Opinions on318 vs. 360 fuel milage

[68D100440]

Hello to all. I have managed to come across a a real clean '87 D150 (Royal SE package) with a blown motor (318). Blown as in cracked block. The motor threw the timing chain and the morons let it freeze up and crack the block. Anyway I'm into this truck for all of 200.00 dollars. So the question is build a 318 or build a 360? I have buildable engines in the garage. I'm not going to go exotic on either one just a good motor that gets good milage. Any opinions are welcome.

[dart662dp]

i fell into a similar deal with my 87d150 as well. clean body, blown slanty six.
if you are looking for any kind of fuel economy go with the 318, and retain the 318 heads. i have a mild 79 360 w/magnum heads in my truck, 904w/999 gear set, 3.21 open rear, thing gets 10mpg on a good day and 8 on average. runs mid 14s on 89 octane
good thing i work at home, mid grade is 3.01 a gallon here.

the last 318 i built for a customer's 84 d150 is getting 18-20mpg, nothing special, rebuild kit from summit, little summit cam, small port edelbrock intake, cheapie headers, 600 edelwebber carb, and msd ignition the engine is a 75 casting, with the 75 smog heads(un-drilled)
the guy can't be more satisfied with the thing , and has referred 2 more engine jobs to me since. he said he wanted it to get good milage, and have enough snot to get his bass boat up the ramp, on 87 octane.

the 360s have always been hogs for me, vs. a 318. you may be able to get a little better economy from a 60 than i do, mine is not tuned for milage. most guys i know with them average 10-12mpg.
the 18 will do the job any you won't break the bank at the pump.

[jd-indy]

I would expect that a 318 would get 1 or 2 mpg better in city driving or 2 or 3 mpg better highway. My 78 power wagon got 12 to 16 mpg with a 360 2bbl with 3.55 gears. My 86 w100 4x4 got 13 to about 17 mpg with a 318 2bbl and 3.21 gears but was a real dog. My 97 318 4x4 Dakota got 10 to 20 mpg and my 99 ram 4x4 gets 11 to 17 mpg.

[rumblefish360]

My old '79 Dodge Magnum had a 360 2bl. in it. The carb was a shot out Carter and a lean burn. I hated it. Poor performance and mileage.
To step up in both departments, I swaped out the intake for a factory 4bbl. A Performaer would do better, but @ $20, it was a steal. On top I put a Carter 625 carb and a early 340 air cleaner. It has a trap door in the base. The lean burn does all the advanceing insted of the distributor. So I swaped that out for a J-yard part. Cleaned it up and poped it in. (Distrib abd intake.)
The distrib was first triggered by an Orange box, but later used a MSD 6 box. This was a great mileage grabber to add.

The exhaust was a simple dual exhaust with ah H pipe and turbo mufflers. The tires were 235/60/15 and the rear ratio was 2.76.
The reward was a quicker car and 20 mpg's.

I never changed the cam. Headers could have added a few more ponies and a tad more mileage. But I never got there.

A 318 should beat it in mileage if the weight of the car/truck isn't to much to overcome.

[michaelmopar]

i have a mild 318 w/ 302 swirl heads, i had them shaved a little to bring up the compression a little. the cam is a 262/272 462/472 good low to mid range.
a Weiand action plus small port intakr with a holley 600 vac second. dual 2.5 exhaust with factory ex manifolds ( unless a high rpm engine you loose torque going to headers on the bottom end) all said i have 276 rea and a lockup 904 i think i get 17 on the highway and 12 city. i only got 10 to 13 all around on my stock 360 in another application. this 18 is in a 82 d 150.

[TK]

318, mild cam, small port heads.
360, with small port heads too, if you have the high gears.

