Need recommendation for a Carb for better MPG!

[Dan the man]

biggies to look for on TQ's

Excessive throttle shaft wear

Metering rods piston free and not excessively worn

The adjust screw for the depth of the
rods frequently is corroded and breaks off

The center plastic body for being wrapped and cracks. My dad's TQ had cracks in the mid section, the carburetor shop that found it said that those carburetors were known for that, is that true? I don't know as I was around 17 at the time

 

[Dan the man]

The only way I can think of in order to get good gas mileage is to do a complete tune up, dial in the carburetor and ignition system, proper size tires and tire inflation. For highway mileage, a good set of gears and a overdrive transmission. And use the cruise control if you have one if not driving 5-10 mph under the speed limit helps. The 2010 Colorado I had got the best mileage for a pickup truck, it was a extended cab wheel drive, with the cruise control set at 65 mph and the ac on I got 27 mpg highway, that's something that a mopar won't get

 

[toolmanmike]

This will stir the pot for sure. Just my own personal experience with the small block Mopar. I had a 1989 D-150 318 a/t and 2.73's 2 wheel drive and it's best was 14-16 on the highway. My 1998 wasn'tmuch better.Even my dad's 1998 D-150 only got 18 on the highway. My parents 1985 5t Avenue got 28 on the highway, but that was probably due to the fact that had the lean burn system on it. I've never known anyone who got good mileage from a 318, I'm not saying that it hasn't happened or that it's impossible. But I will say that I've heard more people say that mopars are not known for mileage and for my experience it's true

A pick up to a 5th avenue is apples to oranges. The Lean Burn engines were pretty efficient. Those cars also ran a low rear gear and a lock up torque converter. The pick ups of that era didn't have any of that.

 

[Dan the man]

A pick up to a 5th avenue is apples to oranges. The Lean Burn engines were pretty efficient. Those cars also ran a low rear gear and a lock up torque converter. The pick ups of that era didn't have any of that.

I know that they didn't. I was only making a comment, wasn't meaning any harm.

 

[RustyRatRod]

This will stir the pot for sure. Just my own personal experience with the small block Mopar. I had a 1989 D-150 318 a/t and 2.73's 2 wheel drive and it's best was 14-16 on the highway. My 1998 wasn'tmuch better.Even my dad's 1998 D-150 only got 18 on the highway. My parents 1985 5t Avenue got 28 on the highway, but that was probably due to the fact that had the lean burn system on it. I've never known anyone who got good mileage from a 318, I'm not saying that it hasn't happened or that it's impossible. But I will say that I've heard more people say that mopars are not known for mileage and for my experience it's true

Then that right there is the telling point of your experience. None. The 318 has always been a good mileage motor. The small bore lends itself well in that arena. I can tell first hand you don't know what's goin on here.

 

[273]

Other than a good tune, it's generally hard to recoup money spent on gaining mpg a lot of time it's just cheaper to put it into the tank. Gains are generally small especially for dollar spent so you would have to be putting a lot of miles on to break even nevermind save.

 

[RustyRatRod]

Other than a good tune, it's generally hard to recoup money spent on gaining mpg a lot of time it's just cheaper to put it into the tank. Gains are generally small especially for dollar spent so you would have to be putting a lot of miles on to break even nevermind save.

If he will confirm what gear he's running......a 3.23 for example ain't gonna get what I call "good" with a 340. 17 would be about what I'd expect. He could probably bust 20 with a change to a 2.76, for example. But he needs to know what he has now.

 

[273]

If he will confirm what gear he's running......a 3.23 for example ain't gonna get what I call "good" with a 340. 17 would be about what I'd expect. He could probably bust 20 with a change to a 2.76, for example. But he needs to know what he has now.

I just mean for the OP he's got to be careful and keep $$$ investment low to actually save money, he could easily spend 1000's of dollars for relatively small mpg gains. Generally for it to be worth it the mpg mod should pay for itself in at least a year or two.

Say at..
5,000 miles at 17 mpg x $3.25 a gallon = $956
5,000 miles at 20 mpg x $3.25 a gallon = $813
$143 a year savings minus cost of mod.

