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Turbo-Torture-Testing a Stock BBC Short-Block

Big Bang Big-Block Chevy

By Richard Holdener, Photography by Richard Holdener

Big-block Chevys have long been a favorite among enthusiasts, and for good reason. The performance offered by their sheer displacement has proven time and again that there really is no replacement. We all know and love what a big-block can do, but how does it compare to a modern engine? We recently ran a series of destruction tests on an LS to determine just how much abuse the stock short-block would take before releasing the magic smoke. We were amazed at the ability of the cast crank, powdered-metal rods, and cast pistons to exceed 1,000 hp in the virtually viral Big Bang Theory. The question on the table now was how well would a stock 454 BBC stand up to the same punishment? Only one way to find out.

In the previous Big Bang Theory on the LS (run on both a 4.8L and 5.3L), we performed a few minor tweaks to the motor before subjecting it to boost. The stock short-block components (including high-mileage rings) were all left intact, but we replaced the heads, cam, and intake to help improve the power output under boost. We wanted more than just big boost when it all went south; we wanted a big power number to go along with it. The mild cam timing and restrictive head and intake flow would both limit power production and artificially increase boost pressure. Knowing this, we applied the same philosophy to the 454 BBC. The 7.4L Gen V test motor was pulled from an early '90s 1-ton truck and given minimal love before hitting the pump. Off came the stock heads, cam, and throttle- body intake and on went a mild Crane cam, Procomp Electronics single-plane intake, and a set of aluminum Brodix Race Rite heads. Any improvements in the normally aspirated power would be multiplied once we added boost. This also gave us the opportunity to dramatically increase the ring gap on the stock rings (to 0.035) and do a quickie deck surface with a whizzy wheel and Scotch-Brite pad.

The factory dish pistons provided only minimal piston-to-valve clearance, which necessitated a mild cam profile. The power could have been improved by stepping up one or two notches, but the used Crane hydraulic flat- tappet was what we had at hand. The mild Crane profile offered a reasonable 0.529/0.525 lift, a 226/234 duration, and 114 LSA. The double roller timing chain and HV oil pump were indications that the 454 had seen service some time in its life, but it was many moons and many miles ago as the chain slop staggered cam timing by at least 4 degrees. Naturally, we used it anyway. The aluminum Brodix Race Rite heads represented a huge performance step up from the stock peanut-port heads. With flow numbers capable of supporting more than 700 hp (NA), they were actually much more cylinder head than this junkyard motor deserved. The Race Rite heads featured a 26-degree valve angle, a 2.25/1.88 stainless steel valve package, and springs set up for our flat-tappet cam. Though a dual-plane would be a much better choice for this mild motor, the single-plane was chosen to work with the turbos. Before stepping up to boost, the motor was run in normally aspirated trim to verify that it was indeed a runner, and then to measure power output before getting serious with boost. So equipped, the Gen V 454 produced peak numbers of 442 hp at 5,200 rpm and 477 lb-ft at 3,900 rpm.

Despite the use of 110cc combustion chambers, the static compression ratio of our Big Bang big-block checked in at just under 8.0:1. The minimal compression did little to help normally aspirated power production, but it did produce an ideal candidate for turbocharging. Adding boost to the junkyard jewel was a simple matter of gathering up the necessary components. Rather than rely on a complete kit, we did a little shopping and found a pair of 76mm turbos, assorted aluminum tubing, and a trick dual-inlet, single-outlet, air-to-water intercooler at Connecting the exhaust to the turbos required a pair of exhaust manifolds. Hooker came to the rescue in the form of a set of shorty BBC headers. The standard three-bolt flange was replaced with a V-band and then connected to our U-bend adapter that featured a V-band receiver on one end and a T4 turbo flange on the other. Also included in each fabricated adapter was a provision for the 45mm Hyper-Gate wastegate from Turbo Smart. Turbo Smart also supplied Race Port BOVs, a manual wastegate controller and a second pair of 7-psi wastegate springs. This allowed us to start tuning at 7 psi, work our way up with the controller to 14 psi, then add the second springs. The air-to-water intercooler was on hand to keep things cool at the elevated boost levels expected during testing.

Oh, we hammered on it all right—to the tune of 29 psi—and it just seemed to shrug it off.

Humble beginnings, indeed, this Gen V TBI 454 was pulled from an early '90s truck. The seatbelt is a dead giveaway to its wrecking-yard origins.

We tossed the peanut-port heads to find stock, cast, dished pistons with minimal valve reliefs and plenty of carbon buildup.

Deck the block on a motor we were trying to blow up? Not on your life! Instead, we pulled out the whizzy wheel and had at the deck surface.

We then removed the pistons to regap the stock rings. Weak cast pistons are not the problem; rather, it's the rings heating up and butting together from insufficient end gap. The ends touch, stick momentarily in the bores, and then snap—the ring lands off the pistons.

This Gen V block was the desirable four-bolt variety, but stuck inside was a cast crank swinging (seemingly) equally fragile connecting rods.

The factory cam was replaced with a mild Crane hydraulic flat tappet that offered 0.529/0.525 lift, 226/234 duration, and a 114-degree LSA. There was sufficient clearance for a slightly more aggressive cam profile, but we had this used cam on hand and stuck it in for the test. The cam and lifters were treated to a liberal dose of assembly lube and Lucas high-zinc, break-in oil prior to starting.

The one upgrade we did to ensure adequate head sealing was to install new Fel Pro head gaskets and ARP head studs. We were amazed that this was all it took to seal over 1,300 lb-ft worth of cylinder pressure.

To improve the power output of the normally aspirated combination, we installed a set of 26-degree Brodix Race Rite heads. A serious step up from the stock, peanut-port heads, these Brodix heads were more than this humble short-block deserved.

By Richard Holdener
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Marc Kitchin
Marc Kitchin

Isn't RPM the limiting factor for crank and rod durability???

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