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Old 08-24-2005, 02:05 PM   #1
71chevylongbed
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increasing gas mileage

is it possible to detune a motor to get better fuel mileage. now that gas is over $2.50 a gallon for regular i no longer care about going fast
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Old 08-24-2005, 02:34 PM   #2
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My 69 lwb use to get 10 mpg going up hill, down hill, loaded, unloaded it made no difference. Now, at 80 mph I get just a little over 16 mpg and feel great about it. Rejetted the Performer, went too lean and had to come back some, one stage lower on primary and secondary. Edelbrock states that the Performer are factory jetted rich and may have to be custom jetted. Then the 700r4 WITH lock up. When the lockup went out I dropped about 1.5 to 2 mpg. Fixed that in a hurry. And finally got rid of the 373 gears and went to 307s. Still got alot of power to impress the youngsters but I do like delaying that right turn into the gas station.
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Old 08-24-2005, 03:36 PM   #3
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i had my motor dyno tuned for max power and they used a gas analyzer so i know that the way it is right now it isnt too rich.if i put in the smaller jets will i need to retard the timing. are there any adjustments that can be made with out rejetting to increase mileage?
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Old 08-24-2005, 04:00 PM   #4
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Since they used a gas analyzer that option seems to be out. The next is the gearing and the type of transmission. If you read the post scripts our setups are very simular. What kind of mpg are you gettin now?
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Old 08-24-2005, 05:58 PM   #5
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Thought about a two barrel? They do atomize fuel a little better...but you have to have the right intake, ignition curve, etc.

For you...look into changing the curve on your distributor - both the mechanical and the vacuum advance.
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Old 08-24-2005, 08:26 PM   #6
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You could always take the fan off the engine and go with an electric unit.

The amount of drag the fan creates really drags down the power. The fan alone is good for 2-3mpg. I started out with a stock motor that had been bored .030 to restore the compression. With this setup I was getting mid 9-10mpg. I then went from points to a Pertronix ignitor and re-gapped my plugs. This helped but only a minimal amount. I then pulled the stock intake and replaced it with an Edelbrock performer. Hell the valve covers were off so I went ahead and installed Comp Cams 1.52 roller tip rockers. At this point I saw no need to install the old distributor. It was replaced with an HEI unit with an MSD coil and wires. When I put the breather back on the carb I put a taller element in it so it could breathe a wee bit better. After all this I was getting a solid 12MPG. I then installed my electric fans at the same time I put on the Vintage Air and March Performance underdrive pulleys. My mileage the last time I checked it was 14.75. By the way this is real world driving in the left lane of the interstate, running the air. I don't ease around babying it just to see what kind of MPG I can get.
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Old 08-24-2005, 08:46 PM   #7
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Quote:
Originally Posted by see ten
You could always take the fan off the engine and go with an electric unit. The amount of drag the fan creates really drags down the power. The fan alone is good for 2-3mpg.
WOW!

Is that a fan kit you used? Which one? 3MPG is worth $10 a tank to me!
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Old 08-24-2005, 10:06 PM   #8
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Originally Posted by farside847
WOW!

Is that a fan kit you used? Which one? 3MPG is worth $10 a tank to me!
It's a flex-a-lite 295 series. It is a universal fan but it is designed to be used on a radiator of the same core width as 67-72 chevy trucks. I built the upper bracket to bolt on to the factory upper shroud mounts. I modified some of the brackets that came with the kit to build the lower brackets. This is not a cheap fan but neither is gas. It will pay for itself if you drive your truck enough. I have the same fan on both my C10 and my K10. I also have a Flex-a-lite fan on our Jeep Wrangler.
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Old 08-24-2005, 10:17 PM   #9
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Everybody chime in with some good ideas, then we'll copy this over to FAQ.
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Old 08-24-2005, 10:54 PM   #10
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2x4 bolted to floor under gas pedle works wonders
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Old 08-24-2005, 11:46 PM   #11
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I would say adding a fuel injection with a computer and all the sensors would do wonders. An overdrive transmission is also high on the list.
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Old 08-25-2005, 12:45 AM   #12
71chevylongbed
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Quote:
Originally Posted by 355
Since they used a gas analyzer that option seems to be out. The next is the gearing and the type of transmission. If you read the post scripts our setups are very simular. What kind of mpg are you gettin now?

