318 MAX fuel economy builds?

Dan the man

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maybe start another thread or possibly add to one that you have currently going on for that build?

hijacking this member's thread with a question that's not within the paradigm is kind of poor form.
Thanks for reminding me about that. I get interested in the article and get off track.
 

RustyRatRod

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maybe start another thread or possibly add to one that you have currently going on for that build?

hijacking this member's thread with a question that's not within the paradigm is kind of poor form.
You beat me to it. lol
 

AJ/FormS

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Cruise power requirement in an FMJ car is only around 40/45hp.
At WOT, that would be about 21.25 pounds of fuel per hour. But cruising at 2000/2200rpm, I'm guessing maybe half of that, so say 11pounds per hour; rounds to 1.83 gallons. At 60mph, that maths to 32.8mpg . That could be your target.

Effective cylinder pressure would be your best friend; it makes torque; but it will take a lotta miles to recoup the buy-in.
Easier and cheaper by far, is to dial in the cruise timing.
and a 318LA with a 2.45 rear gear @ 65=2000rpm, should be barely on the MainJets to make that....... so any old carb will get you there. The smaller the primaries the better, but the higher the vacuum at 2000, is even better.
If I was planning this out, I would start with a closed chamber /tight squish design, and way more than factory Cylinder Pressure. For cruising on, you can run a ton of cylinder pressure.... you just have to figure out how to get to that cruising speed without detonating the poor girl to death. I vote variable-flo water/meth injection. Ignition timing at cruise rpm will be the key.
Sure this will be pricey, but you want bragging rights so who cares ....... right? Lol.

OK but, since we're talking theoretical, I would start with a smaller bore or more stroke, or both........ and maybe long-runner intake tuned for cruise-rpm. I think a Magnum would be a logical choice ..... with an A500 and a rear gear between 3.55 to 3.91, for a cruise rpm of 2000 to 2200. And if a Magnum is on the table, Ima liking a Magnumized 273, with custom pistons.
Or maybe 3.65 x 3.58= 300 cubes, and 65=1660 with 2.94s, and that A500. Yeah I like it!
Wait a sec, I think I still have a lil 273 kicking around somewhere........ hmmmmmmmmmmmmmmmm

And then; there's a certain super high-compression Alloy headed 367, with Plasma-Moly rings, and a manual trans with overdrive, that runs 65mph just off the transfer slots, @ 65=1600rpm, hmmmmmmmmmmmmmmmmmmmmm, that's a small bore/long stroke 1.18ratio, same as the 318, but with a lil more inherent torque to get that tank-Dippy/FA rolling, and to give it some passing-power.
 

Darter6

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In the mid 70's I drove a 1970 bare bones Duster 318 4 speed 2.94 gears with the tallest rear tires I could find. The engine had a factory spread bore 4 bbl 340 manifold with a thermoquad,secondary's disconnected,headers and full dual exhaust. I would drive it from Pittsburgh Pa to Denver Colorado ruffly 1600 miles.I woud do it 4 times a year.I would average between 24-26 mpg running the then speed limit of 55 to 60 mph.Weight is a big factor.
 
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rumblefish360

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I've been reading up on intake manifolds and a lot of guys say that the edelbrock performer isn't much of then the factory intake, is the weiand action plus any better?
It’s about equal. Build dependent.
What's a good dual plane intake?
Factory dual plane, Edelbrock Performer & the SP2P for mileage builds.
Just a driver with a extra zip
Any dual plane except the SP2P or the Offenhauser dual port.

The thing here on a mileage build is beating the factory intake in the low rpm range. The SP2P intake would be a disaster for a performance intake. Though it was never built for performance. It was introduced during the gas crunch days.

I had a coworker tell me it was a good help in his van. It is possible but more likely improbable to find a two barrel SP2P.
Crazy hard to find they are.
The one below is a picture gleamed from the web.
AKA - Not mine.

4A03C8CD-8FE8-4A07-93C8-23E9C2AE5226.jpeg


The below standard Chrysler 4bbl Thermoquad intake is all you really need for a mild performance build or a mileage master searching intake. For its design, it’s hard to beat.

AD6F6D30-C577-41F1-AD68-B82ADBD9E145.jpeg
 

rumblefish360

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Years back a fella on Moparts did a mileage 318 build. IIRC, he was able to achieve 32 mpg’s. I don’t remember the details of everything, but, again, IIRC, he used a high compression ratio to help.

