When we decided to do something different and build a two-ton station wagon for occasional track duty we knew we needed big power to get all that mass into motion. Actually, what we needed was torque and the quickest way to get there was boost. Yep, physics and Newton (Isaac, not the fig) tells us that objects at rest really want to stay that way, and we estimate that our 1971 Chevelle wagon will weigh in right about 4,500 pounds when done. That’s over 1,000 pounds more than the typical Pro Touring Camaro.
So we knew we wanted a boosted mill and that it had to be in the form of an LS engine. To shave a little weight off the nose, we chose a Chevrolet Performance LS3 block from Scoggin-Dickey Parts Center, combined with a Lunati stroker crank. Our game plan penciled out to 415 cubes. Having the extra displacement will give us extra grunt down low while the boost spins into the equation.
Now, we’ve built a lot of LS engines, but we’ve always been impressed with the work done by professional shops such as Shafiroff Racing Engines in New York. Long known for their killer big-blocks, they’ve also been churning out some impressive LS mills. To be honest, how we sometimes assemble an LS engine and how a pro shop like Shafiroff does it are pretty different. Yeah, we do the basics, such as checking bearing clearances, but Shafiroff checks everything, every part and every possible variable involved. It’s why their engines survive in race cars. So, a huge crate of parts was shipped out to their shop in New York and they turned it into one very well sorted, boost-ready long-block.
That still left us missing the boost part of the equation. For that, we hit up the guys at ProCharger. We’ve made great power on the dyno with their centrifugal blowers, but haven’t gotten to stuff one into a project car yet. They offered up a track proven D-1SC blower with their quieter gearset. We’ve made close to 1,000 hp with one of these in the past so we knew it was more than capable of getting us where we needed to be, which is around 700-750 pump-gas horsepower at the crank. We will make more on the Westech dyno just for giggles, but in the real world anything over 700 in a street car starts to become excessive. Of course, we padded that number a smidge to cover the added inertia of our four-door wagon.
Now, the wagon will hit the track, but its main use is a cruiser. Need to grab some sticks of lumber? No problem. Take the kids to a sports deal, equally as easy. With a blower we can get big power while still running a mild camshaft. The stick specified by Brian Tooley offered us a mild-mannered LSA and realistic lift numbers that would ensure a rock solid and long-lasting valvetrain.
So with all of that potential energy simmering on the burner, it was time to get this big project in motion.
The starting point for our 415 build was this Chevrolet Performance 6.2L block from Scoggin-Dickey Parts Center (PN 12621769). Since the block was new we decided not to mess with it and source Mahle pistons for the stock 4.065-inch bore.
With the torque plates installed, they used their Sunnen Diamond Hone to finish the cylinder bores according to the type of rings and the intended use: naturally aspirated, turbocharged, nitrous, or, in our case, supercharged. The bores were honed but, as mentioned, left at the factory bore of 4.065-inch.
Every block that goes through Shafiroff’s shop gets play time in the Rottler CNC block machine. Here they are decking for a specified height and head gasket finish. The target was for the pistons to end up 0.012-inch in the hole.
All of the blocks go through the labor-intensive process of hand deburring practically every edge of the block.
Once the ARP main studs (PN 234-5608) were installed, Shafiroff’s Sunnen Line Hone unit got the mains to spec. This is especially critical when moving to new fasteners, such as our ARP main cap studs.
With any engine build, especially with increased stroke and aftermarket connecting rods, you must check where the rod bolts swing past the cylinder bottoms. This area typically needs a notch for clearance.
Shafiroff’s Rottler was used to notch the cylinder bottoms for ample rod bolt clearance.
Every short-block, long-block, and complete engine that Shafiroff builds has its own buildsheet. They measure and record everything that you would expect, including crank sizing, rod sizing, block sizing, piston clearance, ring endgaps, torque specs, cylinder head chamber size, pushrod length, and a myriad of other important bits of information.
Every rotating assembly is unique and gets balanced according to the custom bobweight. Sometimes it’s just a small drill hole to remove material or it might require the installation of “heavy metal.” Our crank was a 4.000-inch stroke Voodoo piece from Lunati (PN 70840001) made from a 4340 non-twist forging. It was nitride heat-treated and micropolished before being sent over to Shafiroff for our project.
