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Re: MPG 318 vs 360
[Re: Magnum]
#776009
08/23/10 12:44 PM
08/23/10 12:44 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
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Quote:
Quote:
I think you just hit on something here. The 5.2
version of the Magnum motor may be the ticket
to higher mpg. It's already blessed with a low-friction valvetrain and very efficient heads with
decent sized valves. All it needs is a good "torque type" cam to get the job done. 
The cam you are looking for is already in there. They are ridiculously small, I think even smaller than a LA318.
similar duration, more lift.
if you want a good cam for a roller 318 that is a good balance of power and economy, get the stock cam reground by bullet cams, and use their HR259/316 lobe for both the intake and exhaust. pulls very hard in my magnum headed 318 roller motor.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: MPG 318 vs 360
[Re: OrangeProwler]
#776011
08/23/10 06:29 PM
08/23/10 06:29 PM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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I think the 360 ports are just too large for cruise economy.
The smaller 318 heads will velocity up at the low rpm. That's going to give you much better cylinder fill at low throttle opening.
The Magnum heads are simply a better design but may be a tad large for maximum economy.
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
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Re: MPG 318 vs 360
[Re: feets]
#776012
08/23/10 07:31 PM
08/23/10 07:31 PM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
Joined: Jun 2008
Posts: 10,847
Oakdale CT
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Quote:
The Magnum heads are simply a better design but may be a tad large for maximum economy.
My 5.2 Durango 2WD would pull down a confirmed 20.5 mpg (calculated from fillups) while cruising through Ohio and Kentucky at 70 mph.
Not bad for a heavy brick with no mods other than a Hooker max-flow muffler.
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Re: MPG 318 vs 360
[Re: HYPER8oSoNic]
#776016
08/31/10 03:28 PM
08/31/10 03:28 PM
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Joined: Jan 2007
Posts: 23
Peyton, CO
Mad Max
member
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member
Joined: Jan 2007
Posts: 23
Peyton, CO
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I'm going through a similar quandry with my '93 Ramcharger 4x4. Just got it locally, really nice condition, about 150,000 on the clock, has the 3.55 gears and 30" tires.
Discovered the overdrive isn't engaging, and my highway rpm has been a nice 2400-2600 rpm, and I've been getting ~ 15 mpg - not too bad really. But that's with the tranny in 3rd, not overdrive. When I get the od functional my 65 mph cruise rpm will be 1650-1850 rpm, and I can't help but think those rpms will pull the 318 out of it's sweet spot, and likely my mileage will go down.
I've always felt the small blocks 'enjoy' a bit more rpm, and I'm thinking seriously about replacing the 3.55s with 4.56's.
With 4.56s and a 31" tire, 65 = 2250 and 75 = 2600, and that sounds pretty good to me.
I can't help but think the 4.56's would be a better gear ratio, especially considering I do a lot of around town driving and the gears should help get the truck around lots easier.
What rpm range do y'all think a Magnum 318's 'sweet spot' is?
'68 Charger R/T
'71 Demon GTS-R
'78 M350 Cummins Power Wagon Crewcab
'93 Ramcharger W150 LE
'93 Cummins Ram
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Re: MPG 318 vs 360
[Re: Mad Max]
#776017
08/31/10 03:39 PM
08/31/10 03:39 PM
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Joined: Jan 2003
Posts: 1,978
Southaven, MS
BossRide
top fuel
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top fuel
Joined: Jan 2003
Posts: 1,978
Southaven, MS
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My '73 has a 904 with a 318 torque converter, 2.73 gears, 275/65/15 tires, a rebuilt '79 360 from a Volare wagon, a 650 Holley on an Offy intake, a semi-lumpy cam, a decent valve job, TTI headers with dual exhaust and an H-pipe, all the A/C stuff and power steering, and I drive like a lead-footed monkey - regularly cruise to Birmingham and back at 80-85mph... I get between 15 and 19 mpg whenever I check it.
The Blue Goose
My instagram: Bossride
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Re: MPG 318 vs 360
[Re: Mad Max]
#776018
08/31/10 05:13 PM
08/31/10 05:13 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
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I Live Here
Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
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Your truck will get better MPG with the 3.55 than the sub 4 something gears you want. Nothing at all wrong with running a 318 magnum 1800 RPM. You will have less vacume in the intake for the pistons to pull down against. It will also make less friction inside the motor. You will be takeing a step backwards. If the truck would get better MPG with the lower gears the factory would have put them in it.
2600 RPM is way beyond the "sweet spot" for MPG(I am guessing you mean tourque peak, but even that don't make sense because you don't cruise at WOT so that tourque peak means nothing at cruise).
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: MPG 318 vs 360
[Re: HotRodDave]
#776019
08/31/10 05:38 PM
08/31/10 05:38 PM
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Joined: Jan 2007
Posts: 23
Peyton, CO
Mad Max
member
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member
Joined: Jan 2007
Posts: 23
Peyton, CO
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ya my 'sweet spot' query was more along the lines of 'where is the optimum rpm range for a 318 for maintaining speed', not for max power. More like, where in the rpm band is 'good/enough' torque generated.
I really wish there were dyno results generated where the engine isn't at full throttle, IOW a half-throttle dyno run showing how much power is generated in a 'normal' driving condition verse WOT. WOT isn't what I'm concerned with - I want to see the power levels for an engine in the rpm range where it spends all its life.
Thanks for the reply. If 1800 rpm is an efficient/maintain speed rpm for a mag 318 then I'll be happy to leave the gears alone. Conveniently, 1800 rpm is also the sweet spot for a 4bt Cummins....
'68 Charger R/T
'71 Demon GTS-R
'78 M350 Cummins Power Wagon Crewcab
'93 Ramcharger W150 LE
'93 Cummins Ram
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Re: MPG 318 vs 360
[Re: Mad Max]
#776020
08/31/10 06:04 PM
08/31/10 06:04 PM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
Joined: Jun 2008
Posts: 10,847
Oakdale CT
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Quote:
ya my 'sweet spot' query was more along the lines of 'where is the optimum rpm range for a 318 for maintaining speed', not for max power. More like, where in the rpm band is 'good/enough' torque generated.
My 5.2 magnum 1500 Ram tools down the highway at 2000 rpm.
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My thoughts exactly!! 
