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Big-Block Chevy Build - Super-Sized Rat

A Fully Streetable 711hp 540ci Pump-Gas Fattie

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This is for all the guys who are addicted to super sizing. You know, the largest soda at the 7-11, the Camaro with the widest rear tires on the planet, and a Rat motor that must displace at least 500 ci. While the small-block has enjoyed plenty of attention when it comes to displacement enhancement, the Rat continues to be King of the Street.

So this got us thinking about what kind of street-driven, pump-gas, normally aspirated big-block we could build that would automatically be branded Neolithic by the tree-huggers and blasted as anything but cost-effective by the monetarily challenged. If you are either of these and are considering firing up your poison pen, save yourself the trouble because we'll ignore your bleating. This is an in-your-face Rat that we wanted to build mainly because we could.

OK, so our pal Tim Moore stumbled across a good deal on a Gen VI 502 iron-block at a swap meet, so right away we were off to a good start. That led to the selection of a Scat 4340 steel crank with a 4.250-inch stroke to add a quarter-inch arm to a stock 454's swing. Since this had to be a pump-gas motor, we went with Sportsman Racing Pistons' (SRP) streetable forged aluminum-alloy pistons with a flat top to keep the compression realistic. With a 4.500-inch bore allowed by the 502 block and the coffee-can-sized pistons, we ended up with Max the Rat at 540 cubic inches.

Flow Chart
The key to power with any engine, from the lowliest four-cylinder to the manliest supercharged Top Fuel engine, is cylinder head flow. But while ultimate flow is always attractive, there are other considerations that often become critical. The most important for us was to retain the street nature of the cylinder head. Many good Rat heads raise the exhaust ports to improve the exhaust flow. While this is an excellent plan for power, it requires very expensive custom headers-something we wanted to avoid.

This led us to Edelbrock's Victor Jr. Chapman CNC heads. These heads feature a stock-location exhaust port, yet sport a healthy 320cc intake-port volume and a fully CNC-machined 112cc chamber. The valve sizes come in at a manly 2.250/1.90 inches. The heads are shipped with valves but without springs, because Edelbrock realizes that a head like this will require custom springs to match the cam.

Next it was time for a camshaft. Tim is good buddies with Flowmaster's Kevin McClelland, who also did us the favor of helping spec the camshaft. The idea was that we didn't want to worry about detonation, but we also didn't want to short-change the heads with a wimpy cam. Tim was also smart enough to realize that the cam would have to be ground on a Gen VI-style cam blank in order to properly mate with the Gen VI block. We ended up with a custom grind from Crane. This may sound expensive and time-threatening, but the truth is that Crane handles custom orders like this every day and got us the cam in a few days. You can find the specs in the accompanying spec chart, but needless to say, it's a thumper.

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 2 1/4-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.

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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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