 

[Dan the man]

Then that right there is the telling point of your experience. None. The 318 has always been a good mileage motor. The small bore lends itself well in that arena. I can tell first hand you don't know what's goin on here.

You don't have a clue as to my experience with the 318's. FYI everyone has had a different experience. Seems to me that you're not happy unless you are stirring up ****

 

[Dan the man]

Then that right there is the telling point of your experience. None. The 318 has always been a good mileage motor. The small bore lends itself well in that arena. I can tell first hand you don't know what's goin on here.

Show proof of good gas mileage for the 318's. I never said that they didn't or couldn't get mileage I was simply talking about my own personal experience.

 

[Brooks James]

A pick up to a 5th avenue is apples to oranges. The Lean Burn engines were pretty efficient. Those cars also ran a low rear gear and a lock up torque converter. The pick ups of that era didn't have any of that.

Yeah it was an 8 1/4 rear at 2.45 ratio on its own special carrier

 

[1971 CY Dodge Dart]

You don't have a clue as to my experience with the 318's. FYI everyone has had a different experience. Seems to me that you're not happy unless you are stirring up ****

Rusty isn't stirring up anything but rather speaking from experience. Instead of attacking people and showing your ignorance at times you need to read more and post less. Just a helpful tip.

 

[Restomod]

If the car runs well, you might be happier just changing the rear differential gearing. An 8 3/4 isn't that hard to change, and you could probably find a 2.76 or 2.94 gearset that wouldn't cost too much.

 

[66fs]

OK, I get it. My expectations were probably a bit absurd.

You expectations are not absurd. I'm slightly amused that people answering you, don't know how to get 20+ mpg from a 340. You are in Nebraska, nice mid-western state with relatively flat terrain, highway driving, 55-60 mph (takes a lot of aerodynamic drag out of the picture), 2,200 rpm @ 65 mph sounds about right for 3.23 gears. What do you know about the 340 in your car? Do you have a timing light? Is your rear an 8 3/4?

So much bad info in this thread... Are you running good solid core wires? What ignition and distributor are you running? Platinum plugs? Anyway, start with a timing light and disconnect the vacuum advance from the distributor and plug it. Where is your timing set at now? Bump it up 2 degrees at a time, reconnect your vacuum advance tube, and check mpg on your normal drive. That is the starting point. Then, you can start swapping mixture rods in the Edelbrock carb, same scientific steps going richer and leaner in small steps.

I have gotten mid 20's (25 mpg average) mpg around 70 mph in a 4 speed, 1964 Barracuda, 2.76 gears running very steady (that's where the vacuum gage comes into play) and with the lightest pedal pressure that will maintain speed, with 72 340 heads, the stock 340 cam, and "71" 340 intake and TQ on a high compression 273 short block. I've done almost as good with a stock "72" 340. So much for "the 340 cam will never give good mpg" pronouncement.

The TQ, Quadrajet, and Street Demon have triple boosters and very small primary throttle bores, which have the potential of running very well and getting good mpg. That said, every time you accelerate, even the slightest amount, you are pumping more fuel into the engine. The TQ is IMHO the best street carb ever made. Like everything made, if abused or misused they can have problems. I still run 50 year old TQ's on my "68" 383, "73" 318 and the "67" 273. No problems yet with probably 400,000 on the 3 combined.

 

[Valveguy]

Well then, start working on the timing. Rusty has been asking, and me too,
However if that 340 has a factory cam, then 17 is pretty good. That cam was terrible for fuel economy.

I can tell you how to set your cruise-timing, but that doesn't mean that you will automatically get any better than the 17 mpg that you are now getting, and in the process, it might mess up your power-timing, and or PT timing.
Just make sure you have a working Vacuum advance system.
Part of the problem is that with the factory cam, 2200 is almost too slow to run a 340. Another is that the power stroke is very short.
Another is that most everybody recommends to run that cam advanced, which just aggravates things.

