663hp 434ci Small-Block Street Engine

"Hardcore Horsepower's 434ci Street Ultra"

small block chevyBuilding powerful street engines when customers place a lot of restrictions on the parts you can use makes life tough for engine builders. This thumpin' 434ci "Bowtie" small-block was built for a customer to terrorize the back roads of Florida in his '72 Corvette.

The owner invested a lot of money in custom-made stainless headers and side-pipes, and was afraid that heads with raised exhaust ports would no longer match his  exhaust system.  But it's those same raised exhaust ports that we typically rely on to make tons of modern power. So, it's back to the drawing board to serve the customer's expectations.

Dart Pro 1 CNC aluminum heads carry 2.1/1.6-inch stainless valves.

When tasked to build a 650hp+ street engine with lots  of restrictions, Mike Petralia's Hardcore Horsepower, LLC in Franklin, TN crafted this 434ci beast to the tune of 663hp and 590tq. Besides building an engine that would meet the power requirement with his existing headers, Hardcore Horsepower's customer expected  to see a minimum 650hp on pump gas with a hydraulic roller cam so he wouldn't have to mess with the valves. He also wanted an engine that would start and run with ease, even when it's cold so that meant incorporating a carburetor  with an electric choke. Blowers, turbos, or N2O need not apply.

This will be a one-carb, naturally-aspirated wonder.
He did offer ample hood clearance with a big scoop however, and he's running a manual trans, so we can make it idle nice n' nasty! But wait, one more thing.
He's running vacuum-assist power brakes, but the cam will be way too big for that, so he'll just have to add an electric vacuum pump for his brakes instead. Problems solved.

All good engines evolve from a healthy recipe of performance components carefully chosen to accommodate the specific requirements or in some cases the restrictions of the intended application. Here's the recipe chosen to meet the particular goals of this application. It is built around a Dart SHP block with 350 mains, a 4.155-inch bore, 4-inch stroke and standard small block cam location.



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Any build like this has to have a strong foundation and Dart's 4-bolt "SHP" block fits the bill. Petralia always file-fits the rings in every motor. The engine's bore diameter is 4.155-inch, but a 4.125-inch ring-squaring tool works in that size too. The Scat H-beam rods have been stroker-profiled and then measured and cataloged at Mike's shop for future reference. You can also see the fully-coated Mahle Motorsports forged pistons in the background.

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After micc'ing the rods, Petralia measures for bearing clearance and logs those numbers too. During assembly of every engine, Petralia records how much torque it takes to spin the crankshaft. It took just 12-inch/lbs., (1.0-ft/lbs.), to turn the crank with all five main caps torqued and just 20.16-ft/lbs. to turn after all eight pistons were in. Joe Gibbs Racing assembly lube makes this all so easy.

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Calculating the exact compression ratio of an engine means you have to measure everything. The Mahle pistons' dish measured 78cc with the piston installed -.250" down the bore. That calculates out to a -22.5cc dish volume. The pistons were advertised as -20cc, so the extra volume is from the area above the top ring and some minor machining discrepancies. After fully CNC-porting the Dart Pro 1 aluminum castings, the pro's at High Velocity Heads (HVH) in Knoxville, TN angle-milled them down to 60cc chambers and corrected all the bolt hole angles to fit.


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The finished 228cc intake runners were first CNC-ported and then retouched with a hand grinder in some of the more complex areas and finished off with sanding cartridge rolls.
Petralia won't reveal the cam specs, except to say it was .640" lift at the valve and ground with a 4/7-firing order swap. He did reveal that he used a trick new spring/retainer set-up from Comp Cams featuring a small-diameter double spring and light, yet very strong Tool Steel retainers to control the large valves up to 6,750rpm.


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The Moroso oil pan will clear a 4-inch stroke, but not the oversize 3/4-inch diameter pickup used on the Melling Select oil pump. So Petralia had to cut part of the rear windage tray for clearance. The Melling Select oil pump puts out a lot of pressure. In this case, 68psi which Petralia feels is too much. So he swapped out the yellow by-pass spring for a lighter pink spring and tested pressure at 60psi with his bench-top fixture before installation.


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With .640"-lift, taller valve were required and this required some custom parts be fabb'd up for the correct rocker geometry. Steel spacers had to be used to raise the rockers up, but that made the bolts too short, (see original bolt on left and installed in left rocker). Petralia had to fab up his longer bolts to get enough thread engagement in the heads (right side rocker and new fabb'd bare bolt on right). You might notice that the cam's dowel pin is not poking through the hole in the locking plate. Petralia purposely installs the lock plate over the dowel pin so it cannot back out. Comp Cams has confirmed that this is a good practice, but it will bend the locking plate a little (see hump, lower right).


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HVH was also tasked with porting, polishing, and milling the Edelbrock Super Victor intake manifold to fit the custom Dart heads. During the initial dyno tests, Petralia was not satisfied with the power produced from his first cam choice. So he ordered a new stick from Comp with the same lift, but a bit less duration, and a wider lobe separation angle.


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Combined with the new cam Petralia also installed a larger set of 1-7/8-inch headers from Kooks and installed stiffer Comp Cams pushrods too. These three changes, and a few tuning adjustments netted 53-more peak horsepower. That's a benefit of having an in-house dyno and not being ashamed to admit when he was wrong.


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Hardcore Horsepower LLC
109 Beasley Dr.
Franklin, TN 37064