Saturday, December 15, 2007

Devin - H-Mod Special

Using the Panhard crankcase, roller bearing crank assembly, and rods as a base, Devin has affixed a pair of Norton "Manx" motorcycle cylinders which are topped by an overhead cam layout. To drive these cams, one per head, a notched rubber transmission belt is used. It sounds easy enough and looks quite natural when viewed in the completed shape but the whole project has been carried on in the face of "it'll never get off the ground" type of predictions. "Anybody will tell you that you can't use a rubber belt for valve timing," Devin says, "but we are doing it anyway."

The use of notched rubber power transmission belts to operate cyclic or timed mechanisms is not unique, naturally, being in constant industrial usage, but this marks the first successful automotive application to our knowledge. Advantages of the 1.5 inch wide belt of molded rubber, bonded to a continuous steel wire base, over the more conventional chain or gears, are many. Lighter in weight, therefore lower in inertia, far more likely to disintegrate slowly than to snap suddenly, and needing no lubrication nor housing, the U.S. Rubber product certainly gets the nod .. if it doesn't stretch.

Such belts have been tried on super-chargers to replace V belts, which suffer from considerable slippage, but sheared pulley keys and pins soon proved that their action is too positive. In this cam driving application the belt has proven admirably suited, although many prophesied that under severe acceleration there would be enough resiliency or backlash to foul up valve timing. But, no stretch!

A machine adaptation for the front of the cam housing on the Norton head, with its hairpin springs, eliminated the tower shaft and several gears. As she sits, a notched pulley with 28 teeth on the end of each camshaft is driven through its own belt by a 14-tooth pulley on the front end of the main shaft .. a spot formerly occupied by the generator pulley, Two idlers maintain tension. Grafting the Norton cylinders onto the Panhard case required filling the original stud holes with 1/4-inch aluminum bolts and drilling new holes to accommodate the 7/16-inch Norton studs.There is no difference in displacement as a result of the switch, inasmuch as the bore diameter of both makes is the same: 3.12 inches. The Panhard stroke of 2.94 inches produces an oversquare engine. Although the Norton barrels are somewhat larger in overall size due to the greater fin area, there is no appreciable gain in weight, inasmuch as the Panhard is cast-iron-sleeved and the Norton all lightweight alloy.

Superimposed over the stock but overstressed bottom end, we find a big-ported head, straight-through porting, monster valves... 1-27/32 inch intake and 1.75 inch exhaust. A compression ratio of 9.5 to 1, effected through the use of Norton hi-dome pistons, is about the maximum desirable for gasoline fed replacement Weber carbs on Y inlet manifolds... one for each cylinder. The flywheel has been lightened through replace-mentl Not to overlook details, Devin whittled out a duplicate in aluminum and pressed on the steel starter ring gear... saved 8 pounds and gained much acceleration.

With cams designed for cycle racing, a normal opening and closing sequence reads something like this: Intake valve opens 571/2 degrees BTC and closes 60 degrees ABC, Exhaust opens 85 degrees BBC and closes 421/2 degrees ATC. With 42 degrees spark advance this can be considered a bit radical but the best is yet to come: The cams are assembled, and lobes can be fitted onto the shaft at any degree relationship. Want to try opening the intake a couple of degrees sooner? Fine. Disassemble the cam, move the lobe a notch and put it back together! Endless possibilities.

What actual timing he will run on a different "New" engine, Devin keeps to himself. Data on the improved model is also confidential but, as one who has been permitted to view some of the actual construction, we can say that the latest crossbreed will employ FOUR overhead cams, twin ignition and fuel injection.

"What kind of a small car can a fellow buy today that can be driven to the track and stand a chance of winning," Bill asks, "and what do you have to pay for one? Almost as much as for a much bigger car. Anything in the 750cc class you have to build yourself. I've spent $75,000 developing this thing and if I had another hundred thousand I'd build a hundred push-rod Devin Panhards. I've made arrangements with the factory for components and the bugs have been worked out of my new body. I could make and sell such a car, complete, for $2,250 or $2,450 with a hardtop. You could drive it on the street every day and yet go to the track and run with the best of them. I think I've proved that." The story is familiar but the ending is yet untold. The difference in the plot as it looks from here is in the one word, "ability". Here is a man with ability. A man with a dream, true, but backed by enough persistence and know-how to go far beyond the conventional for a solution to his problems. Perhaps a financial solution will be found as well and we will be thrilled by the pants-ripping snarl of a Hock of Devin-Norton-Panhards in future races.

Mini Cooper Performance Parts & Accessories

1 comment:

Unknown said...

why is some of the right side of the text cut off in the Devin-H-Mod Special post?