Does anyone know the factory rating of the city and mpg specs of the L69 auto 3.73 geared, OEM quadrajet f-bodies? I need to know because I'm debating on going to the same gear ratio on my 86 LG4 firebird project.

 

Highway was 24 or 25.

3.42 gives better mileage, if you're concerned.

 

You can check EPA.gov....but may be too old.

 

The original window sticker shows 18mpg, but the old tests to determine mileage were done in a controlled environment. Not sure how accurate the number is.

 

I distinctly remember a layout with the City number on the left, a fuel pump image, and a Highway number on the right.

Was there an average number below that too? I can't get to any of my WSs.

 

I had an '84 L69 with 3.73s and a 5-speed. I want to say I never cracked more than 20 MPG on a good tank. Seems like I was closer to 16-18 MPG with a lot of in-town driving. The 3.73 were a hoot to drive, that's for sure. As JMD said, if you are worried about gas mileage the 3.42 are a better choice.

 

I calculated a bit less than 12L/100km with mine, which would be around 23-24MPG on mostly highway driving at an average of 80mph

On my last trip it did a lot less than that, maybe 14-16MPG...but I found out once home there was an air leak because a plug on a vacuum port fell off...

 

The "Official" Highway/City Combined in 1986 numbers had to be at least 22.5mpg... Or the EPA would have dinged GM $4000 per car...

I think they take 80% Highway and 20% city for calculating the figures...

Keep in mind they changed the ratings to all vehicles around 2008 lower, they stated to make them more "real world" when in fact it was around the same time they mandated 10% ethanol in gasoline... go figure... I know I get a lot better MPG with pure gasoline...

John

 

1984 Z28s that had the L69 came with 3.73 gears. Here's a window sticker that shows only the one mileage that I mentioned above.

 

Maybe it was 1986 that when the average had to be 22.5

I believe all L69's came with the 3.73 gear btw... Might be wrong about 1984, but 85 & 83, that is mostly all I have seen...

 

For 1983 you could only get the L69 with the T5/3.73 gears.

In 1984 the T5/3.73 combo was still available. Could also get the 700r4 with the L69 - came standard with 3.42 gears but 3.73 gears were available with the 700r4 with the G92 option.

 

There was no G92 option available with the L69 in 1984. The 3.42 gears were standard with the auto trans and the 3.73 gears were standard with the manual trans.

In 1985, you could only get the 3.73 gears with a manual trans. There was no auto option that I see.

In 1986, on the 50 produced, you got a 3.23 gear standard with the MC4 manual trans and you could get 3.73 gears with the optional M39 manual trans.