340 gas mileage

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kevindahle

kevindahle

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I have a 71 dart that I over hauled a 68 340, built it as close to stock as possible, electronic hei distributor, edelbrock carb. The cam was a summit, other than that put new rings and bearings had the heads done. Runs good. 727 8 3/4 with 2:76(?). I'm not a super tuner but the car runs well. When I drive it to work about 70 miles, I get about 10 mpg. I had a Duster with a built 360 4 speed & 3:23 and would get 15 ish. My next step with the dart I think is a air fuel gauge. Any other suggestions?

20200306_154101.jpg
 
kevindahle said:
I have a 71 dart that I over hauled a 68 340, built it as close to stock as possible, electronic hei distributor, edelbrock carb. The cam was a summit, other than that put new rings and bearings had the heads done. Runs good. 727 8 3/4 with 2:76(?). I'm not a super tuner but the car runs well. When I drive it to work about 70 miles, I get about 10 mpg. I had a Duster with a built 360 4 speed & 3:23 and would get 15 ish. My next step with the dart I think is a air fuel gauge. Any other suggestions?

View attachment 1715494735
Click to expand...

Doesn`t have enough power for that tall of gearing w/ an automatic ???
 
thats not very good mileage i get 14 to 14.5 with my 530 hp 418 with a 950 hp and no vacuume advance .

thats an imperial gal .
 
You left out a LOT of important information. Tell us what's in the engine from air cleaner to oil pan, including exhaust. We don't have crystal balls. Well, I do, but the cats knocked it off the table and broke it.
 
^^^ What he said. So we all know what assuming means right? But other than a few mods it sounds basically stock.

I don't know which Eddy carb you have, but, if its a newer version like an AVS series I have no experience. If its a 1400 series, they like no more than 3.5-5psi of fuel pressure. Most mechanical fuel pumps exceed 5psi. So, if you don't have a fuel pressure regulator on it, get one with a gauge and dial it into 4.5psi. You should also pull the airhorn off of the top and check the float level. That small amount of pressure can over come the floats and pour raw fuel down the throat of the carb.

Edelbrock's web site has tutorials in their Tech section with videos on how to adjust your carb.

I think at best you're gonna see 12-15mpg, an improvement over 10ish, but that's life with old technology.
 
Don't really need an A/F gage.
Assuming this is mostly a highway drive to work.
Increase the restriction on primary side main circuits - one step at a time.
Test it to make sure its still drivable. If so, take it to work.
Repeat until it too lean (you'll know - it will be undrivable at interstate speeds)
Go back to a less restrictive rod or rod/jet combo.

If you want to buy vacuum gage, that's nice tool to have, relatively cheap, and can help your driving habits too.

Use the drag strip best mph to determine the jetting. Work the opposite direction, go richer as the first tests.

Finally you can experiment with the step up spring. Car should go leaner and faster with more pedal until some point over half throttle. Then it needs enrichment or it won't accelerate. There will be a dead spot. vacuum gage is a useful reference tool, but again not neccessary. Performance is the measurement that determines the best tune.
 
With 2.76 gears you should be able to get around 20 mpg on the highway. You should have initial timing set around 10 degrees BTDC, Total around 35 degrees without vacuum advance. Does your distributor have vacuum advance? Try a vacuum gage and let off on the accelerator until you drop speed. You can tune for mileage without gages by leaning the mixture, larger diameter rods till it "hunts" or slightly surges holding steady throttle at about 60 mph. Then richen it up, smaller diameter rods, just a bit.
 
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A lot about mileage can be cam related.
 
It is a 1406 edelbrock carb. Out of the box basically. Pistons are the factory ones, it was pretty low mileage engine I just honed and put new rings and bearings, no machining on block. The heads are '68 x. Hardened seats and new exhaust valves. 68 340 exhaust manifolds with dual exhaust. Cam specs I would have to look up it's been 2 years since I bought it summit brand, close to stock 340 specs. I just wanted in to be what you would of got off the lot in 1970. And I am happy how it runs but gas mileage stinks. And it may be above my tuning skills, may have to find someone.
 
Now is the perfect time to learn how to tune a carb. You tube and threads here should keep you busy.
How is your distributor set up?
 
When I had my 72 Duster, it had a Thermoquad, and 15-17 was easy to get but I kept an egg under my foot to do so..
 
Bassically agree ^^^^with Rob rumblefish
If you can install an engine and hook it up, you can change the rods in a carterbrock.

I just looked at the 1406 chart.
It starts with the largest diameter rod, so you can't go larger on the rod.
To go leaner, you have to change the rod and jet.
The chart is on page 12. The next leaner rodjet combo is listed on line 8.
https://www.edelbrock.com/pub/media/wysiwyg/documents/carb-owners-manual.pdf
 
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Which cam exactly do you have in there?
The other guys are also dead on. Between carb tuning and the distributor timing, much can be gained in power and mileage.
 
kevindahle said:
It is a 1406 edelbrock carb. Out of the box basically. Pistons are the factory ones, it was pretty low mileage engine I just honed and put new rings and bearings, no machining on block. The heads are '68 x. Hardened seats and new exhaust valves. 68 340 exhaust manifolds with dual exhaust. Cam specs I would have to look up it's been 2 years since I bought it summit brand, close to stock 340 specs. I just wanted in to be what you would of got off the lot in 1970. And I am happy how it runs but gas mileage stinks. And it may be above my tuning skills, may have to find someone.
Click to expand...
I normally dont have a problem with the tuning part it's my right foot I have the problem with for getting good MPG.
 
