Big Power, Small Dollars

Make Big HP For Little Money

Steve Warner Sep 1, 1998 0 Comment(s)

Step By Step

This basically stock production 468-inch big-block equipped with a cast crankshaft, stock rods, and 8.5:1 forged TRW pistons with the addition of a 15 percent over- driven Weiand 8-71 supercharger made close to 700 hp. Accomplished with 92-octane pump gas and 26 degrees of total timing, this engine installed in the right car could do some serious quarter-mile damage.

Internally this Duttweiler-built 468 big-block is essentially stock. But it does run a Comp Cams CB-280AH-14 hydraulic tappet camshaft that specs out at 232 and 237 degrees duration at 0.050-inch lift with valve lift at 0.547-inch intake and exhaust, set on a 114-degree lobe separation.

Production cast-iron cylinder heads were used. The only difference over stock is the intake valve diameter, which was opened up from 2.19 inches to 2.250 inches to help bring more air into the combustion chamber. Would this engine have made more power with square port heads? Maybe, but who can argue with 694 ponies and an overdriven 8-71 supercharger screamin’ at you?

Even Manley factory-style long-slot rocker arms were incorporated into our 700hp big-block. Comp Cams supplied the valve springs, locks, and retainers as well. Manley guideplates keep the valves in proper alignment.

With the addition of a Weiand 8-71 ’huffer, you’ll get an additional 40-50 percent gain in power. A big-block should make roughly 1.1 hp per cubic inch, give or take a few ponies. So on just the motor alone, our engine should make in the neighborhood of 480-500 hp. Our 620- and 694-blown hp figures were right on track.

The beauty of the Weiand 8-71 supercharger is that swapping the pulleys from the top to the bottom makes the blower either under- or overdriven. In this case, Duttweiler ran the engine both 15 percent under- and overdriven. The 468 made the most power with it overdriven, but this puts more strain on a stock bottom end. Underdriven, the supercharger made less than 10 pounds of boost and still made roughly 620 hp and gobs of torque in this configuration.

A MSD ignition consisting of a Pro Billet distributor and coil helped light the 92-octane pump gas, with total timing set at 26 degrees for each test.

One of the hardest parts about running dual carbs is getting the linkage adjusted properly. Weiand offers complete dual-carb linkage assemblies that are designed to work in conjunction with both superchargers and dual-quad Hi-ram manifolds.

How many ways do you know to make 700 hp? Nitrous oxide is obvious, but that puts severe limitations on the engine and you’d have to run the snot out of it to generate huge horsepower numbers. However, there is another way. Ken Duttweiler built a simple big-block and bolted on a supercharger. With a 468ci Rat and a Weiand 8-71, Duttlweiler made 700 hp without really trying. Let’s see how he did it.

The Foundation

Making this kind of power requires a few things. Big cubes, a big supercharger, and big carburetion. The foundation for our success is a very basic 0.030-over 454 big-block equipped with iron oval port heads, a no-frills Comp Cams flat, tappet blower grind cam, and a pair of 850-cfm Holley carbs. When it was all bolted together, the Rat made 694 ponies. The long-block consists of nothing exotic, and in fact, it could easily be duplicated for about $2,000, assuming you have the block, crank, and rods. Minus the supercharger, this engine should produce roughly 1.1 hp per cubic inch, which equates to an estimated 500 hp. Bolt on an inexpensive Roots-style Weiand supercharger—available from numerous mail-order parts houses for roughly $2,400—and output should rise an additional 40-50 percent.

This engine was rebuilt with a stock cast crank, factory 3/8-inch connecting rods upgraded with ARP rod bolts for added strength, and 8.5:1 forged TRW blower pistons. It has a Comp Cams CB-280AH-14 hydraulic blower-grind camshaft that specs out at 232 and 237 degrees duration at 0.050-inch lift with valve lift at 0.547-inch intake and exhaust, respectively—all set on a 114-degree lobe separation—as well as Comp’s lifters, push rods, springs, and retainers. Typically, the lobe separation for most Comp Cams components is 110 degrees.

Because this grind is specially designed for superchargers, you will have less air bleed-off. The only things slightly out of the norm on the stock oval port cylinder heads are that the valves were replaced with Manley pieces, the intake was opened up from 2.19 inches to 2.250 inches, while the exhaust remained stock at 1.88 inches. Stock replacement long-slot rocker arms from Manley were also used.

To the top end, Duttweiler bolted on a Weiand 8-71 supercharger and a pair of 850-cfm Holley double-pumper carbs. The interesting part of the story is that the Weiand intake manifold was designed to fit both rectangular port and oval port cylinder heads. You might think the engine would lose a lot of power due to the mismatched ports, bu this was not the case with a budget effort, and that’s what the customer had to work with.

Overdriven Vs. Underdriven

To get 700 ponies, Duttweiler relied on a 15 percent overdriven pulley setup, which increases the strain on the bottom end. Another byproduct of a supercharger setup is heat. As air is forced into the cylinder bore, it compresses, and automatically heats up. This happens regardless of whether the supercharger is over- or underdriven, but more heat will be present in an overdriven system. And as everyone knows, heat is an engine’s worst enemy.

An interesting thing happened when Duttweiler swapped the pulleys around and made the blower 15 percent underdriven: the power only dropped 75 ponies, to roughly 620. But an underdriven system will live forever in a daily-driven street machine. As an underdriven kit, the 8-71 supercharger will make around 9 pounds of boost on a 454ci big-block, which is more than enough for a street car.

A key to an underdrive system is not so much the peak horsepower figures generated—in this case 619 at 6,000 rpm— but the staggering torque figures we achieved, perfect for a street-driven car. With this engine making only 2 pounds of boost, torque was an amazing 488 ft-lb at 2,000 rpm. By the time the engine hit 2,500 rpm, torque was up an additional 23 ft-lb to 511. Bolt this 468 big-block and the Weiand 8-71 supercharger with its underdriven pulley at 15 percent in your ’68 Camaro, and the car will fry its hides all day long.

And, being underdriven will significantly increase the engine’s longevity, because the engine won’t have to work as hard, and the boost isn’t as extreme as in its overdriven form. This translates into a healthier bottom end, which will perform adequately in a daily-driven street machine.

Carburetion

This engine was equipped with dual 850-cfm Holley double pumpers. Is this overcarburated? Duttweiler, whose dyno was used to generate our horsepower and torque figures, doesn’t think so. His experience has taught him that you can’t overcarb an 8-71 Roots-style supercharger, because he has found that both the 6-71 and 8-71 blowers need an unrestricted inlet side to really work well. To make this happen, larger than normal carburetors do the job. Could you get away with a single 850-cfm or even dual 750-cfm carburetors? Maybe, but Duttweiler knew that in this case, bigger is better. He has experimented with different carburetor sizes and determined this one to be the best and most powerful for the given application.

It just goes to prove that despite all common logic, which dictates the need for a truly built bottom end to run an 8-71 supercharger, it just isn’t necessary. You can have a basically stone-stock engine and generate incredible numbers by supercharging. Instantaneous power is available all the time, which is something everybody wants. Yes, nitrous may work wonders and is comparatively cheaper than a supercharger setup, but blowers are also just plain cool. If 600-700 hp tickles your fancy, this may be the powerful answer you have been waiting for.

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