Max MPG recipe for an F150

[MechRick]

Lean does not burn valves.

As I understood it, leftover oxygen after the combustion event can extend the heat curve far enough into the exhaust cycle to burn a valve. Particularly in a carb application that doesn't have strict control of the fueling.

I've been skimming through the Microsquirt MsExtra installation instructions. There is no mention of a dual table mode, but the text mentions the load parameter can be picked up from a MAP sensor *or* a TPS, so that eliminates the need to rig a TPS on a carbed setup. Other parameters needed are RPM, vehicle speed, brake lamp switch (for lockup functions). Seems fairly straightforward.

Both my 4R70W cores are out of 2003-ish 3.8L Mustangs with the digital MLP and the weak reverse drum/clutch pack, but they will work.

 

[Frank]

I also need to address a common fallacy of lean-burn and heat. Lean does not burn valves. In-fact, lean burns cooler than stoich (Lambda 1.0 or 14.7:1 for gasoline). Lean is not hot, but burned valves are late. Late timing. The late timing allows very hot or still burning mixture when the exhaust valve opens. Bingo, burned valves, and secondary effects such as increased coolant temperatures. Ignition timing is not only critical to lean-burn efficiency, but all areas of fueling to achieve maximum conversion of fuel to energy. AERA has some interesting data around this, and FWIW, the second most common reason for burned valves and seats is consistent rich fueling.

I'm confused. Repeatedly you say lean does not burn hotter, that's contrary to every chemistry book I've seen. I know about it burning slower and timing, but gasoline is unique in this- lean is hotter, unlike other fuels. IMO discussing the tricks to make a very lean mixture work in a 50 year old truck engine is unnecessary without electronics to manipulate timing and assist with EGR. Reality is, an over lean mixture WILL and does cause an old-school engine with fixed mechanical timing to run hotter. I've experienced it many times.

 

[Bronctopia]

I'm confused. Repeatedly you say lean does not burn hotter, that's contrary to every chemistry book I've seen. I know about it burning slower and timing, but gasoline is unique in this- lean is hotter, unlike other fuels. IMO discussing the tricks to make a very lean mixture work in a 50 year old truck engine is unnecessary without electronics to manipulate timing and assist with EGR. Reality is, an over lean mixture WILL and does cause an old-school engine with fixed mechanical timing to run hotter. I've experienced it many times.

On the chemistry....
With Complete combustion, a stoichiometric mixture will produce the most enthalpy per volume (most heat per cycle).
The trick word here is Complete.
The only things contributing to heat production in a cylinder are fuel, and the oxygen in the air combining with it.
Any excess fuel, OR excess oxygen (and the quadruple quantity of nitrogen that comes with it), will only add passive mass (heat capacity) and will lower the ultimate temperature attainable.
That said....
Most gasoline engines struggle to attain complete combustion.
Field tuning a carb by screwdriver between rich stumble and lean stumble is the most common way we see this.
Missing or late ignition of the mixture means you may be generating less heat total, but at ALL the wrong times and places, like too late in the stroke to extract some as Work, and or in the exhaust ports/manifolds that we hear as lean "pop", most often on decell.

TLDR: lean makes less heat, but at all the wrong places.

 

[PSIG]

As I understood it, leftover oxygen after the combustion event can extend the heat curve far enough into the exhaust cycle to burn a valve.

+1 to previous. Examining the effects, chemistry and Voodoo aside—it's the relatively late ignition timing that extends the burn. Lean slows the burn, and correct timing prevents long burn and restores cruise efficiency by re-establishing optimal peak cylinder pressure angle (PCP). In-fact, the primary job of ignition timing is to maintain best PCP angle for most efficient conversion of fuel to energy at any Lambda or condition. Tuning finds that.

Both my 4R70W cores are out of 2003-ish 3.8L Mustangs with the digital MLP and the weak reverse drum/clutch pack, but they will work.

The 3.8L Mustang version is by far the most popular version for V8 and L6 swaps. Lots of installs for reference, and the reverse drum has not been an issue. I used USShift Q1 as MS didn't do the 4R at the time (not sure they do yet ). With only J-mods, it will handle ±450hp and ±700 ft·lb. I used the same version in my GT-40 turbo daily, stock with only J-mods and Marauder converter, without issues. I have not investigated specifically, but using trans-brake launch function continuously might be an issue for rev, as is driving on/off with the throttle or with a misfiring cylinder beating back and forth. By all means look into it, but I have seen no worrisome evidence. Let us know what you find!

