'84 318 2v Mileage ?

[84ram]

Not sure if this is the right place to post this question, but here goes...

My '84 D150 has the original 318 2v carb. (EGR setup and air pump belt removed, and custom dual 2 1/4" into single 3" magnaflow exhaust w/o cat(s)).

My question is this; What is it about this engine design that will not allow mileage any better than 12-13 mpg? No matter how I drive it, city or highway, this is what I get out of it. The timing is set @ ~12* btc with the vacuum line removed, It has an A727 trans, 28" tall tires, and 2.94:1axle ratio 8 1/4" ring and pinion. I know it is not running too rich because I've recently replaced the plugs with new ones, and the porcelin (spelling?) on the old plugs was barely discolored from its original white color indicating to me that it's most likely running a little bit lean if anything. Is the combination of the original cam and 2v carb the culprit(s) in this case? Maybe it's that the cam is going flat with 125k miles on it? Am I just asking too much to get better mileage from it?

I used to own a 72 swinger with a small block; .060 over 318, 10.3:1 comp. w/forged flat tops, purple shaft cam, 750cfm afb carb, Long tube headers, 727, 2500 stall etc., etc. and it would get 18mpg hwy with 3.23:1 gears in it. So, what gives here? Why does my truck suck so much gas? Just a less efficient combination of engine parts pushing a heavier vehicle with the aerodynamics of a brick wall, maybe? Any opinions here?

J. Campbell

[dwc43]

A stock thermoquad and intake or Weiand 8007 would help some. A true dual exhuast with an X pipe will also help your milage some. Your main problem is the truck weighs at least 5000 lbs and it's about as areo as a concrete block. And if you have wide tires that does not help. Ground clearance lets too much are go under it. Your tail gate collects a lot of air. Leaving it open wont help, it actually hurts. You would need a flush mount hard bed cover to help out areo wise on that end. That's about where you stand.

[michaelmopar]

i have a 82 d150 w/a mild 318 and dual exhaust with the holley vac sec and the weiand intake and a dual pattern cam for good exhaust flow and the best i get is 12 to 13 also.

[84ram]

Yeah, that's what I figured. I guess that I just need to build a power plant for it that makes more efficient use of the fuel/air mixture... OR.... I could build a high compression 360 stroker for it, lighten it up, set up the suspension for the drag strip, and buy an eCoNoMy car for mileage!

J. Campbell

[dwc43]

That's an idea.

[TK]

Originally Posted by dwc43

A stock thermoquad and intake or Weiand 8007 would help some. A true dual exhuast with an X pipe will also help your milage some. Your main problem is the truck weighs at least 5000 lbs and it's about as areo as a concrete block. And if you have wide tires that does not help. Ground clearance lets too much are go under it. Your tail gate collects a lot of air. Leaving it open wont help, it actually hurts. You would need a flush mount hard bed cover to help out areo wise on that end. That's about where you stand.

A stock thermoquad intake is a big port intake, never get any economy out of a big port intake on small port heads. The weiand would be fine.
Me? I would get a single plane 2bbl manifold, and use your carb, or a older carter. (the best gas mileage combo for a 318)
A D150 is lucky to weigh 4200.
You said the rest, the key to gas mileage is compression, too bad we cant buy good gas anymore.
My 74 Dually will get a honest 15, light, with 4:10's, so you may want to look into what kind of condition the inside of your motor is in, just one wek valve can do wonders for your MPG.
Oh, and the single exhaust ain't hurtin' a thing.

[Tarrbabe]

You stated your timing was set with vacume disconnected. You did re-connect the vacume to the dist. I trust.

[jd-indy]

You might try a different carb or rebuild the carb. I don't no why but poor mileage on my 318"s always seemed to be related to the carb. I used to run a 307 chevy carb because it seemed to get about 5 mpg better.

[dusterdood]

I've got an '86 5th ave winter rat that gets 12 MPG. The 100K mile 318 2bl just won't give me better. Maybe there's something to this stroker idea! Might just as well get 12 MPG, and be able to smoke 'em at will.

[dwc43]

Originally Posted by dodgetruckboy

A stock thermoquad intake is a big port intake, never get any economy out of a big port intake on small port heads. The weiand would be fine.
Me? I would get a single plane 2bbl manifold, and use your carb, or a older carter. (the best gas mileage combo for a 318)
A D150 is lucky to weigh 4200.
You said the rest, the key to gas mileage is compression, too bad we cant buy good gas anymore.
My 74 Dually will get a honest 15, light, with 4:10's, so you may want to look into what kind of condition the inside of your motor is in, just one wek valve can do wonders for your MPG.
Oh, and the single exhaust ain't hurtin' a thing.

