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Big-Block Chevy Build - Super-Sized Rat

A Fully Streetable 711hp 540ci Pump-Gas Fattie

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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.

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!

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.

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10 comments
David Carrillo
David Carrillo

Cuando se recalienta tenes que dejar descanzar el motor y enfriarlo un poco .!! porque si no la caja de Aceite puede rebentar y el motor hace una circulación mal

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