[maxwedge413]

i would just put together the 318 avoid buying or scrounging 360 oilpan,360 exaust manifolds,360 torqconverter and various parts 318 small 2barrel enough power better gas mileage.the job will be less expensive less headaches

[SixGunner]

I have an 84 4by with a 360, Edelbrock package, headers, duals (2.25") and a 727. It gets 10 MPG city. I haven't had it on the freeway in awhile.

I also have a 2wd 318 Magnum powered 97 shortbox, ext cab, auto. It gets 12 MPG city. I thought it would have been better than that.

I need to get out on more trips to get freeway milage.

Jay

[68D100440]

I think the 318 is the way I'm going to go. Does anyone know if MP still builds the 9:0-1 cast piston since I'm going to have to bore my other 318 block to put this back together?

[rumblefish360]

I believe Fedral Mogual has what your looking for.

[dart662dp]

8.5:1,flat top with 4 relief, 1.720 cd. cast, full float or press pin. Sealed Power #285NP (NCP with coated skirt)

9.0:1 flat top 1.745cd. cast, press pin. Sealed Power#526P

they also have: hyperutectic stock replacement flat top with .010 more cd than the 9:1 above.
7:1 low compression dish(possibly work for 360 crank in 318 block with a little work) makes 349-351 inch motor ) pretty cheap hybrid to build. small bore+ 360 stroke=wind up pretty nice, have good low end, get ok miledge.
some one has to have built one of theese things???

[cageman]

An 84 d150, getting 18-20, I cant beleive that, There is something wrong with the speedometer, or his math, no way, uh uh.

[TK]

Cage, I have got 17 out of a 2x sweptline, with 5.54's.
Hard to do though, you had to be flying.
20?
I second that.

[dart662dp]

the guys swears up and down the milege as actual, i questioned him as well.
the low first gear and the lock-up may help a bit, as well as the small port intake, msd, taylor wires and edel carb as lean as we can get it without flat spots or surges. my guess for him was 15 mpg, he says no. i do not drive the thing, so i can not say for sure. if i did drive it it would prolly only get 10! i did have the machinist do a 30*angle on the exhaust valves instead of the std 45. he runs a 3.55 rear with 245/60/15s. claims he can run it to and from work for 2 weeks on a single tank. i will grill him on the odometer next time we speak.....

[TK]

Fill it up, go for a drive, and fill itup again, yourself.

[dart662dp]

might be fun to trade trucks for a week. he wont wana trade back tho!
i will call the old redneck tonight and see if he will give me a "real world" average. once again, this is not my truck, i merely built the thing for the guy, with every mpg trick i could throw at it, and only have what he tells me to go on.

[dart662dp]

ok, verified 18 mpg at 60-70mph. he says like any other 4bbl it does real well till you tickle the butterflies. around town 15-16mpg, not getting on it.
start hammering on the thing and you measurement goes to feet per gallon.

[dodger1]

C'mon, guys; the final drive has a lot to do with this question. For instance, my Mirada (at 3675 lbs as scaled) got 18-20 hwy with the tired leanburn 318 and stupid 2.24 rear. Swapped in a mild 9 to 1, 340 cam, stock head and manifold, T-Q and headers, 78 truck 360, still got 16-21 MPG. Swapped the 7 1/4 for an 8 1/4 cop-car 2.94 axle and the mileage dropped to 18 hwy and don't-know city. Tires are 275-15/60's on copcar rims in both cases (about a 28" diameter) So I could see a light-weight D150 getting 20 with tall enough gears out of a well-tuned 318. Finding a truck with tall gears is another story, though.

[FastEddie]

81 Ramcharger with a 318 TQ 3.21 gears. 10 in town 17 with the cruise at 60 or less.

[michaelmopar]

i have a 318 d150 swb and it is a mild 9.5:1 w 302 swirl heads a 265/272 442/462 cam w/ small port weiand dual intake holley dual feed vac sec pre avenger dual 2.5 w/276 8.5 and all i get is 12 average city/highway. so i would love to know how to tume it better to get 17 to 20mpg w/ these gas prices 3.00 for the good stuff it wont run on anything less than mid grade.

