Author Topic: Gas mileage  (Read 8660 times)

Offline 1979C20

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Gas mileage
« on: September 15, 2011, 06:48:49 PM »
Just curious of what I could do to increase my gas milege a bit. I dont want to change gears of transmission or tire size. Im just curious if there is anything I could do to the engine to boost it a bit. Its got a new/clean air filter. New plugs, good wires. New cap and rotor. Fresh oil. Stock qjet. No vacuum leaks. The choke is tied open because it was sticking partially closed, and its summer in az. The A/F mixture is set properly. The idle is at 400-450. The engine is stock except for the 882 heads which are said to be the best of the worst flowing heads, and the Comp Cams 12-206-2 woth 260L .440D. Ive driven my truck easy for a tank and hard for a tank and my gas mileage is always 8.xxmpg. Its the truck in my signature for the rest, of the details. I was considering an.electric fan swap, I know that will free up a few ponies and add mpg. and I was also looking into building a hydrogen generator to feed into my carb, with the propper safety equipment (check valves, flashback arrestors, generator hooked to the key so I dont leave it on). The HHO generators are said to raise MPG by 30%. Any other ideas?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline zieg85

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Re: Gas mileage
« Reply #1 on: September 15, 2011, 07:23:58 PM »
You may be able to squeeze some MPG by going down in jet size in the carb, and unhook the secondaries.  Your real MPG killer is the 4.10 our back IMO.  I don't know about the camshaft choice but you are looking to get the engine running efficiently.  I just look in amazement at my 85 C20 in my signature.  My carb needs rebuilt and I can still squeeze 14 mpg out of it.  I don't lug the engine but I don't wind it up either.  I keep it at 65 or lower and she delivers.  If I run it at the 70 mph speed limit in Indiana she will drop into down near 11.  My $.02
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline VileZambonie

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Re: Gas mileage
« Reply #2 on: September 15, 2011, 07:27:00 PM »
Don't waste $ on snake oil. Your granny tranny isn't helping your situation any. A 700R4 would help and what size tires are you running?
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Offline 78 Chevyrado

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Re: Gas mileage
« Reply #3 on: September 15, 2011, 07:27:44 PM »
best thing to make you drive super easy is a vacuum gauge in the cab.  try to drive without making the neddle move.  thats impossible, so go for making it move the least.

also keep you speed at 65MPH or lower.  When I go on my 165 mile road trip to AL, If I go 75-80MPH It takes 17 gallons to get there, one way.   If I go 60-65MPH and use cruise it takes right at 9 gallons to get there, one way.  which comes out to about 17MPG.  

Ride with your windows UP!

again, the same 160 mile trip, going 75MPH or so.  (windows up, AC running = 16MPG)  (windows down, AC off = 13MPG)

play with the carburator.  you absolutely cannot setup a carb for maximum economy on the spot and not have to mess with it again.  change some settings, drive for a week or two or three and go farther or undo what you did.  its long term testing.  

I dont know how your body looks, but badly fitting parts and big damage kill the aero dynamics.  a door sticking out farther then the fender will screw up air flow or just a wide gap between the two, as an example.

air up your tires a bit more, again you have to do this long term checking and resetting until you find the max your tires will hold without wearing the center of the tread out.

DON'T use super heavy greases in wheel bearings and such.  use a good grease, just not soo heavy. its not a caterpillar.

up the timing as much as possible without pinging.  im about 4 degrees or so above stock and still running 87 octane

keep up with your ignition system, the terminals in the dist cap mess up fairly often

use synthetic oils in everything

put a lower weight oil in the rear end, and make it synthetic.  be careful what weight to choose, so it doesnt burn up!

buy electric fans.  yes they use power like a clutch fan, but they dont run constantly so they do IN FACT save fuel.  there's no question on that.  clutch fan never turns off, EVER.  E-fans turn off most of the time and mine have never run yet on the freeway.  

