Is it possible to improve the mpg?

Posted By: dodgeram440

Is it possible to improve the mpg? - 03/24/13 01:21 AM

Ok, so like I posted a couple weeks ago, I've given up on the 440 swap. Sold a few of the parts and the engine and trans may be sold Easter weekend. I still have the bb truck headers and mount brackets available.

This leads me to my question. I'm considering a job change soon, but it's going to involve a weekly drive of about 80 miles one way. Since the old beast would be once again my daily (or weekly, actually) driver, the 10-14 mpg is really gonna suck. I'm looking for advice and suggestions on what I can do to increase that even a little bit. Here is what I'm working with:

The patient is an 86 D100 shortbed, 2wd, 318 auto as seen in the sig pic below. The truck is 95% stock with the only mods being the 2 1/2" full dual exhaust (planning ahead for the 440) and a distributor swap to eliminate the factory spark control computer. Still has the original carb which is not a feedback model. I can't remember what I did about the vacuum for the advance on the dist, but if I remember, it was an issue I left unresolved. I haven't driven the truck in nearly 2 years, but I will be waking her up next weekend. I do think it is running a bit rich as the bumper had been turning black over the pipes, and it does have that typical hesitation/bog that I have never been able to work out. I saw a post not too long ago about another member having a similar issue and he fixed it, but I couldn't get a response on exactly what he did to it. Something about the power piston I think. Would this also cause it to run rich? The last time I adjusted anything, I used a vacuum guage and adjusted for highest vacuum.

So the basic questions are: Do I need ported or direct vacuum for the vacuum advance? How do I fix the hesitation/bog? Could it possibly be adjusted ok at idle but rich under power? Is there anything else I can do to help with the milage?

TIA

P.S. Since I'm no longer putting the 440 in it, do I need to change my name?

Posted By: NITROUSN

Re: Is it possible to improve the mpg? - 03/24/13 02:18 AM

Did you ever pull the intake and clean the cross over passage?

Posted By: ahy

Re: Is it possible to improve the mpg? - 03/24/13 02:18 AM

MOPAR's are set up for ported vacuum advance. That's what I would use. As you know, that will help mileage. Tires can help also. Not too wide, moderate tread pattern and max pressure. I don't know that carb, but if its black around the pipes agree its rich and needs fixed. How do the plugs look?

I bet she can do at least 2-3 MPG better with some attention.

Posted By: jerseybud

Re: Is it possible to improve the mpg? - 03/24/13 02:19 AM

You should be better than 10-14 in a 2wd on the highway. In town, no. But on highway I would expect closer to 17 @ 63-67 mph

That carb should be a Holley 2280. I always had problems with the choke linkage sticking/maladjusted and vacuum leaks at the throttle shafts. Definitely get the vacuum advance sorted out, that will help mpg on the highway.

Posted By: dOrk !

Re: Is it possible to improve the mpg? - 03/24/13 02:27 AM

Quote:

Did you ever pull the intake and clean the cross over passage?

x 99 ...... A engines are famous for plugging-up the intake heat crossover. How HOT does it get?

Posted By: 340SHORTY

Re: Is it possible to improve the mpg? - 03/24/13 02:58 AM

tune the engine to the best you can. change the auto trans for a OD 833 and you should break the 20 MPG average..

Posted By: poorboy

Re: Is it possible to improve the mpg? - 03/24/13 03:11 AM

I would also consider some kind of bed cover. Of the bunch of Dodge trucks I've had over the years, about 1/2 of them gained at least a couple mpg if the tailgate was down or removed. if your truck falls into that group, a bed cover solves the issue and you still have a useable bed. Gene

Posted By: 76dodgeboy

Re: Is it possible to improve the mpg? - 03/24/13 03:42 AM

Quote:

I would also consider some kind of bed cover. Of the bunch of Dodge trucks I've had over the years, about 1/2 of them gained at least a couple mpg if the tailgate was down or removed. if your truck falls into that group, a bed cover solves the issue and you still have a useable bed. Gene

They did that on myth buster. Tailgate down got worse than tailgate shut.

Posted By: scratchnfotraction

Re: Is it possible to improve the mpg? - 03/24/13 04:38 AM

318, worn out q-jet, a999 HS/LU trans, headers/duels, 8 1/4-2.76 gear, 235/75/15 tires.

19+ mpg at 55 mph 80 miles round trip to work x5days

went to a 727 HS non lock up trans and seems to stay the same this past week for work on milage.

same thing,set timing with vac gauge for highest reading,fine tuning it with the idle mixture screws, set curb idle at 650/750 rpm

use ported vac on the dist unhook and plug when tuning. most times mine have wound up around 10-14 degrees BTDC 750 rpm.

I just slaped a stock cast iron 4-v intake on the 302# headed 318 with the q-jet. and mind you it does have a small lunati roller cam so it runs like a teen should run.

drive it like GrandMa and keep it under 60 mph with nice slow take off from dead stops.

give the finger as the speed junkies go around you.

