Gas mileage improvements for 318 - DodgeTalk : Dodge Car Forums, Dodge Truck Forums and Ram Forums
 
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#1 Old 02-05-2007, 08:07 PM
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Gas mileage improvements for 318

I am in the process of purchasing a 1976 Dodge van conversion (109wb) with 318/2V/727/3.21. This is a relatively light, one owner vehicle with a medium ht. roof.

In the course of restoration, I will be pulling the engine and trans for rebuild and need some advice as to what to add to improve gas mileage. The goal is 18-22 mpg.

My thoughts were the following:
- small 4bbl (Holley 390) with Performer manifold, K&N filter
- what about a throttle body F.I.from a later 318
- electric cooling fan - saw the thread posted
- dual exhaust
- cam - don't know
- any advantage to a lock up converter trans.?

I have also thought about going back to a 6 cyl engine. There are a few available locally and given the motor and trans will be out, the conversion probably won't be too difficult. Had an 88 van a few years back with the 3.9 FI and it was great.

Your thoughts and comments, please.
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#2 Old 02-06-2007, 06:45 AM
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If you want FI, heck why not transplant a Magnum 318 into the '76? My '94 gets pretty good mileage for a high-top conversion van. I also have the 35 gallon fuel tank as well. In my opinion the Chrysler TBI systems of the 80's are troublesome, but the MPFI Magnum engines are pretty stout.

Honestly, you'd be hard pressed to get 22mpg out of a brick. The V6 might get you there, but I'm not sure.

Nate Breece

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#3 Old 02-06-2007, 12:52 PM
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To get 18-22mpg with a slant six you will have to go with a manual transmission, preferably the 833-OD 4 spd.
The automatic 3 spd. isn't efficient enough. The newer OD automatic won't fit the slant six due to different bellhousing.
I would consider the swap mentioned by Nate.
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#4 Old 02-06-2007, 03:59 PM
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Smaller carbs can be counterproductive to fuel economy - the engine actually has to rev higher to pull in the same amount of air, and thus has more friction to work against. With a 318, get a 450-550cfm carb, and you should be good. Jet it just this side of lean so you don't get stumbling and pinging, and you'll be just about right. You could also re-jet the carb that's on there - I don't know about 76's, but most earlier carbs were jetted on the rich side for smooth running and reduced combustion temps, with the side effect of poor MPG and sooty deposits.

Dual exhaust will help a little, if you can keep your foot out of it.

Lockup trannies will help by keeping revs a little lower. If you can, an overdrive lockup trans would be your best bet. I don't know what's available for carb'd power plants, but I assume there's an equivalent to Ford's AOD that uses the standard small-block bolt pattern and a throttle valve cable rather than computers to control it.

E-fan will definitely see you an improvement in MPG and power - it's a mod I've been thinking about myself.

Cam, stay close to stock.

Another thought: run the thinnest oil in your rear diff that you can get away with. Less friction = less power loss = more MPG.

Lastly: your driving style can greatly affect your MPG results. A vacuum gauge and a tach can help you optimize how you accelerate and what speeds to cruise at for the best MPG, as well as other techniques like driving ahead to avoid stopping and keeping your mass moving, etc.

22mpg is going to be very, very tough, and probably unattainable, but I believe 18 is definitely within the realm of possibility (as long as you're talking highway cruising rather than average).

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#5 Old 02-06-2007, 05:58 PM
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I agree 18 on highway is obtainable. We just got 15.5 mpg on a cruise to Texas, pulling a small 1000 lb trailer, and our .96 Ram van is a high top.

Synthtic oil every where is a must, eng, trans & diff. I did the 'side-gap' spark plug trick, used new wires, cap & rotor. I've also done the electric engine fan & remote auto tranny fan cooler.

The 'Fastman' Throttle Body conversion is also worth doing -

It all adds up.

Funny thing. I gained two full mpg from upping our highway cruising speed from 65 to 72 mph. No kidding. It was 13 - 13.5, then went to 15.5 at the faster speed.

Any ideas why ?

1996 Ram Van B-2500 Conversion Van - 318, Electric Engine Cooling Fan - "The Family Bus"
1997 3500 Cummins Ram Truck - 19.5 wheels, pacbrake, Gearvendors OD - "Pocket Peterbuilt"

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#6 Old 02-06-2007, 06:41 PM
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Could be the engine's sweet spot - different on every vehicle, forms during break-in. Or, maybe you caught a favorable stretch of highway or a tailwind? I don't know!

