Troymm

A while back I read that some were getting over 20 mpg with 3.4L supercharged & fuel mods, either with the 7th injector/AIC or URD. I'm sure that driving habbits are some of the reasons, but will I acutally save on gas money if I get a fuel mod.

I only get around 15.5 mpg (but I'm going about 85-90 mph at night going home.) Even If I can get 18 mpg I'll be happy.

mike_d

generally it takes a long time to earn back any money put into a fuel mod.

here's a table. the first colum is miles per gallon. the second column is the amount of fuel you'll save per 1000 miles relative to the 15.5 you said you're starting at. example: if you go to 18mpg, you'll save 8.96 gallons every 1000 miles you drive. the last three columns are how much money that is at different fuel costs. so if gas is $2/gal in your area and you increase to 18mpg you'll save only $18 every 1000 miles (or 1.8 cents per mile). generally maintenance costs and such are estimated around 30 cents per mile, so fuel costs aren't typically a big part of your car budget, it just seems that way because you fill up so often. so weigh the cost of the fuel mod with how much you'll be saving. hopefully all the columns will line up nicely for you.

Troymm

Yeah, I know the savings on the gas money won't add up to much. But just think about it MORE HP, MORE TORQUE, = MORE FUN and less time at the gas stations!!!

roger

The best way to save gas would be to lighten up on the long skinny pedal a bit. Fuel economy with these engines drops off dramatically when you go over 70 mph or so.

I get about 19mpg in town just by not letting the tach go over 2500rpm most of the time. But that might be hard to do with a supercharged truck!

FilthyRich

got that right. Too much fun

Troymm

Its almost impossible for me to stay under 70mph on the freeway. I just filled up the tank and trying to keep it under 80 mph. So far I have 140 on the first half of the tank. I'm usually at 125-130 miles. We will have to see how the rest of the tank goes.

TRDOLMAN

I took a trip to LA from northern California. Did 75 all the way playing in boost some (can't resist) with the air on and averaged 22 MPG. This is with the mods in my sig.

Dave

Roadtripr

I agree with roger, do not use a lead foot and you will see gains. you can also increase tirepressure or check that is not too low. Bigger tires = lower mpg.

X-AWDriver

So,your the guy that takes 30 seconds to get up to 45 on the on-ramp.

Duc Hunter

You guys are all missing one very important thing here. Our ECU's, like most fuel injected cars ECU's do these days, run in "closed loop" mode during cruise. Typically this is below 3500-4000 RPM and below 40% throttle. In those ranges the ECU reads the O2 sensor and corrects the mixture to achieve an air/fuel ratio of 14.7. This is the perfect air fuel mixture for complete and clean combustion, however, it is not the best mixture for power or fuel economy though. Once we are above those areas the car switches to "open loop" where it ignores the O2 sensor and runs based off its fuel map and the knock sensor only (adding fuel and retarding ignition if it senses knock). The stock O2 sensors are very inaccurate, you are either rich or lean, but here is not allot of granularity in the readings. When the ECU see’s a rich condition it adds a set amount of fuel, if it see’s lean it takes a set amount away. No matter how we try to fake the car out by using piggyback computers it will just try to correct itself during cruise because it will see a "lean" condition through the O2 sensor. Mods like the fuel mods for the superchargers (or the AFC's everyone runs on turbo cars for fuel control) are mainly designed to help during "open loop" operation. They also are used to adjust the fuel map in the "closed loop" part of the map so that the car can run at 14.7 when it has fuel injectors that are much larger than the stock ones. With out this the base map would put too much fuel in and the amount of correction the ECU could do is not enough to compensate for radically larger injectors. No matter what though they cannot make a car run at a leaner, more efficient air-fuel ratio during cruise.

On my Galant VR-4 I have tune my aftermarket standalone ECU to run at a leaner 15.2:1 air/fuel ratio and gain a fair bit of gas mileage. Some cars can run up to 16:1 air/fuel ratio at cruise and they see a huge jump in economy. On a smog test though they would fail miserably, because the test looks for 14.7:1. Anyway, I then tell my ECU to run at around 12.5 for max toque just above cruise and before I hit boost and it drops to a very inefficient 10.5 at max boost (this is to fight the detonation that occurs from 21PSI of boost). I can do this because I have a stand-alone ECU that lets me set what air/fuel ratio I want to run at each engine RPM and load point in the map. I also have an aftermarket "wide band" O2 sensor. These are very accurate and are what aftermarket ECU's use to set the air/fuel ratio at specific levels.

To the only way I know of the we can make our trucks more fuel efficient is to increase the engine efficiency. Headers and an exhaust could help as they allow the car to make more torque at a certain RPM. If we can increase the engines torque output at cruise RPM’s it will take less throttle (fuel) to make the amount required to push the car at cruise speeds. The problem here is this is often low RPM, and doing so would sacrifice higher RPM power. That is why muscle car street headers make less power, they are smaller, which makes better bottom end at the sacrifice of top end power. Anyway, long diatribe, sorry!

HaveBlue

265/75/16 BFGs - 27.82 MPG mountain driving
285/75/16 Revos - 25.42 MPG mountain driving

With the larger tires, I average 17.5-18.5 MPG if I drive the 4Runner to work all week (60 miles round trip)

I have a supercharger, 305cc injectors, Apex'i S-AFC, headers, cat-back exhaust, deckplate, etc. etc. etc.

midiwall

heh... I WISH I was getting that kind of mileage!

My mileage dropped to 14mpg (from 17) a couple of months ago (before the S/C) and I've been trying to get it back ever sense. In fact, adding the S/C actually kept it even - even though my right foot is having a TON more fun!

There are a number of "HELP! MY MILEAGE SUCKS!" threads here and I've been through it all, but no luck.

One thing that I'm gonna start doing is killing the morning warm-ups. That's usually 7-10 minutes of running at idle (remote starter) and I know that's not helping anything, but I don't have a way to measure fuel flow in order to compute just how much.

midiwall

I've seen a lot of people say this, and I can accept that it's true, but then how is it that I can use my SMT piggyback to lean out (or richen up) the engine to the point that it stalls?

Again, I understand that the ECU will always seek Stoich. If you watch STFT via an OBDII monitor while adjusting "cell" values in the SMT's map, you can see the ECU working to correct to Stoich, but it still floors me that I can stall the engine through the fuel map in closed loop.

Is it just 'cause I toss a value in that's so far off of Stoich that the ECU can't correct for it in time and the engine stalls?

But then, I know that I can affect how the truck feels in various ways (boggy, "quick", etc) by modifying the fuel map. Even sitting at idle, I can make changes in the map and the engine will respond to them.

weird.

Duc Hunter

In regards to your making the car stall you are dead on. At some point the ECU does not have enough range to richen the motor up to correct for your removing fuel and your car will stall. Often at idle cars wont run closed loop until the water temp is over 140-170 deg. In regards to your boggy/quick, the ECU probably is out of closed loop at 40% throttle. That is really not very much, and some cars go as low as 30%. When you tip in to accel you are over that, then your fuel mods would work.