I remember that post,it was the power piston stuck in the up position IIRC, that will make one run rich and have a bog off the line with light throttle

they can stick up/down/middle ways and cuse poor performance.

also open the carb to make sure it has not suck charcoil from the canister into the carb bowl and clogged things up in it.

if you stay with a BBD carb get the oldest carb you can find 68-75 are much better to work with.IMHO

Posted By: scratchnfotraction

Re: Is it possible to improve the mpg? - 03/24/13 04:42 AM

did I mention q-jet?? I picked my 440 truck up from 10 mpg to 13 mpg going from 600 eddy/3.91 to 750 q-jet/3.23. should gain a couple more with a 2.76

did you use a reman points dist when converting?

i would get a points dist and run the points or a conversion in it.

then ported vac to the advance can.

Posted By: MachoMan

Re: Is it possible to improve the mpg? - 03/24/13 01:56 PM

for me, highway mpgs are hit and miss on model.
had a 76 D100 LB club that increased w/tailgate down slightly, had a 94 F150 SB supercab 4x4, i added K&N dropin, flowmaster catback and toneau cover and picked up 2mpg highway.

Posted By: ahy

Re: Is it possible to improve the mpg? - 03/25/13 02:30 AM

Another option on the carb is a reman OE type. I used an "Autoline" reman from AZ on a '78 brand F PU. It works well.

Posted By: dodgeram440

Re: Is it possible to improve the mpg? - 03/25/13 03:00 AM

Current tires are 255/70/15, not sure about the gears in the stock 8 1/4, but I'm thinking 3:23. I think it was listed on the underhood sticker. Will have to check again next weekend.

Would this 86 have the 302 heads and roller cam? Don't really think this would improve my situation one way or the other, I was just curious if it's what I had.

Would a four barrel be an improvement over the 2bbl? I still have the t-quad from the 440. Would that be too big for the little 318 if I got a manifold? I never did remove the intake to clean out the passages. But it also doesn't run hot.

I think my problem with the vacuum advance was that I didn't have a ported vacuum source. It was full time vacuum. I've thought of getting an older carter bbd carb, either used or reman. Biggest problem always comes down to money. I can dream until Jesus comes back, but that isn't gonna get me anywhere. I guess I'm just gonna have to bite the bullet one of these days and make a decision on what I'm really going to do.

Scratch, the distributor I used was one of those Chinese ready-to-run dizzy's off ebay. Been trouble free so far and the most notable improvement I've seen with it is the once shaky tach needle is now steady as a rock.

Posted By: poorboy

Re: Is it possible to improve the mpg? - 03/25/13 03:02 AM

Quote:

Quote:

I would also consider some kind of bed cover. Of the bunch of Dodge trucks I've had over the years, about 1/2 of them gained at least a couple mpg if the tailgate was down or removed. if your truck falls into that group, a bed cover solves the issue and you still have a useable bed. Gene

They did that on myth buster. Tailgate down got worse than tailgate shut.

I really give a rats butt what myth busters did or did not find.

I know that out of at least 10 73-93 Dodge trucks, about 1/2 of them picked up a couple mpg with the tail gate down or off. Back years ago, I drove my trucks about 10,000 miles a year, year around. I lived 10 miles out of the town I worked at, and drove them to work 5-6 days a week. My next job was 30 miles from home, and I made that trip 5-6 days a week. I lived at that out of town house for 16 years and Dodge trucks were always there and were used as normal transportation. For the record, there was never any rhyme or reason to the gas mileage improvement, it either happened or it didn't, and it didn't take more then a couple tanks of gas to know for sure, the difference was an extra day of driving on a tank of gas.

I don't know if his truck will respond with better mpg or worse, but it sure is a cheap, easy thing to try. Gene

Posted By: NITROUSN

Re: Is it possible to improve the mpg? - 03/25/13 03:49 AM

Quote:

I never did remove the intake to clean out the passages.

All I will tell you is if the passage is plugged you will have a lazy running, hesitating, poor mpg pig. All the other junk is just a band aid. Fix the core problem. I fixed these problems since 1972. Why people will not listen is beyond comprehension. Should have this section titled the axe man fixes, or cave mans garage.

Posted By: dOrk !

Re: Is it possible to improve the mpg? - 03/25/13 04:33 AM

CHECK the intake heat around where the carb bolts on ... spray it with a water mist ....and if it does not steam-away right-away (after the motor is fully warmed-up) ... then you have a MAJOR PROB. I have heard of people picking-up UP TO 10 mpg clearing that cross-over out.

YOURS is probably plugged with carbon ...

Posted By: dOrk !

Re: Is it possible to improve the mpg? - 03/25/13 04:36 AM

....and YES a TQ carb will be a LARGE improvement over the stock 2bbl. But find the smaller primary carb ....1 3/8.

Posted By: Kern Dog

Re: Is it possible to improve the mpg? - 03/25/13 06:35 AM

W H A T ???
The heat crossover is NOT responsible for a 10 mpg difference.
Nice try, Eric....

Posted By: dodgeram440

Re: Is it possible to improve the mpg? - 03/25/13 12:18 PM

Nitrousn, not trying to argue with you here. Like you said, you've done this since 72. I would just like a little more clarification for better understanding. What confuses me most about your advise is all the people who purposely block off that passage with no ill effects. I realize that's mostly done for performance applications, but if I'm understanding the logic right that shouldn't matter.

