[Andyman]

I think you will find that if you advance the camshaft you will hurt your fuel economy. I've tried changing valve timing on four different engines and every time the more retarded setting gave better fuel economy. Normally retarding the camshaft increases fuel economy, reduces low end torque and increases high RPM horsepower. It also makes the idle quieter. If you retard it a lot, you will lose power at all engine speeds. The four engines I used were a Ford 351C, a Porsche 2.2 flat six, a VW 1.7 four cylinder and a Chevrolet 1.8 four cylinder in a Pontiac version of the Cavalier. On the Ford and Porsche engines, I retarded the valve timing and gained fuel economy. On the VW and Chevrolet engines, I advanced the timing and lost fuel economy but gained low end torque. On the Porsche, the engine felt a little weak at low speed but it became very powerful above 4000 RPM. Its fuel economy went up from 24 to 27 MPG on the highway. The VW engine was in a Plymouth Horizon with manual transmission. Its highway mileage went down about 9 MPG when the camshaft was advanced by one tooth. It could get 44 MPG in the more retarded position. I decided to change it back. The Ford actually doubled its mileage from 9 MPG to 18 MPG after I retarded its performance camshaft by 12 degrees. It also lost power at all engine speeds. I later set it to 8 degrees retarded for some extra power when I deactivated four of the cylinders. The highway mileage with that setting was 24 MPG. I would like to have a way of adjusting the camshaft while driving. It could run retarded most of the time but go to a more advanced position for fast acceleration at low engine speeds. The Pontiac was too sluggish with the original timing. I think I advanced it by 4 degrees and reduced fuel economy about ten percent.

I tried asking a mechanic in a garage about the effect of valve timing on fuel economy and his answer was that advancing the camshaft increases torque and fuel economy. That seems to be the prevailing belief of people who want to modify engines. Experiments show that they are wrong.

If you can find a camshaft with less duration it may help you get better economy. I would not recommend increasing the valve lash by more than a couple thousanths of an inch. That causes more stress on camshaft lobes, rocker arms, valves and valve seats. They may wear out fast, especially if you use high engine speeds. If you break a valve, the damage is even worse. You could destroy a cylinder head, piston and cylinder wall.

I agree that car engines are too powerful for best fuel economy. Car engines are most efficient at about 1/3 of maximum power. If you normally use 15 HP to drive 55 MPH, a 45 HP engine would be the right choice. The displacement would be about 750 cc. Of course you would have to accept slow acceleration and hill climbing. Normal car engines usually are most efficient at about 2500 RPM and about 2/3 throttle (not WOT). Some vacuum improves fuel vaporization. If your engine runs on natural gas then it might be most efficient at wide open throttle.

It is possible to remove rocker arms from Honda engines. I tried it in my Accord to see how it runs on two cylinders. Be sure to block any oil holes in the rocker shafts where rocker arms were removed with hose clamps so you keep up the oil pressure to the other rocker arms. Deactivating half the intake valves may increase your fuel economy but deactivating exhaust valves will probably reduce power without helping fuel economy.