Outside of having your timing correct, 1406's are a very simple carb. If you haven't a fuel pressure regulator on it, get one. What happens when its unregulated and there's too much fuel pressure, that pressure will bend the tangs on the float and it will eventually need a place to dump the extra fuel that's in the fuel bowl, it has only one place to go. Well actually 2 places. The 2nd place will require a fire extinguisher as it will seep out from where the airhorn mates with the carb body. Then onto your manifold.

If you pull the airhorn off, there are 2 cavities behind the secondaries. If those cavities are full of gas, that excessive fuel pressure is seeping between the airhorn and carb body.

Pull the airhorn off, check the float height and the float drop. Then put a fuel pressure regulator on it and see what your results are. Make sure the pressure regulator will adjust down to the 3.5-5psi range and stay away from the Mr Gasket dial type gauge. They're junk. Here's a link for you to look at. From there you can go to their tech center and checkout their videos.

https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf
 
Tinmannz said:
Outside of having your timing correct, 1406's are a very simple carb. If you haven't a fuel pressure regulator on it, get one. What happens when its unregulated and there's too much fuel pressure, that pressure will bend the tangs on the float and it will eventually need a place to dump the extra fuel that's in the fuel bowl, it has only one place to go. Well actually 2 places. The 2nd place will require a fire extinguisher as it will seep out from where the airhorn mates with the carb body. Then onto your manifold.

If you pull the airhorn off, there are 2 cavities behind the secondaries. If those cavities are full of gas, that excessive fuel pressure is seeping between the airhorn and carb body.

Pull the airhorn off, check the float height and the float drop. Then put a fuel pressure regulator on it and see what your results are. Make sure the pressure regulator will adjust down to the 3.5-5psi range and stay away from the Mr Gasket dial type gauge. They're junk. Here's a link for you to look at. From there you can go to their tech center and checkout their videos.

https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf
Click to expand...
I have been wanting to add a regulator to mine.
Do you have recommendation for one that you know actually works well?
Say Hi to Dr. Smith for me.
 
512Stroker said:
I have been wanting to add a regulator to mine.
Do you have recommendation for one that you know actually works well?
Say Hi to Dr. Smith for me.
Click to expand...
I think that I used the Summit Racing brand. It worked very well for what I had which was a Eddy 1406 carb on a SBC 350. Make sure it's adjustable to your desired fuel pressure range and you will have to plumb in a fuel pressure gauge. If you're running fuel injection or a high pressure pump then you will need a high pressure regulator. I hope this answers your question.

Edited to add: Some regulators have a fuel bypass port which returns fuel back to the tank when the pump puts out too much pressure. If you happen to pick up a regulator with a bypass port, no big deal, just plug it and go. Or if you have a return line back to the tank, use it as a return line.

Dr Smith has lost his marbles but Will and Penny are keeping us entertained.
 
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Mattax said:
Don't really need an A/F gage.
Assuming this is mostly a highway drive to work.
Increase the restriction on primary side main circuits - one step at a time.
Test it to make sure its still drivable. If so, take it to work.
Repeat until it too lean (you'll know - it will be undrivable at interstate speeds)
Go back to a less restrictive rod or rod/jet combo.

If you want to buy vacuum gage, that's nice tool to have, relatively cheap, and can help your driving habits too.

Use the drag strip best mph to determine the jetting. Work the opposite direction, go richer as the first tests.

Finally you can experiment with the step up spring. Car should go leaner and faster with more pedal until some point over half throttle. Then it needs enrichment or it won't accelerate. There will be a dead spot. vacuum gage is a useful reference tool, but again not neccessary. Performance is the measurement that determines the best tune.
Click to expand...
Just an aside to the vacuum gauge comment. I remember as a young kid the built in vacuum gauge on my school bus......which were the wipers beating like hell in between shifts during a rain storm.
 
kevindahle said:
I have a 71 dart that I over hauled a 68 340, built it as close to stock as possible, electronic hei distributor, edelbrock carb. The cam was a summit, other than that put new rings and bearings had the heads done. Runs good. 727 8 3/4 with 2:76(?). I'm not a super tuner but the car runs well. When I drive it to work about 70 miles, I get about 10 mpg. I had a Duster with a built 360 4 speed & 3:23 and would get 15 ish. My next step with the dart I think is a air fuel gauge. Any other suggestions?

View attachment 1715494735
Click to expand...
Is it city driving, stop and go, or one long highway, or urban back roads or a combination of all ?
 
Did I miss what size the rear tires are? They look kinda small. What RPM are you at on the highway? I love the slots too!

PS: I know nothing compared to those guys^^^^ I'm serious about that! :)
 
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Tinmannz said:
^^^ What he said. So we all know what assuming means right? But other than a few mods it sounds basically stock.

I don't know which Eddy carb you have, but, if its a newer version like an AVS series I have no experience. If its a 1400 series, they like no more than 3.5-5psi of fuel pressure. Most mechanical fuel pumps exceed 5psi. So, if you don't have a fuel pressure regulator on it, get one with a gauge and dial it into 4.5psi. You should also pull the airhorn off of the top and check the float level. That small amount of pressure can over come the floats and pour raw fuel down the throat of the carb.

Edelbrock's web site has tutorials in their Tech section with videos on how to adjust your carb.

I think at best you're gonna see 12-15mpg, an improvement over 10ish, but that's life with old technology.
Click to expand...
We had a '70 Dodge truck I had put a 340 in, with a MP cam and was running a TQ. We took it on a 2,200 mile round trip and averaged 17 mpg at 65 mph. 727, stock converter and 2.76 gears
 
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