How can I improve fuel economy?

[Paul Y]

OK I will chip in here. Admittedly not a truck but similar aerodynamics and weight so give me a break...

My 56 Chevy Sedan ran a 454 with a +100 bore for 476, Comp Cams 282H, Edelbrock Performer RPM manifold, Holley 830 with Mechanical secondaries, MSD Dissy and Electronics, Vac advance, Ported Oval heads, Doug Nash 4+1 trans and 3.25 gears with 29" tall Mickey T Sportsman Pros.

On my last trip to the Drag Strip it averaged 18.7mpg. That included 420 mile round trip to the track( cruising at between 70-80mph on the motorway and 'spirited' driving on the B roads), 11 1/4mile passes at a best time of 12.2 @ 115mph.

Motor dynoed at 478HP and 510lbft.

So, choose the right components and gear it accordingly and you can have your cake and nearly eat it too.

Only down side of this combo was it would cost about $8000 to replicate the engine and drive train.

What about a junkyard LM7/4L60 swap? And a Turbo...Yea...Turbo...If you are only getting 11MPG at the moment you might as well get it going fast!

No real help but....

P.

[highwinger]

Originally Posted by Average Joe

tuning...wideband o2 sensor...qjet... Call Sean Murphy Induction...Why no vacuum advance? A clutch fan or electric...12 mpg city and 14-15 mpg highway should be doable without overdrive and your current 3.42's if you keep it under 65.

Tuning is first on my list. Been shopping the O2. I'd have to replace my intake with a Qjet since it's a spreadbore, correct? I think I have a clutch fan, but I'd have to check. I did add vacuum advance Friday (and driveshaft support). Also changed one of the dizzy springs to give quicker response, which it did. I might fill up tonight to see if it helped.

Originally Posted by CaptRMW

1- Lose the Edelcrock carb and get a Q-jet.
2- electric fan
3- overdrive trans.
4- 3.08 gears.
5- aftermarket cruise control.
6- tune carb and ign. timing for max efficiency.

A "good" 700R4 and a Q jet is the best investment you can make just steer clear of folks like Munster sp? transmissions.

Reoccuring themes for sure. I'd really like a 700R4, but $ keeps me from jumping on that option. I will search for reasonable tranny, while I tune.

Originally Posted by 60sIron

...vacuum gauge...Is your speedo/odometer calibrated for your tire size? Be realistic, if you're getting 10 mpg what kind of increase is realistic 10, 20, 50%? How many miles do you drive?...mpg would improve with a change but the cost out weighs the gains...You could buy a Prius and use your Suburban to park it in...I'll stick with poor mpg too...lol...

So what does the vacuum vs mpg curve look like? How do you use it? The burb is my primary driver now. I work is 17 miles from home. I can drive a few more mile & use the intersate, but I prefer the more direct route with lights and the occasional river view. I heard too many interstate driving horror stories to want to use it daily. I am trying to be more right-foot conscience. We put a lot of miles on our vehicles. In the recent fleet swap, my wife got a '14 Camry hybrid. She's averaging 3k miles per month. This offsets my burb & Camaro I am trying to be realistic with my mpg and just get what I can for with dumping a ton money I don't have into it. learning to tune will benefit both my rides.

Originally Posted by Old Truck Man

...Im building a 283...I hoping for a average of 16 MPH.

I'd be interested to hear if you are successful. When do you expect to have it completed? The weekend I looked at the burb, I drove my '04 4.7L Dakota that's EFI & OD, cruise control (albeit set to 80ish), mostly interstate driving. I got 16.9mpg on a single tank. I could get 14mpg on a full size Dodge conversion van 318 EFI, OD. I'm trying to stay realistic, but hope to improve upon my current 10-11mpg.

Originally Posted by Paul Y

...My 56 Chevy Sedan ran a 454...averaged 18.7mpg...What about a junkyard LM7/4L60 swap? And a Turbo...Yea...Turbo...If you are only getting 11MPG at the moment you might as well get it going fast!

Dang...this gives me hope. If all else fails, go BB

I really appreciate the inputs. Doing my best to implement them.

Bill

[highwinger]

So, in tuning the carb, is this what I'm aiming for?

[theastronaut]

Originally Posted by Old Truck Man

All the things you have accomplished defy the laws of Physics. You should quit whatever it is you do for a living and concentrate on pepertual motion. There is a old saying that a million dollars is nothing to a liar because they can have as many millions as they want.

Thank you for pointing out that I lied. I needed to be corrected. The Trailblazer only got 23.7 instead of the 23.8 I quoted. Have a nice day.

[theastronaut]

Originally Posted by highwinger

So, in tuning the carb, is this what I'm aiming for?

That looks pretty good. You can go as high as 17:1 on light cruise and no need for richer than 12.5-12.75:1 at WOT.