The Weaind intake is the same port size as the stock 318 Thermoquad intake and there is a big gain to be had by using it along with the Thermoquad for better milage. And the single exhaust causes a drop in volumetric eff. which hurts gas milage, and torque. With a dual system and an X pipe torqie is increase at lower rpm levels maknig it more effecient and therefore it will save your milage.

[dwc43]

Originally Posted by dodgetruckboy

A stock thermoquad intake is a big port intake, never get any economy out of a big port intake on small port heads. The weiand would be fine.
Me? I would get a single plane 2bbl manifold, and use your carb, or a older carter. (the best gas mileage combo for a 318)
A D150 is lucky to weigh 4200.
You said the rest, the key to gas mileage is compression, too bad we cant buy good gas anymore.
My 74 Dually will get a honest 15, light, with 4:10's, so you may want to look into what kind of condition the inside of your motor is in, just one wek valve can do wonders for your MPG.
Oh, and the single exhaust ain't hurtin' a thing.

Oh, by the way, my firends long bed weighed in at 5500 on a certified weight scale and my Ram Charger weighs in at a 1000 more due to it being a 4x4 and all the glass and extra seats that a normal truck does not have.

[Tarrbabe]

of the later 2bbl carbs. Never could get mileage out of them except the one that came on my 78 Volare. ( I got 21 most of the time but got 26 on one trip from Motor City to TN. My Cordoba has the 318 2 bbl and I have never got over 16. I now have that carb apart for the 300th time. Most of the time I'm happy if I can just get it to run right. Wish I still had the carb off the Volare but it got lost in moving. I took it off and replaced with 500 cfm Holley 2 bbl for fun. Ran great, mileage sucked but I wasn't worried about that then. I just wanted to beat that damn 350/4 bbl Nova in town. Still didn't beat him till I put the 340 in.

[84ram]

Yes, Tarrbabe I did re-connect the vacuum line, and the advance shows to be working with the light on it and the line connected. J/K!

The GVWR on the door jamb sticker says 4800 lb., so being a 1/2 ton truck would mean that it weighs ~3800 lbs, isn't that right? My truck really looks small sitting next to a newer model body style Dodge. I know that it's MUCH lighter than those big azz things are.

As for the "single exhaust" that I have; It is designed such that the main point of restriction is the stock exhaust manifolds. There is a custom-built "Y" similar to the one that flowmaster sells just to the right of the trans pan which brings the two 2.25" downpipes together and transitions into a 3" I.D. single pipe. This pipe leads into a 3" straight through Magnaflow muffler and the 3" tailpipe finally exits in the stock location just behind the right rear wheel. I'm pretty sure that this will allow much more flow than the stock carb and heads will ever be able to achieve.

I do agree that an X or H crossover would give better scavenging effect than the Y does, but the fact that I have a "single" pipe does not make it more restrictive than a dual system. Two 2.25" diameter pipes have a total area of 7.952 square inches. One 3" pipe is a 7.068 square inch opening. Not much difference, especially when you consider that area of the the stock exhaust opening is going to be less than half of either of these (one 2" dia. pipe).

I'm thinking of buying an edelbrock dual plane and a 500-600 cfm 4v edelbrock carb for it, and also a set of long tube headers. Maybe these things will help some...

J. Campbell

[olde_ram85]

Originally Posted by dwc43

Oh, by the way, my firends long bed weighed in at 5500 on a certified weight scale and my Ram Charger weighs in at a 1000 more due to it being a 4x4 and all the glass and extra seats that a normal truck does not have.

theres no way, unless thats a 4wd truck, my powerwagon weighs around 5,300lbs and it has 38inch swampers, dana 60 in the back, thats w/o me in it....... moms liberty weighs about 4,500lbs

[olde_ram85]

Originally Posted by dwc43

Oh, by the way, my firends long bed weighed in at 5500 on a certified weight scale and my Ram Charger weighs in at a 1000 more due to it being a 4x4 and all the glass and extra seats that a normal truck does not have.

theres no way, unless thats a 4wd truck, my powerwagon weighs around 5,300lbs and it has 38inch swampers, dana 60 in the back, thats w/o me in it....... moms liberty weighs about 4,500lbs

my 85 2wd ram i used to own, got about 15mpg on the highway mabey better, it had 600cfm carter 4bbl with an edelbrock torker 340 intake and headers, 5pd 2.92's.. thats not too bad

[dwc43]

Originally Posted by 84ram

Yes, Tarrbabe I did re-connect the vacuum line, and the advance shows to be working with the light on it and the line connected. J/K!

