How can I improve fuel economy?

[68 TT]

Originally Posted by 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.

Changing to synthetic gear oil in the rear end while you are at it will make an improvement in efficiency and in power to the wheels too. Not a huge improvement but for the minimal cost difference from dino oil it is worth it. Every little bit helps.

I saw a solid full MPG improvement in my 78 K20 with the change of both diff's to synthetic. Big difference going from 8 mpg to 9.

[chris mc bride]

Ok first too lazy to read all replys so may repeat some.
Trans with overdrive is one of best things for mialage.
350 can be made to get great milage.My best milage engine have been bigger stronger
If motor has to work to do the job it will need more fuel.A powerful engine can just cruise down the road and not need lots of throttle a weak one will need more throttle to do same thing.

Eldebrock carbs work great and can get good milage.That said its hard to beat a well built quadramess.Trick is finding someone who can make them work to their best.I can tune Holley fairly well,a Eldebrock is easier but a quadrajet is some what of a either your good or lousy with things and there is 10x more who think they are good than there are one who are good with them.
Rear gears are another approach,but with trade offs.
Really good flowing exhaust will help.
Proper tune of all will give best result for what you have.

Example .Not a suburban but performance engine. I had 350 .040 over,10.5:1 eldebrock performer rpm intake,carb and cam,ported heads 2.05/1.625 valves and headers. Had 700r4 trans with 3.73 rear gears. I could get 23 mpg if I kept my foot out of secondary and drove reasonable.Now you start to play and it dropped into 12 to 15 mpg range.Now this is in a lite weight camaro but it shows driving habbit has huge effect.

My panel has 454 with stroker crank 489 ci and Im working on getting late model OD trans for it along with new exhaust and little engine work.I figure the trans will pay for itself in short period.Not expecting 20 something mpg but figure I can get 16 to 18 on highway if I can get driver to behave,lots of luck there.

[highwinger]

Thanks for the last couple replies. I will check rear when I get a chance. I expect the gears have been changed so the oil should have been too. It's probably several years ago but less than 10k miles.

I've heard the compression ratio is a big factor in economy. I assume the valves too since they impact flow. I will have to read up on this.

I would like to do more eddy tuning, but I need an O2 sensor first.

[BK72BURB_3/4Ton4x4]

I read this reply on a forum where a guy with a 94 chevy 2500 w/ 7.4L 454was trying to improve gas mileage. Printed it and kept it my pocket but have not tried personally. I think some items mentioned have merit:
*********
Here is an instant 2-3 MPG: Remove valve covers. Using a 11/16 socket, back each rocker arm off about 3/4 turn, with engine at idle. Do one rocker arm at a time. After you loosen 3/4 turn. try loosening another 1/8 turn or so. At this point, you should begin to hear that rocker arm ticking, slightly. Also, once that happens, it should start oiling that rocker arm pretty heavily.

Now, slowly tighten that rocker arm just until the tick ceases. At that point, give the rocker arm nut another turn about another 45 degrees. A 45 degree turn is about equal to the hour hand on a clock going from 12:00 to about 1:30.

After you do one rocker arm, move on to the next one.

To make your job easier and quicker, I would loosen each rocker arm nut between a half of a turn to 3/4 of a full turn before I ever even start the engine. Then you should have very little loosening to do before you get to the 'ticking' part of the process.(Assuming nobody has been in there once it was assembled from the factory.)

When you are finished, your adjustment (lifter pre load) will still be within factory specifications.
You should find a noticeably cleaner idle, snappy response, and very noticeable power increases throughout the entire RPM range.

Next, I would try some ultra slick oil such as Royal Purple 5W30 or Amsoil 5W30. I would also use a Wix oil filter. Either of these two oils will go well over 6,000 miles between oil changes, in their sleep.

Make sure you have a fresh 195 degree Thermostat in the cooling system. That will also make a difference in the mileage. It will keep the internals of the engine cleaner, too, as it keeps condensate out.