I also tried a set of those E3 spark plugs.  i know dont laugh.  my dad got one for the leaf blower and it made such a difference, I tried it in my truck and noticed just changing those, my idle RPMS went up almost 100RPM, felt a bit more power everywhere.  they work for me and im sticking to em.  they also havent worn down yet like normal plugs always do.

in short, i get a tad more than 17MPG out of a 5200lb 3/4 truck with the old 70's front sheet metal, with a 3 speed tranny, 350, 3.73 rear gears and 33.5" tires.  you just have to put in lots of time to get it truly dialed in. and then drive slow with a light foot.
Kenny

1978 C-20, 350/400, 3.73, Graystone Metallic, Raceline Renegade 8 Wheels - 18x8.5, 275/70R18 BFG KO's

Offline 1979C20

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Re: Gas mileage
« Reply #4 on: September 15, 2011, 08:47:42 PM »
Theyre 30in tires. My timing is advanced as far as it can go without the starter kicking back and no pinging. Like I said, driving habbits dont seem to matter. I can drive without pushong the pedal more than a quarter way in and shift with no clutch, or full throttle often banging gears, and my.gas mileage is only different by like .6. And I never go.on the free way, so the highest speed I tend to reach is 50.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline VileZambonie

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Re: Gas mileage
« Reply #5 on: September 15, 2011, 08:52:08 PM »
Get a Hyundai  ???
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Offline big bear

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Re: Gas mileage
« Reply #6 on: September 15, 2011, 08:57:23 PM »
im with vile... you know as well as i do man, if you want superior gas mileage, driving an old  heavy chevy around with a v8  isnt going to impress the number chart whatso ever.  i understand squeezing what you can out, but after a point its just not too realistic. 

Offline big bear

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Re: Gas mileage
« Reply #7 on: September 15, 2011, 09:00:08 PM »
im not against you working on the motor  updating it ect, or  finding a beater, or whatever. but,  the money your dumping into the engine to help boost your mpg by 1mpg?  could just go in gas anyway . so, your giggered if you do, giggered if you dont.

Offline 1980c10

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Re: Gas mileage
« Reply #8 on: September 15, 2011, 09:45:03 PM »
8 mpg is terrible, your engine is needing more than a tweak or two. something is very wrong with this equation.
the way I see it you have a 350 and manual trans in a 2wd truck. Even in city driving you should see a minimum of 12.
In my experience the power adders ussually add fuel effeciency as well. Check your spark plugs to see if your getting a good burn (med brown color) this is the easiest and quickest indication of a/f mixture. if they look good then maybe free up your exhaust some by adding headers duals etc. (depending on what you have).

It also might be possible the cam is hurting your mileage.

The electric fan swap to me is a no brainer as it is simple and cheap but fix what is broken first.

Also reconsider some taller gears.

Offline 1979C20

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Re: Gas mileage
« Reply #9 on: September 15, 2011, 09:55:58 PM »
I have headers and free flowing glasspacks that dump under my cab. Can you guys recommend a spark plug for it?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline wildcatjason

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Re: Gas mileage
« Reply #10 on: September 16, 2011, 11:49:34 AM »
I had a stock suburban getting the same gas mileage as you. Your not going squeak much out and any old carbureted 350 with 4.11's as alot of these guys have already said. I put a 4bta in mine with a ford zf5 and going to move my 3.42 to a 2.73 so I can use the granny as a first is used in a 700r4. I am planning on at least 25mpg. You will have to do something drastic. New plugs won't help much unless it's really bad and you know your driving style keeping you foot out of it only works for so long.

Offline 1980c10

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Re: Gas mileage
« Reply #11 on: September 16, 2011, 06:31:27 PM »
I always run the factory recommended a/c delco plug for whatever head I am using.
How do your plugs look?

Offline lukieg

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Re: Gas mileage
« Reply #12 on: September 18, 2011, 07:05:21 AM »
 Not to sound silly.... but go for a more modern roller cam engine setup... or enjoy your ride for what it is... mileage and old trucks dont seem to go hand in hand. Not what you wanna hear... but from my limited experiance... you will just be wasting money.... msn ignition helps a touch... never driving it seems to also.

Offline lukieg

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Re: Gas mileage
« Reply #13 on: September 18, 2011, 07:07:26 AM »
 Sorry big bear... I duplicated your responce.. im with you... love it for what it is... or go to the dark side.... vroom vroom....mazda commericial rip off

Offline big bear

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Re: Gas mileage
« Reply #14 on: September 18, 2011, 08:36:45 AM »
haha its kool man. great minds do indeed think alike