The GVWR on the door jamb sticker says 4800 lb., so being a 1/2 ton truck would mean that it weighs ~3800 lbs, isn't that right? My truck really looks small sitting next to a newer model body style Dodge. I know that it's MUCH lighter than those big azz things are.

As for the "single exhaust" that I have; It is designed such that the main point of restriction is the stock exhaust manifolds. There is a custom-built "Y" similar to the one that flowmaster sells just to the right of the trans pan which brings the two 2.25" downpipes together and transitions into a 3" I.D. single pipe. This pipe leads into a 3" straight through Magnaflow muffler and the 3" tailpipe finally exits in the stock location just behind the right rear wheel. I'm pretty sure that this will allow much more flow than the stock carb and heads will ever be able to achieve.

I do agree that an X or H crossover would give better scavenging effect than the Y does, but the fact that I have a "single" pipe does not make it more restrictive than a dual system. Two 2.25" diameter pipes have a total area of 7.952 square inches. One 3" pipe is a 7.068 square inch opening. Not much difference, especially when you consider that area of the the stock exhaust opening is going to be less than half of either of these (one 2" dia. pipe).

I'm thinking of buying an edelbrock dual plane and a 500-600 cfm 4v edelbrock carb for it, and also a set of long tube headers. Maybe these things will help some...

J. Campbell

The H pie is not that good and it needs to be custom made while on the dyno to see where it goes, how big and how long it must be. THe X is the only way to go. The Weaind 8007 and TQ would be a better intake carb combo. And your exhuast is still pretty bad and if you go long tube headers it will make it worse than what it is. You will have to weigh your truck. That decal does not tell the trucks weight.

[dwc43]

Originally Posted by olde_ram85

theres no way, unless thats a 4wd truck, my powerwagon weighs around 5,300lbs and it has 38inch swampers, dana 60 in the back, thats w/o me in it....... moms liberty weighs about 4,500lbs

Sorry, but that's what it weighed. Saw it on the scale myself. We just dropped off a load of scrap and weighed it loaded and empty in order to get paid. My 4x4 weighs more than his truck that's for sure.

[TK]

Originally Posted by dwc43

Oh, by the way, my firends long bed weighed in at 5500 on a certified weight scale and my Ram Charger weighs in at a 1000 more due to it being a 4x4 and all the glass and extra seats that a normal truck does not have.

So, your friends longbed 1/2 ton weighs almost 1000 pounds more than my Longbed, one ton dually?

[TK]

Oh, and By The Way.
My 3/4 ton 69 SWEPTLINE, has a lot more steel than a newer D, and three gas tanks, two full, one half full, was 5680#'s, with me in it, and Swepts are VERY HEAVY.

[72Challenger]

Either someone played games with the scale at the scrapyard so they didn't have to pay full price for the load, or DW forgot to get out when they weighed out!

[teddy1500]

I have an 84 D150, 318 and the 4speed OD. with an eddy 650 carb, performer intake, it will get about 13 to 15 mpg. spent alot of time tuning it, the carb is too big for the engine. I am runing a comp cams 268 hi energy cam, headers, MP ignition, a performer intake, and 29 inch tall tires, with a 3.23 sure grip. I used to get 10 mpg, but I've really leaned out the carb, 2 steps lean according to the edelbrock booklet
My truck doesnt seem to care about what it does, empty or loaded, the MPG stays the same. Went to Fla to dolly a car home not too long ago, I think it used less gas coming back than it did going down. but with what gas costs today I bought a Honda, It gets 35 mpg, and the truck sits.

[84ram]

...but with what gas costs today I bought a Honda, It gets 35 mpg, and the truck sits.

I'm not biting on the weight-of-a-d150 argument because apparently, it won't matter what I say concerning the weight of my truck anyway... but I will state that I try to ride the scooter as much as I can because it gets ~40mpg even with the performance enhancements that have been made.

J. Campbell