Fuel Economy estimate?

[WDoherty]

i got 25.5 mpg on a 5 hour texas highway drive yesterday with the a/c blowing( i think that sucks about 2mpg). That's better than it used to get i think the last time i checked it was getting 22mpg highway without the a/c so the only thing i can think of is the new spark plugs i put in, sweet!

 

[xirforever]

you can also get a piggyback to alter the a/f ratio as some sources on the internet say it runs rich stock. So lean it back to stoich and youll get better gas mileage.

 

[jtjerry]

but only on open look. on close loop ecu try get stoch mixture all the time so piggy back do not work on closed loop.
there is needed stand alone or piggy that can affect oxygen sensors signal (say it give ecu signal o2 little rich so ecu turn it down little lean)

 

[stevechumo]

Why would you guys want to alter the stock fuel/timing while the engine has no modifications? Normally, if you pull out the fuel, the timing is advanced and that's not a good thing. But if you carefully tune it, then you might gain some hp. That's what most aftermarket ECUs do with stock engine. However, it costs like $1000 or more for this, which I don't think is worth.

My experience was that I took my ECU from one of my Hondas (stock engine) to JETCHIP and guess what, they gave me some misfires along with damaging the cylinder walls. After that, I don't trust any ready re-programmed ECUs, unless the programmer put my car on the dyno, hooking up all the sensors, monitoring it and tune it. You can see many programmers advertise that you can send in your ECU for a re-tune. That's very risky because every car is different based on its mileage and condition of each car, although the tuning was tuned on other cars with the same model/year.

So before you do this, ask yourself a few questions. How do you know if the ECU is still in specs, fuel injectors working properly, combustion chamber is cleaned with no damaged pistons/rings/walls...etc? How about other sensors?

Again, if you really care for the gas consumption, this V8 is not a right choice. The V6 might be a better choice. But if you look for more power, then this V8 maybe the right choice. Power and gas consumption are always linear. You may ask David (Lextreme) about his turbocharged LS400 or Jibby about his NOS SC400, they'll show you how powerful their car are, but also show you how fast the gas needles drop down after each rev.

 

[Spooled 7M-GTE]

Man i love sc400's but their fuel ecomony is brutal... My heavy ass van eats less gas. lol
BTW, are there any ways to make your sc400 burn less fuel? Other than not punching it, i mean like any mechanical stuff or things to add on to it.

1- remove the "power" mode
2- try to swap a lower differential gear (but performances will be affected)
3- check for tire pressure
4- use the economy mode with the A/C (A/C compressor uses 10-15HP that's 15 horses you need to make drink
5- if you've got a bad ass sound system (1200W and more) Alternator will suck you a good 5-7HP too
6- good, O2, clean catalitic converters, good Air cleaner, NO COLD AIR INTAKE, good fuel pressure (within specs) good fuel filter clean oil in trans/diff, all the mud guards under de car (air flow) will help.

 

[WDoherty]

i was saying that i was impressed by my gas mileage on my last trip, but that i think the diff swap like spooled said would be a big one. Swapping diff's from an ls400 would ad some mpg and in return lose some accleration.

 

[UZZ30-Québec]

1st tank this week

I filled 65.353 liters of 91 octane for 550km, 85% city driving.

I'm pretty amazed by the fuel economy the car gives!