IF I myself was going to do this, and I have thought about doing it for fun, I’d look towards the following parts.

@Bewy recommendation of a small primary TQ
The factory 4bbl. or a SP2P though they’re hard to find.
An Edelbrock Performer would also be a viable intake.
Stock cylinder heads with a 3 angle valve job.
Earlier years 318 pistons for more compression due to the pistons height. A KB replacement flat top is also a good idea.
Iskendarians (Isky) Mile-a-more camshaft

That would be the list of basic starting engine parts that should do very well. The transmission would be A lock up 904 or a LU/OD 904.

Gear ratio with the 904 would be a 2.45 if I could find one. Or work the math backwards with the OD trans ratio to find a suitable ratio to end up numerically as low as the 2.45.

A multiple spark ignition is something I have found helpful in low speed, low rpm driving in order to burn the most fuel possible for added mileage. While I have had the most crappiest luck with MSD, only one box worked longer than 30 days…. A multi spark box is a great help.
 

Jadaharabi

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Back in 1976 my dad bought a new Volare. He was always tweaking on the carburetor and the timing to get better fuel mileage. He was making trips from Illinois to California and Massachusetts. I think when he was finally done with his tweaking he was getting 26 to 28 miles to the gallon with that car. It had the lock up transmission and I think a 2.76 rear gear. But I could be wrong on the gear.
 

AJ/FormS

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In the mid 70's I drove a 1970 bare bones Duster 318 4 speed 2.94 gears with the tallest rear tires I could find. The engine had a factory spread bore 4 bbl 340 manifold with a thermoquad,secondary's disconnected,headers and full dual exhaust. I would drive it from Pittsburgh Pa to Denver Colorado ruffly 1600 miles.I would do it 4 times a year.I would average between 24-26 mpg running the then speed limit of 55 to 60 mph.Weight is a big factor.
as is rpm. and the type of trans.
You had the exact combo that I was referencing earlier, namely: the Hi-compression engine, in which 60mph = 2100 or so, but yours had a manual trans. Not to mention, the Duster is not as much of a brick/shoebox, as are the cars that the OP is considering. Plus your 318 had a real and decently calibrated distributor, headers, and dual exhaust.
Those hi-compression 318s were pretty darn nice; advertised at just 45hp less than a 340, but at the same maximum torque, albeit 800 rpm sooner. IIRC it was 340 ftlbs at 2400rpm. That's the kindof torque you need for a cruiser. And 26/32 is 81% of my imagined target (32.8) so you were doing pretty darn good. And that, with a factory engine! no less.
Btw,
in those years, I also had one of those hi-pressure 318s, but in a 71Demon, and it did about the same, with 2.76s and a 904 which was by far, the best-shifting trans I ever owned. So I cloned it, making 3 copies. Over 45 years later, I'm pretty sure that I still have one left.........
 

AJ/FormS

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The below standard Chrysler 4bbl Thermoquad intake is all you really need for a mild performance build or a mileage master searching intake. For its design, it’s hard to beat.
I found one of those with 318-sized ports. I was very pleased with it.

A multiple spark ignition is something I have found helpful in low speed, low rpm driving in order to burn the most fuel possible for added mileage. While I have had the most crappiest luck with MSD, only one box worked longer than 30 days…. A multi spark box is a great help.

I have no experience with those, but the idea seems really good for an engine, set up to run on the lean side.
I had really good success with the hi-amperage Square-top Accell Super Coil, and it has taken my Barracuda to around 135,000 miles, with nary a complaint. About a 100,000 of those were with the 367, from which I just took the plugs out last month, that were installed in 1999; I kid you not.
 
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volaredon

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My 76 charger with a 318, 2.45 rear, and 360 2 barrel Holley carburetor was good for 23. As is my current 78 fury 2 door (also 318) dead stock 2 barrel motor tht actually still has working lean burn... Only deviation from stone stock is true dual exhaust 2-1/2 all the way to the back bumper
That one has 2.76 in the rear end. No lockup in either one, charger was 727 fury has 904.
 

rumblefish360

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I found one of those with 318-sized ports. I was very pleased with it.
When I did the 2-4 swap on my first Magnum, the intake was $20. Glass beaded it at work, a rattle can of Chrysler blue for IIRC, under $7, good cheap performance and good looks, can’t beat it.
I have no experience with those, but the idea seems really good for an engine, set up to run on the lean side.
I had really good success with the hi-amperage Square-top Accell Super Coil, and it has taken my Barracuda to around 135,000 miles, with nary a complaint. About a 100,000 of those were with the 367, from which I just took the plugs out last month, that were installed in 1999; I kid you not.
The one and only MSD that has worked for me was a gem. It added about a 1-1/2 to 2 mpg’s on the Hwy. It was easy to hook up. I did tweak the carb (Federal-Mougal 625 AFB ) a good bit over and over until I was happy with it. The car was heavy-ish at 3700+ dry. I was a skinny fella back the at time at around 160/170 max.

