I completely forgot that the Magnaflow V6 exhaust had the outlets on the same side of the muffler and one routed back to the passenger side. That exhaust should be perfect for what you're looking for. But don't try to compare your current winter gas mileage now to what it does if you install it later on when the temps are closer to 60 degrees out. I think I'm getting my worst mileage of the winter right now looking at my readings.

yeah i figured they would just use the same system as the v8's

Looking inside the muffler, it is straight through. There are two perforated pipes welded into a V shape with a mini-two pipe collector at the input side, and each leg of the V angles to an output. It literally splits the input flow into two output pipes. You can look right through, but you have to look at an angle to see through each leg.

Heard that winter gas gives lower economy, but I never tested it. I'll take your word on it. Hate working in the cold with hand tools, so I'll wait until March or April to install it. Also have the aluminum drive shaft to install too.

It does. I still watch my fuel usage like a hawk, its a good indicators of issues. I lose ~5% on winter gas. The snow tires I used to run cost me another ~5%.

Magnaflow built the V6 system specifically to enhance V6 performance, rather than selling the V8 with a few V6 mounts tacked on. For a stock 3800, the 3" V8 system is reported to cause a loss of bottom end torque. I always thought the Magnaflow was too expensive for my budget, but when I could get it for less than $300, I just couldn't pass it up. Thats even cheaper than some of those "aluminized" steel cat-backs.

Wow, I didn't realize winter fuel could cause as much as 5% economy loss! That is the pits....

That could also account for the 0.5 - 1.0 mpg fuel economy loss since changing the rear gears early in winter.

Update: Found this on the Chevron website:

They go on to say other winter factors increase the loss of economy. I'm surprised I was not really aware of how significant the impact of winter is on fuel economy.

seems like win win with magnaflow then 8-)

Yes, winter seems to cause a loss of 2-3 mpg regardless of the engine. I've watched my mileage drop that much with 4cyl, V6 and V8 vehicles.

Yup, I go from 17-18mpg to 15-15.5 in my Jeep from summer to winter.

- Justin

MPG Update time!

FYI... the average MPG has risen 1.5 mpg. Thats a 6% increase over the average of 25 mpg. I bet your happy and relieved that its quite a bit better than your prediction of "very unlikely that you will notice a difference in MPG.....be the same or slightly a tenth better".

Yep, I am getting similar results with the V6.

Just as I expected, there is a very measurable increase in fuel economy. Seeing as there were a few trips on rt80 that were bumper to bumper, I expect the long term MPG to be even better.

Magnaflow claims a 2-3 mpg improvement (iirc).

Rather than starting a new thread, I decided to find this old one and update so all the info is in one thread.

The "winter" gas is pretty much gone from the fuel tanks in these parts. I also learned its not just a Summer/Winter blend. The fuel is modified to match the degree days throughout the year. So late winter/early spring gas is different than mid winter gas, and different than summer gas.

Anyway, to the point of the post.....

To recap, the mods to the car are: 3.73 gears w/Truetrac posi, PCM tune (PCMflorless.com), Magnaflow V6 exhaust, 180 Thermostat, and low restriction intake.

My last 4 tanks have averaged 26 mpg. That includes some traffic backups due to accidents in the commute that I thought would ruin the numbers, but didn't happen.

So keep in mind that changing gears like I did (3.08 to 3.73) is not going to blow your fuel economy out the window (like so many posts said). When you drive with a light foot, and keep your speeds under 67 (I cruise at 65 mph @ ~ 2300 rpm when possible) the fuel economy should not be impacted, depending on mods done.

I have to admit, that the week I was off from work, and working on the car, I was hammering the throttle often, doing 0-60 tests, peel outs, etc and also just doing around town driving, and short trips such as taking the kids to school. The fuel economy for that week dropped to 20 mpg. Apparently WOT sucks the fuel. :mrgreen:

So, what did you learn?

- The claims that changing gears will drop fuel economy 3-5 mpg in our V6 are proven bogus. Especially if other mods off set the change, like PCM Tune and Exhaust.

- The 2-3 mpg improvement claimed by Magnafow is probably closer to 1-2 mpg, and along with the PCM tune, offset any loss of MPG due to the gears. Claims that the exhaust will only give a "tenth" of a mile per gallon are most likely bogus.

- Yep, winter fuel does give lower MPG than summer fuel.

- WOT sucks fuel. So if you are wondering why your car does not get good economy, its probably due to your right foot, and not the cars mods.

