Chevrolet 396 Big Block - Mean Little Rodent

Making Big Power With A Small Rat

Mike Petralia Feb 1, 2001 0 Comment(s)
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The Chevrolet 396-cid, big-block's destiny was decided long ago. After punching the block out 0.030-inch and increasing its displacement to 402-cid back in 1970, a couple years later, GM stopped offering the little big-block in cars and trucks altogether.

It probably didn't help that GM kept calling this engine a 396 big-block, further adding confusion to the already vague big-block market. Following its official retirement the 396 will forever go down in history as second fiddle to the big, bad 454. Now with newer and bigger displacement Rats like GM's new 8.1-liter (496 cid) truck engine being introduced the little old 396 gets pushed further and further into big-block obscurity.

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After our 31-year-old Rat was checked for defects it was align-honed and hot tanked in preparation for cylinder boring and deck machining. It gets its deck surfaces squared relative to the crankshaft's centerline to ensure every machining operation that comes afterwards will be true to the crank.

Without going into tremendous details of production figures and years of availability, it's safe to say that there were more 396-cid big-blocks installed in cars than there were 427s or 454s combined. Yet, to date the 396 is still often cast aside by the performance crowd whom usually have hailed the credo, "If you're going to build a big-block, build it as big as you can." While that's certainly a good motto to live by, it's also an expensive mantra to uphold.

A byproduct of the 396's outcast into obscurity has been the reduction in the cost of its parts. While a forged GM crank for a 454 could cost as much as $400 today, a forged 396 crank sells for about $75. And a rebuildable 396 short-block will usually only set you back less than $200. While a 454 short-block could fetch $500 easily. Sure, with cubic inches comes cubic power, but what if we showed you how to build that 396 you've been neglecting in the hopes of adding some inches to your diet and make power equal to or beyond the average street 454? We'll show you how to do it right the first time on a reasonable budget. Sorry, this isn't a totally down and dirty low-buck engine, but it certainly doesn't carry a cubic price tag either.

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With the crankshaft secured by the No. 1 and 5 main caps and bearings, we installed the No. 1 rod and piston without its rings, and checked installed height. Note the position of our thumbs, which we use to "rock" the piston in its bore and determine how far below the deck the piston sits at TDC. After this, we reset the block in the mill and "deck" its surface for a "zero" piston installed height, meaning the piston is very close (+/- 0.005) to the deck at TDC.

We figure that today it takes at least 500 hp to be a street hero. Anything less and you're just paddlin' upstream while the big fish are sailing by you in their new powerboats. And you've got to make your power from the pump, since race gas is still taboo in most street car circles. So what's it take to make 500 hp with an old street 396? About $5,000 and a few gallons of 92 octane. Follow along as we detail the buildup and testing of our fearsome little Rat and maybe you'll forgive your 396's cubic-inch deficiencies and give it a new lease on life as a street brawler, instead of a dust collector.

The Dyno Dance

Our little Rat puffed out its chest and pumped up some mighty big dyno figures for us. The average power numbers from 4,000 to 6,250 rpm (where it carried over 400 lb-ft of torque) were 438 hp and 450 lb-ft of torque. While power peaked at a high 6,400 rpm, low-end torque was still plenty respectable with the motor peaking 483 lb-ft at 4,700 rpm. Here is a sampling of its best power pull with the cam four-degrees retarded and 38-degrees of ignition advance.




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