With the bearings installed and the rod bolts torqued to spec, a dial bore gauge was the only way to accurately determine what the bearing clearance was. The goal here was a main bearing clearance between 0.0028- and 0.0032-inch. For rods, we went with Lunati Voodoo H-beam 6.125-inch pieces (PN 70361251-8). These 4340 forged rods featured ARP2000 bolts and will easily hold up to the power we’re expecting to make.
The small end of the connecting rod is typically bushed. The Sunnen gauge was dialed in using a pair of wristpins in a special fixture to “zero” the gauge. Once the gauge was set, they could hone the bushing to size. Bearing clearance here is adjusted to between 0.0030- and 0.0032-inch.
Since the gauge was already set for wristpins, they then measured and honed the pistons to size where needed.
Once the rings were squared in the bore, the endgap was measured. Each ring was custom fitted to the cylinder bore and kept in specific order. This engine will see moderate boost so the top ring was gapped to 0.024-inch and the second ring was dialed in with a 0.026-inch gap. This should give us plenty of room for expansion due to the heat generated by boost.
Once the rings had been gapped, they carefully hand installed the oil and compression rings for each respective cylinder onto the pistons. Remember, every piston has a specific cylinder it’s been assigned to.
With the main bearings and caps in place and torqued to spec, the inside diameter of each main bore journal was measured and recorded. This measurement was then used against the crank journal outside diameter to determine which bearings will be used to achieve the proper clearance. We used Clevite bearings and it’s not uncommon to use different sized bearings in the process.
It’s easier to fit the camshaft first, before the other components. For this cam we went with a stick spec’d by Brian Tooley Racing specifically for our boosted LS stroker. The cam penciled out at 231/248-degree duration, 0.598/0.596-inch lift, and an LSA of 117+5. The result should be a smooth idling cam that makes good power all across the powerband. The lift numbers may seem low, but boosted engines aren’t lift sensitive and this will give us better valvetrain control.
This Allstar Performance tool made easy work of removing the main caps after measuring the main bores. It’s not an inexpensive tool, and if you regularly work on LS engines, it’s worth every penny since it lifts the main caps straight up instead of rocking them out, which can cause damage.
Once a fastener was torqued to spec, their engine builder applied a dab of paint to confirm it had been done. And yes, each builder has his own color.
Shafiroff used a BHJ “tapered ring” to install the pistons. A simple push is all that was required. The sleeve is specific to the bore, in our case 4.065-inch. Having the right tools on hand makes the whole process much easier.
It took two hands to torque the ARP cam gear bolts (PN 134-1003). You can also get a good look at our forged 2618 PowerPak Mahle Inverted Dome pistons (PN L92105065P25). They came fully coated with a -25cc dish. They also featured a Forced Pin Oiler for increased wristpin lubrication. The grey color comes from Mahle’s proprietary lubricant coating. The skirts, which you can’t see here, have their Grafal anti-friction coating.
The GM oil pump was installed by using equal thickness shims to center the pump over the crankshaft drive sprocket. This step is often skipped by other builders, but having the pump properly centered over the crank drive gear will greatly improve the life of the pump.
You need all of these tools to accurately degree the cam, measure piston location, check events, and verify TDC. It’s steps like this that result in a better, more reliable engine.
Once the front timing cover was installed, we could tackle the Holley oil pan (PN 302-2BK). The forward rods just barely touched the pan so we machined a groove for clearance. Since we plan on hitting the turns hard, we also ran Holley’s trap-door baffle system (PN 302-11) along with the shorter F-body-style windage tray.
Heads are critical if you want to make good power so we went with a set of big-bore CNC-ported AFR 245 cathedral port heads (PN 1680). These featured 65cc chamber volumes and were rated to flow 356 cfm intake and 257 cfm exhaust at 0.600-inch lift. Big 2.165 intake valves and 1.600 exhaust valves will move plenty of air. We’ve always had great luck making big power with AFR heads.
Every valve was checked for the installed spring height using this special micrometer. This was especially critical since we replaced the springs on the AFR heads with Brian Tooley Racing’s Platinum Dual-Spring Kit (PN SK001) that were matched to our camshaft.
Once we had the installed height measurement, each spring was checked against it for installed seat pressure. Shafiroff doesn’t make assumptions that all the parts in any given set are the same.
Each valve stem was liberally coated with assembly lube before being inserted into the guide. Then the spring locators and shims (if necessary) were put in place. The valve stem seals were then carefully installed. Note the red numbers on the valve cover rail are from the earlier height measurements. Once done, the springs were installed using their air-operated Sunnen Head Station.