[Old Truck Man]

A tri five chevy weighs about 3200 lbs. a chevy pk weighs about 4200 pounds. A 325 gear is good for keeping rpm down. Most of our trucks have 410,s or at best 370,s. fuel economy on a highway will be much improved over stop & go traffic or when pulling a trailer. I got what I thought was great fuel economy from a 64 3/4 ton we used for a wrecker. It had 390 rear gears and tall 19.5 tires a SM 420 trans and a 84 intergrated head 250 engine. the engine was the 1 bbl version. The integrated head engines have a stainless steel gasket between the intake & exhaust. this will get a hot as a frying pan. With a 195 degree thermostat the fuel was really vaporized & greatly expanded before it ever got inside the combustion chamber. We where traveling together and I was pulling a 84 ford ranger from little rock. My wife was driving a 92 GMC 1/2 ton with a V6 throttle body & overdrive. We ran 68 MPH on 4 lane hwy 67. We filled up at the same times & places at the start and finish. And My wrecker used less fuel than the 93 GMC.

[highwinger]

...found an interesting vacuum pic...

[Keith Seymore]

Originally Posted by highwinger

How can I improve fuel economy?

Slow down.

The aerodynamic drag increases with the square of the velocity, so the relationship is exponential (rather than linear).

K

[Keith Seymore]

Originally Posted by Old Truck Man

I knew a guy who worked in the chev dealers shop in 73. those trucks all got crappy fuel economy. He was getting a lot of bad negative complaints because he couldn't tune them up and improve the fuel economy. one day the shop foreman came to the rescue. he obtained a number of speedometer gears. they would increase the speed indicated by about 5 MPH. the customer drove a little slower and that helped to use less gas. and the odometer showed a few more than the actual correct milage so the calculated fuel economy was a improved result.

Whoa. That's pretty sneaky...

K

[highwinger]

Originally Posted by Keith Seymore

Slow down.

The aerodynamic drag increases with the square of the velocity, so the relationship is exponential (rather than linear).

K

That is a drag

[Old Truck Man]

It wont help the fuel economy but it will make you feel better. Drive a early 60,s truck with the V6 engine even the 305,s used lots of gas. After you go back to your 11MPG truck it will seem to sip fuel. You gotta take everything with a grain of salt the fact is for every action there is an equal & opposite reaction. If something sounds too good to be true don't believe it. A over worked small displacement engine sometimes will use more fuel than a larger that doesn't strain to do the same job. I knew a guy back in the fifties that drove a car hauler on the old Route 66. He would haul brand new 55 chevies from St Louis Mo to Oakland Calif. They had two 54 snub nose trucks. one chev with a 261 ,four speed two speed rearend. the other a 54 GMC with a 270 four speed & two speed rearend. He claims it took ten days to make the trip in the chev. and 8 days in the GMC and the GMC used less fuel. He thought the extra torque made the difference. the GMC would pull many hills in second gear that the chevy had to take granny low.

[Old Truck Man]

I have a motor minder vacuum guage permanently installed in my 66 GMC. old school you watch it as you drive and try to keep the needle in the optimal position.

[Old Truck Man]

H ighwinger wrote .I'd be interested to hear if you are successful. When do you expect to have it completed? The weekend I looked at the burb, I drove my '04 4.7L Dakota that's EFI & OD, cruise control (albeit set to 80ish), mostly interstate driving. I got 16.9mpg on a single tank. I could get 14mpg on a full size Dodge conversion van 318 EFI, OD. I'm trying to stay realistic, but hope to improve upon my current 10-11mpg. Ok Ive drove 283 powered trucks that got between 14 and 18 MPG and they all where stick and has 410 or 390 rear gears. Im using the 602-305 heads because I want the hard valve seats and they have about 58 CC combustion chambers. the stock Power Pack heads are about 64 cc. Ive polished and cced all of the combustion chambers. they now all are 66 CC,s. I will use a thick head gasket should be about 8to 1 compression ratio. I also needed heads that have the bolt holes for my power steering and air conditioning. It will have a HEI ignition. The 283 intake has a exhaust crossover under the carb. that heat vaporizes the fuel and ill make shure the heat riser works also. use a 195 degree thermostat and it should be a lot better than the 350 Q jet engine ever was. Its a light wrecker sling with a electric winch. Nice handling, comfortable truck that really has cold air cond. my wife really likes that truck. When ill get it back together is a good question. At present im working in the hay fields, have fence to build and have too many projects. Ive got the engine all assembled just need to get them swapped out.

[highwinger]

Nice to see things working a bit. I filled up today and got 11.6mpg which is probably the best I've measured. I assume this primarily due to adding the vacuum advance and weaker spring.

I'm going to try putting the original rod & spring back in the carb to see if the timing was causing the hesitation.

[Average Joe]

Originally Posted by highwinger

Nice to see things working a bit. I filled up today and got 11.6mpg which is probably the best I've measured. I assume this primarily due to adding the vacuum advance and weaker spring.

I'm going to try putting the original rod & spring back in the carb to see if the timing was causing the hesitation.

