318 MAX fuel economy builds?

toolmanmike

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Going against the grain here, but if mileage is the primary concern it is hard to beat the lean burn set up.

If it is still working after all these years I would leave it. It leans AFR out at part throttle cruise to 17 or 18 to 1. Exactly what is needed for best mileage.
There were many issues with it even when it was new. Parts aren't reproduced that I know of.
 

mgoblue9798

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Probably get 20+ out of one of those. Most of those had a roller cam, the #302 heads, and a lock up 904 transmission with a low rear gear (like 2.87 or whatever) Heck, my 70 318 2 barrel with a standard 904 and a 3.23 gear gets a steady 19 on the highway.
Lots of the M bodies have a 2.20 gear rear end.
What's a good dual plane intake?
In this instance I would use the one I had on hand, including an oem one.

To go all out for mileage if I were buying one I would use the SP2P with a small thermoquad.

If I were building a low buck motor from scratch I would use a magnum crank, rods, pistons and zero deck the block. Would use magnum heads, long tube headers, and factory 318 magnum cam.

Even the low compression 2bbl smogged out 318's that came factory in the M bodies would knock down 20mpg plus with no problem. If the engine was good I would just change the timing chain out, tune it up, and run it as is with the 2bbl.
 

mgoblue9798

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There were many issues with it even when it was new. Parts aren't reproduced that I know of.
I know I have owned a bunch. Have switched over a bunch to regular electronic ignition when the computer failed as well.

The computer either worked or it didn't though. Never had one give problems other than dying.

If the car still has one that is in working order after all this time it is not likely to give any problems as the newer orange boxes sold by ma mopar now.

If there is an issue with it, or someone wants to change the setup from stock, then they have to go.
 

AJ/FormS

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My question is does it absolutely have to be points to benefit or can it be a newer electronic style? Is there something to benefit from setting the points differently or what? I have never touched a points style.
No, points are fine for a modest rpm engine, but; they have to be readjusted periodically, because they tend to lose their setting over time as the various parts wear/wear out. As they wear, the point gap changes, which changes the timing.
With the electronic distributors, you just set 'em and forget 'em.
Here's the thing, not too many years ago, every Internal Combustion Engine had points, including lawnmowers and such. I made good coin rescuing old yard-equipment from the scrap bin, and just giving them a tune-up, (which included cleaning and re-gapping the points), then peddling them.
 

MopaR&D

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I had a 1988 5th Ave, converted it to TQ carb on a Performer intake, electronic distributor and old MSD box I got for free, homemade 2 1/4" duals and swapped in an 8 1/4" rear with 3.07:1 (Jeep XJ ratio) gears. MPG still averaged around 20 (got maybe 22-23 stock) but the 0-60 dropped from like 25 to 8-10 seconds and overall performance was drastically better. Heck just changing the gearing alone makes the biggest difference, mine came with the 2.24:1 or whatever and it literally couldn't keep up with modern traffic.

Those roller-cam 318s are great engines all- around; good power, good gas mileage, bulletproof.
 

Bewy

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Elec ign conversion should be on the list. At the top. It has two important benefits that aids mileage & performance:
[1] it does not start to retard the ign from day one like points do because it does not have a rubbing block that retards ign as it wears. Retarded ign hurts performance AND mileage.
[2] you can run a bigger plug gap, which exposes more of the A/F mixture to the ign source, which is the spark. The best/simplest/best bang for buck system is the GM HEI conversion with a an E core coil such as the MSD #8207 & run 0.060" plug gaps.
 

273

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If the goal is to save money you got to look at the gain and $$ reward of each mod.
Depending on yearly mileage savings per average mpg gain probably between $50-150, so say $100 savings per 1 mpg average gain, so you got to be careful with the cost, say you do intake carb ignition duals headers with a gain of 3 mpg depends how you go about it could take 2-5 years or more to break even.

First you got to figure out what each mpg gain will save you a year.
Second how many years do you plan using the car as a daily driver, if say 5 years your gonna want most mod to break even in a year or two.
 

RustyRatRod

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Not new, no.
Someone disagreed with me when I said the Edelbrock SP2P is not available new. So post up an current up to date ad of one for sale somewhere NEW. I don't mean an individual, either. A vendor.
 

junkyardhero

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there are a whole lot great suggestions and ideas here and I think that you need to decide if you just want to plus a few miles on the ticket of your current set up or if you're looking to build something to wring out every last drop of mileage.