im getting 10mpg now. im running a th400 tranny and 3.73 rear gears
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Old 08-25-2005, 07:35 AM   #13
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Replacing the turbo 400 with a 700r4 should help considably, especially if your doing a lot of highway driving, I also am assuming the crower cam is 240 advertised duration and not @.050 unless you have serious compression to back it up.
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Old 08-25-2005, 12:53 PM   #14
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I don't know that the EFI is going to help much. I have the TPI, 700R4 and 3.73 gears. In town I get 10 and 14 on the highway. I'm going to drop down to 19lb/hr injectors though and see if that brings it up any more. Jeff.
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Old 08-25-2005, 04:38 PM   #15
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you can just look at newer vehicles that are fuel injected with similiar gear ratio and same engine size and see it is not going to help gas mileage by much if any.
you may still have some room to play with the carb jetting even though they set it with a gas analyzer, as it was probably set to run good and not for gas mileage.
700r4 or changing rearend gears or both.
depending on your camshaft your using you may be able to go with a more efficient running camshaft that would be closer to stock lift and duration.
if you can run taller tires it may help lower your rpm a little at cruising speed also.
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Old 08-25-2005, 05:26 PM   #16
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Get a cheap beater Honda Accord. Probably costs less than all these MPG saving mods.
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Old 08-25-2005, 05:43 PM   #17
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Originally Posted by Jim_PA
Get a cheap beater Honda Accord. Probably costs less than all these MPG saving mods.
Maybe so , but how many thumbs up is that going to score while cruisin down the road?
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Old 08-25-2005, 11:06 PM   #18
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Maybe so , but how many thumbs up is that going to score while cruisin down the road?
Agreed, but if you care that much about a thumbs up, suck it up and pay the extra gas money.
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Old 08-25-2005, 11:58 PM   #19
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A cheap beater Honda Accord does not help us get better fuel milage in our trucks. We could get a motor cycle but we are talking about getting more miles out of a gallon of gas for our trucks.
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Old 08-26-2005, 12:09 AM   #20
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Quote:
Originally Posted by walker
I would say adding a fuel injection with a computer and all the sensors would do wonders. An overdrive transmission is also high on the list.
Well that defeats the purpose of why I bought this truck... being able to work on SOMETHING WITHOUT all that complicated computer stuff in it. I partially agree that you need to suck it up when choosing to drive these classics or get a beater lil car, but we should try to conserve as much as we can while still having fun in these trucks.

I also have an electric fan on mine and agree that it seems to do wonders. I recently switched to a lower profile air filter element and surprisingly that seems to be lowering my MPG, so I may go back to a taller one. Just my two cents.
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Old 08-26-2005, 12:13 AM   #21
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I've been driving around like the roads are icy. Easy acceleration saves tons of gas. Keeping the pedal off the floor saves alot too. I've been trying to keep it under half throttle most of the time.
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Old 08-26-2005, 03:35 AM   #22
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I put a quart of Slick-50 into a 1-ton Ford Van I used to own and my MPG got better
by 3 miles per gallon immediately. I don't know if that stuff does what they claim, but
it paid for itself within 6 weeks of using it. At today's gas prices, it'll probably pay for
itself after the first fill up.
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Old 08-26-2005, 05:46 AM   #23
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Do a mileage check, then change the engine, diff, and manual trans (if so equipped) oil to a quality synthetic (preferably Amsoil, IMO). Repeat mileage check with same driving technique and usage (all highway or all city or daily commute with no differences, etc.). Cheap thing to try for maybe up to one mpg increase. Possibly two.
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Old 08-26-2005, 09:13 AM   #24
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see ten
I really like your set up with the electric fan, but flex a lite web site does not recommend for the main cooling source on a 4 core radiator. What do you think about this. I have a big block with air and a 4 core.
David
Attached Files
File Type: doc flex-a-lite.doc (19.0 KB, 74 views)
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Old 08-26-2005, 10:47 AM   #25
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Quote:
Originally Posted by 71chevylongbed
is it possible to detune a motor to get better fuel mileage. now that gas is over $2.50 a gallon for regular i no longer care about going fast
Gas up here in Canada is near 5 bucks a gallon I hope this will make your truck seam a little easyer on gas.
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