So I've been planning to do an engine swap in my car to get rid of the 305... but its also my daily driver so I need to be thinking about fuel economy. I haven't been able to find any threads about mileage people get so I figured I would start one.
It would be nice to have:
Your engine; size and maybe injection style(carb'd/TBI/PFI)
Modified or not
Transmission
Rear axle ratio

It would also be nice to have it all in MPG (I'm sure most people can relate to this better than L/100km)

 

Ive got an all stock 85 Firebird, with a 305 TBI, and an automatic behind it. Gets about 18 MPG with me rodding around. Fueleconomy.gov says it should get 22 MPG, but if you really babied it you could prolly get 24.

 

6mpg with the current carb'd 327/TH350.

 

Not possible, the LO3 wasnt introduced until 88. You have V6 MPFI, 305 carb or 305 TPI. A LO3 in there is a swap

My 92 LO3 gets 27-29mpg full HW and around 24-25 mixed. Only mods are LTs, and LM1 headerback

 

I have a swapped 350, very mild cam with a VS carb and manual trans. I get around 12-15 around town I believe. It all depends on how hard I run it. Haven't taken it on a long enough highway trip to gauge that.

 

357 HSR with a 5speed 3:73 Many mods I get 25 - 27 MPG...Until I drop the hammer
outstanding for the power to weight ratio

 

On my 84
I have a 305 carb with an auto trans. Depending how I am driving I get 12 to 15 drving well but driving fast I get 8 to 10.
My bad all are in mpg

 

My IROC managed 26mpg cross country tbi305/700,3.27s,headers stock wheel/tire size.....then i swapped to tpi350/5spd 17" wheels,pulley kit,K&Ns,cut out air box,slp muffler.mpg jumped to 28 and ran 13.7 on 285/40/17comp TAs at 3000' DA car was totaled

 

my carbed 84 z28 gets 12 or so but I have the intake off and found the EGR was clogged solid so after I get it back together with the carb rebuilt I would expect a little better just a little maybe 16 tops.

 

'82 Berlinetta #1, ZZ4 clone with LG4 induction/ignition, Hooker 2055 headers & 3" exhaust out back, TH700, 3.23 gears, 1400 mile round trip including 5 passes down the 1320, 23 mpg.

 

Stock 305 TPI with simple bolt-ons & exhaust, - no emissions, 700R4 with 2.73:1 rear
- 29 MPG highway.

Swapped to 383 with carburetor & mild roller cam, same trans & gears
- 24 MPG highway.

 

Stock LT1, T56 3.70 rear and get usually 28mpg on a long trip, 23-25 on my normal 52 mile round trip from work every day.

Stock LS1 T56, 3.42 rear and get 30mpg on a long trip 25-27 on my normal 52 mile round trip from work every day in my '98 (would be a little better in a 3rd gen)

 

383 Carb
700R4
3.27 rear
8mpg

 

im sorry but there is no way in hell that you guys are geting 20+ miles to the gallon with a old v8. i no for a fact that there is nothing you can do to a 383 to get 24 mpg that a flat out lie. no need to bs the guy he looking for real world mpg not what you would like to get out of your car.


if you swap in a 350 with a th350 and leve it stock youll be looking at 15 hw 10-12 city

 

I get around 13mpg (combined city/hwy)

1991 GTA L98
SuperRam, compucam 2032, bolt-ons, 3.73

 

it's not the age of the motor... it's there is not much efficiency in a carb
and a combo of a 3 Speed<<< if traded with a TH 350 resulting in a huge MPG loss

 

The precision of EFI coupled with an overdrive gives amazing numbers. This isnt 1970, these number are real and consistent. Do a search on gas mileage, this isnt the only thread with numbers in these ranges

 

Totally possible, car craft or popular hotrodding did a 67 camaro they called bad penny or something like that, fuel injected SBC and overdrive trans and they were getting 25 mpg out of a 60's camaro... I cringe everytime I read someone saying they are tearing the fuel injection off and putting carb setup on... Would you buy a new computer and tear out the motherboard and put the guts of a commodore 64 in the case???
86 IROC 305 TPI auto trans... I have gotten 23 mpg highway in the Pennsylvania hills and I'm not real light on the pedal either. Sorry guys, carbs are old tech, and will never be as efficient as fuel injection. Too many guys just rip them out and never take the time to learn how to work on them. This is an awesome website with tons of info, sometimes too much info to sift thru, but it's there if you just take your time...

 

Fueleconomy.gov I just looked up my iroc's fuel rating according to the EPA.... Guess what??? 23 mpg highway for a 1986 chevy camaro with a v8. I'm assuming they used the TPI for their testing. Now let's put better flowing exhaust and air intake improvements and imagine the possibilities...

 

1985 camaro Z28 5.0 TPI with ram air fabrication, headers and dual exhaust.
14 - 16 miles per gallon city.
21 - 23 miles per gallon highway.

 

406SBC 770 Holley 3.73 T5
9 MPG mixed driving.

 

My old LG4 got around 22-24 highway, the 350/330 may be 18.

JamesC

 

I started to build a 383 to replace the 305 in mine, but in the interest of drivability and fuel economy I Have been looking at this crate engine instead... GMPP 12530283 it's a brand new 350 with 250 hp vortec heads, roller cam, 4 bolt mains with 1 piece rear main seal, originally used in 96 to 2000 gm trucks. Give me approx. 50 more horse power than my stock 305, and with those vortec heads I think I'd get equal or better mpgs.... Anyone tried it??? Should be basically a bolt in swap, change knock sensor etc...

 

11 mpg in town with 305 V8 TPI and stock tranny.

 

450 h 383 lt1/t56 17mpg around town and hwy driving.

 

I had a TPI 10.8:1 383 with dart iron eagle 215cc heads a 700r4 and 2.73 gears and custom ground cam for max torque and it got 30+ on long road trips.