 

[PSIG]

Just to cap this off by pulling the points made by others together...

Reality is, an over lean mixture WILL and does cause an old-school engine with fixed mechanical timing to run hotter. I've experienced it many times.

Yes - fixed mechanical - which will cause a retarded condition without appropriate variable vacuum advance to correct timing. For another example, this is why aircraft using 1940s and '50s technology (most even today) would lean all the way to just shy of rough-running (lean!) only under 75% power as a general rule. They did not have vacuum advance, so only 'fixed mechanical'. Indeed you are correct, and why corrected timing is required for any lean running above 75% power.

Still they are at full-lean all the way to 75% power, equivalent to most of us cruising on the expressway. So, carb tuning in cars and trucks is done similar to the tried and true method used by aircraft on every flight. Below is the leaning routine established by the AOPA, used by every pilot (including me) on every old technology engine out there, with the car/truck equivalent below it. Lean isn't "bad", but we must give the engine what it needs to burn it properly.

1. At altitude, set cruise power.​

​

2. Lean by reducing the mixture gradually until the engine runs a little rough. You may see a slight increase in rpm before the engine starts to roughen.​

​

3. Slowly enrich the mixture until the engine smooths out. This is what’s known as a “best economy” setting.​

​

4. If you need to climb, enrich the mixture before adding power if at or above 75-percent power, then lean again at your new altitude.​

​

For us an added step for our variable vacuum advance timing, to increase efficiency and remove late-burn heat:

1. Set stable max cruise speed.​

​

2. Lean the AFR gradually until the engine begins to run rough or surge (slow cyclic push-pull feeling). Ignore AFR.​

​

3. Slowly enrich the mixture until the engine smooths out. This is what’s known as a “best economy” setting. Note AFR.​

​

4. Increase vacuum advance just until maximum manifold vacuum is found. This is what's know as "lean best" timing. This is required.​

​

5. If increased power is required (hill, passing), enrich the mixture with carb power circuits and allow falling vacuum to reduce timing.​

Tada! Max economy with max power available.

 

[Bronctopia]

Just to cap this off by pulling the points made by others together...

Yes - fixed mechanical - which will cause a retarded condition without appropriate variable vacuum advance to correct timing. For another example, this is why aircraft using 1940s and '50s technology (most even today) would lean all the way to just shy of rough-running (lean!) only under 75% power as a general rule. They did not have vacuum advance, so only 'fixed mechanical'. Indeed you are correct, and why corrected timing is required for any lean running above 75% power.

Still they are at full-lean all the way to 75% power, equivalent to most of us cruising on the expressway. So, carb tuning in cars and trucks is done similar to the tried and true method used by aircraft on every flight. Below is the leaning routine established by the AOPA, used by every pilot (including me) on every old technology engine out there, with the car/truck equivalent below it. Lean isn't "bad", but we must give the engine what it needs to burn it properly.

​

For us an added step for our variable vacuum advance timing, to increase efficiency and remove late-burn heat:

1. Set stable max cruise speed.​

​

2. Lean the AFR gradually until the engine begins to run rough or surge (slow cyclic push-pull feeling). Ignore AFR.​

​

3. Slowly enrich the mixture until the engine smooths out. This is what’s known as a “best economy” setting. Note AFR.​

​

4. Increase vacuum advance just until maximum manifold vacuum is found. This is what's know as "lean best" timing. This is required.​

​

5. If increased power is required (hill, passing), enrich the mixture with carb power circuits and allow falling vacuum to reduce timing.​

Tada! Max economy with max power available.

Fun fact.
Early, Early automobiles did not have timing advance in the distributor at all
It was actually a lever on the steering wheel/column.

 

[Wesman07]

Fun fact.
Early, Early automobiles did not have timing advance in the distributor at all
It was actually a lever on the steering wheel/column.

The saying was “Start late and arrive early”. What that meant was retard the ignition to start the engine and advance it once running.

 

[PSIG]

Heh, same as today.

