Our theory about the slide valve carburetion netted us a very fine batch of horsepower plus a couple of big carburetors that you can stick your foot in anytime and any place. They don't cough, hesitate or spit back...they just GO!
For a good all-around setup, it would be difficult to beat this one. When making the changeover, it is advisable to use the manual choke setup which is operated most easily by a Bowden cable.
Our final rating showed an additional 10 horsepower. The added carburetion was letting the engine really come on in the higher rpm bracket, and we were belting out a solid 115 rear wheel hp up at 4800 rpm. Translated into a 0-60 time, this amounted to a 9.4-second clocking (or close to a second off our previous time at the end of last months alterations). A trip down the quarter-mile netted 81 mph in the low 16-second bracket. One further benefit here; the gas mileage was beginning to show decline, but not as much as one might suspect as the car was still capable of consistent 18 to 2O mpg at normal cruising speeds.
With the carburetion and cam changes, the engine still had a more-than-reasonable idle at a steady 600 rpm, leading me to believe this setup could be used very nicely with the little C-4 automatic transmission.
When we had put on an additional 1000 miles or so with this setup, the urge to go to the four Honda Keihin carburetors became too strong. Having previously brazed the four flanges onto the manifold, the transition was only a matter of two or three hours work. When installing the Honda carburetors, we noticed they did not care too much for high pulsating fuel pressure (due to their small float assemblies), so a regulator was installed to limit fuel pressure to 3 pounds. This did the job very nicely. The first run-up on the dyno indicated lean mixture conditions in the medium rpm range. This was cured by removing the .028mm jets and replacing them with .042's. The main jets were subsequently enlarged to .070, and a set of adjustable needles were installed. These are available from Honda agencies. The metering rods have five notches for adjustments, and we found the "number two" notch (from the top) to be the ideal setup.
These changes seemed to bring the air-to-fuel ratio into balance, so we decided to give the little six a full blast on the dyno and see what we could get in the way of additional horsepower. I was also very interested to find out what the small carburetors would do for horsepower in the lower rpm ranges, so we took a reading at 2800 rpm and netted 75 hp at the rear wheels. At 3800 rpm we had l05 hp, and we reached the top of the ladder at 4800 rpm, with 125 hp. This proved to us that our idea on the soundness of this type carburetion was right. When you jump on the throttle with the little bears, it is just like having fuel injection. It feels like all the horsepower unloads at once. In driving the car on the road, we found we could still stabilize the idle, very nicely at around 600 rpm. As a matter of fact, the idling adjustment on these Keihin carbs proved to be something to behold. This setup came with a smoother idle than 99 percent of all the stock cars I have ever played with. We did, however, encounter flat spots in the extreme low end of the rpm range, but, after all, when playing around with 5.8 square inches of carburetion on such a small engine, one must learn to expect that all cannot be "peaches and cream." To offset the flat--spot disadvantage, the price of these units is only $25.00 each.
Exploring still further the possibility of using side-draft carburetion, we decided to check a couple of the Tillotson diaphragms used on the American Harley-Davidson motorcycles. This is a very simple, straightforward carburetor of 1 5/8-inch venturi dimensions. Testing proved this arrangement to be capable of equaling the SU's in all-out horsepower, but having more flat spots than a thief would encounter in robbing a banana factory.
The general behavior of the car in normal stop, go, and cruising ranges was a most pleasant surprise. Later tests proved this car to be capable of 84 to 85 mph in the quarter-mile. With 4:1 gearing and 27-inch rubber, 5500 rpm could be had at any time, and this is 110 mph. This performance proved more than equal to several versions of the 289 2-V and 4-V jobs that we found willing to try us on for size.
We also tried the 4:1 gearing in conjunction with the four-speed tranny, and our conclusions would be to forget this setup since it wreaks havoc with gas mileage and is certainly not conducive to good smooth road speeds at 70 mph. Instead, stay with the three--speed synchro with the 3.20 rear gear set. As for the remainder of the work, take your pick. It all proved very exciting and rewarding for us since we have always felt that true hot rodding is venturing into the unknown or unusual.
I have personally gained a tremendous respect for the latest version of the seven-main, six-cylinder engine and sometimes wish one could purchase such a Package, call it a GT Six, and add some minor heavy-duty equipment to the chassis. This combination would give a good accounting of itself when compared to many foreign sporty Jobs that cost considerably more.
So as we close our hood and roar off into the setting sun. We can only say come on and join the six-cylinder parade for more fun with less money than you ever could imagine!