Hey guys, out of curiosity I was browsing the EPA fuel mileage ratings for a 1992 firebird. According to the EPA, the 3.1 with the 5 speed gets the same city mileage as a 5.0/5.7 (15 mpg and strangely the auto gets 16 mpg) with highway mileage only being 1 mpg better (25 vs. 23/24). Wow does anybody experience this?
http://www.fueleconomy.gov/feg/bymake/Pontiac1992.shtml

 

As I understand it, many of the EPA ratings on government websites mysteriously changed right before cash for clunkers. Hence the disclaimer You can still find the old numbers here... http://www.fueleconomy.gov/feg/calculatorSelectYear.jsp

However... From first hand experience, those revised numbers aren't too far off. My daily driver for about 4 years was a 1991 Firebird 3.1L Auto. My nice weather driver was a 1991 Formula 5.7L Auto. Around town I got better mileage in the Formula. Out on the highway the 3.1 got much better mileage then the EPA rating. Part of the reason the V6 is such a gas hog in town is because it's a heavy car, with a numerically higher gear ratio, that needs to be worked hard to make the car move. The V8 version of the same car can get around town without coming nearly as far off idle.

 

OFF TOPIC

My 1992 Lumina with a 3.1 gets horrible city fuel mileage. I get around 270 miles per tank (16 gallons = 16MPG). Miles per tank goes way up on the freeway, close to 28MPG.

The final drive ratio is 3.33:1 and the 4t60 OD transaxle never gets into OD below 45-50 MPH. I think this is why the car gets crappy around town mileage.

I think the rear axle and the transmission calibration have a lot to do with the V6 and V8 F-Bodies getting comparable mileage.

 

That sounds like normal 3.1 mileage to me... We had a 3100 Grand Am GT and it didn't get any better gas mileage then my Firebird. Same with all the 2.8 and 3.1L Lumina and Grand Prix's my friends were driving. It's not like they were ever gas sippers.

 

the 3100 in my '98 lumina gets about the same mileage. 16/26-28.

 

That makes sense. My 94 Jimmy (4.3 port injection) suffers from the same situation. During the mixed driving that I usually do, I usually get a tick over 200 miles to a tank. But once I was driving to New Hampshire (actually to check out my 91 T/A before I bought it! ) from CT and on the highway I squeezed well over 300 miles on my tank! So I guess if you want an f-body as a daily runner (especially if you do mixed driving) you might as well get a V8, comparable mileage and more power=more fun.

 

Lets not make this a thread about the gas mileage a non 3rd gen get. Drew mentioned and confirmed that the 3.1 gets similar mileage and it was also mentioned as to why. I don't want to read about every car with a V6 and what mileage it gets. The 4 posts above mine should establish the standard for GM V6 mileage.

Sorry, I don't want to sound like a jerk, but in the 6 posts made, 4 were related to other cars and what they get!

 

1 - Weight, For every 10% weight reduction, you get 8% better economy. It should go without mentioning that the heavier the car the more energy it takes to accelerate it. The use of aluminum & Zink, Magnesium & other white metals that are lighter started in the 70's for reducing the weight of a car.. I have even noticed in recent years that there was a trend to more aluminum parts, my 1995 Riviera for example had an aluminum hood, aluminum front bumper support etc. And my wife's Chevy venture also had an aluminum hood.

2 - Aero, The aerodynamics of the car really do not matter much until you get above 55 mph, it does matter a little, but not as critical below 55mph, that is why most newer SUV's get the optimum fuel mileage at about 60 to 65 Mph. But the more aerodynamic the car, the better highway mpg. Other factors related to aero are obviously frontal area and drag, all which play a part into the Coefficient of Drag.

3 - The least obvious factor is related to the Technology. Although it would seem that an automaker would strive to have the best economy possible, there are limitations, IE the government is probably the biggest limitation. On the one hand they want cleaner, more eco-friendly cars. on the other hand they want more fuel efficient cars. These do not go hand in hand as one would think, so as they put more emissions on a vehicle, the fuel economy decreases, either by Weight, or some other factor that limits the progress of fuel economy. There is also the fact of crash zones and such that add to the weight of the car that limit the advancement. Another interesting trend is the more powerful engines seem to be getting, the better MPG they are also getting. A late 4th gen, fully loaded, V8 car gets 30Mpg highway, according to many owners...

ADD moment: Have you ever wondered why a Geo Sprint in the 1980's & 90's got 50 Mpg, but they struggle to get 35 mpg now out of a new small car that is not a hybrid?

