Vannin' Home Forums Dodge Performance (Dodge) tweaking a 318 for better mileage....

so i picked up a '69 A100 that was someones not-quite finished project. it had a brand new 318 crate engine. ... i gave the carb a good cleaning, actually got rid of the 3.90 something rear end for a 3.55, put in a pertonix electronic ignition trigger- replaces just the points- and got the timing to 35BTDC at full mechanical advance. Staying under 65, going down the highway- 10 mpg. This aint right. Did some reading- got a cam w/ some lift & duration, currently being installed, and a 2150 motocraft 2bbl w/ 20% larger venturis. I put dual exhaust in it already, 2 long cherrybombs keep it quiet. So, ill be interested to see how greater breathing- greater efficiency effects my mileage. i need to snag a couple neighbors to help me lift the radiator/doghouse nose assembly up & over so i can get to the timing cover- the radiator got a scvant inch of clearance from the hungry fan blades. im a gearhead and like tech boards. my last van was a 80 econoline w/ the 300 six. Cal smog legal it got 12-13 MPG. a bunch of suppoasedly criminal mods later, i had a ton more power and was getting 17MPG up.

Don’t expect a miracle but with the size of that van, it should be a good combo. Some say if you go with a 4 bbl, and take it easy, especially at cruising speed, you’re using less fuel since the primaries are smaller than a 2bbl. That being said, I have smog era 318 with exhaust, and everything else is stock, including the e control carb, 3.21 gears and get about 13-14 in a fully loaded lwb Ram van

318 in my fuel injected 94 gets 10mpg. I've just learned to live with it- it's probably my fault for many reasons though... Bigger tires, 3.90 gears, 360 PCM, loving to hear my exhaust note...

The carburetor mixture adjustments on these engines were aimed at smog, and at preventing the engines from burning up in hilly terrain by running excessively lean. Running rich cools them down. What makes the bean counters eyeballing warranty claims happy, doesn't necessarily make the van owners all that happy...

I installed instrumentation on my 318 and it's exhaust system, then tested it while driving in various conditions. I found that even with the very latest updates to the dealers service info on timing and carburetor adjustments , the engine was running excessively rich, all the time. It was far happier being leaned out quite a bit. The specified 14.7:1 AFR was definitely not its happy place... Fortunately I live where there are no emissions tests. I found AFR settings around 15.7-16.0 worked the best overall. I may have higher NO than a smog state would allow, but the HCs vanished.

Also, I found that the choke mixture adjustment detailed in the service manual was specified so insanely rich (the measured AFR was richer than 9:1) that the engine was loping, actually close to stumbling. And once started, it produced a lot of smelly, dark smoke during warmup. The engine started far easier and ran far smoother, with no tendency to stall, and with no smelly sooty exhaust during warm up, with a considerably leaner setting, out closer to 11:1. It's easy to partially manually simulate this particular test without the instrumentation I used; simply start the cold engine and move the choke plate by hand, opening and closing it gradually to determine its positions effect on how the engine is performing.

Also make sure the heat riser is functioning normally, and that you use the correct temperature thermostat; they can have a profound impact on fuel economy.

I’m gonna go with a spread bore intake and carb. My goal is 20mpg.

Modern American v8 SUVs with LS engines don’t even get 20mpg

20 MPG does seem to be extraordinarily unlikely from an LA-318 in a van on the highway.

I did once get 21.5 mpg across a ~ 200 mile section of I-10 in Arizona, but had steady 35mph tailwinds with 50mph gusts, driving 65 to 70mph. It was bizarrely quiet.

I recently have tried some sparkplugs with the same heatrange as the champion rn12yc spec'd for this engine, but they have an extended reach.

I Have not yet gotten back on the highway, to drive back to the other coastline, to see if they improve mileage, but the engine idles smoother hot and cold and the throttle response is noticeably improved. I thought it might just be placebo effect, a smoother idle when cold, but my old plugs were still in excellent condition, and the hot idle smoothness and throttle response was much better when I last drove it.
Been driving this same van 20 years come July.
I can tell.

NGK 3459 ZFR5N V-Power Spark Plug.

https://www.ngk.com/ngk-3459-zfr5n-v-power-spark-plug

These were recommended to me by Daniel Stern, the Automotive lighting expert. He had a 1989 D250 truck with a 318 TBI. Said he also used fuel injectors for the smaller 3.9 v6 and used a custom made fuel pressure regulator at 21PSI instead of the stock 15.

I'll soon be driving 2500 miles in a few days. The trip here to SW Florida, with mostly favorable winds, I averaged 15.7mpg. Best 16.67 mpg, worst 14.01mpg.

1989 b250 318 TBI with LT 30x9.5x15 AT tires( speedo reads dead nuts accurate with GPS and radar, reads nearly 4mph fast @61mph with stock size LT 235/75/15) and 3.55:1 differential.

The 235's inflate the mpgs, falsely, as the odometer is counting 65 miles when only ~61 have been traversed.

My Next tires will not be all terrain tires, but I want to keep the 30x9.5x15 size for the accurate speedometer/Odometer, and the slightly larger size looks better as well, in my opinion.

Getting to 20mpg is going to require slower speeds and some aerodynamic tweaks in addition to whatever can be done to make the engine/drivetrain run more efficiently, and keeping internal weight to a minimum.

Try some Schaeffers 293 in the diff, if it is due.

https://www.schaefferoil.com/documents/180-2937590-td.pdf

I've also found Pennzoil Platinum SN+ 10w-30 to be the quietest oil I have used in my 318.

On my 78 3\4 ton 318 I put a Holly Economaster carb on and did the "plug this tube and that tube" on the engine and it would still perform well and yet got 19 miles to the gallon. Don't know if they still make that carb or not.

Not sure about mileage, but my 5.2 TBI is happier, after I went into my engine bay on the 88 B250. Put everything back together with the stock configuration operating the stock air cleaner air door at 100 degrees. Thank you Sir.

Running Roy Purple 10/30, after freeing a sticky lifter, using the Catfish recommended drain a quart, put in a quart of Tranny fluid,,drain, and refill with Quality oil.
Thank You Sir! Quiet as a Mouse.

The 5.2 A500 setup gives you a decent freeway cruise. Not sure what the rear end gear is, but I know it's not Posi.
I like the 5.9 Port injection, A518 for moving the 1 ton. Geared well for the application. 94 Xplorer 230
14 mpg, less pulling the boat, which it will do.

Any smallblick V8 should give you at least 15 mpg, IMO. If you can enjoy driving the V8 and achieve 15mpg? In a Van?
Thanks again for the help.. High Fives all around!!