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318 gas milage build? #1670242
09/12/14 08:35 AM
09/12/14 08:35 AM
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Weatherford, Texas
RapidusMaximus Offline OP
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Just bought my son a 77 SWB with a 360 auto, carter afb, duel plane 4bbl intake, stock exhaust, stock rear with 2.73 one legger, it is a gas hog (about 10 mpg or less)...considering pulling the 360 and installing a 318. Any suggestions on a gas miserly 318 build? 2bbl/4bbl, cams, induction preference? Or....is there any way to improve the milage of this 360? Thanks


1968 Plymouth GTX
1974 Dodge P/U Long Bed Stepside 318
2019 Ram 2500 6.4, auto, 4WD
Re: 318 gas milage build? [Re: RapidusMaximus] #1670243
09/12/14 10:40 AM
09/12/14 10:40 AM
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Florida
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a 318 with a good BBD 2-v,stock 360 4-v cam, stock high stall TC,headers/duels with that 2.76 gear would help it.

I am getting 18+ with a JY-91 #302 headed 318, whiplash roller cam,Holley street dominator intake,6210 Holley spredbore 650cfm,headers/2.5" - 2 chamber muffs/duels out the side, NV4500 5-speed, 8 1/4-3.21 gear turning 235/75/15.

cam sweet spot is 1800 rpm, 55mph is 1500-1600 rpm.

great street/cruzer cam.

try swaping on a set of #302 heads on the 360 to get some torque down low to help the 2.76 gear. add a holley street dominator with a q-jet/spredbore Holley.

not a high reving race engine but does make a nice stump puller in a stockish daily driver work truck.

just bumping the axle to a 3.21 - 3.55 gear is gonna help get it rolling.. IMHO, thats where it is sucking the gas, getting it rolling with a 2.76 needs a heavy throttle.

Re: 318 gas milage build? [Re: RapidusMaximus] #1670244
09/12/14 10:55 AM
09/12/14 10:55 AM
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Irving, TX
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Ditching the gears would be a big help for an in-town truck. It likely has an 8-1/4" rear. If so, grabbing gears out of a Dakota would likely help.

You can always drop in the steeper gears and a 518 OD to get the cruise RPM down. There's plenty of room under the truck.

What happened to the 360 mileage build thread? It went several pages and the engine had good numbers all the way around.


We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
Re: 318 gas milage build? [Re: feets] #1670245
09/12/14 11:35 AM
09/12/14 11:35 AM
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Lincoln Nebraska
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RapidRobert Offline
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I would checkout the 360 mileage build and in your current eng I would put a 3 keyway timing set in & adv it 4 deg and dial in the dist subsystems in order: initial/total (initial+slots) at 35 (vac capped) then springs then plug in/adj the can. Not sure if a razor sharp built 318 would be better than a razor sharp built 360 but Scratchn is getting incredibly good mileage numbers with his 318 & he is a truck guy so I would go with his plan. definitely get .035" quench/some mild porting & especially some small tube 1&1/2 or 1&5/8 headers and a free flowing exhaust (mandrel bends/free flowing (somewhat loud) muffs. EDIT the 2.73's and 15" (I'm assuming) tires are hurting you also. As said I would go to a deeper gear

Last edited by RapidRobert; 09/12/14 11:38 AM.

live every 24 hour block of time like it's your last day on earth
Re: 318 gas milage build? [Re: RapidusMaximus] #1670246
09/12/14 01:47 PM
09/12/14 01:47 PM
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Salem
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Chances are the truck has been really neglected by the previous owner and it needs a full, proper tune-up.

In a 2wd it should be doing 14 maybe 15mpg without too much trouble.

The biggest weakness I see for lack of fuel mileage is no lock-up converter and lack of dual exhaust. My other guess would be hopefull it has a viscous fan and not a direct-drive.

You may gain little going 318, and if you have the 727 maybe nothing at all. I find that 727 is a power-robbing turd to a 318. Right now I have the a833OD with a 318 and it's night and day difference to every other 318 auto I have/had: With 2.94's, 2bbl, 2wd, and single exhaust it's doing 17 to 20mpg on the highway.

However, if this is all in-town driving you are talking about, then 10mpg is about right.


Mo' Farts

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Re: 318 gas milage build? [Re: Grizzly] #1670247
09/12/14 02:21 PM
09/12/14 02:21 PM
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QuickDodge Offline
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I'd agree that 10 mpg or less is low for a stock truck, unless that is city mpg, driving in mountains, or driving with a VERY heavy foot. My 360 Ram always got 12 mpg. It had a rather tired 360, 727 and a 3.21 gear. The 12 mpg most likely could have been improved. I never even bothered to tune it up.