Nice work! Its cool to see positive results weather its lower ets or better mpg. You can buy an adapter to run a qjet to a square bore manifold. Probably around 25 bucks. If you go this route you might look for one in phenolic plastic or wood to isolate the carb from heat. Demon has recently came out with a new carb that looks promising for fuel economy as well as crisp throttle response. Small primaries with huge secondaries and triple boosters for better atomization. This will bolt to either a square or spread bore intake.Just some food for thought Im not a huge fan of the 700r4. I think they are ok behind a small block but I would be hesitant towing any significant weight with one. Personally I would run a junkyard 4l80 with a stand alone controller before going the 700 route. JMO The other thing to remember with an o/drive tranny is any mpg gain will only be seen with highway driving on flattish ground not in town mileage.

[DWilbur]

The most expensive would be diesel conversion. My Nephew's 2005 Chevy 2500 4 door with a 6.6 durmax get 22 mpg at 70 mph. My 2012 Dodge 2500 4 door Cummings get 17 mpg around town and 20+ mpg freeway at 70 mph.

[highwinger]

What makes the Qjet better? I can see the spreadbore benefit with smaller primaries. Is Qjet the best spreadbore too? Also, reading Sean Murphy's tuning, his has more non-invasive adjustments, plus they are scews opposed part replacement.

The Demon, as previously, described, sounds great. I didn't readily find which one that is tho. I don't know much about them, but it appears the company has "returned" into business in the past few years.

[Average Joe]

http://www.demoncarbs.com/Types/Street%20Demon.asp Part #1901 would help, especially in a hot climate, with vapor lock. I have personally not run one of these but everyone I have talked to who has one really seems to like it. You can find them a little cheaper on Amazon. The edelbrock is really not a bad carb but can be tough to tune the notorious flat spot off idle. A properly tuned qjet usually will outperform it in terms of MPG. Holley now owns Demon carbs so I can only speculate that quality control has improved over previous units.

[highwinger]

Originally Posted by Average Joe

...Im not a huge fan of the 700r4. I think they are ok behind a small block but I would be hesitant towing any significant weight with one. Personally I would run a junkyard 4l80 with a stand alone controller before going the 700 route....

For my future refence: http://67-72chevytrucks.com/vboard/s...d.php?t=470855

Originally Posted by Average Joe

http://www.demoncarbs.com/Types/Street%20Demon.asp Part #1901 ...

Thanks for the link. I will beat on the Eddy for a bit longer before I jump ship. I noticed the tuning is like the Eddy with rod, jet, spring swaps. SMI's Qjet appears to be all screw adjustments unless you have a radical cam. That's a nice feature.

[highwinger]

I installed a vacuum gauge last night. Cool thing about it is 1) it's pretty cheap (~$20), 2) it's used for engine diagnostics and health monitoring and 3) used for driving characteristics. I've never used one before in any vehicle, so it's a great addition to the tool box/panel.

As we found with the Camry Hybrid, acceleration is the arch enemy of efficiency. I'm to get it on the hwy to see when speed becomes an issue.

[LuckyScott]

I get 13mpg in my '72 suburban. Here is what I did.
Stock quadrajet, but I took it to a carb shop that does racecar rebuilds and had them build it for milage. Also, with the small primaries on the carb, if you drive like there is an egg under the gas pedal you will be mostly using just the primaries and that helps.
Next, a good exhaust system. Have a good muffler guy redo the pipes all the way to the manifolds. I tried flowmaster mufflers but they were just too loud. I have dual exhaust with free flow mufflers but I dont remember which brand.
Last, I replaced the distributer with a HEI and put all good MSD parts on it. (cap. rotor, etc) Also, good plug wires.

[DreamRyder1963]

I have a 625 Demon on my dd C10. I love the carb! It fires up without question, has lots of power, and killer acceleration when the secoundaries are kicked in. I also have a customer that rebuilds old cars and he said that he also loved the demon he put on one of his rides. He is even going to get another one for his 352 powered F100. I have not any benefit in mpg from the carb swap, I have trouble staying out of the secoundaries. I did see some milage gain from changing the worn out fliud in my diff. Don't forget that worn fluid can increase drag in the trans and diff. You might want to think about changing them.

[highwinger]

Originally Posted by DreamRyder1963

... I did see some milage gain from changing the worn out fliud in my diff. Don't forget that worn fluid can increase drag in the trans and diff. You might want to think about changing them.

Hadn't considered that. How often are you supposed to change diff fluid?


I am consistently getting 11.8 mpg now. I had one 3/4 tank around town and one on hwy using AC @ 70-75mph. Both fill-ups gave the same results. I think mostly attributed to the vac advance & watching the acceleration. Now that I have a feel for driving with the vac gauge, I may pull it out since I don't have a place I'd like to mount it permanently.

I'm not going to be able to work the mileage much more for a while. I've got to get the weatherstripping in...amongst other things.

[DreamRyder1963]

I believe its about every 15000 miles. Most vehicles never get it changed so think about how well 45 year old oil works.

[Johnnyhotrod]

The next big jump in MPG could be gained by what Theastronaut said in an earlier post, "air/fuel ratio gauge to see how rich it is running, then re-jet accordingly". Changing fluids is a good idea but will increase MPG only slightly at most if any. Lots of info on the net about idle and part throttle being lean while full throttle being rich for power when needed.