When my 79 l-82 was brand new, I yanked off all the smog crap and installed 1 5/8th headers with true duals and no cats. It was maybe a 15 in town and 18 something hiway. I installed flat top pistons, Crane cam, better heads, single plane intake and I used to get 21 mpg with my modded L-82 3.55 rear and highly modded TH350 on 3000 mile trips

When i went with a low to mid 500 hp 383 solid roller 4.11 and 700R4 the same 3000 mile trip dropped to 18.2

When I went to a 600ish hp 427 small block solid roller 4.11 and 700R4 the same 3000 mile trip dropped to 17.4

The real change was the speed. As motor size went up so did speed. I drive over 100 mph for hours on end.

MPG is a function of the state of tune and having enough HP to not even be in the throttle to cruise at speed.

 

gkull's mileage is great!
IMO
his HIGH compression is largely responsible
along with it being tuned about perfect.
wind resistance is horrible at higher speeds,
but
his motors are efficient at those speeds.
Nevada is wide open spaces .
.
george
how was the mpg, new in 79 wth stock exhaust?

 

Matt, I really can't tell you. It was very long ago and I bought the 79 with only a few miles on it. You had to take the car back to the dealer for a 500 or 1000 mile warranty check up. as soon as it got that i started tearing out the stock stuff and installing mods because the L-82 was such a dog.

I would research Motor Trend or consumer reports on original true road tests.

Back when the nation speed limit was 55 mph I drove about 30 over. tickets never have bothered me. Now that the speed limit is 75 I still drive about 30 over.

I think the key is compression, lean primary jetting, running the rpm in the cams efficiency range, ease in and out of throttle, don't use your brakes unless you have to, and aerodynamic adds like the later C-3's had. I used body rake to create downforce and not the stock front end lift with all it's added wind drag.

 

Just took a trip of about 97 miles from Wichita to Pnoca City this past weekend.

On the way down into a headwind I got about 12. On the way back I got 13.

This is with a rebuilt Tomco carb from Advance Auto on a stock 72 LS5. Next fill up will be with a carb tuned by Lars.

cc

 

My last fill up I got 22mpg in my 80 and the time before that I got 18mpg. But when I speed around or hit the freeways I get around 15mpg sometimes less.
No smog and runs good?

 

I'm getting 16MPG with my stock L48/auto with 3.08 gears..

 

I honestly think you guys should stop keeping track - it's too depressing. I don't think I've ever once in my life tried to calculate the mpg on any vehicle - I guess I'm just not **** about it. Maybe I should start though. McCain was talking about it on Good Morning America and apparently doesn't think it's gonna change to ever be any lower than it is now. During the interview I also learned that our government is giving these oil companies hand-outs - yep millions & millions in "aid/subsidies" to assist them with the expense of exploring for oil even though their profits are already through the roof. That pisses me off!!! On top of all these oil companies are ripping us off for then I learn our government turns around and funnels them even more of our money that they don't need. It's obviuosly a huge scam and they are sucking us out of every penny and then some. Sorry - off the topic but also related in a way so worth mentioning.

 

Whoops - I apologize - just realized I steered an already depressing topic into an even more depressing one. Sorry - back to cars....politicians and oil companies suck!!! Let's all say it together now. At some point were gonna have to put our foot down and get together on this though and speak out as free Americans before we can't even afford to enjoy our hobbies - or get to work & back for that matter while these corp idiot nerds count our money. Anyway - my '82 is allegedly supposed to get 26mpg but haven't verified it yet. 5 spds. are great. I have a '68 Camaro w/383, 3.73s & tremec and it's barely purring along at 75mph. Excellent option to save gas over the long haul.

 

383 ,performer heads, hooker headers ,roller rockers ,stealth intake
edelbrock 750 carb , 20 to 22 mpg if i keep my foot out of it .
forgot the 336 gear and keisler 5 speed

 

20-22 on the freeway (driven properly)
about 12 in city (impossible to drive for economy )

 

I only have kept track because: During a trip out west it might be 300 miles to the next gas station. So i need to know when to stop and when to skip onto the next bigger town.

Once I got a rough idea I'm not **** about it. Two days ago i was getting low so I put in 22 gallons of fuel $160 dollars worth of 110 leaded race gas. My motor kind of needs it with 11.8 compression.

The good thing about the high price of gas is that i noticed allot less rif raf out on the highways during my Memorial day two week 3000 mile drive

 

About 15-16 on the highway. GM over the counter motor between 275-300 hp, M-20, 3.08 gears. At 60, rpm's about 2300.
Now I try to never let the tank go below half empty, so it's not to bad at fill up.

 

I average 12-13 mpg with the 406, but most of my driving is on twisty back country roads doing 45 mph or so. The mileage really suffers when I hit the highway and lay six feet of rubber catching second while coming up the on ramp.

 

My 69 427/390 is pretty much stock, right down to the Q-jet. I've never actually measured the gas mileage because I regard some things as not fit for human knowledge. If I were pressed, I'd guess somewhere between 15 and 17. I've got 3.36 gears and an M21. My 69 SB Mustang only gets 12-14 on the highway and who knows around town? It's a bigger guzzler than the Vette. My DD is an LS1 Camaro. It pulls down 20 mpg in commute traffic and I got 24 mpg on a 400 mile road trip last week. All that and it's way faster than the two vintage cars.

A comment on speed vs mileage: In April I took the Mustang convertible from the S.F. Bay Area to L.A. for a weekend of Ford fun and games. On the way down (around 400 miles) I caravaned with about fifteen other vintage Mustangs. We kept the speed at a steady 70 mph and I got 12.7 mpg. On the way home I was alone and cruising at 80 mph. Mileage was 11.4 mpg. I think the optimal highway speed for good gas mileage is around 60, for the Mustang at least. If you try doing 60 on I5 or most other interstates, you'll wind up road kill. The Mustang has a balanced 302, a single profile .224/.500 cam, a 625 cfm Road Demon carb (you can smell the unburned gas for a block), Edelbrock Performer intake, GT40 heads, roller rockers, headers, a C4 (3 speed auto) tranny and 3.55 gears. Not such a great highway cruiser anymore.

 

I have a 1974 L-82 4 speed with a Holley Street Advenger Carb and I can squeeze 14-16 MPG if I don't get on it too much

 

I get 14-15 in my 79. 4 spd, 3.70 gear, headers, unknown bigger cam, Q jet, Edelbrock performer intake, etc, etc. The trick is to tune for maximum vacumn, which will get you maximum mileage.

 

1980 18mpg daily driver. No smog

 

My '75 gets 18-22 highway with properly tuned engine. The '70 with a 330hp crate motor and holly carb gets about 12 - if I'm lucky.

 

My stock '75 L-48 Automatic is averaging about 13.5 with a mix of local and highway driving.