be due to the fact that you have a manual tranny and a lighter car.

 

IS250 and IS350 dont weigh that much differently to make that big of a mpg difference. The 250 automatic actually makes better mpg than the manual according to lexus, check it out if you dont believe me. Shifting early and getting to top gear earlier will save you gas, you will be a little slower than someone else who doesnt but you save gas

 

I've consistently gotten between 22.5 and 24.5 mpg per tank. 90% highway but when i sit in traffic it really kills the mpg which is often.

the most gas I've put into the tank was 16.5 gallons and I had over 410 miles on that tank!

The gas light comes on at about 13 gallons consumed, and 0 miles left hits at about 15 gallons.

 

According to the brochure, there's about a 2% reduction in weight, 9% increase in final drive ratio (no mention of tranny gearing), and 3.6% increase in estimated highway mileage for the 250 manual. Of course, it also lists a 4.7% decrease in estimated city mileage...

Even still, I think the difference is more easily disregarded by differences in driving styles, climates, altitudes, and break-in mileage.

 

Some cars don't always make better mpg in the lowest RPM. Some vehicles make better MPG at 2,5k-2.8k, RPM, where the engine is not lugging along, trying to create power with a partially open throttle, while injecting loads of fuel to match the torque. For example, putting your car in highest gear, then trying to accelerate may have you in low RPM, but you're not getting good MPG for the above reason. I'd say keeping it in low RPM really depends on your vehicles speed/load.

 

I think I drive pretty conservatively, and i've been average ing 15.5-15.9 mpg. Not what i had expected. Tank average shows an even more dismal 14.5 avg. What gives? Do I relly need to baby the thing to get in the 20 mpg range?

However, this is still better than the 9-11mpg my STi was giving me.

Greg

 

Are you confirming these MPG numbers with actual mileage per fill-up? That seems REALLY low. I haven't gotten less than 18 MPH yet, and I've done a lot of aggressive driving.

 

What do you consider conservative? and how many miles on your car? Off the top, most of my gains come from coasting whenever possible, and accelerating at a good pace up to speed, then applying light throttle to maintain a 'cruise'. Traveling around 45mph give or take, usually offers the best compromise in distance vs fuel usage for me.

Edit:

Aside from your exhaust, I see you've also changed your wheels/tires; this alters the revolutions a wheel spins per mile. This can affect your speedo readout, and the two in combination may just as well affect the MPG calculation your car is attempting to determine.

 

Wheel and tire changes won't change gearing (or speedo / MPG calcs) unless the new tires have a larger or smaller outer circumference.

 

I commute 154 miles roundtrip a day in my 250 MT with 17" stock wheels, only 20 miles of city driving so what, 85% HWY using cruise control. Lifetime MPG is 30.1MPG.

@65mph with AC On, 42 MPG
@70mph with AC On, 34 MPG
@70mph with AC Off, windows up, 36MPG
@75mph with AC On, 28 MPG

Here is a picture after driving at 65MPH for 60 miles and includes 10 miles of city driving, but still, the city driving is only 5 lights in the 10 miles. All miles were virtually flat driving, not many hills:

I'll have to take a pic when the tank is almost empty and still over 40 MPG. Maybe next week. Won't happen over the weekend when the wife takes the car

 

I get 22.1 AVG MPG. FWIW, I filled up this morning and with 3mi left on the diplay, the car took 14.886 gallons.

 

The size difference was the point I was making reference to, however regardless of this change, gearing will remain the same.

 

IS250AWD,,, tank average 27 to 28 mpg
80% highway
Average since I have had the car 27.4mpg
and i use 89 oct. gas
40mpg WOW!!!!!!!

 

That's awesome! I wish I could get 30+MPG. Right now I only drive about 7 miles round trip to work so my MPG is only 18 on average. When I drove to San Diego I got it up to 27.4 MPG, but never higher. Me and my lead foot....