The fuel and ignition systems should be examined carefully. I'd guess the fuel / air mixture is overly rich or there is a problem with the timing not advancing. (Make sure both the mechanical and vacuum advance are functioning properly!)

An overdrive transmission is often worth 1-3 mpg on the highway. It would take a while for the fuel savings to pay for the swap, but the overdrive makes highway cruising MUCH more enjoyable! I'd seriously consider making such a swap just for the better highway manners. Any mileage improvements would be icing on the cake.

I'd give the truck a complete going over before considering an engine swap. (Assuming the existing engine is in good shape.) I'm guessing the low mileage can be significantly improved without resorting to major wrenching.

Swapping from a 360 to a 318 should improve the fuel mileage. If you have to buy the 318. Rebuild the new engine, and swap it into the truck, I'm guessing the truck would have to be driven for many, many miles before any savings would be realized.

Re: 318 gas milage build? [Re: QuickDodge] #1670248
09/12/14 06:43 PM
09/12/14 06:43 PM
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st.cloud fl
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find a 318 magnum donor computer and all and install.more power better milaege

Re: 318 gas milage build? [Re: d-150] #1670249
09/12/14 08:21 PM
09/12/14 08:21 PM
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Weatherford, Texas
RapidusMaximus Offline OP
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Thanks for all the replies and tips...I'm going to start with the basics this weekend and see what it looks like from a tune up perspective before I do something nuts like swapping engines...it was early this morning when I posted and I have a 318 sitting on the stand that needs freshened so I kinda went into f-it mode and jumped straight to engine swap...


1968 Plymouth GTX
1974 Dodge P/U Long Bed Stepside 318
2019 Ram 2500 6.4, auto, 4WD
Re: 318 gas milage build? [Re: RapidusMaximus] #1670250
09/12/14 08:40 PM
09/12/14 08:40 PM
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Back home in PA
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BulletBob Offline
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If you want good mug use a Magnum engine

Re: 318 gas milage build? [Re: BulletBob] #1670251
09/13/14 12:01 AM
09/13/14 12:01 AM
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Freeport IL USA
poorboy Offline
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Your son's gas mileage problem might be driver related. If it is, adding performance parts will probably not improve mileage at all, and may make it worse. Gene

Re: 318 gas milage build? [Re: RapidusMaximus] #1670252
09/14/14 01:12 AM
09/14/14 01:12 AM
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Manitoba, Canada
DaytonaTurbo Offline
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Is the 10mpg city , highway or a mixture? 10mpg in town for that truck while being driven by a kid is quite normal.

Re: 318 gas milage build? [Re: DaytonaTurbo] #1670253
09/14/14 01:00 PM
09/14/14 01:00 PM
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Weatherford, Texas
RapidusMaximus Offline OP
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Yes it is quite possible that the mpg is driver related...but he has driven my 74 318 2bbl auto truck quite a bit and it never used this much gas so I'm kinda leaning toward tune up on this 77...we shall see once I get some time this week to wrench on it...


1968 Plymouth GTX
1974 Dodge P/U Long Bed Stepside 318
2019 Ram 2500 6.4, auto, 4WD
Re: 318 gas milage build? [Re: RapidusMaximus] #1670254
09/15/14 01:01 AM
09/15/14 01:01 AM
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Freeport IL USA
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Al of the 360s I've owned would get about 2mpg less that a 318 version of the same thing. 77 was about the worse case for trucks concerning fuel mileage, it was a time when the car companies were prolonging adding the converters, so the motors were choked with hang on emissions stuff. Gene

Re: 318 gas milage build? [Re: RapidusMaximus] #1670255
09/15/14 01:16 AM
09/15/14 01:16 AM
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Manitoba, Canada
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The 4x4s use a lot more fuel than the 2wds do too...

Re: 318 gas milage build? [Re: DaytonaTurbo] #1670256
09/15/14 03:41 PM
09/15/14 03:41 PM
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dogdays Offline
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Get a roller cam 318 from a Fifth Avenue, '85 or '86 up through '89. Have someone do a good valve job and assemble it with the Mr. Gasket thin head gaskets. Use the rest of what is on your current engine. You should pick up a few mpg, that engine in my '64Dog D100 gets 20mpg at 70 on the highway.

R.