Don't hesitate to replace the Oxygen Sensor. At 180,000 miles, even if it does not trigger a code, it's very tired and slow. Therefore, you can trim up some fuel economy with a new one, I assure you.

You can also try the Amsoil or Royal Purple 75W90 gear oils in the rear differential.

Keep tire pressures where they belong.

If it were my truck, I would not hesitate to put either a single 50 series or 80 series Flow-master muffler in place of the factory one. Stick with the factory pipe diameter and only change the muffler itself. Those 2 series of mufflers are very calm. So do not worry about excessive noise or interior noise.

Follow my suggestions, and if you were in person, and if you were to follow ALL of these suggestions, I'd shake your hand with a bet that you will see 3-8 MPG gains and a hell of an increase in all around performance, or I'd give you $100.

At this stage of the game, if you don't want to change the camshaft, I would definitely take the step to replace the timing chain assembly. Email me and I will give you an exact part number for the 'right' chain assembly.

Email: camshaftshaun@gmail

In addition to my experience source I will list below, I will also share you this information: We survived without issue, and for 550 continuous hours, a wide open throttle and heavily loaded torture test at Mercury Marine, with a production 454 which they used one of our camshafts in. I also do occasional hush-hush secret engine or valve train development projects for a special program here and there for companies such as G.M, Ford, Roush, etc.

That said, I know how to make these engines live, perform, and get decent mileage.

It is also worth it for you to install a one inch thick TBI spacer and also an Injector Spacer. You will more than likely have to bend fuel lines to reconnect them to the TBI, once you install the TBI spacer. Other than that, it's plug and play.

Source(s):

Camshaft design/manufacture, full competition race engine building/development, failure analysis of internal engine components, carburetor blueprinting, drive-ability/MPG/durability expert.

[chris mc bride]

expensive way to do it but ceramic bearings will help a lot. They are hot ticket in racing world. A car that runs 7 second 1/4 mile times can pickup.02 and 1 to 2 mph just from the reduction in drag. A guy I know in Kansas said his tow ropes retractor would actually move his car on level ground since he went to full ceramic bearings in car. Now front bearings alone run 200 to 300 bucks,but are good for million miles or so. How long to regain 300 if you pick up 1.5 to 2 mpg? Just throwing it out there.

[Jurassic-1]

I have a 1972 K5 Blazer with 32" tires and 373 gears. I previously could not go too far out of town at 70 miles an hour. I get 8 MPG . I replaced the engine with a rebuilt Napa short block and a set of 194 double hump heads. It now has around 100K on it. I installed a 700R4 in it about 16 years ago and it improved drive ability but the mileage was un changed. I can now cruise at about 2600 RPM at 70 and drop that another 250 RPM when I lock the converter. I also have a 1970 C-10 that gets 10 MPG with a rebuilt 350 using vortec heads and a mild cam. Both trucks have a Q-jet style edelbrock on them.

[Cumminpwr11]

I went the diesel option. First gen Cummins diesel ve fuel pump, built 47rh transmission 4x4 with 33 all terrains. My best hand calculated was driving 70 from Phoenix to Las Vegas. Averaged 24.7 mpg.

I ran the truck hard and I would get 15. Now she is getting stripped to become a pretty pig!

Chris

[highwinger]

I've been doing a lot of work on the burb lately some of which addresses the efficiency. I added the O2 sensor, changed the tranny shift points, changed the vacuum advance port on the eddy... I'm still playing with the timing, mixture and idle to get rid of the dieseling. Last mpg was 11.8, but I was still playing with it. I hope to get to 12 once I make some more eddy tweaks.

[highwinger]

I got up to 12.7mpg on my last fill up. About 3/4 was highway miles doing 65-75 (no A/C). I did another tuning adjustment since and will see how that works. The A/F seems to be pretty good. I would have expected the plug to be a bit cleaner (tan) though.

I'm curious how many folks here use ported vs. manifold vacuum for timing advance.