[cageman]

Im trying to get 20 or so out of my 273 Valiant, I go 100 miles and fill, Have no speedometer yet, so I can only go by the distance I went and the gas I filled, I have gotten 16 with it, but I just put a Edelbrock on it, I think it will be in the 20's now. When I heard what that truck got, I just went yeah right, My 95, on a good good day with a tail wind gets 16. I would think my truck is a bit more sleek thru the wind, and fuel injected too, I just cant see how the 84 gets better mpg.
Oh well, some people like to validate the money they spent on gas mileage goodies, by bragging a little bit over what it really is, just so they feel better. I visit my Favorite junkyard when I'm back home, and when im sitting there, I hear the craziest stories from people getting parts. my truck gets this, my duramaxx gets this, my cummins gets this, but then they tell you how they put different sized tires on, and the gears were changed, but they never say they got the speedo redone. Oh well.

[dart662dp]

cage: the 95 IS a little (lot) more aerodynamic than the 84 (brick barn door) BUT the 95 is a lot heavier than the earlier (pre-magnum) trucks. my 87 weighs in at 3650, with me in it! (unless the calibration of the land-fill scales is off, so i weigh on the way in, turn around and weigh on the way out, 20 lb variable) the newer rams are around 4,500-5000, i think, correct me if i am wrong. if 100 lbs is worth a tenth of a second, what is 1,000 lbs. worth for mpg?
all the magnum truck guys (at least around here) are crying about their guzzling injected, lock-up overdrive 5.2 trucks getting 12 mpg on a good day.
small motor in heavier truck works harder, uses more fuel. You can also have your computer reprogrammed and pick up the economy a bit. factor in the rolling resistance of those '03-20's.....
The 84 i speak of is a very fresh, purpose built motor. with all new electronics, carb, etc... went through the trouble of finding the old SP edelbrock (small port) 273-318 intake. not the more common performer 318-360 with "uni port" design (works on 318 but overhangs ports, works on 360 with port match) with a small (204/214-.420/.442) cam from summit(made by crane)
How many miles are on your 273? we both know old tired motors use twice the fuel of a fresh tight one, oil getting into combustion chamber kills octane, makes a 8:1 motor want 89 octane or better to run right. along with a myriad of other factors.
My 87 D150 only gets 8-10 with the 360 magnum conversion, but was not built with economy in mind . Kinda curious to see what the 413 will get vs. the guzzlasaurus 360. magnum heads (in stock form) flow real well on the intake, but the exhaust leaves alot to be desired, even with headers.
that 273 should get 18-22 if the car/engine are in optimal condition to work together. if the alignment is even a little bit off 20 goes to 15!
the motor in my truck was in my last (not current) 66 dart, with 3.90 gears and the 650dp carb it got 15-16mpg at 65mph, through the 340 manifolds.
same motor in truck with headers is measured in FEET per gallon!

[cageman]

Hmm, what alignment settings would I need to keep her at 20 mpg's, I aligned it myself.
I think the 20 inchers helped my mileage too, as it rolls right along. I think the stiffer sidewalls could be why. It is also a manual trans. 3.55. I just bought a lowering kit for it and I hope to cheat the wind a bit by doing so, it should be here tomorrow. when I first go the 20's I aired em up to 45, and I wore the centers right out of the rear tires, I pulled trailer alot that summer though.
I weighed it with me at the highway scales and it was 3450, if I remember right. But that sounds right, reg cab shortbox 2wheeldrive.

My valiant has a fresh 273 with magnum heads, I figured that with those heads, I would exceed the factory heads, but I think I went backwards, as I used to get 21 mpg with it back in the day with a 3 speed 294 gear, now I have 391 with a 5 speed, it comes out to 2.89 I think final in 5th gear. I had fat tires on the front of it and I switched to some skinny buggers now, to try to save, I still have the 10 inchers on the back though, that could be hurting me too, mpg wise. It sucks, I want it to look cool, and utilize the mini tub, but man, if it kills me everytime I fill it, Ill be doomed to cruising in the Honda, and that only gets 31.

