Random curiosity to see if a fun daily can achieve decent fuel mileage. I've seen one car on here that claims ~27mpg in a 6.0/T56 swapped 2 door Volvo. Anyone think a fairmont wagon with a 6.0/4l60e and some highway gears(3.08-3.27) would even come close to that number? I know doing a LSx swap and hoping for good gas mileage is laughable but let's entertain the idea at least. What's your swap get?

 

I get 21-22 going 75-80MPH.

Remember, aerodynamics play a big factor with MPG. 3rd gen Firebirds had one of the slipperiest shapes around.

Andrew

 

My swap is far from done, but seeing as I own an 08 G8 GT (6.0, 6L80e, 2.92 rear gears) and I can get about 25mpg hwy @65-70mph with the DOD disabled... I'm HOPING I can at least get 24-26 hwy after swapping the 6.0/6L80e out of an 09 G8 GT into my 72 Chevelle. Planning to run either 3.08 or 3.42 gears in the Chevelle...

The Chevelle doesn't seem like that big of a brick in the wind (in my mind) compared to some cars, and considering it could be appx 500lb lighter w/ driver than the g8, I don't think my estimate is too far fetched?

I don't think a Fairmont wagon is super aerodynamic? What's that beast weigh?

 

I've had up to a 24 mpg avg in my chevelle on the highway with LS1/T56 combo.

 

I had 30mpg in my reg cab shorty 98' S10 that was lowered 6". L33 5.3l LS6 cam and intake with a GTO T56 and 3.73 gear and 26" tall tires. I ran it SDOL and AFRS at cruise where about 15.5:1. It ran 12.9@109.

 

My '33 gets right around 20 with LS1//4l60e, my Nova does about the same, LS1/4l60e. My 71 swb gets 17 5.3/4l60e and my LTD wagon gets around 18. These figures have been checked over the course of many thousands of miles, so I say they're pretty accurate. Checking one or two tanks just doesn't give an accurate measurement of mileage.

To the OP, I wouldn't hold my breath hoping a Fairmont wagon will get close to those numbers.

 

My aerodynamic brick '39 Chevy MAY be getting very good MPG. I say may because I don't have enough time on it to tell for sure. Most of the 400 miles I have on it is local and not filling the tank all the way but I'm noticing a very slow gas gauge. I think it really comes down to my rear gears. Not sure what they are but guessing around 2.73 (Chevy 10 bolt). Been prepping a Ford 8.8 with 3.73 trac loc gears to install when I build the new frame. Mileage will drop but overdrive rear gear ratio should be 3.5 to 4.0 for best results.

 

I've got 13 to 15 mpg in around town and highway mixed use. '51 Ford pickup with L92 + 6L80 with 3.5 rear end ratio and very low to the ground, 3300 lbs. This is 6.2L from the Escalade with VVT.

Maybe mine is running too rich? Engine is stock. Trans gets me to higher gears real quick, unless I get on it hard. And I do that only once or twice per tank (maybe every 150 miles) (11 gallon tank).

Don't see how these swaps could outperform the new corvettes unless they have better aero.

 

Hi, did you say your rear end gear ratio is 3.5?

 

My rear end may not be 35 / 10 teeth, exactly, but very close to that, if not. 3.5 to 1.

So yes, with 18 x 35 x 275 tire. I think 25" diameter. 72 mph cruise is around 2200 to 2300 rpm.

I didn't do the swap for the mileage and perhaps I'm an outlier, but folks thinking they are building a v-8 powered Prius shouldn't have that expectation.

cheers,

Doug

 

Best ever in my 6.0 68 vette with Richmond 6 speed was 26mpg. Realistically probably closer to the 22mpg the 5.3 that my 72 Olds gets as a DD. Lots depends on how you drive and gearing.

 

I run a slightly modified 5.3 in my 72 Chevelle wagon...(the one in my avatar)...

I get 23 highway all day long...4l60e, 3.73 ratio rear end.

Z06/LS6 cam, dual exhaust, F-body manifolds, stock pickup converter.

 

See sig below.

 

My SS gets 26mpg highway with a T56 and 3.73 rear gear, The mileage didn't change between stock 5.3 with intake and headers to magnacharged 5.3 pullied down to 3.0in pulley and picking up 150whp.

 

Before mine had electrical issues last fall I took mine up to PA to visit /show my friend the car and it has these specs:

85 Monte Carlo SS full wieght car
2008 l92 (vvt deleted ) stock besides :
231/239 .617/.624 lift
Ls3 intake

4l80e transmission
3400 stall

Long tube headers
3 inch exhaust

8.5 GN rear with 4.10 gears

28.3 inch 295/45/18 tires

It got about 18.5 mpg on the highway.

I want to see if I can squeeze out 20+ mpg come spring .

 

Fuel mileage is going to be a combination of:
1) how you drive it (both speed and acceleration)
2) cam overlap (more overlap = less mileage)
3) tune quality (crap tune = crap mileage)
4) gearing (reasonable cruise RPM on highway)

My 04 GTO got about 27mpg on the highway with a stock LS1 and the 6 speed and 3.46 gears (cruise control set at about 75 mph).

It an be done with something less aerodynamic it just requires a lot of attention to detail.

 

+1

My old 04 GTO stock LS1 auto would get about 16 in town, but 26 on the hwy.

Old 2010 SS Camaro M6 w/ a cold air intake, and HFCs would get about 18 in town and 27-28 hwy

Current G8 GT stock w/ DOD disabled I'm only getting 14 in town, and 24-25 max on the hwy.

Of course none of them were swap cars, just basically stock production vehicles.

 

A Fairmont wagon has about the same aerodynamics as a large cylinder block, but it will probably weight about 600 lbs less than the GTOs did. Probably means better mileage around town and worse on the highway. I think 25-26 mpg is doable though, unless it's all roof racked and wood panel sided out.

 

don't forget:
5) weight of the vehicle. affect around town.
6) aerodynamics / frontal area of the vehicle affect highway mileage.

I have never really checked highway mileage. Perhaps it is worth checking if I do a highway - only trip soon.
I'll conclude from this that maybe my tune sucks. I do smell rich mixture at idle, though the truck idles smoothly and doesn't miss. Check engine light is off, too.
And at 6.2L my engine is a bit larger than some with an auto trans, which is probably a little less efficient.

Doug

 

I have 2002 LS6 H/C in a 2000 Miata. T56 with 3.23 rear gear. 80 mph is 2100 rpm. Best was Daytona to Miami (no hills) around 75 to 80 mph. 28 mpg. I feel there is more in the tune, just haven't got there yet.