OK lets have some discussion, I been slowly gathering parts for the 92 dakota 318 auto truck and the time for much improved MPG is here, I have an a-500 to swap in place of the 518 and am preparing some heads to throw my suite of mods at but really wish I could get more compression while still keeping the flat tops.

Cylinder head mods are going to be opening the intake valve seat to match the size of the valve as the seat diameter is much smaller, then run as sharp of valve seat angles as I can get on the intake while mirror polishing the ex valve to reject heat. I have found nice gains just opening the port at the PR pinch especially on the PR side because the fuel sprays there instead of the back of the valve and opening it up allows more to hit the valve where it belongs. Also I will be running ferd yellow 4 hole infectors. Top it all off with about .030 head milling and I just might try the "singh grooves" this time.

I will zero deck the block again as I have done in the past and run a .028 head gasket but I still am only going to have just under 11 to 1... I would really like to try at least 12 to 1 and retard the cam timing to bleed off some of the compression and let the cylinder pressure work on the crank a little longer before opening the ex valve. I really don't want a dome screwing up the flame front... maybe I should build some heat stoves to suck hot air off the exhaust manifolds?

When I did this basic engine in a 1/2 ton it would not ping with nearly 11 to 1 on 87 octane, it actually seemed more octane tolerant than it did stock. It gained some MPG from that but really wanted to try more compression but could not easily figure that out... that truck benefited from slowing down the RPM by installing 265-65-20 tires (stock had 245-75-16 tires and 3.55 gears) . Recently I was going to put some 2.76s in this dakota that also has 3.55s but much shorter 235-75-15 tires but when I pulled the gears out of storage they were rusted beyond usable... I am looking for another nice 2.76 or maybe 2.94 for the 8.25.

I will not make the bed unusable so no tonneau cover. I will not switch wheels and tires as I drive on dirt roads and can't have rubberband tires getting holes in them and bending wheels.

I have thought about finding some slightly smaller injectors and unplugging the O2 to make it run leaner but I know that could be a crapshoot. I read once upon a time about a wideband A/F sensor someone sells that will send a false o2 signal signal to the computer to change the ratio to whatever you set it at, anyone know who sold such a thing? How would that work if I wanted run 16 to 1 or something at cruise but normal A/F 12.5 or so ratio at WOT?

Anything else I am missing (besides EGR, still not buying that)?

You know, I was reading your super mileage 273 thread earlier today.

Since your 92 is OBD1 you might consider replacing the stock computer with a megasquirt unit. Then you can control the AF ratio, timing, etc to your hearts content.

How hard that would be, I do not know.

Unfortunately for me I can grasp physical/mechanical stuff pretty well but I really struggle with electronics, megasquirt hurts my head just reading about people trying to get it working.

I would really like a TBI holley style injection and eddy RPM intake to give the fuel longer to evaporate but that would be tough learning curve for an old brain.

Might want to upgrade to 96+ sequential injection, More efficient and you can get "caned tunes" for it.

Perhaps it should be a Super-Duper 273 ?

The dual sparkplugs of a 5.7 V8 are such an advantage that engine should be the starting point.

(Since even the late dual sparkplug 4.7 have bad reputations I will not consider those.)

An air to fuel ratio of more than 20, perhaps even 25
can gain a lot,
and you “probably” need fuel injection to keep all 8 cylinders even.

Dodge Ram, or maybe Dodge Magnum station wagon?

Better aero of Magnum would help a lot.

Couple things as I have actually driven and modded a 1992 ext cab long bed dakota for mileage. Combo was 5.2 518 8 1/4 with 3.55 gears.

I did not do internal engine mods though.

A vinyl roll up soft tonneau cover picked up over 1/2 mpg on the interstate.

Electric fan setup was worth a little.

31"x 10.5x 15 tires helped trim rpms and upped fuel mileage. Better choices than those for mileage purposes out there though.