Re: 318 gas milage build? [Re: dogdays] #1670257
09/15/14 08:24 PM
09/15/14 08:24 PM
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Weatherford, Texas
RapidusMaximus Offline OP
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Quote:

Get a roller cam 318 from a Fifth Avenue, '85 or '86 up through '89. Have someone do a good valve job and assemble it with the Mr. Gasket thin head gaskets. Use the rest of what is on your current engine. You should pick up a few mpg, that engine in my '64Dog D100 gets 20mpg at 70 on the highway.
Sweet! That's some good mileage... I'll keep my eye out for one of those engines.

R.




1968 Plymouth GTX
1974 Dodge P/U Long Bed Stepside 318
2019 Ram 2500 6.4, auto, 4WD
Re: 318 gas milage build? [Re: RapidusMaximus] #1670258
09/16/14 12:51 AM
09/16/14 12:51 AM
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Florida
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any of the 85-91 318 2-v carb or tbi roller cam engine is a good starting point.

the 2-v carb or tbi roller cams respond well to a small 4-v carb/headers.

the whiplash roller is a very street friendly cam with a nice chop at idle.

Re: 318 gas milage build? [Re: scratchnfotraction] #1670259
09/16/14 02:56 PM
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dogdays Offline
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I like the Fifth Avenues for a lot of reasons, most have to do with the car itself:
1. 2-barrel carb is small, engine never developed a lot of cylinder pressure so rings, bores, etc. are not worn out.
2. The cars came with 2.24 rear ends, meaning the engine didn't see much high rpm use.
3. They were "grandma" cars, meaning they were driven easy.
4. Many of the "grandma" cars I have encountered were very well maintained. Grandma knew she couldn't afford a new car so she took it to the garage every 3000 miles.


Other things:
The cast iron used in these engines is pretty hard.
The hydraulic roller cam stuff is already there.
You can have the stock cam (it's a single pattern cam with 110LSA) reground by Bullet for something like $120. The largest lobe that will fit is the 209 degree@ 50, 0.316 lobe lift. That's from Patrick, who is the patron saint of this engine. A note about going to a higher lift: Retainer-to-guide clearance will probably have to be opened up, the tool costs less than $50 and I did all mine in around 15 minutes. Also, valvesprings become an issue because of the short installed height of the stock setup. Patrick used Hughes 1110 springs, IIRC. On my engine I used Crane 833 springs, and actual valve lift will have to stay under 0.474". There's also the old favorite Comp 901s, and those too have a maximum lift of less than 1/2 inch. The stock retainers worked just fine on my Crane 833s and will work on the 901s I have on the shelf.

Another note: The 318 roller cam valvesprings are stouter than stock 318 flat tappet springs and would be a cheap upgrade for a mild cam in a flat tappet 318 or 360.

About the 302 heads: They have a lousy stock valvejob. They are quite easy to open up to the 360 gasket size, at least on the outside side of the runner curves, where much of the flow is. There is quite a lot of material clogging the topside of the port around the valve guide. The air holes into the exhaust port can be plugged with 1/4" setscrews or bolts. Run the correct size drill through the hole before tapping and be careful tapping. I broke a tap off and had to use some goop to plug the hole. The AIR holes in the exhaust manifolds are not connected to the exhaust after you plug the holes in the heads.

The 5-blade fan clutch assembly on the Fifth Ave is the same as the MP low drag fan.

R.

Re: 318 gas milage build? [Re: dogdays] #1670260
09/16/14 09:59 PM
09/16/14 09:59 PM
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Weatherford, Texas
RapidusMaximus Offline OP
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Now that's a lot of info


1968 Plymouth GTX
1974 Dodge P/U Long Bed Stepside 318
2019 Ram 2500 6.4, auto, 4WD
Re: 318 gas milage build? [Re: RapidusMaximus] #1670261
09/23/14 09:44 PM
09/23/14 09:44 PM
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Cleveland Ohio
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holley street dominator for sale on cl.



http://detroit.craigslist.org/wyn/pts/4650051559.html

Re: 318 gas milage build? [Re: sportfury70] #1670262
09/25/14 12:38 PM
09/25/14 12:38 PM
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Irving, TX
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Quote:

holley street dominator for sale on cl.



http://detroit.craigslist.org/wyn/pts/4650051559.html




That's a crap intake. Much better pieces are available these days.


