Project #002

Vehicle: 1975 Ford F-250 Camper special
Engine: 390

Objective: Improve/maximize efficiency

It has been over a year since I last posted. Many things did not go to plan. But now I have a new project.

The truck tows a fair sized boat and is presently getting 4 MPG. I think that can be improved to at least 8 or 12 while it is towing and perhaps even twenty when it is empty. The issue is efficiency. This means that a properly metered mixture is well atomized and evenly distributed to the cylinders in a way that keeps the fuel in suspension and is then introduced into a well designed combustion chamber with enough swirl to completely burn the air fuel mixture when it is ignited by a very reliable ignition system with a well chosen advance curve and the exhaust leaves through a nearly zero back pressure exhaust system.



I see this job having many phases. There are a few that may overlap.

Phase 1
Eliminate all exhaust leaks.

The Ford 390 is notorious for its manifold gaskets failing. I've throw down the gauntlet and bought some Remflex exhaust manifold gaskets. I have not installed them yet but I have heard a bunch of good things from various people in various fields. I personally had a very good experience with the company. They are located in Washington state where they make the gaskets. I called them up and spoke to a human being who actually cared whether I got what I needed. I really hope their gaskets are as good as their service.

When I do this I will need to replace the manifold bolts. The gaskets are a lot thicker and the bolts are 33 years old.

The reason this is important (besides the exhaust leak) is that I don't want to get a reading on my wide band O2 sensor that is falsely lean. This will lead me to make the mixture richer than it should be and that will hurt the MPG.

Phase 2
Make the ignition system reliable.

There are two parts to this.

First I will replace the spark plugs, plug wires, and cap and rotor. This will make that side of the ignition system solid. I will be using spiral core wires instead of the usual carbon filament type. They cost about two or three times as much but almost last forever.

Second, I am in the middle of researching ignition enhancements. Specifically the multiple spark discharge type of ignition. David Vizard says in his book "Performance With Economy" that they virtually eliminate misfires and greatly reduce the time the choke needs to spend on. This is an obvious potential economy improvement. The question is how much will it cost. This may be a later addition.

Phase 3
Tune carburetor.

I have purchased a Zeitronix wide band O2 sensor. This was not cheap but considering the features you get it's a great value (It plug into your computer and gives you simultaneous data-logging of RPM, A/F ratio, manifold pressure (vacuum in this case), exhaust gas temperature, throttle position, and a user determined input of 0 to 5 volts. I bought the additional MAP (Manifold Absolute Pressure) sensor so I can look at the screen and get a pretty good idea of what is going on. I have attempted multiple times to dive into this carb using a single wire lambda sensor but it only got me close. This setup gives me an actual air/fuel ratio. With a real A/F ratio there is no guessing. . .as long as there isn't any air getting into the exhaust system up stream and there aren't misfires sending cylinder fulls of air and unburned fuel into the exhaust (hence phases 1 and 2). I did a quick check and I found the A/F ratio was around 11:1 full throttle/full load (It shouldn't be any lower than 12:1 and in this case I'm shooting for 13:1 or 13.5:1) and it got as lean as 15:1 only for brief moments. So it looks like there are some sizable improvements to be made.

That covers the immediate future. At some later date I will delve into the following

Phase 4
Design and install new exhaust system.

Phase 5
Major work
- Port heads (for efficiency - see here)
- Enlarge exhaust valve (perhaps)
- Address any valve shrouding
- CC Heads
- Intake with good flow and mixture distribution (Stock, modified stock, or aftermarket. Whichever looks to be the best)
- Wide LCA (Lobe Center line Angle) cam.

Phase 6
- IR intake system.

Builder