Mopar performance midlength headers and y pipe with a magnaflow muffler.

Used the yellow Ford injectors as well.

I could knock down 20mpg at 75 to 80mph on I 20 between Atlanta and Birmingham. Made the trip at least once per week for over a year.

As far as compression is it the lack of valve cutouts in the piston tops or the shallowness of the combustion chamber that is limiting you? KB167 would help with the former.

KB piston would also help bump the compression a little with the higher top ring land.

The magnum head chamber is very efficient when set up with quench and doesn't need the help of a dual plug deal like the hemi chamber does to get a complete burn.

I have the Dakota, use it a lot, it won't sell for much here (2wd) and it would be much harder to set engines and things in the bed when I go to the junk yard, machine shop and such...

I do have an eagle 5.7 I could swap some early 5.7 pistons in for a big compression bump, they are slightly taller and have a bigger dome that should not interfere with flame travel...I would love to have a hemi in it, I just think it would be a much bigger project than I want to do. It would require me to build motor mounts (don't know how) build headers maybe/probably (don't know how) building a wiring harness (could do it but I hate electrical) then I got to figure out how to get tach to work, CEL, kickdown...

I would also think a 273 would be better suited to this project but again I would have to build motor mounts and a crank sensor mount, buy a block, run a flat tappet cam or spend a pile on retro roller lifters if they are even currently available or run a flat tappet (not the end of the world) compression would be even harder to increase...

The question of compression limit in the 318 magnum is when you mill the heads much more than .030 you will end up with the valve poking below the surface and after about .060 you are gonna start getting too close to the seat it's elf. Also poking it below the surface means valve notches in the pistons witch gives the fuel and air a small place to hide from burning quickly. If I do this I will notch my stock pistons only as much as I absolutely have to for valve clearance, the valve notch in the kb167 (I ran them in the first MPG 318) is huge, nice for a big cam but will negate the compression I am after by milling it so much in the first place. I suppose I could turn the diameter of the valve down to match the seat instead of opening the seat to the valve... then I could probably safely mill them to .060, anyone know what size the chamber would be on a magnum if milled .060? Assuming I can get it down to 58 CC and .028 quench would only give me about 11 to 1 witch is pretty good in a normal build but I really want it very high so I can retard the cam to bleed pressure and take advantage of a dramatically increased expansion ratio.

What about improving the transmission? Roller bearings instead of thrust washers? Better torque converter? Have you given thought to a custom ground cam?

Missed part one someplace...maybe this stuff was covered in part one...maybe not.

Anyway, look at what manufacturers are doing today to improve MPG. Fuel injection is obvious, the 92 Dak should have it. Leave the O2 sensor, let the computer control the fuel, it will do a better job of controlling fuel use at all RPM ranges than you could do. Low tension piston rings. Look at any gen3 hemi or LS engine with over 100K, you can sometimes still see cross hatch in the cylinders. That's low ring tension and fuel injection with no fuel wash. Look at eliminating other friction in the engine; roller cam/lifters/rockers. Let the engine breathe, nice big cold air intake. Free flowing exhaust includes headers.

You mention not looking at tires. While you don't want/need rubber band tires, you do need an smooth, even tread pattern, the big, knobby, mudder tires will kill MPG. With the trans, A-500 with lock-up converter and a reasonable rear gear ratio. Might have a lot of takers on that 518 trans you're taking out...might fund other things.

Think about driving habits. Using AC is better than having windows down. Using no AC and windows up is best. Trim the fat on the truck, low weight will help the cause. Fiberglass hood, bumpers, remove the tailgate for a net. Try to trim 200-400lbs from the truck. Funny how some of the MPG improvements are also things done on a race car.

Anybody see the video on youtube where the guy put a lawn lower carb on a 302/4 speed Maverick, he got 40+ mpg.

