Hot VWs - August 2007 - Project Mileage Motor - Part 8
Installing a 'Freeway Flyer' Gearbox






Project Mileage Motor
Part 8: Installing a "Freeway Flyer" Gearbox

BY BRUCE SIMURDA

This month, we're adding something that actually has nothing to do with our Project Mileage Motor, but everything to do about the mileage that it gets - a new gearbox. You see, with the fantastic low-end torque this new engine is now producing (120.8 ft.-lbs. @ 2,500 rpm, as seen in the March 2007 issue), there is no need to buzz the engine as fast as the stock gearing in our 1972 gearbox does in order to maintain highway speeds. Our tests showed that with the stock 4.125:1 ring and pinion and 0.88:1 fourth gear, our engine was turning 3,200 rpm at 65 mph. Some earlier transaxles, with the 4.375:1 ring and pinion, will be revving even higher! Of course, because cooling is dependant upon engine speed you cannot turn the engine too slow either. But with high output of the late model doghouse fan we used, the engine's mild compression (8.25:1), and the fact that the engine is not working as hard as a stocker to maintain freeway speeds, we estimate that a drop of about 300-400 rpm at 65mph should not adversely affect engine temps - but could have a big effect on mileage.

But before chaning anything, we installed a few gauges into our test '72 and went out for a test drive. With an outside temperature of 84°, we took all measurements (except idle oil pressure) midway through an 80-mile test drive, at 65 mph. As stated earlier, at 65 mph our 1745cc engine was turning 3,200rpm, with an oil temperature of 195°, head temp of 260°, and oil pressure of 48 psi. Immediately upon stopping, our oil pressure dropped to 20 psi. This test run netted 29.9 miles-per-gallon. Another test we ran was more performance oriented - as we wanted to see just how strong this engine would perform on the race track. For these tests we installed a Gtech Pro SS Performance Meter (www.gtechpro.com), which uses some military technology to determine a car's 0-60 mph and 1/4-mile times, along with maximum G-forces during a test run. You simply attach the Gtech meter to your car, plug it in, and it does the rest! We should not that the performance runs were not included in the mileage tests. Averaging three runs, our stock trans netted a 0-60 mph time of 8.05 seconds, with a 1/4-mile time of 16.13 seconds at 85.2mph. Maximum launch G-force attained during these test runs was .74.

With this information in hand, it was time to change the gearbox. Our stock 1972 transaxle was equipped with a 3.80 1st gear, 2.06 2nd, 1.26 3rd, and a 0.88 4th. Our new gearbox, which was a 1973 model with single side cover, featured the same first through fourth gears, but a lower 3.875:1 ring and pinion. In stock configuration, the '73 box would have a 0.93 fourth gear with the 3.875s, but 4th was changed to the 0.88 4th years ago when it was converted to "freeway flyer" gearing. The only factory gearbox that came with the gearing in this new gearbox was the 1971 - 1974 Karmann Ghia. We should also mention that this gearbox is not new, and was not built specifically for this project. It has been used in a staffer's other Bug in the past, but for the last several years has been resting in the Hot VWs back room. For those interested in this style of gearbox, several Hot VWs advertisers offer a "Freeway Flyer" box for both swingaxle and IRS application with the same gearing used here.

Before installation, we contacted AC Industries and So. Cal. Impors, both in Long Beach, California, for a few items that we felt needed replacing - while we were in the area. These included new engine/trans mounted, CV-joint/axle assemblies, rear wheel bearings and seals, new "bowden tube," and nose cone-to-body seal. We also drained the gearbox and filled it with 75W-90 Royal Purple synthetic oil, the same lubricant used in the last test with the original trans.

The processes on our IRS equipped '72 included pulling the Mileage Motor and stock gearbox, removing the CV/axle assemblies, swapping the starter motor and throw-out bearing from the old to new trans, and then bolting the new motor/trans mounts to the new gearbox. Before installing the mileage trans, all new inner and outer axle bearings were lubed with a quality synthetic wheel bearing grease before being installed with new seals. The gearbox was then connected, and the new AC Industries CV/axle assemblies bolted in using a 6mm "star" wrench. It should be noted that these axle assemblies come with the inside of the CV (boot side) pre-greased, so it is only necessary to grease the outside of each CV-joint. This is always a dirty, messy job, but the special grease applicators supplied by AC makes the job a lot cleaner.

With the engine back in place, we were ready to do a little testing. Right away we could feel a difference in how the car drove, as first gear was now a much longer pull, and more "usable" than before. As expected, performance dropped somewhat with the new gearing, with an average 0-60 mph time of 9.17, 1/4 mile time of 16.57 @ 80.60 mph and a maximum G-force of .71. With the outside air temp a little cooler at 80°, we hit our 80-mile test run. On the freeway, we saw a drop of 300 rpm at 65 mph, as our tach was now pointing to 2,900 rpm. This rpm drop was quite noticeable as we drove, as noise level dropped, and keeping up with traffic required no more than a slight pressing on the throttle. At midpoint on our drive, oil temp showed a slight drop at 185°, but head temp remained the same as in our previous test at 260°. Oil pressure was still solid at 49 psi @ 65mph, and dropped to 20 psi at idle.

But what we were looking for most what was going to happen to our mileage, and we were happy to see a healthy 9.03% increase to 32,6 mpg - we had passed the 30 mpg mark! With premium gasoline here in Souther California nipping at the $3.70 per gallon mark, this was a good news indeed.

Next month we'll continue our search for improved mileage with jetting and timing changes. Could 35 mpg be far away?