As far as cams go, the factory 340 cam, being on a 114 LSA is just too far apart. this chews up compression degrees all rightee to help keep it out of detonation, but it also chews up power stroke, which leaves a lot of cylinder pressure escaping into the exhaust, which could have been sent to the crank, to power the vehicle down the hiway. Instead it just puffs out the tailpipes.
Everybody used to rave about that cam, but not me. IMO, it was a terrible street cam. I mean I kindof understand why that cam got in there, but back in the day, it was one of the first things to get rid of, right after installing headers.. Today we have many better designs. IIRC I got 4 or 5 boxed up around here somewhere.
But you know, 1972 was a long time ago, and chances are that the original cam is long gone.... and who really knows what cam is in it...............

Excellent info, Thank You!!

 

[harrisonm]

I will try to say this as nicely and politely as possible. I don't want to sound condescending. 17 MPG is good for a 340. The 340 was a performance engine. It was never designed or expected to be a 'good mileage' engine. In fact, the 340 is one of the few 'performance only' engines ever made. You could not get the 340 in a station wagon, truck or a 4 door car. It was a performance option only available in a 2 door car. There have been reports of 340s being put in station wagons, trucks and/or 4 door cars, but they have not been substantiated that I know of. Most other high performance engines are variants of engines available in all other cars and trucks. When Chrysler put the 340 into their cars, it was as a performance platform. It was never meant to be an engine to deliver maximum gas mileage. Personally, I think if you are getting 17 MPG, that is about as good as you can get. You might be able to boost that a little with tuning, but any significant increases might get expensive and destroy the performance you have from your 340 now.
You could get a highway gear put in your car. You could put a 2 barrel carb and manifold on it. You could rebuild the engine with lower compression and fuel mileage in mind to include a milder cam. You could put fuel injection on it (some people on this forum have claimed better gas mileage). You could possibly put some slightly taller tires on the rear. You could swap a /6 into it and store the 340 in the corner of your garage. That way you could always put it back in. In my opinion, the bottom line is that the only way you can significantly increase your gas mileage will be expensive and lessen your performance. Some people are going to disagree with that statement, but please notice that I said 'significantly increase'. I am not talking about the small increase you might get from tuning, and it sounds to me like you are looking for a significant increase.

 

[Valveguy]

I Live in Lincoln Nebraska. I wish I had one of you guys close enough to hire to spend a couple hours with me and my Demon to see what might be going on because there are other symptoms that might make a diagnosis easier.
I sure appreciate all the replies! THANK YOU!!

 

[toolmanmike]

I will try to say this as nicely and politely as possible. I don't want to sound condescending. 17 MPG is good for a 340. The 340 was a performance engine. It was never designed or expected to be a 'good mileage' engine. In fact, the 340 is one of the few 'performance only' engines ever made. You could not get the 340 in a station wagon, truck or a 4 door car. It was a performance option only available in a 2 door car. There have been reports of 340s being put in station wagons, trucks and/or 4 door cars, but they have not been substantiated that I know of. Most other high performance engines are variants of engines available in all other cars and trucks. When Chrysler put the 340 into their cars, it was as a performance platform. It was never meant to be an engine to deliver maximum gas mileage. Personally, I think if you are getting 17 MPG, that is about as good as you can get. You might be able to boost that a little with tuning, but any significant increases might get expensive and destroy the performance you have from your 340 now.
You could get a highway gear put in your car. You could put a 2 barrel carb and manifold on it. You could rebuild the engine with lower compression and fuel mileage in mind to include a milder cam. You could put fuel injection on it (some people on this forum have claimed better gas mileage). You could possibly put some slightly taller tires on the rear. You could swap a /6 into it and store the 340 in the corner of your garage. That way you could always put it back in. In my opinion, the bottom line is that the only way you can significantly increase your gas mileage will be expensive and lessen your performance. People are going to disagree with that statement, but please notice that I said 'significantly increase'. I am not talking about the small increase yo might get from tuning, and it sounds to me like you are looking for a significant increase.

Along those same lines, The 340 never came in a 2 barrel version.

 

[Killer6]

A pick up to a 5th avenue is apples to oranges. The Lean Burn engines were pretty efficient. Those cars also ran a low rear gear and a lock up torque converter. The pick ups of that era didn't have any of that.

Well, that's just the beginning, lets not trip over the fact that that 5th Ave. would've had the roller cam & the fast-burn chambered heads with ~9:1 squeeze....that just might matter along with the feedback carb/electronic timing controls...apples to cantelopes....