[cageman]

I also three years ago bought a wrecked 98 Dodge, 4 wheel drive, and it had a 360, I got it done and drove it and I only got 12 empty, and it rode funny, I dont like the way a 4wheeler drives, and the mpg empty was wahat I was getting pulling with my 318, I sold it. No need for 2 4wheel drives any ways.
Speaking of 318's, I have a built up one in my 71, and if I am nice, it gets 8, Now, my 70, which has 35 inch boggers, it gets 13. It too has a 318 with headers and a 4 barrel, 4 speed. Sure the 71 makes way more power, but it is thirsty too, But you would think that the 35x14 1/2 tires would kill that thing, My 62 with a 440, it gets 8, no matter what. So in my situation, it seems the bigger motors, get worse, and the stock ones get better.
I think there is some magic in getting mpg, some motors have it and others dont. I wish I knew the magic recipe, but it seems as soon as you get some performance out of an engine, down goes the mpg. that simple I guess.

383's are supposedly good for mpg, I wonder why. All the ol timers I talk to tell me about their ol 3883 monaco or polara, how it got so good gas mileage. I Just never hear of a 360 owner bragging about mpg.

[TK]

Smaller bores get better MPG, period.
The best MPG manifold made, for a SB, IMO, is Offey Dual port.
20MPG?
Not with a brick with disc brakes.

[cageman]

Do you think that discs drag that bad. I never even thought of that, I had 4 wheel drum back in the day, now the thing has 4 wheel discs, I think all the cool things hurt mileage. uuuuuuggghhhhhhhhhhhhh.
I have 4 wheel discs on almost all my rides. well half. ok 4, soon 6, well 7 if my race car counts, lol.
Oh, and they are all bricks, whats your point, I like bricks apparently
Oh I know, I shaved the marker lights and antannae, so that should theoretically cancel out the 4 wheel discs, right, well, ahhhh, never mind.

[TK]

Well, take your disc brake wheel, and spin it, and then go spin a drum in good condition/adjustment.
I do know I sure can feel it when pushing them. (don't ask)
Tellin ya cage, offey Dual Port, 252/252 comp cam with 3:54's and down, 260/260 Comp with lower gears.................
I could get 17 out of my 69, with that combo.

[rumblefish360]

I Just never hear of a 360 owner bragging about mpg.

Heres one for ya. Right here baby!

Stock '79 360 in a Dodge Magnum, swapped out the leanburn for a Orange box, later went to a MSD. Very important feature in mileage IMO.
Swapped out the distrib for a vaccum advance unit from a truck.
Add a Carter 625 AFB on top of a stock T-Q intake, added dual exhaust off the manifolds with an H pipe and turbo mufflers.
The air cleaner was a '70's 340 trap door OE unit.

The tranny, a 904 got a cooler.
The rear was a 2.76 with 235/60/15's all around.

20 mpg's Hwy.
Stock compersion and cam.

[dave571]

I was getting high teens for mileage in my van when it still had the 360.(keep in mind the imperial gallon is bigger than a us gallon, probably low teens for you guys) It was a shorty with 276 gears.

It got far better mileage than the 318 it replaced. About twice as good as the 400 that replaced the 360, but that's another story...LOL

You do hear lots of stories of poor economy in 360's, but 360's were usually in heavier rigs. Bigger cars, trucks, vans, etc.

I have found that when tuned correctly, and in decent shape (compression etc) they get decent mileage. Application can be a big variable.

[TK]

I had a 78 adventurer, with a stock 360, it got a honest 16mpg, with 3.2? gears. It was the only 360 I have seen get decent MPG. (Compared to a 318)
413's got damn good MPG................