Another thing that I seem to notice is that they have not improved as much on the city driving as much as they have improved on the Highway driving aspect, maybe its me, but it seems to be the trend.

 

I've had similar results with my thirdgens. I knocked down a consistant 18mpg with my two different 2.8 5-speed thirdgens, 18mpg with my LB9 5-speed GTA, 18mpg with the stock LB9 auto in my 85, and I get roughly 16-17 mpg with the worked TPI 350 & 5-speed that's in my IROC now.

 

Not to beat this subject to death, but My first new Camaro was a '89 RS with a 2.8/Auto combo, with about 5000 miles on the odometer I drove it from Wisconsin to New York, it got the best of 29 mpg on that trip, after the '89 I bought a New '91 RS, this time with the L03/5-speed combo, I took it on the same trip and averaged 26-27, The next year I drove it out west and coming accross New Mexico, A/C on, cruise set and actually got 31 mpg which was the best for that trip. even my '87 Camaro LG4/Auto got the best of 29, going out to Camaro fest in Ann Arbor. There wasn't alot of difference in Mileage between the V-6 or V-8, I'd take the V-8 anyday

 

The biggest factor for mileage is not the size/type of engine, it's how you drive. The big torqy V-8 labours much less than a V-6 trying to perform to the same level. Out of all my family's vehicles (5 of them), my Camaro gets the best mileage. On the highway with that LB9 in 5th gear, 3.08 rear end, it just coasts along getting high 20's.
Drive any V-8 hard and everything gets thrown out the window. But it's more fun!

 

Oh of course! My 305 TPI with the 700r4 and 2.73 gears (yuck) is probably capable of sipping fuel but I almost always burn rubber when the light turns green!

But the first time I put the car on the road I filled it up to the top. I think I got well over 200 miles on that tank, and that's with a heavy right foot. What's the fuel tank capacity?

 

Wow, this is great to read! I have been looking for a super low mileage 91/92 V6 Firebird as a commuter, I might rethink as the commute is in town.

Just to add, when I got my GTA 10 years ago with 69K miles, I on 3 or 4 different drives to the bay area, got about 330 miles to a tank with my 2.73s! It was great! Now after all my mods I get about 300 miles to a tank with 3.42s and a 2400rpm converter.

 

Oh wow, I'm planning on putting those gears in as well and I didn't think that the mpg drop would be so subtle, well that's good though!
And regarding the V6 car as a DD, yeah I thought the same thing! Might as well get a V8! More fun for similar mileage

 

Keep in mind too that both those numbers are driving on I5 up through CA going about 68-69mph with the cruise set and highway mode NOT enabled in the tune.

The minute I touch the gas to pass or something, guzzle guzzle guzzle lol!

 

In my opinion, mpg numbers are almost meaningless. My DD is a 1989 Firebird, 2.8 (now heavily modded stroker) with a 5-speed. My daily commute is 80km each way. I used to get 3 1/2 days per tank, now it's about 2 1/2. The reason? Almost half of my commute is now bumper-to-bumper creaping.

As soon as you get stuck in that kind of traffic, your emissions go up, efficiencies go down and as I said, mpg becomes meaningless.

 

Yep gotta love it. And you stroked a 2.8?

 

Very easy to do - the 3.1 is basically a stroked 2.8 (but I did do a few other things as well - - check on the V6 forum for the possibilities - and as soon as I get done with the tuning, I'll easily stay with a stock V8).

My other point, at least as far as a 5-speed goes, is that the clutch on the V6 is so much lighter than on the V8. I have a Centerforce clutch on one of my GTAs and I could hardly walk after I got out of that car followimg my commute. The V6 clutch is so much more friendly on knees, etc.

 

Haha nice. I can imagine someone asking "Why do you walk with a limp?" "I have a trans am with a 5 speed." haha. I thought that the 3.1 also had a difference bore?

 

Not to take the thread into a different realm, but the bore is the same on the 3.1 vs the 2.8. The stroke is different. So, when I did my rebuild (after about 425,000 km), all I did was replace the rotating assembly. The mods, well....pretty extensive (you can PM me for the details if interested).

But on the original topic, I'm about the same for mpg vs my 305 GTA's. Again though that relates to the fact that I spend a lot of time idleing in traffic. If the road is clear and I drive the V6, I come out better than the V8 - by about 20-25%.

 

Oh that makes sense, thanks. We all learn something new everyday lol. And was 425,000km your first engine rebuild on that car?

 

Yep!!

 

Not bad!