700hp Super-Sized Rat

Most performance Rat heads also raise the exhaust ports in an effort to gain flow. The exhaust ports feature a D-shape floor but will locate the headers in the stock location to make these heads easier to use in popular performance chassis like a Chevelle or Camaro.

We also lined up a Victor Jr. 4500-style intake along with a Demon 1,090-cfm Race Demon carburetor-a big-inch motor like this wouldn't be happy with an 850- or 900-cfm square-bore carburetor. We also acknowledge that it will take some effort to ensure that this big Dominator gets a little attention when it comes to part-throttle tuning for the street.

Along with the induction system, we also added a complete MSD billet-aluminum distributor, wires, and an MSD-6A box to boldly light the fire. On the exhaust side, we chose a set of Dynatech 21⁄4-inch headers to vent the exhaust along with a Flowmaster 3-inch exhaust system and a pair of matching mufflers. After Ed Taylor bolted all these parts in place on Ken Duttweiler's dyno, and after gently warming up and breaking in Max the Rat, we were ready to make some noise.

Since this is a big-inch motor, the long stroke can accommodate a very healthy cam. This led us to a custom Crane grind, required because we were using the Gen VI block. In addition, we added custom Crane triple springs, titanium retainers, and Crane Gold roller rockers.

WOT Fun
Big-inch Rats have a sound all their own. This motor doesn't thump at idle like some you've heard mainly because with a big cam and only 9.5:1 compression, the cylinder pressure's not overpowering. But the cam matched nicely with the rest of the package, and this allowed Ed to pull this rotund rodent all the way down to 2,500 rpm. If you've ever wondered why many dyno-tests start at 3,500 or 4,000, it's often because the cam is so rowdy that the engine literally won't hold a wide-open-throttle (WOT) load at that low of an engine speed. Tim's super-sized Rat, on the other hand, was more than happy at 2,500, so our test data starts at 2,600.

The first minor difficulty our gallant testers ran into was that Max wanted a bunch more fuel. Even using the largest jets we had in the 1,090-cfm Demon, our Innovate air/fuel-ratio meter reported a lean 13.5:1. This necessitated increasing the power-valve feed restrictors in the primary as well as increasing the restrictor size in the Demon's intermediate fuel-delivery circuit. This was worth sufficient fuel to bring the air/fuel ratio closer to 12.9 to 13.0:1, where we felt the engine would be safe and also make the best power.

The Gen VI block incorporates a taller lifter body, so we used Crane's taller solid-lifter body (right), which allowed Tim to reuse the stock factory lifter tie bars and spider arrangement.

And power is what we had. We ran Max both with open headers and with 3-inch Flowmasters, but we'll deal with the muffled exhaust numbers for the sake of our street intentions. Our big-stick big-block started out at 2,600 rpm with over 500 lb-ft of torque and then pushed peak torque up to 632 lb-ft at 4,900 rpm, with peak horsepower coming in with 711 hp at a reasonable 6,200 rpm. That's a 1,300-rpm powerband, which is a little narrower than we would have liked-but hey, we're talking about 711 big ones here.

For fun, we plugged that power into the Quarter Pro simulation for a 3,500-pound body style with a TH400 automatic and a conservative 3,500-rpm stall, 5 percent slippage, a 3.91 gear pushing sticky 18-inch tall slicks that are 10.5 inches wide on a decent 72-degree-F day at sea level with a 29.00 barometer. The simulation spit out a 10.55/132-mph number using a 1.60-second sixty-foot time while shifting at 6,500 rpm. That's a great effort from a heavy car, but certainly achievable-and that's without any power adder. Imagine pumping a 150 or 200hp shot on top of that! Yahoo!

Ed Taylor bolted our rotund Rodent on the dyno at Duttweiler Performance using an Edelbrock Victor Jr. 4500-style single plane along with a Demon 1,090-cfm Race Demon carb.

Conclusion
So what have we learned here? Max the Rat isn't cheap and it isn't conservative. But it does make excellent power, and since it only spins to 6,500 rpm, it should be dead reliable. With 500 lb-ft of torque on demand at 2,600, traction will be difficult to achieve. But that's the kind of problem that every car crafter dreams of. So there you have it-a Rat for all seasons, because it's never too hot or too cold to go fast. CC

Tim and Ed discovered that even with the biggest jets in the Demon carb, the 540ci Rat wanted a bunch more fuel to maximize peak power. That's an Edelbrock Victor Jr. 454R intake for the 4500-style Demon.	The solution for feeding this thirsty Rat was increasing the size of the power-valve channel restrictor (arrow 1) and eventually increasing the intermediate circuit (arrow 2) to make the air/fuel ratio safer and to make best power.
To reinforce that this is no max-compression, race-gas-only motor, Ed performed a quickie compression test, revealing a mere 175 psi of cranking pressure.