Throw in a vacuum gauge. Try to keep it as far from 0 at all times- that'll give you the best milage.

yup that worked well in my supercoupe. kept it away from 0 or going into boost whenever possible to do so and ended up getting mid to upper 20s. its all in driving habits :nod: it also makes things easier when trouble shooting for little things

I was running my stock 3.8 with a 4.10 rear end. I had Whisper lid, WS6 ram air hood with ram air box, MSD Coil packs, headers, 3 inch y-pipe w/o no cat, 3 inch S pipe, 3 inch I pipe, and a Flowmaster 80 series with 3 1/2 inch tips! It sounded so mean. I was also getting around 28 miles per gallon in the city and 32-34 mpg on the Highway! I would drive up to Jersey from VA beach with only using 1/2 tank of gas. It was 260 miles to my parents house! When I did the built motor I was still getting 25mpg in the city and around 30 mpg on the highway!

Here's an interesting one for you. The 2001 Silverado Z71 I bought a month ago has pulled down 14.8 mpg on the first half tank which was daily commuting and not getting into overdrive or above 50 mph, then another week of daily commuting and a 130 mile highway trip(65-70 mph in overdrive) averaged out to 14.8 mpg as well! :-? My last tank with daily commuting came out to 14.8 mpg. I just changed the plugs, put in a 160 t-stat, a ported TB and took off the mud tires and put on some BFG AT's. Already it rides quieter and actually coasts when you take your foot off the gas. I think the worn mud tires were really hurting it big time. I'll see what this next tank does before doing some tuning, the LTFT's are running around 8 so I should be able to adjust the fuel curve and spark to get better cruise conditions. I need to see what the first set of changes did first though.

Jeff, tires can make sure a big difference in MPG. Width, compounding, etc.,

I actually went 1 size up on the tires from 285/75 to 295/75 but I'm sure the tread pattern is going to be the big difference. I can really feel it and hear it in normal driving and the block size on the Mickey Thompson Baja MTZ tires is huge compared to the AT tires. But looking at the LTFT on the scanner after the ported TB vs stock is showing how much better the air is flowing in. I also cut back the EGR tube that sticks into the intake like I did on the SS and that is probably helping airflow as well.

Mark, that makes me wonder what the EGR setup looks like on the V6 cars? If the tube sticks into the intake as bad as it does on the V8 cars you might want to look into trimming that tube back to allow better airflow.

It goes in about a 1/2 inch. I removed mine from my old V6 to save on weight.

Will make this update short and sweet.....

Now that construction is done on RT80, and no more winter gas, the fuel economy is now 27.45 average compared to a best average of 26 when the car was bought last summer.

So, even though a few trips showed a best of 27 mpg average for the one 15 gallon trip last year, now I am showing a weekly average of 27.45 for regular commuting (without construction backups/delays), including some strictly around town driving.

I will be doing some long highway drives from NJ to LI all through the summer. Will be interesting to see what the MPG is for those long highway trips. Bet the car averages better than 30 mpg.

Again, I have to admit that the PCM tune and Magnaflow exhaust have offset and/or exceeded any loss due to changing from 3.08 to 3.73 gears.

Your mileage may vary... :mrgreen:


Hmmmmm. See above. AND, its time to start posting your MPG and driving habits. OK?????

And all you guys should do the same. Its not hard to write down the mileage and gallons. It helps everyone because it gives them a reference. If enough folks post their milage, maybe this thread will become a sticky.

My mpg is more painful when you write it down.

youd think the six cylinders would get better mileage than the v8's :?: damn gm

Yeah, and the milage went UP after a gear swap. :mrgreen:

Well, that is the average for that cars use. The type of driving the car gets is documented earlier in the thread. How does your driving compare to the V6 Firebirds use? More highway, less highway?

If you question yourself about your driving habits compared to what is in the thread, then you will have the answer to your inquiry about 6 vs 8 economy.

Let us know how it turns out for you.

Good luck,

Mark.

i got upper 20s in the past few ls1 cars ive owned. id label the driving style as ''Spirited'' :nod:

On the Highway my LS1 and V6 were pretty close. Best I got about 27 mpg in my T/A and the best ever in my V6 was 33mpg! Around town the best I can do in my T/A is 300 miles per tank! I use to avg between 380-420 miles per tank in my V6 around town! All of this is by using skip shift in my T/A and 1st-3rd-5th in my V6! Normal driving in my V6 I never took it above 3000 rpms! The car sounded mean as hell up to 3000 then it started to sound like a V6 after that!

In Virginia the track was 75 miles away from Virginia beach. I use to cruise up there in my V6 with the other T/A guys. We would fill up before leaving Va Beach, then I would make 5-10 runs there and when we got home I would still have between a 1/4 -1/2 tank left. All the LS1/LT1 guys would have to fill up when we left the track!