Early on in the block process, the lifters bores were honed and yes the lifters only go in one way. The lifters are link-bar style hydraulic pieces from Lunati.
Once the ARP head studs (PN 234-4317) were installed, the AFR recommended Cometic MLS head gaskets (PN H1069SP1040S) (4.20-inch bore and 0.040-inch compressed thickness) were laid in place. After doing all of the calculations (piston dish, chamber volume, gasket thickness, etc.) the compression ratio ended up at 9.37:1. And yes, they are that precise.
The AFR heads were then carefully slid over the ARP studs.
Once the heads were torqued, the rocker arm pattern was checked on the valve tips to determine the appropriate pushrod length, which ended up being 7.350-inch.
To prime the oiling system, Shafiroff used a pressurized tank. Note the oil flowing through the pushrods. The crank was also rotated during the procedure. The rockers are bushed Comp pieces, which removed needle bearings from the equation and still gave us the benefits of a lightweight stock-style rocker. Since this story, we upgraded the rockers to Comp’s new Max-Lift BSR shaft rockers, which will add even more valvetrain stability and squeeze out a bit more lift.
This is where the work at Shafiroff ended, with one badass long-block. Before shipping the mill across the country, they did toss a Holley carb and intake on the 415 and ran it on their dyno just to make sure everything was perfect, which it was.
Once the mill arrived in California we finished the stroker with an MSD intake, Holley billet throttle body, ACCEL ceramic plug wires, MSD coils, Meziere electric water pump, ATI damper that was right for our ProCharger, and a set of long-tube headers from Ultimate. Naturally aspirated, the low-compression LS churned out 560 hp (at 6,300 rpm) and 528 lb-ft of torque at 5,000 rpm. Not bad, but now it was time for some boost.
In this case, boost was supplied by a ProCharger D-1SC centrifugal blower. We opted for the quieter helical gears and the oh-so-fashionable black coating.
After plumbing the ProCharger through an air-to-air intercooler, the SuperFlow 902’s tank was filled with 112-octane Rockett Brand fuel and we were ready to spin up the new ProCharger.
After a few pulls and some pulley swaps, we hit 983 hp at 6,400 rpm and 857 lb-ft of torque at 5,400 rpm. As you can see by the graph, that’s a huge gain over the NA pulls with a 423hp bump from baseline. The D-1SC was about out of air, so we might run the newer D-1X before we hit the chassis dyno. Of course, this was with race gas, so for the street we’re going to dial down the boost a bit, but it’s nice to know all that extra power is just a pulley swap and some octane away.
Choosing Supercharger Cams
We asked Brian Tooley, who chose the cam for this build, his thoughts on selecting a blower cam. As Brian explained, “Positive displacement supercharged cams need different specs from centrifugal supercharged cams. There’s a big difference in how the two blowers build boost. Centrifugal superchargers continue to build boost as rpm’s increase. They almost always make good top end horsepower so we crutch them to make more average torque. And because they make so much air we can get away with running more overlap on those cams to make even more power.
“Roots blowers make so much low and mid-range torque that we crutch those cams to make more top end horsepower. And because they’re more sensitive to ‘boost leak’ due to camshaft overlap we tend to run less overlap on those cams.
“For example, our Positive Displacement Supercharged Stg III cam we really stretched out the Exhaust Valve Open and Intake Valve Close to maximize peak power and also reduced overlap to zero. Those resulting specs are 231/248 120+5 and the valve events are 69 EVO, -1 EVC, .5 IVO and 50.5 IVC. So you can see the IVC and EVO are really moved out compared to your cam, and the overlap has been minimized as well.
“The LSA on the cam for this engine was 117 due to the EVO being 66 degrees BBDC. So, the total specs were 231/248 117+5 for the cam in this build. If we pulled back your EVO to 62 degrees BBDC that would make your cam specs 231/244 116+4, but I know that 62 isn’t really enough EVO for a supercharged 400+ inch engine. Once again, a stock LS9 cam has an EVO of 60. The LSA is also wide because we wanted to reduce overlap to make the car drive and idle better.
“You would be shocked at how many aftermarket supercharger cams have less than 60 EVO. But those cams are designed by guys focused on duration and LSA, rather than focusing on the valve events and letting the duration and LSA be the derivative of those event like we do at Brain Tooley Racing.”
Photography by Steven Rupp; Tom Tilford