Project Mileage Motor: Part 13
Advancing and Retarding cam timing

BY BRUCE SIMURDA

In the last segment of our Project Mileage Motor, which was way back in the February 2008 issue, we ran a variety of tests to see if we could improve the mileage of our 1745cc test engine with CB Performance's "Quick Tune" electronic fuel injection, which was installed in a 1972 Super Beetle in stock trim. Up to that point our best mileage had been 36.13 mpg at a steady 65mph on the highway, but with a little tweaking on the ignition timing - which was set at 38° in the midrange - we netted a best with fuel injection mileage of 36.56mpg. To date, we still have not yet achieved our project goal of 40 miles-per gallon in a stock trimmed Bug at realistic highway speeds. (Note: best to date mileage was 38.46mpg with Dual Weber ICT carbs and Berg-Jet-A-Vator in the October 2007 issue.)

This month we're going to try something completely new on our Project Mileage Motor - advancing and retarding the camshaft timing. If you have been following this series since its inception in the November 2006 issue you may remember that during assembly we used an adjustable timing gear. Well, here it is, about a year-and-a-half later, and we're ready to utilize this feature. Actually, we were a bit timid before tearing into our engine to make this adjustment, because it certainly looked like a difficult job with the engine installed in a sedan. But it proved not very difficult after all, with the toughest part of the job being the actual removal of the oil pump.

Tearing into the rear of the engine, it was neccessary to remove the rear breast plate sheet metal, and then the fan belt and pulley. The small tin behind the pulley came off next, as well as the header. At that point we removed the oil pump cover, and struggled to get the CB Performance full-flow oil pump out of the case - it was in there tight! Unfortunately, we did not have the correct oil pump puller on hand, so it was a slow process of carefully tapping and prying the pump housing out of the case - we did not want to risk damaging the seating surface. But once the pump was out, our adjustable timing gear was easily accessible.

One thing to remember when performing this modification is that the cam rotates in the opposite direction as the crankshaft. So if you are advancing it, the cam should rotate counter-clockwise in relation to the slots in the adjustable cam gear. The adjustment is made by using offset washers, placed in the correct position for the advance or retard that you are trying to achieve. For our first test, we used the 4° washer, and placed it in the advance position (cam rotated counter-clockwise). We should note that it is a good idea to loosen each cam gear bolt, remove its washer, and then replace the bolt, (but not tighten) before installing the first offset washer, to ensure that the cam does not turn beyond the slot in the cam gear. Also, be extra careful not to drop a bolt and/or washer into the case, as it will be very difficult to remove!

With the cam advanced 4°, we put it all back together and went for our standard mileage test run, using the same fuel injection program we used to get the best run in our last segment. Interestingly, we netted a respectable 36.13mpg - which was slightly less than the best of 36.56mpg we got last test with the cam ran "straight-up". Apparently, advancing the cam had a slightly negative effect on our mileage, although we did feel that the throttle response was a bit quicker.

With our curiosity peaked, we again tore into the engine, this time to see what would happen if we retarded the cam 4 degrees. Luckily, the oil pump was much easier to remove this time around, adn the entire job took only about three hours. Without touching the fuel injection's settings, we ran the mileage course, but were disappointed to net only 33.07mph. Mileage-wise, our engine certainly didn't like the retarded cam timing - but you don't always make gains while testing.

At this point the cam was adjusted back to its original best mileage "straight-up" position, as we plan to run additional tests next issue. Until then, we certainly are enjoying our time spent behind the wheel of th Project Mileage Motor Super Beetle - both when cruising the highway in search of the hard-to-achieve 40mpg, and throttling stoplight to stoplight.