I’d pack the car up and travel to Georgia or the Virginia off of Long Island NY. The best I did was running it near empty to the tune of 400 miles per 20 gallon tank. That was really pushing it. The car was listed as having a 20 gallon tank.

I never tried headers back then. NY State demanded cats on the car, so off of the exhaust manifolds was a dual 2-1/4 H piped exhaust with twin high flow cats & simple turbo mufflers from Walker IIRC. A 2.76 rear gear rolling 235/60/15’s and keeping I-95 speeds down to 70 or less was key. Through the night traveling makes that very easy and being young, non-stop unless the car was hungry.

Once I got the tune nicely in, that was the last set of plugs I had until the car left me. I had gotten 3 years out of the plugs when I last checked them, they were looking good, so I threw them back in and off I went.

I don’t want to say get a MSD, since they were most crap boxes for me but I will say get a multi spark ignition onto your car and then re-jet the carb if need be. I ran mine pretty lean.

Missing a couple of more tricks, I would have liked to have tried them out. Headers with a larger exhaust and a TQ are among them. But a solid 20 out of a 360 in a loaded ‘79 B body worked OK for me back then.

LMAO - FWIW - a knthe. 93 octane was a grossly overpriced amount of $1.50 and I was outraged at that!
LOL!
 

rumblefish360

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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.
 

gagembassett

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Apologies for the lack of responses on my own thread fellas, I'll get caught up and reply to them. Happy Thanksgiving to you all as well!
 

gagembassett

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If it has the original "Lean Burn" ignition get rid of that. Just a Mopar electronic or even a Pertronix in a old point type distributor.
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.
 

gagembassett

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Use a small [ 800 cfm ] TQ carb. To resist the temptation to use the secondaries, disconnect the link connecting the pri to sec. The extra booster ring in the TQ primaries provides exceptional fuel metering & atomisation, a must for good economy.
Not a bad idea at all. Never once in my mopar mind have I thought about using a Thermoquad for economy but I can see how the small primaries would benefit very well. The big secondaries would help for passing situations as well
 

toolmanmike

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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.
Original point type distributors can easily converted to electronic ignition with a Pertronix kit. You could do that with a used or new replacement distributor. There are Mopar Electronic ignition kits available but the quality if the electronics seem to be a bit iffy lately.
 

gagembassett

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I've been reading up on intake manifolds and a lot of guys say that the edelbrock performer isn't much of then the factory intake, is the weiand action plus any better?
I run the action plus on my 360 in my D150. Seems to be a really good and torquey intake. That or the stealth may be a good option.
 

gagembassett

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It’s about equal. Build dependent.

Factory dual plane, Edelbrock Performer & the SP2P for mileage builds.

Any dual plane except the SP2P or the Offenhauser dual port.

The thing here on a mileage build is beating the factory intake in the low rpm range. The SP2P intake would be a disaster for a performance intake. Though it was never built for performance. It was introduced during the gas crunch days.

I had a coworker tell me it was a good help in his van. It is possible but more likely improbable to find a two barrel SP2P.
Crazy hard to find they are.
The one below is a picture gleamed from the web.
AKA - Not mine.

View attachment 1716014565

The below standard Chrysler 4bbl Thermoquad intake is all you really need for a mild performance build or a mileage master searching intake. For its design, it’s hard to beat.

View attachment 1716014564
Not long ago a 2 barrel version was for sale in the town over from me for $100, didn't realize it was worth anything, should have jumped on it. I would think those runners are better for the street even compared to the 4 barrel due to the 2 barrel base plate but maybe I'm just over analyzing that?
 

mgoblue9798

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If it has the original "Lean Burn" ignition get rid of that. Just a Mopar electronic or even a Pertronix in a old point type distributor.

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.
 
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