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Improve Fuel Economy on 360

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sctvguy1 View Drop Down
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    Posted: Nov/22/2012 at 7:43pm
I have a 360, two barrel, 3sp. automatic. It is in a 1971 Matador 4 door.  The car has dual exhausts, and I was thinking of putting smaller jets in the carb, HEI ignition.  I have radial tires.  I have looked at many sites trying to find the average fuel economy of this engine/combination, but it is too old.  Are there any other things that I could do to get more miles per gallon from my car.  It is in beautiful shape, only 26K miles.  I drive very lightly.  I do not have cruise control, is it available somewhere for this model?  Thanks for any tips.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/22/2012 at 8:58pm
First, gearing and rpm's will have the biggest effect on your mileage...once the engine is in tune properly.

Want electronic ignition?  Why go with HEI when AMC actually used a Ford Duraspark unit from the factory, from 1978 on?  It's not THAT hard to wire up on an older 360...but then, I'm a fan of using what was factory designed to work, as long as it works well.  Take a Duraspark, add a Cap-A-Dapt setup to use the larger diameter Ford electronic cap [and the corresponding rotor], add an e-coil, and you've got as good a setup as any HEI system.

The fact that AMC never used an overdrive with the V8 is a bit of a problem.  You could swap in an AW-4 out of a 2WD Jeep with a 4.0 six, but that has its own problems...but answers can be found in the transmission section of this forum.

If the carb is properly jetted now, what do you hope to accomplish by running smaller jets?  Running an engine lean doesn't necessarily equal better efficiency [and therefore better mileage]...and may create driveability issues on top of the mileage issues you already have.

You mention having radial tires; for "ultimate" fuel economy, you should be running the tallest yet narrowest tires that will fit your car. Smaller contact patch from the tire = less friction with the road = more mileage...at a cost of a loss of handling and braking because of that same decreased road friction.  Nothing's free; it all comes at a price.

You aren't going to get anywhere near 30 MPG from a 360 in a car as heavy as a Matador.  In fact, over 20 MPG may be a pipe dream.  Decreasing the weight of the car significantly will increase your mileage, as the engine doesn't have to work nearly as hard to get the car rolling or to keep it rolling.

BUT...the biggest problem is the weight of the car, the final gearing in the top gear [rear end ratio x high-gear ratio]; and driving like you have an egg under your right foot...as well as anticipating stops, and taking your foot off the gas earlier as opposed to using the brakes as much to slow the vehicle...will have about as much effect on your mileage as anything else you can do for under $1000.  Also, doing more highway driving vs. stop-and-go city driving will make a big difference because, on the highway, you're running in the top gear for a larger percentage of your driving.

But there is no magic carb or ignition tuning specs that will dramatically change your mileage...unless your car is already in a poor state of tune to begin with.


Edited by Buzzman72 - Nov/22/2012 at 9:08pm
Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/22/2012 at 10:02pm
You should get 15-17 on the hwy and around 12 in the city if everything is in good shape.  better ignition will not get more MPG unless the old ignition is weak.  If you are only city driving, then you could get rid of the 2.87 rear gears and go down to 3.15 ratio.  That will help around town but hurt on the Hwy.  Alos, don't run too much pressure in those radials.  The gas mileage increase with radials comes from the flexible sidewalls and too much air makes them too stiff.  Start with about 30 psi and no more than 35.  As said before, smaller cross section tires roll better.  Like the difference between riding a mountain bike and a good road mike.  Big tires means big resistance.  Air dam in front will help keep the air out from under the car and side skirts would help too.  They would be ugly though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fluffy73 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/22/2012 at 10:17pm
Or just lower your expectations. A heavy car with a 6.0 liter, cast iron engine under the hood is not going to be economical. Just sayin'.  Another ignition alternative would be the Pertronix systems. Keep your stock distributor, but eliminate points. You can usually get a much more powerful coil from them as well.
 
You could also switch to a 4bbl.  I know this seems counter-intuitive but 4 barrel carbs usually have smaller primaries than straight 2-barrels.  4 barrels can give you the mix of both economy, and power when necessary.
 
Aluminum wheels can also help a little.
 
Or, invest in things like Fuel Injection, Aluminum Heads, 700R4 transmission.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Nov/22/2012 at 10:49pm
As said, if I can average 13 MPG combined highway and city in a 4000 pound Wagoneer, you should be able to get 17 or so in that. It weighs a couple hindred pounds less with a more efficient transmission and is more aerodynamic.
 
Factory AMC axle gearing for the auto boxes tends to be pretty good all around.  The 2bbl carbs are the best fuel economy and low torqueing carbs ever made, but a slight increase in mileage can be had with a carb off a later Jeep 360.  Motorcraft made quite a few improvements to the carbs in the name of power, fuel economy, and emissions, all of which improve together.
 