If I understand the purpose of the crossover correctly, it is to warm the manifold and air charge when cold by directing hot exhaust gasses thru the intake underneath the carb plenum. I can see where warming the air charge on a cold winter Ohio morning would be a benefit, but in my situation, the hesitation occurs winter or summer and first start in the morning or after driving for 30 miles. And although it would be really great, I'm not going to buy the 10 mpg improvement claimed by Doc Fiberglass. I could see a small mileage increase, but that much would be a small miracle.

I probably should have done this years ago when you first suggested it, but I didn't and now I'm moving into a situation where it's going to be prohibitive. I'm moving into an apartment complex and they generally tend to frown on major engine work like that. If I can get them to allow me to remove the intake, it will probably be a one time deal, so I need to decide if I'm going to stick with this 2 bbl or go with a 4 bbl. The 2 bbl would be cheaper, but I would rather have the 4 bbl. Either way, it's not anything that's going to happen soon. Right now I'm just looking for possible tuning advice that would improve the drivability and increase the mileage even just a little.

Thanks

Posted By: NITROUSN

Re: Is it possible to improve the mpg? - 03/25/13 12:35 PM

Basically two things are happening when the crossover is plugged. The lack of heat causes the choke to stay on and not open properly. Along with the electric assist not working properly. The second is the hesitation. The intake needs to heat up for proper fuel mix. As designed the cold dense fuel mix will cause a hesitation. Where the proper heated mix will not. With this plugged you could easily lose 4 mpg or more along with the hesitation. Most all that we have done include replacing valve seals along with the heat passage cleaning. You also need to verify the heat riser is working properly if equipped. If you do the needed repairs there is no reason that you cant get 18 to 20 mpg at sensible highway speeds.

Blocking off the passage is a performance mod and thats a totally different set up.

Posted By: RUNCHARGER

Re: Is it possible to improve the mpg? - 03/25/13 03:47 PM

You need to unplug that passage. The choke is sticking on if it is operable at all and you are coking up the engine if it's plugged. You are losing 5-10MPG if it's plugged and gumming up the engine as well.

Sheldon

Posted By: dodgeram440

Re: Is it possible to improve the mpg? - 03/25/13 06:27 PM

Maybe my issue isn't so much with the crossover as you all seem to think. In Nitrousn's explanation, he commented about the choke operation as did Runcharger and his comment about if the choke is even operational. Well, the choke is fully operational and when the engine warms up the choke fully opens. I'm not saying that the passage might not be plugged as suggested. I'm just saying that maybe this isn't the absolute cure for my problem.

I would also point out that not too long ago another member posted about a hesitation/bog with his 318 equipped with the same Holley 2280 2bbl I have and no one told him his passage was plugged. Turns out his problem was the power piston and I had asked for more specifics but never got an answer. EVERY 318 I've ever owned, either with the Carter BBD or this Holley has always has this same bog. I've just learned to drive with it. I know my main question with this thread was about increasing fuel mileage, but in this case I think the two may be related. If my power piston was stuck in an enriched position, could it cause the hesitation and also allow it to run rich at cruise, reducing mileage? Also, I don't think the mileage with this truck is too far off average. I'd say about 10 or so around town and about 14 on the highway. I was just looking for a way to improve on that if possible.

Posted By: hooziewhatsit

Re: Is it possible to improve the mpg? - 03/25/13 08:34 PM

If you really want to chase the best mileage you can get, I would highly recommend finding a wideband O2 sensor.

Without knowing exactly what's going on AFR-wise, every modification is a SWAG.

Posted By: NITROUSN

Re: Is it possible to improve the mpg? - 03/26/13 02:49 AM

My last 87 4x4 318 auto would do 17 mpg highway all day long and 14 city. My 84 2wd 318 would do 20 hwy and 15 city. So you are easily 4 to 6 from what it will get. 50 bucks in parts and a good 4 to 6 hours could get you where you would like to be. What other mod can you do for so cheap??? One tank of fuel the savings would pay for the parts. I am done with this post.

Posted By: RUNCHARGER

Re: Is it possible to improve the mpg? - 03/26/13 03:58 AM

I bought a new 86, 318, D150 and it got 17-18 MPG dead stock with 3.21's so that's what you can shoot for with it totally stock.
BTW, I have never swapped a 2 bbl to a 4 bbl and gained mileage ever. I've tried it on 318's, 360's, 383's, 400's and they always got worse, TQ, AFB, AVS, Holley it didn't matter and I am a much above average carb. tuner.
Stock 2 bbl, dual exhaust (headers too) and an optimized advance curve along with tight ring seal and good timing set are key elements to fuel economy mechanical wise IMO.

Sheldon

Posted By: dOrk !

Re: Is it possible to improve the mpg? - 03/26/13 04:44 AM

Quote:

W H A T ???
The heat crossover is NOT responsible for a 10 mpg difference.
Nice try, Eric....

Oh really ? ... I said I have HEARD of 10 ..... and I have actually SEEN 8 ...with my old 318 van.