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Re: 318 gas milage build? [Re: sportfury70] #1670262
09/25/14 12:38 PM
09/25/14 12:38 PM
Joined: Jan 2003
Posts: 28,063
Irving, TX
feets Offline
Senior Management
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Senior Management

Joined: Jan 2003
Posts: 28,063
Irving, TX
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
Joined: Mar 2005
Posts: 792
Earth
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Rob C Offline
super stock
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Posts: 792
Earth
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
Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar Offline
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Joined: May 2008
Posts: 5,399
Aurora, Colorado
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
Joined: Jan 2006
Posts: 8,162
USA
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360view Offline
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USA
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
Joined: Feb 2003
Posts: 10,178
Someplace you aren't
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SomeCarGuy Offline
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Posts: 10,178
Someplace you aren't
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
Joined: Dec 2004
Posts: 1,176
Crockett ,TX
9
98RAM1500 Offline
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Joined: Dec 2004
Posts: 1,176
Crockett ,TX
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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