 

[66fs]

I will try to say this as nicely and politely as possible. I don't want to sound condescending. 17 MPG is good for a 340. The 340 was a performance engine. It was never designed or expected to be a 'good mileage' engine. In fact, the 340 is one of the few 'performance only' engines ever made. You could not get the 340 in a station wagon, truck or a 4 door car. It was a performance option only available in a 2 door car. There have been reports of 340s being put in station wagons, trucks and/or 4 door cars, but they have not been substantiated that I know of. Most other high performance engines are variants of engines available in all other cars and trucks. When Chrysler put the 340 into their cars, it was as a performance platform. It was never meant to be an engine to deliver maximum gas mileage. Personally, I think if you are getting 17 MPG, that is about as good as you can get. You might be able to boost that a little with tuning, but any significant increases might get expensive and destroy the performance you have from your 340 now.
You could get a highway gear put in your car. You could put a 2 barrel carb and manifold on it. You could rebuild the engine with lower compression and fuel mileage in mind to include a milder cam. You could put fuel injection on it (some people on this forum have claimed better gas mileage). You could possibly put some slightly taller tires on the rear. You could swap a /6 into it and store the 340 in the corner of your garage. That way you could always put it back in. In my opinion, the bottom line is that the only way you can significantly increase your gas mileage will be expensive and lessen your performance. People are going to disagree with that statement, but please notice that I said 'significantly increase'. I am not talking about the small increase yo might get from tuning, and it sounds to me like you are looking for a significant increase.

I never built specifically to get mpg, always performance. But, the mpg came for free with the better efficiency. With a TQ you got both in spades, if you could stay out of the secondaries. You can easily get into the 20's with a gear change. I always had, and still do, have a 2.76 pumpkin for long distance driving.

 

[RustyRatRod]

I Live in Lincoln Nebraska. I wish I had one of you guys close enough to hire to spend a couple hours with me and my Demon to see what might be going on because there are other symptoms that might make a diagnosis easier.
I sure appreciate all the replies! THANK YOU!!

If you will follow instructions, we can help you from here. But understand, there may not be much room for improvement if your tuneup is right.

 

[Ottmundr]

I just mean for the OP he's got to be careful and keep $$$ investment low to actually save money, he could easily spend 1000's of dollars for relatively small mpg gains. Generally for it to be worth it the mpg mod should pay for itself in at least a year or two.

Say at..
5,000 miles at 17 mpg x $3.25 a gallon = $956
5,000 miles at 20 mpg x $3.25 a gallon = $813
$143 a year savings minus cost of mod.

^^^^^^^^^^^^^^^^^^^ This.

Back in the 70's when Lincolns weren't selling for **** because they 'got bad gas mileage,' my uncle bought one for real cheap. Pennies on the dollar cheap. Yes, he spent more money on gas, but his overall cost was still lower than a car that got better mpg.

Look at your overall cost.

 

[Valveguy]

If you will follow instructions, we can help you from here. But understand, there may not be much room for improvemThis is ent if your tuneup is right.

This is Wonderful!

 

[Valveguy]

I just mean for the OP he's got to be careful and keep $$$ investment low to actually save money, he could easily spend 1000's of dollars for relatively small mpg gains. Generally for it to be worth it the mpg mod should pay for itself in at least a year or two.

Say at..
5,000 miles at 17 mpg x $3.25 a gallon = $956
5,000 miles at 20 mpg x $3.25 a gallon = $813
$143 a year savings minus cost of mod.

This is some pretty great perspective, and you are spot on! I didn't think of it quite like this but also thought if I could get maybe 3-5 more mpg I wouldn't have to stop for gas so much with our 16 gal. tanks. My commutes are 60 miles a day. I am very good at driving in an efficient way so I know my 340 can do better. Thank You!

 

[Valveguy]

I never built specifically to get mpg, always performance. But, the mpg came for free with the better efficiency. With a TQ you got both in spades, if you could stay out of the secondaries. You can easily get into the 20's with a gear change. I always had, and still do, have a 2.76 pumpkin for long distance driving.

Efficiency sounds good to me!