273 makes a note of what the ROI is on mods while looking for that mileage and that's something that you should have in the back of your mind.

giving your current motor a mileage master glow up with a few bits and bobs won't break the bank; but building out a full blow motor would ultimately negate any savings in fuel mileage you'd come up on.
 

Jadaharabi

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Elec ign conversion should be on the list. At the top. It has two important benefits that aids mileage & performance:
[1] it does not start to retard the ign from day one like points do because it does not have a rubbing block that retards ign as it wears. Retarded ign hurts performance AND mileage.
[2] you can run a bigger plug gap, which exposes more of the A/F mixture to the ign source, which is the spark. The best/simplest/best bang for buck system is the GM HEI conversion with a an E core coil such as the MSD #8207 & run 0.060" plug gaps.
In regards to your number one. Proper lubrication of the follower is very important. You can wear out a set of points and nothing flat if you don't lubricate them. As for the variance of the Gap from where if you set your points Gap to the high side as they wear in they will be right on the money. Of course there is your annual maintenance for winter tune-up whatever you want to call it when you replace the points. And a lot of people do not realize that you can set the point tension by how much you slide the spring under the nut where the wire hooks up. More Point spring tension less Point bounce. People got high mileage with points for 100 years so it's not necessary to go to electronic ignition to get good gas mileage.
Jmho
 

Darter6

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Those roller-cam 318s are great engines all- around; good power, good gas mileage, bulletproof.
I agree.Yes they are. I put one in a 88 D350 Dodge, unknown mileage that I got for free.10 years still going strong.
 

volaredon

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The RJ12YC also has a smaller hex equivalent, same plug Edelbrock suggests with their head. The heat range works fine for most builds that aren’t to radical. Going a step cooler for strong “Hot Rod” builds would be a good route.

For the task at hand, I think it’s a good starting point.
No the rj series is still a 13/16 hex. It just has shorter threads so the electrode end won't reach down far enough into the combustion chamber. The rj plug is what the big block engine calls for and "if I remember right" the older poly series engine as well.
I think that you want "re" prefix plugs if using champion. There's 2 that will work. One listed for the magnum series engine til 96, the other listed on 96- newer magnum heads. The difference between these two is that the 97+ version has a longer ground electrode, the inside insulator seems longer to compensate, (it isn't but sets into the threaded portion farther)
I remember when my kid had his 90 w250 with a. Gas 360. He had gone to the parts store and asked for plugs for it, and they gave him the plugs for a magnum, I went back with him to return them for the regular *RN" series plugs as LA motors always used and they showed us that "their" listing showed many of the LA engines had been superseded to the newer style peanut plugs.
So with that I called the Federal Mogul (Champion) tech line myself and was told that besides the difference in wrench size that these peanut plugs were identical to the original plugs that we were used to seeing in the LAs and could use either/or. The main reason why magnum engines went to the different style plug was because of the pressed in tubes around the plugs to insulate the plug wire boots from heat.
 

volaredon

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Going against the grain here, but if mileage is the primary concern it is hard to beat the lean burn set up.

If it is still working after all these years I would leave it. It leans AFR out at part throttle cruise to 17 or 18 to 1. Exactly what is needed for best mileage.
In my case the lean burn is going away. The last 2 years I had the car out (fair weather cruiser) it started pinging randomly at weird times (not when you'd expect with over advanced base timing) and quite intermittently at that. I have everything to convert to the 4 pin ecu, but the more I hear about it the more I'm considering trying an HEI setup instead.
I have had many 318s over the years.
On another one I had, an 83 d250 I went inside the engine and put in a stock replacement cam for a 360-2 barrel, a set of EQ heads (converted to a magnum drivetrain) added a performer intake (original performer, not air gap or RPM versions) and a Carter afb 625 and I was quite amazed at how much better that engine ran plus a quite noticeable improvement in mpg (wasn't my main goal in the cam and 2 bbl-4 bbl swap but I wasn't complaining)
I plan on doing exactly the same thing on the 318 in my fury that still currently has it's lean burn. I have all the parts here for it. My "cam of choice" happens to be a Melling SPD 25. The only difference in this case is that instead of the EQ heads like I put on the hay truck, I have a fresh from the machine shop set of '302s sitting here for that engine's upgrades.
All that remains before the parts are swapped is to get inside those '302s with a die grinder and a set of burr bits while hoping I don't "oops" the fresh valve job.
 

