gas mpg

[lytemup454]

ok i know this is a general question and i can't get any real sold answers so bear with me. I'm looking at a 62 chevy with a L6 it looks to be stock motor, carb ect. the guy said he had valve work done on it a few years ago and it has been sitting since. it has a four speed ans it's a 1/2 ton so i don't think it has too low of gears but i'm not sure. i'm looking for some ball park #'s on mpg. i drive just under 60 miles a day and that is a big factor. the guy said it get's good mpg but he also trying to sell me a truck. any help would great thanks.

[wibilly]

i wouldn't expect much over 12 - 15 keeping your speed under 55 will sure help but thats no fun

[davidh]

tuned up and not going over 2200 rpm think 15mg. find a T5 (5speed) for more mpg.

[WorkinLonghorn]

I kinda doubt that thing will have any kind of freeway cruising rear gears. You need to test drive it and see how it buzzes on the highway. The guys above pretty much said it.
I am writing because I always see a big flag go up when someone tells me they had a bunch of work done but it hasn't been running ? Like they tore into it and found major problems,siad "F. I. ",let it sit for years then finally got around to looking for a sucker to offload it on. If you really like it,take a very good look,ie.,compression check etc.

[Longhorn Man]

moved to 60 - 66 board.

[Fred T]

Since it has the 4 speed it probably has 4.10 gears. With 30" tires that means 60 mph is 2750 rpm. That's the setup I have in my 52 with the same engine, a 235. On the highway, I get 12-14 mpg.

One thing that I learned years ago is that too many people will stretch the truth when they are selling a vehicle.

[lytemup454]

thanks guy's your help means alot

[rickf]

Originally Posted by Fred T

Since it has the 4 speed it probably has 4.10 gears. With 30" tires that means 60 mph is 2750 rpm. That's the setup I have in my 52 with the same engine, a 235. On the highway, I get 12-14 mpg.

One thing that I learned years ago is that too many people will stretch the truth when they are selling a vehicle.

I truly do love the L6, but that 12-14 MPG is annoying. When my 230L6 was 20 years younger (in the 1980's) I got 16 at best. Add a load and it dropped to 12/13.

I now have a 350v8 and (if I drive somewhat gently) the mileage is roughly the same. Load? What load? 800 lbs of cycles and gear plus 700 pounds of driver and passengers make diddly difference.

[greg64]

Hey lytemup, my 77 has an L6 with a non-overdrive 4 speed. I get between 15-20 canuck MPG, which is 12-16 yankee MPG. I think to do better, you need two things; a fuel injected Gen III engine and an overdrive tranny. This is my plan for my 64 (4.8 or 5.3 with a TKO). All the old stuff we love just wasn't created with mileage in mind.

[Fred T]

Problem isn't the load, but the gearing. To get the best milage you need to be turning 2,000 rpm or less at cruise. When I upgraded to the 235 I had 4.57 gears and 29" tires. That made 60 mph 3,000 rpm, and I got 11-12 mpg.

When you get down to 2,000 rpm is when weight starts to make a difference. And you should see milage in the 17-19 mpg range.

[PrerunnerRob]

Originally Posted by Fred T

Problem isn't the load, but the gearing. To get the best milage you need to be turning 2,000 rpm or less at cruise. When I upgraded to the 235 I had 4.57 gears and 29" tires. That made 60 mph 3,000 rpm, and I got 11-12 mpg.

When you get down to 2,000 rpm is when weight starts to make a difference. And you should see milage in the 17-19 mpg range.

I know this may be sort of irrelivant, but with my 01 silverado I went from 17mpg on the freeway at 65mph and I think around 1700rpm, to regearing for my lift with 4.88s, and turning 2200 rpm, and now getting 13mpg at 65mpg.

[rickf]

Originally Posted by Fred T

Problem isn't the load, but the gearing. To get the best milage you need to be turning 2,000 rpm or less at cruise. When I upgraded to the 235 I had 4.57 gears and 29" tires. That made 60 mph 3,000 rpm, and I got 11-12 mpg.

When you get down to 2,000 rpm is when weight starts to make a difference. And you should see milage in the 17-19 mpg range.

Yes, I agree totally about the gearing. My point about the load was intended to be that when my truck is doing useful work I am getting the same MPG from the 350V8 as I got from the 230L6 (with same gearing). The little 230 just had to work so hard to do what the 350 does in stride. The L6 I suspect is more robust longevity-wise than the V8 (259K miles on my 230 when swapped out, and still running) but the L6 is not particularly fuel efficient in my experience.

[Brad54]

I got 17mpg in with my tired 283, granny 4 spd and whatever gears are in the back, in my '62 Suburban. I'm still surprised.

I swapped in a new crate motor, 4bbl carb (which I'm SURE is killing me!), 4spd OD manual trans, and the same gears. I can't figure the MPG yet, because 2nd gear turned out to be wasted in the trans, so I was making the jump from 1st (3.09) to Third (1:1 ratio), couldn't downshift effeciently (with no second gear, it was either OD to Third, or Third to First), and the speedo didn't read correctly with the new trans.

However, for your truck: Make sure you have the proper height tires (they'll be tall), and if you want mileage, one of the easiest things you can do is knock that stock rear gear down to 3.23 or even lower if you're going to keep the Granny 4spd. The Granny 1st will still let you pull stuff.

I BELIEVE the gears in my truck's rear end are 4.11; I haven't pulled the cover off yet, and don't have a tach to do the math. With the OD manual trans, my next big project on it will be swap in 3.55 or 3.73 gears. And after that, I'm going to clean up the aero on it a little bit with a subtle, black chin spoiler set behind the bumper, a filler apron between the bottom of the front bumper and the K-member like new vehicles have, and close off the 9-inches of un-used grille opening in the core support on each side of the radiator opening, behind the front grill. I see no reason to have a parachute 18 inches wide and 9 inches tall that grabs air from behind the grill (hitting the core support) that isn't directed into the radiator. Don't know if it will help, but aero can't hurt! Even if I realize a half mpg from it, the 5,000 mile round trip to Bonneville will make it worth the effort. I put over 20,000 miles on the truck in a year and three months, so I'm with you on the whole MPG thing.

-Brad

[Tomsriv]

If you drive slow you will get ok mileage. If you go over 60 the lack of aerodynamics will kill your mileage.

[greg64]

With the L6, peak torque is usually at a low speed, around 1500 RPM (for my 250). This means that the max volumetric efficiency is at this same RPM. Now, on the highway at 65, I'm turning around 2800 RPM, and the efficiency is pretty crappy, and on top of that, the engine is working to maintain speed, especially on uphills. So, if you were geared such that 65 was 1500 RPM, AND the engine had enough torque to drag the vehicle along, the mileage would be pretty good. But, I don't think that's realistic for a 4000 lb truck with the aerodynamics of a brick. Maybe in a light Nova. I really wish GM had built larger displacement L6s, because they're great engines. Can you image a "big block L6"? 454 size pistons and canted valve heads. That's a 340 ci L6.

[merlin65]

put her in neutral going down hill. what i do is floor the sucker until up to posted speed limit and then put her in neutral. she will coast for quite a long time. plus you can tell your honey that the engine died and she better get ready to walk.. hahahahahaha... everytime i crank my truck, a terrorist shoots his a.k. and yells...... Oh and you should try filling up and doing a burnout on the extra gas that you poured on the ground under your rear tires and through out your empty beer cans out as you totally smoke your tires as you drive off and not pay the towel head at the counter. im out......

[Micmac]

I get around 13 MPG, 3 on the tree.