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Tuning for economy?
#1
Planning a 3500-4000 mile road trip in my 73 vert this spring and sure would like to do something to improve fuel economy. 351 2-v with eldelbrock intake, summit 600 cfm carb, maybe small cam but unknown specs. Engine rebuilt by PO approx 15000 miles ago and runs good. FMX with 2.75 rear gears

Current fuel mileage is 10.5 to 11 mpg mixed highway/city. Everyday driver.

Any suggestions?
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#2
OUCH! I get close to that with my current set up and I don't baby it by any means., see signature below for my specs. You should be doing better than that considerably, especially with the smaller carb, 2.75 gears, I assume by your comment not nearly as aggressive cam. Is it running rich now? What is your timing set at?

73 Grandé H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

- Jason


[Image: 082-hot-rod-power-tour-2017-1970-1970s.jpg]
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#3
Do you have a stock ignition with points? If so I would install a new set and adjust them by dwell angle, not feeler gauge. Replace the cap and rotor if you can't remember when the last time they were replaced. If the points are fairly new adjust them by dwell angle. Make sure your mechanical and vacuum advance are both functional. Set the timing.

After getting home, from driving it for 10 miles or so, pull a couple of spark plugs to see how they look. I like to pull one from the front and one from the rear. First, what kind of condition are they in? Is the gap correct? Is the center electrode burned down? If they are in decent condition what color are they? Black and carboned means either the carburetor is too rich or you're getting oil past the rings or through a bad PVC valve. Check and gap the plugs, or replace them, if needed.

How old are your spark plug cables? Insulation in good condition on them? Check the resistance of each cable.

Check your tire pressures. If you don't already have them, radials have less rolling resistance, which equals better mileage.

Put synthetic gear lube in your differential and manual transmission (if you have one).

New air filter.

Change oil and filter. Full synthetic will give you the least friction (best mileage), either 10w30 or 10w40 (for warmer temperatures).

Chances are, no single item will give you a big increase in mileage, but a little here and a little there will add up.

Finally, and this is the toughest for me, don't show every Chevy what you got, take it easy on the gas pedal.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#4
(01-17-2019, 03:18 PM)mbrew2 Wrote: Planning a 3500-4000 mile road trip in my 73 vert this spring and sure would like to do something to improve fuel economy. 351 2-v with eldelbrock intake, summit 600 cfm carb, maybe small cam but unknown specs. Engine rebuilt by PO approx 15000 miles ago and runs good. FMX with 2.75 rear gears

Current fuel mileage is 10.5 to 11 mpg mixed highway/city. Everyday driver.

Any suggestions?

...and here I am afraid to drive Christine 178 miles one way to Carlisle next May for the Ford Nationals.

[/url][Image: mbpsrsig3_zps456db2cb.png]

[url=http://s165.photobucket.com/user/MPBsr25/media/mbpsrsig3_zps456db2cb.png.html]
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#5
11mpg is pretty bad for a mild 351C with highway gears. I had two 4v cars, one got a best of 20mpg, the other managed 16mpg, but the engine was a bit tired and had a larger cam in it.

As mentioned, do a complete tune up. For a 4000 mile road trip, if you haven't upgraded to electronic ignition, you'll be miles ahead in reliability if you do. It's tough to beat the Ford Duraspark for dirt cheap performance and reliability improvement. If the plugs look good with a nice light tan color on the insulator and no excessive buildup on the threads, your carb is probably pretty close and the engine in good shape. Verify that the mech advance is working in the distributor. Set your static timing to 12* BTDC or so and tweak to what the engine likes.

Before you start really digging in, verify that none of your brakes are dragging or hanging up.

First and probably the largest contributor to poor gas mileage - vacuum advance. If it's not hooked up or the diaphragm is bad, you'll lose 3-5 mpg on the highway. I hook mine up to ported vacuum, so there's an instant boost in advance when the throttle is cracked. Kinda gives you a power boost without requiring more throttle.

Second, if you have any type of fan other than a clutch or electric, you're throwing away mileage. On my 71 XR-7, I netted 3mpg alone by switching from the factory AC flex fan to an aftermarket clutched unit.


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#6
+1 on what has already been said on tune up, lubricants, and vacuum advance. In addition, adjust float level down a bit, decrease jet sizes, decrease accelerator pump discharge nozzle size, advance initial timing to about 14 degrees, and if equipped with a modern ignition amplifier open plug gap to about .045-.050. This will require trial and error tuning to make sure you don't go too far (detonation, hesitation, flat spots, etc.). As someone said, a good place to start is reading the plugs and continue to read the plugs as you make changes. http://4secondsflat.com/Spark_plug_reading.html  Please let us know what progress you make. Chuck
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#7
You have the best advice from the best on the forum. All of the guys know their stuff.  It was suggested to change from points (if you still have them) to a Duraspark ignition. That is a great idea and can be affordable. However, if you have a GOOD Motorcraft distributor and what I mean by that is not worn out, no play on the shaft, then drop in a Pertronix Ignitor II module AND matching coil, very important!!!!.
I'm not too familiar with 2V's, but I have my '71 4V engine set with 16 degrees initial, 20 deg. on the crank plus about 4-6 deg. vacuum with a Holley 670 4V carb, stock intake. Plugs at .045 gap and I easily get between 15-16 miles per US gallon, (18-20 imperial) on the highway at 65-70 mph.
Note though, most stock Motorcraft distributors are typically made with a 15L slot, which equals 30 degrees on the crank. This was when engines were coming out of the factory with only 6 degrees of initial timing. Jumping up to 14-16 initial will certainly result in spark knock or pinging. There has been lots written and posted on the subject of reworking the slot plate to allow only 20 deg. crank. i.e. 10L slot which is .410" across. This has been my own experience and what I taught myself to achieve a strong running yet fuel efficient (if one can call it that!!) motor.
Geoff.

I learn something new every day!
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#8
On a drive like that a vacuum gauge inside the car to tell you when you are getting highest vacuum (can't remember if that's carb or manifold, off hand) will help control the right foot and maximize your highway mpg.
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#9
2 yrs ago i did a complete rebuild of engine.. no performance stuff only a 30 over. edelbrock carb and intake. my first trip within a week of finishing it got 20 mpg's . haven't checked in a while but i'd say i'm still very close to that.. as said TRASH the points and go pertronix. cheapest way and works great.
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#10
Thinking a bit more on this and it is out of my experience level, the 73 is a lot lower compression than what I was dealing with. So why not first try installing the Pertonix II and coil, then gradually bumping the timing a couple of degrees at a time to find out exactly where it start to ping under load. The back it off a degree and try again. You may be able to get to 10-12 degrees initial.
Worth a shot and if it works then you've saved yourself all the work of rebuilding and modding the distributor. However my thought on that would be to redo the dizzy at some point regardless..... or I could be talking out the back of my head!!
Let us know if the tips offered will work for you
Geoff.

I learn something new every day!
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