YY1

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I will agree with keeping the lean burn and electronically controlled 2 barrel- that's what they were designed for.

...and it's $0 if they are working.
 

YY1

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For the cost, a better plan might be replacing the long block with a 5.2 Magnum.

More HP and better efficiency.

Keep the 2 barrel.

I bet it will be hard to get better MPG with anything else, but if we're really shooting for max MPG, EFI and a controlled distributor is the true successor to Lean-Burn.
 

rumblefish360

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I will agree with keeping the lean burn and electronically controlled 2 barrel- that's what they were designed for.

...and it's $0 if they are working.
The Leanburn was a recall! It tends to suddenly stop working when it gets hot. This will happen when you’re driving. The Leanburn should be replaced with an earlier style ignition at the minimum. AKA - orange box though I like the chrome box better. IMO, go see Don @ 4secondflat.com for an ignition system.
 

Rat Bastid

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Champion 12s, with the 5/8s hex for plug clearance
maybe RJ12YC, or something like that. I mean, I've only seen them 3 times since 1999, lol.

RC12YC is the 3/4 reach, 5/8 hex plug.

The “C” denotes that.

The “J” series plugs are 5/8 reach, 13/16 hex plugs. They used those junkers in big block Chryslers.
 

rumblefish360

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No the rj series is still a 13/16 hex. It just has shorter threads so the electrode end won't reach down far enough into the combustion chamber. The rj plug is what the big block engine calls for and "if I remember right" the older poly series engine as well.
I think that you want "re" prefix plugs if using champion. There's 2 that will work. One listed for the magnum series engine til 96, the other listed on 96- newer magnum heads. The difference between these two is that the 97+ version has a longer ground electrode, the inside insulator seems longer to compensate, (it isn't but sets into the threaded portion farther)
I remember when my kid had his 90 w250 with a. Gas 360. He had gone to the parts store and asked for plugs for it, and they gave him the plugs for a magnum, I went back with him to return them for the regular *RN" series plugs as LA motors always used and they showed us that "their" listing showed many of the LA engines had been superseded to the newer style peanut plugs.
So with that I called the Federal Mogul (Champion) tech line myself and was told that besides the difference in wrench size that these peanut plugs were identical to the original plugs that we were used to seeing in the LAs and could use either/or. The main reason why magnum engines went to the different style plug was because of the pressed in tubes around the plugs to insulate the plug wire boots from heat.
Thanks. I miss typed I think. I was thinking of the plug Edelbrock recommends. The RN?
Good write up though!
:thumbsup:
 

Rat Bastid

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Thanks. I miss typed I think. I was thinking of the plug Edelbrock recommends. The RN?
Good write up though!
:thumbsup:

The “N” series plugs are 3/4 reach, 13/16 hex plugs. I pretty much never use an “N” plug any more. The ”C” is the same plug without that clunky 13/16 hex and required bigger plug socket.

It appears that Champion and NGK are eliminating plugs in the “N” series very quickly. There is no real reason to use them except maybe a 100 point restoration or similar.

I can’t remember the NGK nomenclature for the 3/4 reach 13/16 hex plugs or Autolites. I have looked at the NGK catalog and Autolite’s web page and they are eliminating that plug series too.
 

Bewy

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The NGK 3/4" reach/13/16" hex is a 'BP', eg BP5S for Mopar V8s. I no longer use the 13/16" plugs in any engine I build/service, I use the 5/8" hex.
 

Dmopower

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Great thread. I am building a 67 Cuda and i'm putting an A-500 and a 3.55 gear this spring. I'm building a 360 for it right now and am looking at high mpg as a big part of the goal. Thinking of running 273 bushed rods to reduce rotating weight. I'm looking for a set of 920 heads and I plan to port them and put larger valves in them, hard seats and bronze guides. Running the KB step up dish pistons get me around .040 quench and I will be running the Performer manifold port matched an air-raid 1" 4 hole carb plate and an Edelbrock AVS 650 annular venturis with the Edelbrock distributor as it's tunable both mechanical and vacuum advance. I'm looking at running a cam in the 215 to 220 at .050 range and I'll be running Rhoads lifters to get it back close to the factory 2 barrel cam specs below 1500 rpm. This is what I thought may get me over 20 mpg and still have some git up while I build my stroker. Thoughts?
 
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