I saw that lawn mower carb 302, it is basically acting like a governor to keep from making any power (burning fuel). I also thought about something like that and how it could maybe tolerate a very high compression ratio based on the fact it is never filling the cylinders so it won't build as much cylinder pressure, then it could reap the benefits of a very high expansion ratio.

Are the aluminum Magnum Mopar Performance sold cylinder heads too rare to find?

Seems like I remember Larry Shepard writing they were “about” 52 cc combustion chambers and the deck could be milled a lot.

Didn’t Ebogger find some aluminum MP Magnum cyl heads for the Magnum 5.9 V8 he transplanted into a v6 Dakota?

Long ago we had a Mopars thread about whether aluminum heads
affected either max hp or max bsfc,
my reading of what reliable data there was led to concluding no measurable differences.

Mazda’s 14 to 1 engine used aluminum heads.

On a 5.2 Magnum I would stay below 12.7 static cr

Are there any production 4” inch steel pistons out there for industrial engines,
like natural gas or 2 stroke heavy bunker oil?

I toyed with this idea for a long time maybe using a flattop LS1 Piston with probably an maybe an offset ground crank and 2" rod journals and the Late 302 heads and a ported SP2P (dual plane with isolated near equal length runners) intake with a tremec. Small tube shorty headers and a single 3" exhaust with a flowmaster Y pipe. Late model roller block probably a reground stock cam for more lift.

With the right gear in a semi aerodynamic car like a late 80's Chrysler Conquest (easy v8 swap my buddy has one) I was going to shoot for easy 30's on the highway. Build a broad torque curve with decent power and high manifold vacuum at cruise speed for efficient burn.

I had a 94 Firehawk LT1 that ran in the 13's stock and would cruise on the highway at 70 MPH barely ticking over 1700 RPM and 31 MPG.

https://bringatrailer.com/listing/1980-volkswagen-rabbit/

Took my drivers test in one of these. On any serious hill it struggled to do 30-45mph. The engine had so much blow by dad ran a hose to the rear bumper to keep the oil from undercoating the car. People didn't tailgait for long... they passed or dropped back. That thing worn out got 40mpg. Lawnmower carb Maverick and diesel rabbit would be compelling drag race. Car and Driver says the VW 0-60 was 21.3sec with a 22.2sec 1/4 mile.

Our family had one of those and my youngest brother made 800 mile round trips in “Smokey”
to mining school in Rolla, MO
routinely getting high 30s and low 40s MPG.

That is also the VW diesel engine that the EPA lab in Research Triangle Park NC
converted to spark ignition and ran on methanol without changing the compression ratio,
as described in their very educational late 1990s scientific paper.
Diesel cycle and Otto cycle energy efficiency was within 1% of each other.

That's very interesting. If you have any links to those tests I'd love to read them. Thank you

Yes I would love to find a pair of the aluminum magnums or eddelbrocks or heck even one of the iron EQ, R/T, RHS... to use as they all have a much larger pushrod pinch that keeps the fuel injector from spraying on the side of the port. I can't find my old notes but I do seem to remember they all had smaller chambers than the stock head, even the chinese crap has a smaller chamber but even worse PR pinch. I just can't find any and when I do find them they are very expensive.

This tread got me thinking about my 65 Sat with the 273. This might be a fuel efficient car to drive. Think so? Can any aluminum intake fit this engine (with a little work)? I have an SP2P thing.

Not a 273 expert but if I recall correctly the intake bolt angle is different on those somehow. The sp2p could likely be made to work enlarging or slotting the bolt holes on the intake though.

Is the car currently running? If so what kind of mileage are you getting now?

Yes I think this could be a good car for highway fuel mileage depending upon the rest of the combo. 25mpg should be within reach with possibly slightly more.

I have an sp2p for the 440 I am building for my RV. I'll be doing some testing with it along with a stock 440 thermoquad intake, stock 413 intake with 450 holley, and possibly a performer 440 with a thermoquad. When you only get 6-8 mpg even just a small increase can make a big difference.