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#7 Old 02-06-2007, 08:01 PM
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Thumbs up

Sweet spot, that's probably it.

The most efficient spot on the torque curve or somesuch. I'll try it at 75 mph (N.Mexico & Arizona) and see what that does.

My point was how so many factors influence MPG - I'd heard that above 55 mph that aerodynamics were the biggest factor worsening mileage, so I reasoned, going slower is better MPG, right ? (especially on a 'high top')

Apparently, not if you're below the 'efficiency curve' speed....there is probably a better term I'm ignorant of...so to Pittwagen; don't neglect a single thing you may hear discused here; including testing your mpg at different highway speeds !

1996 Ram Van B-2500 Conversion Van - 318, Electric Engine Cooling Fan - "The Family Bus"
1997 3500 Cummins Ram Truck - 19.5 wheels, pacbrake, Gearvendors OD - "Pocket Peterbuilt"

Tyranny Rising ? The answer to 1984.....is 1776 !

"Evil is powerless, if the good are unafraid."
Ronald Reagan

"You never have to give up an ounce of Liberty to obtain security."
Ron Paul

"Stand fast, therefore, in the Liberty wherewith Christ has made us free, and be not entangled again in the yoke of bondage..." - Galatians 5:1
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#8 Old 02-06-2007, 09:12 PM
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Thanks all, for the comments. In talking to my machinist today he said the one best addition would be a vacuum gauge, keep your foot out of it and vacuum high as much as possible. His view was that you need to drive a lot to recover the costs of the mods and I probably won't be doing that.

Given this thing has literally no pollution equip. on it, I will check on the idle settings to see if the screws can be tightened a bit. Unfortuately if it is leaned out too much the NOX will go through the roof (no cat. on this baby) and the vehicle fails our BC Canada AirCare test. Had a 74 camper van a few years back and with a 360/2V and in order to get the CO to spec. the idle screws were almost turned completely in.

Another question, do these Autolite plugs (saw a reference on the truck site) really make a difference?

Thanks again for the help.
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#9 Old 02-06-2007, 09:53 PM
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Thumbs up

Pittwagen:

I just installed the standard Autolites, but one range colder, # 3923's if I recall, and I did the 'side-gapping' method of cutting the electrode prong back to allow spark propagation to go down, instead of just 'out'.

Now the prong doesn't block the spark 'kernel'.

Very nice performance mod, very affordable. Plugs were but $ 1.69 ea at NAPA, and boy does she scoot. Mileage is up, too. Beats paying $ 9-15 for plugs with fancy tips !

The thread is just back on this index page or two, where three weeks ago we throroughly discussed this method.

I just drove her 3200 miles to Texas & back and it's a winner of a mod.

That thread had a link to the article I discovered about it.....

1996 Ram Van B-2500 Conversion Van - 318, Electric Engine Cooling Fan - "The Family Bus"
1997 3500 Cummins Ram Truck - 19.5 wheels, pacbrake, Gearvendors OD - "Pocket Peterbuilt"

Tyranny Rising ? The answer to 1984.....is 1776 !

"Evil is powerless, if the good are unafraid."
Ronald Reagan

"You never have to give up an ounce of Liberty to obtain security."
Ron Paul

"Stand fast, therefore, in the Liberty wherewith Christ has made us free, and be not entangled again in the yoke of bondage..." - Galatians 5:1
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#10 Old 02-06-2007, 10:08 PM
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Here is the recent thread we discussed some relevant plug & mpg ideas:

http://www.dodgetalk.com/forums/show...0&page=1&pp=20

1996 Ram Van B-2500 Conversion Van - 318, Electric Engine Cooling Fan - "The Family Bus"
1997 3500 Cummins Ram Truck - 19.5 wheels, pacbrake, Gearvendors OD - "Pocket Peterbuilt"

Tyranny Rising ? The answer to 1984.....is 1776 !

"Evil is powerless, if the good are unafraid."
Ronald Reagan

"You never have to give up an ounce of Liberty to obtain security."
Ron Paul

"Stand fast, therefore, in the Liberty wherewith Christ has made us free, and be not entangled again in the yoke of bondage..." - Galatians 5:1
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