 

[Frank]

Fun fact.
Early, Early automobiles did not have timing advance in the distributor at all
It was actually a lever on the steering wheel/column.

More fun facts:
The electric starter motor was invented by Mr. Kettering Sr (1912? or so) after his close friend stopped to help a lady on the roadside to re-fire her car. She forgot to retard the timing lever on the steering column. The engine kicked backward when it fired and the crank handle killed the man. This is the same Mr. Kettering who's son invented the 2-cycle locomotive diesel. They were small-time engineers in Dayton, OH. Their company was Dayton Electric Company. GM snapped those guys up, and the name DELCO lives on. As does Electromotive.

 

[Lazy JW]

I also need to address a common fallacy of lean-burn and heat. Lean does not burn valves. In-fact, lean burns cooler than stoich (Lambda 1.0 or 14.7:1 for gasoline). Lean is not hot, but burned valves are late. Late timing...

Yup

On the chemistry....
With Complete combustion, a stoichiometric mixture will produce the most enthalpy per volume (most heat per cycle).
The trick word here is Complete...


TLDR: lean makes less heat, but at all the wrong places.

Yup

... Lean by reducing the mixture gradually until the engine runs a little rough. You may see a slight increase in rpm before the engine starts to roughen...

My Dad taught me this tuning procedure on chain saws more than 50 years ago; with chain installed and properly tensioned, run wide open and lean it out until it blubbers, richen it up until it blubbers, and then lean it out until it just smooths out. This provides maximum power without burning up the saw, and it will speed up just before running out of fuel, which gives you enough warning to shut it down RIGHT NOW. Those old McCulloch saws were a real bugger to start if you ran it out of gas.

Of course there is no need for a 'lean cruise' setting on a chain saw.

 

[MechRick]

Paul's recipe has been firmly filed as a solid option, but as a gedankenexperiment, let's pursue what form the EFI version might take.

When adding EFI to the recipe, the first thing that comes to mind is turbocharging. In fact, let's pretend Ford was going to create an Ecoboost truck in 1986. One form that might take is a 240 crank in a 4.9L block, EFI of course. Running the numbers, a 300 carb head with flat tops with the 3.18" stroke and some judicious relieving ends up slightly less than 8:1 compression. 5.0L forged pistons will work. Keeping boost to 6 psi (for a reason I'll share in a moment) the software dyno shows about 114 HP and 300 ft. lbs at 2000 RPM (with a small turbo) and peaks of 281 HP at 5000 and 344 ft. lbs at 4000.

With knock-sensing and the low boost it might be possible to run cheap 87 octane.

Every small turbo car I've built show a 10-20% improvement in fuel economy, the trick is not to wipe out the savings by having to run 93 octane fuel.

Is the 240 crank set up for a two-piece rear main with an oil slinger? And if so, can it be machined off for use in a one-piece block?

 

[Lazy JW]

...
I know there are hurdles such as the water outlets on the radiator...

Would it be practical to simply use two radiators and leave them connected, thus obviating the need to drain and disconnect them?

 

[MechRick]

I thought of that, but I think a simpler approach would be to put drains in both blocks, and cross one lower hose connection to the other side with metal piping. I have an air evac that allows coolant to be installed in about 30 seconds. Upper hoses are both centered, should not be an issue.

A/C will be the issue, I don't think I want to evac/recharge the system every time. The A/C compressor hangs off the left side of the engine, I would probably just leave it charged, move it to the left and have a bracket above the frame rail to bolt it to. Tough it out without A/C on the V8.

The V8 can remain carbed, if I EFI the six I can have a fuel pressure regulator set up to use the stock quick connects.

 

[Frank]

I thought of that, but I think a simpler approach would be to put drains in both blocks, and cross one lower hose connection to the other side with metal piping. I have an air evac that allows coolant to be installed in about 30 seconds. Upper hoses are both centered, should not be an issue.

A/C will be the issue, I don't think I want to evac/recharge the system every time. The A/C compressor hangs off the left side of the engine, I would probably just leave it charged, move it to the left and have a bracket above the frame rail to bolt it to. Tough it out without A/C on the V8.

Moving AC out of the way to remove an engine is not too tough, done it. Just caution not to flex the fragile connection at the evap. It seems fabricating a bracket for AC for the 8 wouldn't be unreasonable?