Hot VWs - February 2008 - Project Mileage Motor - Part 12
More tests with CB's Quick Tune EFI
BY BRUCE SIMURDA
Our Project Mileage Motor series began way back in the November 2006 issue of Hot VWs, when we set a goal of obtaining 40 miles-per-gallon in a stock trim, street-driven VW Beetle. The engine we designed to achieve this goal was a 1745cc with stock 85.5mm pistons and a stroker 76mm counterweighted crank-shaft. The little mill went together inside a stock VW magnesium case, with lightweight CB Super Race H-beam rods and Cheater Cam running straight-cut timing gears. Up top, a set of Mexican fuel-injected dual-port heads were chosen, due to their small 33mm intake valves. Before assembly, they were "flapped" clean, but no head work performed to increase flow. This combination was topped off with a set of dual Weber 40 ICT (single-barrel) carbs, Bosch mechanical advance distributor, and trick merged 1-3/8-inch header system. On the dyno at Jack Sacchette's JayCee Enterprises the engine stunned even us, producing a maximum of 92.5 horsepower at 5,000 rpm, and 120.8 ft.-lbs. of torque at 2,500 rpm! While our goal was mileage, we knew it would also be a blast to drive.
Since that time the engine has been installed in a stock trim 1972 Super Beetle, and had a freeway flyer gearbox added to maximize the engine's great torque curve. To date, our best freeway mileage had been 38.46mpg, which we achieved in the October 2007 issue while testing the unique Jet-A-Vator from Gene Berg Enterprises, which was placed between our Weber carbs and their manifolds to act as a restrictor/fuel atomizer/reversion plate. In a nutshell, it worked great for improving mileage, although performance suffered.
In our last installment of the Mileage Motor series, the December 2007 issue, we made a big change to the engine by installing CB Performance's Quick Tune Electronic Fuel Injection system. While not really designed for obtaining maximum mileage from an engine (it has 48mm throttle bodies!), its adjustability makes it a great candidate to supply the optimum air/fuel ratios at our 65mpg test cruising speed, and provided an impressive 36.13mpg while adding a big boost to performance
This month, we're testing a few more tuning mods, which is easy to do with the Quick Tune EFI, as both ignition timing and air/fuel mixture are easily adjusted via laptop, using CB's own "Dashboard" software. By simply changing the setting on your computer screen, it is instantly modified in the fuel injection's Electronic Management System (EMS, or brain). Altered programs can then be downloaded and stored in your computer for future use.
In the December issue we attained a best mileage reading of 36.13mpg, and best performance of 16.05/81.8mph using the original program settings supplied by CB Performance. So this month we went back to that original program, and made a few modifications. First, at full throttle we dropped the timing from 32° to 29° and leaned the air/fuel ratio from 12.8:1 to 13:1, and at midrange we dropped the timing from 36° to 32°, and richened the mixture from 15:1 to 14:1. The change provided our best time in the 1/4-mile test to date, with a 15.63 second e.t. at 86.6mph! The mileage tests were not so favorable, however, as the engine didn't seem to respond well and we only netted 33.59mpg. Happy with the top end performance, we left those settings alone, and for the next three tests concentrated on mileage only. First we changed the air/fuel ratio back to 15:1, which netted a better 34.1 mpg, but still off our fuel ignition timing to 38°, and were rewarded with a new best of 36.56mpg - not bad, considering the great performance of this engine. Thinking we were heading in the right direction with the timing, we then changed the fuel/air mixture to 14:1, but dropped our mileage as well, to 34.77mpg. Obviously, the proper combination of both air/fuel ratio and ignition timing is everything.
At this point in the project we are very happy with the results - even though we have yet to reach our stated goal of 40 miles-per-gallon at 65mph. But who can complain with a 1972 Super that gets over 36mpg and can run the 1/4-mile in mid-15s at 86mph? It is an absolute pleasure to drive, with smooth powerband, fantastic torque, and driveability more like a modern car. Of course, we'll be doing more tests in the coming months, and will keep you updated with Project Mileage Motor's progress.