We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
Re: 318 gas milage build? [Re: RapidusMaximus] #1670263
09/25/14 02:30 PM
09/25/14 02:30 PM
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Rob C Offline
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Quote:

Just bought my son a 77 SWB with a 360 auto, carter afb, duel plane 4bbl intake, stock exhaust, stock rear with 2.73 one legger, it is a gas hog (about 10 mpg or less)...considering pulling the 360 and installing a 318. Any suggestions on a gas miserly 318 build? 2bbl/4bbl, cams, induction preference? Or....is there any way to improve the milage of this 360? Thanks




The hardest part if mileage is the vehicle itself. Being a huge brick moving through the air is a problem in itself. Things I did for improved mileage to 20 MPG's in my '79 3700lbs. 360 powered Magnum were;

Open air cleaner
625 Carter well jetted, slightly lean
A stock intake was used but a RPM would be better once under power going down the road.
While I used stock heads, a rebuilt set with a good valve job to improve low lift flow would help here.
I used dual exhaust of the manifolds @ 2-1/4 inch pipe with an "H" connection into a set of Thrush mufflers.
A junk yard distributor w/vacuum advance (since in 1979 the vacuum advance was on the leanburn computer) and a MSD fired it all off.
The trans was a 904 & the rear was a 8-1/4 w/2.76 gears and 235/60/15 tires on all 4 corners.

Being a low powered emmision year engine saddled with lots of equipment, which was removed, I'm not sure if headers would help much or a larger exhaust pipe would help. More compression would increase power and mileage but I never milled my heads.

Re: 318 gas milage build? [Re: RapidusMaximus] #1670264
09/26/14 04:26 AM
09/26/14 04:26 AM
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Aurora, Colorado
451Mopar Offline
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There are a few things you can do, but fuel mileage on the old trucks was not that great (unless it is a two wheel drive.)
Headers and dual exhaust. Good ignition system (plugs, wires, coil, re-curved dist with vacuum advance adjusted.)
You will need the above with either engine.
Fix any vacuum leaks, tune carb.
Some non-engine related item may help get one or two additional MPG: Redline or other light weight synthetic gear oil in diff. If it is a 4x4 front diff too, depending on transfer case synthetic gear or trans fluid. lockout hubs, properly adjusted and greased wheel bearings, maximum rated tire inflation, correctly adjusted brakes, just the normal stuff.

If you get 15-mpg that would be good.

Re: 318 gas milage build? [Re: RapidusMaximus] #1670265
09/26/14 12:21 PM
09/26/14 12:21 PM
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There might be as much as a 10 percent fuel economy improvement if you were to "equallize" the eight cylinder intake runners so that they got a more nearly equal air to fuel ratio at highway cruise rpm and throttle opening.

The cheapest way to do this would be to buy or borrow an electrical multimeter with a type J or K thermocouple probe, and then measure the cylinder head metal temperature beside each sparkplug. The highest reading cylinders will be the ones closest to an AFR of 16 or so.

It would be better to drill holes in the exhaust manifold to measure EGT but this is obviously more work and expense.

Even better still would be bleed some exhaust gas from each cylinder across a wide range oxygen sensor and measure AFR. Individual header tubes make this more straight forward but it can be done with exhaust manifold holes "collecting" gas to sample.

Port the runner of any cylinder's intake manifold that is too rich and therefore is lower in temperature.

Boosting static compression ratio from 8 to 11
would give roughly 8% fuel economy gains
at part throttle cruise,
but detonation at full throttle unless you used water injection or cooled EGR.

Back around 2004 then Chrysler chief Tom LaSorda wrote that switching to optimum economy camshafts instead of 4500 rpm max power grinds would improve fuel economy about 6%

Re: 318 gas milage build? [Re: 360view] #1670266
09/26/14 01:27 PM
09/26/14 01:27 PM
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10 MPG is low for a SWB 2WD. I was able to get 12-13+ in a 79 1 ton w/ a 12 foot bed. That was with a TQ. I would change out the afb and probably the intake unless a good tune gets you there. Headers make a night and day difference, as those logs are really bad. Have to watch the $$$ though or it is just hot rodding. The carb would be the most bang for the buck I think.


I want my fair share
Re: 318 gas milage build? [Re: RapidusMaximus] #1670267
09/27/14 12:01 PM
09/27/14 12:01 PM
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Crockett ,TX
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98RAM1500 Offline
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Don't forget about terrain has a lot to do with fuel mileage as well, flat open ground vs hilly country, The best I have ever gotten out of a truck was my 81 ram stepside with a stock 318 2 bbl, auto, 2.94 gear it got 17-18 hwy at 55 mph.

Last edited by 98RAM1500; 09/27/14 12:06 PM.
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