1290 HP, 421ci Small Block Chevy
PUMPING UP A DRAG RACING SMALL BLOCK WITH PROCHARGER BOOST
Sportsman racers have pretty much gone big league thanks to a broad performance market that offers a remarkable variety of supercharging options and supporting components. Whether carbureted or fuel injected, the responsive aftermarket has provided racers with all the tools they need to make big, reliable power for their racing ambitions. Drag racer Patrick Carrigan teamed up with Basham Motorsports in San Bernardino, California to stack a deck of these performance tools with all the right cards for maximum dragstrip performance from his Vega. Combining a Dart Little M block, a Scat rotating assembly and Dart 18 degree cylinder heads with a robust Procharger F2 centrifugal supercharger, they tweaked a 421ci stroker small block to almost 1300 horsepower with a mild tune and plenty in reserve if needed. The era of big boost has set sportsman drag racers free to make all they power they can handle and they are all stepping up to claim their share of the fun.
In most cases a centrifugal supercharger like this Procharger F2 permit a lower profile hood to reduce the aerodynamic drag associated with a scoop. The Procharger is centrally mounted in a stiff aluminum plate and all accessory drives are easily accommodated around it.
BUILDING THE SHORT BLOCK
This combination is based on a Dart Little M iron cylinder block capable of accommodating the large 4.155-inch bore and lengthy 3.875-inch stroke to achieve 421 cubic inches. Block prep included extensive deburring with custom decking and surface preparation for the MLS head gaskets. The cylinders were hone with a torque plate to ensure roundness with the heads installed and all bolt holes were checked with a tap for proper thread depth. The high boost application called for cylinder head studs instead of bolts. The studs were installed using the common practice of dropping a BB in each blind hole to allow the stud to center up and provide clamping force from the threads only. Studs install finger tight and are not locked in the block.
The Dart Little M block has billet steel main caps on all five main bearings. The center three caps have angled outer bolts to help spread the clamping load into the block.
Basham's also selected the Little M block with raised 50mm cam tunnel that accommodates roller cam bearings to reduce the friction associated with regular babbitt bearings.
To further reduce friction, Basham's installed precision honed bronze lifter bushings that provide perfect lifter alignment for the roller camshaft. The bottom of each bronze insert is carefully checked to ensure no interference with the cam lobes. As a further performance measure, Basham's installed a set of BLP pin oilers in the main bearing bulkheads. These squirters capture oil from the main bearings via a tiny trough in each main bearing saddle. The pin oilers help cool the bottom of the pistons and ensure adequate pin lubrication.
Patrick's SCAT rotating assembly uses 6.000-inch SCAT connecting rods and flat top CP Pistons which you can specify when ordering your components. These pistons provide a compression ratio of 9:1 for the supercharger application. The full floating pin applications incorporates a robust pin. The ring pack is a .043 stainless top ring with an .043 second ring and 1/8 oil ring.
The top ring is .250-inch down from the deck to put some distance between the ring and the high heat source. A reinforced piston skirt with a robust ovality profile provides good thrust support for the boosted application.
The flat top pistons are not gas ported as found in some applications. The pin bosses feature extra reinforcement to ensure sufficient strength for the anticipated cylinder pressure generated by the boosted operating environment.
The front and the rear billet main caps are also four-bolt components with a combination of center studs and outer bolts.
The premium SCAT connecting rods used in this rotating kit feature ARP 2000 rod bolts with a tensile strength of 220,000 pounds and a fatigue life nearly double that of 8740 chrome moly. Note also the ARP supplied main stud kit with a combination of main cap studs and bolts. ARP designs all of its kits to provide full thread engagement on the nuts as seen here. They check this fitment frequently and suggest that if your studs protrude more than one full thread past the nut, you likely have the wrong kit and should call for consultation. Unless there are bearing clearance issues or lubrication problems, this is pretty much a bulletproof setup.
Here is a view of SCAT's big block post which essentially is a big block Chevy spec crank snout machined on a small block crankshaft. It is essential for added strength on all crank driven supercharger applications.
To ensure rock solid timing, Basham's untilized a COMP Cams big block Chevy belt drive with idler tension pully. It is accompanied here by an Innovators West aluminum crankshaft damper.
Camshaft endplay is critical when running a roller camshaft. COMP's popular small block Chevy belt drive system permits easy adjustment by rotating this plate on a ramped surface until the indicator reads correctly. Then the bolts are installed and locked down.
Loosening the six bolts on the cam drive allows you to rotate the assembly to advance or retard the cam. The marks at the top indicate up to ten degrees in either direction. This cam was installed 1 degree retarded to meet the rfequired centerline spec.
The bottom end is buttoned up with a CVR high volume oil pump and pickup inside a deep sump Kevco oil pan with full internal baffling and side kickout.
CYLINDER HEADS AND TOP END
A set of full CNC ported 18 degree Dart aluminum cylinder heads was chosen for this project. These heads have an intake port volume of 252cc and they come with 2.180 intake valves and 1.625 exhaust valves in a full ported 66cc combustion chamber. The valve angle is 18 degrees and they have angled spark plug ports. According to DART, they flow 371 CFM at .750. lift and 262 CFM at .750 lift on the exhaust side; both flowed at 28 inches of water. Both the intake and the exhaust side are fully CNC ported, including streamlined valve guides. The intake ports are raised 5 degrees and measure 2.150-inch tall by 1.290-inch wide. According to DART the heads weigh 32 pounds fully assembled, but that does not include valve gear. DART specifies a DART #42711000 single four barrel intake manifold and Mr. Gasket #113 intake gaskets or equivalent.
The proof is in the pudding as they say and it was time for a visit to Verbancic Brothers Racing in Ontario for a dyno session to break in the engine, get a base tune and some power numbers. The engine had good oil pressure right from the start and a preliminary check showed that all the pipes were lit and no valve train distress was evident when we peeked under the valve covers. sneaking up on the tune and keeping the boost conservative we advance to 1240 horsepower at 20 psi boost without much trouble. With that as a baseline Patrick knew he could begin establishing a proper track tune when the car is finished. With than much power in a tube chassis Vega it should be a plenty hair raising ride.
Here's some more shots of the engine in the car getting the headers fabricated.
1904 Riverview Dr # 101
San Bernardino, CA 92408