What kinda MPGs witha stock 3.8 2v? UPDATED


Amateur Racer
Mar 9, 2009
Spring, Texas
Re: What kinda MPGs witha stock 3.8 2v?

Well.....just for reference I had an 81 g-body in college with that engine. The rear gears were something in the 2.90 range and I kept it under 70. MPG was about 18 or so if I remeber correctly. Lots of variables though in these age of cars.


Pro Stocker
Thread starter
Re: What kinda MPGs witha stock 3.8 2v?

Ran the codes , this has a 2.41 rear . The trans upshifts way early so she is a dog in drive.

Tried just leaving it second and feels pretty good, engine is in it's power band.

Does not feel likes it's revving cruising at 45.


MalibuRacing Junkie
Oct 21, 2007
Lederach, PA
Re: What kinda MPGs witha stock 3.8 2v?

2:41 would have been my first guess.

I would expect the rated mpg was about 20/24. Have you been able to find any documentation citing original mpg ratings for the car?


Top Fueler
Mar 22, 2005
Mississippi Gulf Coast
Re: What kinda MPGs witha stock 3.8 2v?

My longroof had 2:73's from the factory.

Was a pretty good gear for the 3.8 buick V6.

I put 3:42's in it and while it woke it up, it was way to tight at highway speeds with a turbo 350 transmission. Overdrive or a lock up convertor would been a great thing to have.
Put some 255-60-15's on it and took a few rpm out of it.

If you do nothing but city driving, 3:42's would be cool.



Pro Stocker
Thread starter
Re: What kinda MPGs witha stock 3.8 2v?

Finally got my 85 Bonnie inspected and on the road.
Ran a tank of gas threw before started keeping track of MPG , had to fix the trans etc.
Anyway , getting a hair under 17 mpg.
That is suburban, drive to work, driving, rarely sees over 50 mph. Did get the a/c working and used that 1/2 the time.
What are you other 3.8 V6 guys getting?


Frequent Racer
Sep 18, 2005
Wichita, Kansas
The last time I checked, Darwin's anything but stock 4.3 was getting 16-18mpg in mixed driving even with a leaky 4160 and 2.41 gears.

Her best mpg was recorded during my only major road trip back when she had 2.73 gears, a Comp 252H camshaft and a freshly rejetted Holley. I saw mileage in the low 20s running 65-70mph with the windows up and the AC running. My best mileage was 24mpg at 65mph


Daily Driver
May 21, 2012
Canton, GA
when my el camino still had the chevy 3.8 I got 21mpg's on on the highway going 55. It had a rebuilt 229 with all the emissions equipment removed, a th350 and I'm pretty sure 2.73 gears
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