The exhaust system might be too big. If they're duals, I hope they are no bigger than 2" each pipe.
 
Cold air intake in the summer, thermostatic warm air in the winter. Make sure the choke is set properly. I know my fuel mileage takes a hit in winter just because the choke is on longer.
 
Ignition timing: 5-8 degrees BTDC. Period.
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 17tamx Quote  Post ReplyReply Direct Link To This Post Posted: Nov/22/2012 at 11:05pm
Put the 360 in a Gremlin or 2door Hornet and pickup a few miles per gallon easy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dbomb Quote  Post ReplyReply Direct Link To This Post Posted: Nov/22/2012 at 11:50pm

We had alot of complaints about fuel economy on the grand waggoneers and j10s and 20s  when i was at the dealership. They were  pigs espescially the full time 4x4  trans case models . We had good luck advancing the timing a bit and  using water injection  as well as making sure the clutch fan was working properly as well as installing flex fans on some models . If the  EGR system is clogged or not opening it can hamper MPG espescially if youre "road timing" the ignition timing .Road timing is advancing ignition a few degrees the backing off when you hear a ping. Old carbonned up motors will ping easily as well as a disabled or malfuntioning EGR or a stuck Heat riser at the exhaust manifold . I dont know why everyone hates egr valves and disconnects them they actually can help stop detonation and allow lower octane  fuel  to be used or more lead timing to be run  while cleaning up the NOx levels emmitted .On some vehicles espesciallt like fords with a sandwich egr plate under the carb the cars and trucks were dogs with a death rattle  when the EGR plates  clogged or warped up. Later Model Grand Cherokees as well had problems  with vaccum delay valves and timing  advance  mods under AMC tech service bulletins.  Newer fords had campaigns on the 46 and 54 crown vic type intake manifolds clogging up egr. Wheel alignment can play a role as well espescially on an old car cambered out and too much toe out.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote smills61074 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/23/2012 at 12:33am
dbomb mentioned probably one of the best ideas to help with fuel economy.  A clutch fan is definitely a step in the right direction.  Should be relatively cheap.  An overdrive trans would be your best option, if there is something out there that will interchange.  If you don't drive a lot of miles.  Do the math.  The difference between 15 and 20 mpg is not much, if you only drive a thousand miles a year.  In reality, anything expensive will never pay for itself.  Good Luck and keep a light foot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BassBoat Quote  Post ReplyReply Direct Link To This Post Posted: Nov/23/2012 at 9:10am

I would advise against changing the jets in the carburetor.  Leaner does not give you better mileage.  Of course, neither does richer, but the way it works is you get the best mileage when the calibration is right.  These cars tended to be tuned on the lean side for emissions to begin with, so save that for last.  EGR is particularly egregious on these old cars.  Plug it off, by disconnecting the little hose to the valve and sticking a screw or a golf tee in the hose.  Undo all the things that were done to improve emissions, all of which are at the expense of performance and efficiency.  Quicken up the advance curve with one lighter spring in the distributor, increase the initial timing with vacuum advance disconnected to 14 or 15 degrees or the most you can run and still get it to crank over and start  when hot.  You might have to limit the mechanical advance in the distributor, but that is pretty easy to do with either the brass bushing included in an advance curve kit or a piece of vacuum hose on the advance limit pin.  Some distributors actuall had two different slots, one for retarded (pun intended) US emissions and one for export.  In theory you can get too much timing, but in practice on a low compression early 70's  motor there is no such thing.  Crank it and see.  You should find that advancing the timing and running premium fuel will give you a mileage benefit beyond the increase in fuel cost.  It takes a bit of patience to fine tune everything, but do it. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote dbomb Quote  Post ReplyReply Direct Link To This Post Posted: Nov/23/2012 at 11:51am
If youre looking for economy  learn to road time the engine and listen for spark nock and advance the lead timing as you go  once it knocks on accel  back off a little bit.I guess i kinda see it the other way on the EGR thing  not to get in a debate here but I know that affective EGR lowers  the peak combustion temperature and allows engine torun more lead timing  Disabling an accurate working system is actually going backwards  for an economy and performance standpoint . Just take expample of chryslers leanburn system as well as other where manifold vacuum and ported vacuum are taken and used  sycroniously to control vacuum advance  and egr function . Theres plenty of patents on it just google EGR and Ignition Timing for a better example. Nowadays theyure tuning EGR lift with Knock Sensor S ignals and boost pressure to provide best possible performance and economy. Bass Boat is right though on old cars especially like thge AMC V8 intake design its arcaic at best but still functional. Try this take an old loaded up engine with regular gas  and run like 14 to 16 degrees timing its gonna ping  a bit  then disconnect the EGR valve  it will sound like a popcorn popper till you burn a hole in a piston or break the ring lands out. ping ping ping. Im glad i got an EGR valve on my AMX . If all else fails wax the car to streamline it
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