Power is an addictive thing. No matter how much you have, eventually you'll want just a little more. It's like buying a new big-screen TV. At first, that 55-inch version seems huge, but as the months go by it almost seems to shrink in size, and soon you're eyeballin' the 70-inch version. Engines are no different. What feels fast, eventually seems less so, and soon the gearhead itch for more power starts to tingle.
That's the story with our '01 Z28 project car, Black Betty. We recently added a set of ceramic-coated 409 stainless JBA long-tube headers that shot the power output of our cammed LS3 to 448 hp and 445 lb-ft to the rear tires. Certainly respectable, but wouldn't just a bit more power be even more fun?
Before long we had the idea to stroke the Camaro's engine out to a 416 and gain 40 inches of power-making displacement. To keep our downtime to a minimum (and not tie up a rack at Don Lee Auto), we picked up a fresh block from Chevrolet Performance so we could have the short block assembled and ready to rock. We don't want to drop any spoilers here, but the newfound power still has us grinning from ear to ear. Will the euphoria last? We hope so. Then again, we heard power-adders can easily be installed using common hand tools, so who knows? But follow along as we pump up Black Betty with just a bit more power.
01. The starting point for our new powerplant is this Chevrolet Performance 6.2L aluminum block. When used in an LS3, it works out to 376 ci, but our plan is to massage the cylinder bores out to 4.070 inches and stuff in a 4-inch-stroke crank. This combo will give us an additional 40 cubic inches of displacement, and that equals more power throughout the curve.
02. The crank is the heart of any stroker build, so we opted for one of Lunati's Voodoo units (PN 70340001, $706). This 4-inch-stroke forged crank is an affordable way to get Lunati quality. Made from 4340 steel, this piece is a non-twist forging known for durability and strength. It came nitride heat-treated with micropolished journals and lightening holes in the rod journals to reduce inertia.
03. The GM block wasn't designed for a 4-inch stroke and required a little work to allow for the longer rod throw. We installed the crank, bolted on a rod, and marked where the rod bolts were running into the bottom of the cylinder bore. Once we found one, it was easy to transfer that mark to the other seven cylinders. We then used an air grinder to remove the material.
04. For pistons, we went with a set of forged Mahle PowerPak slugs (PN L92105070F04). These flat-tops came with a Grafal anti-friction coating on the skirts and were phosphate-coated to reduce pin galling. Street price was just under $700.
05. Working with the crank to get us the right stroke are these 6.125-inch Lunati H-beam rods. They are forged from the same aircraft-grade 4340 steel as the crank and are then heat-treated, stress-relieved, shot-peened, and magnafluxed to ensure they will last. After all, connecting rods are subjected to some of the highest stress levels any of the bottom end engine components endure. When the piston direction reverses from top dead center, the forces on the rod can exceed 12,000 pounds. To hold up to that kind of punishment, we are utilizing ARP rod cap hardware.
06. Don Lee Auto's (Cucamonga, California) Tim Lee then went about the task of file-fitting the rings and mating the Mahle pistons to the Lunati rods. The wristpin locks are the split-wire-ring type, so be careful since they tend to want to shoot across the room when you're trying to remove them.
07. We then slid the rod and piston assemblies into place and torqued them to spec. Made from 4032 low-expansion aluminum, these flat-top pistons should yield us an 11:1 compression ratio, which is perfect for a pump-gas EFI LS engine.
08. Friendly reminder: just as there's a top and a bottom to a piston, there's an inside and an outside edge on the rod. When installed on the crank journal, this is how the rod end should look.
09. Since this engine is destined for our '01 project car, we made life simpler by ordering the Lunati crank with the requisite 24x reluctor wheel installed and ready to rock.
10. We don't mind a little cam, but being too aggressive can be a pain to live with. At first we wanted to try Lunati's new line of high-lift cams, but they weren't playing nice with our bone-stock LS3 heads. So, we instead went with a profile that should make good power and have decent off-track manners (PN 20540731, $430). The final specs on the bumpstick were 227/238 (at 0.050) with lift numbers of 0.583/0.600 on a 112 LSA.
11. The plastic GM lifter trays are convenient, but at higher rpm they can flex and cause valvetrain issues. For a hard-running engine, these 0.842-inch diameter captured link bar lifters from Lunati (PN 72332-16, $375) are a much better solution. They dropped right in and should easily support 6,500 rpm.
12. There wasn't anything wrong with our stock timing chain, but since we're this deep into it, we decided to upgrade to something a bit stronger. This billet Lunati timing set (PN 95603, $165) came with a pre-stretched double-roller chain and had three points of adjustability on the crank sprocket.
13. Before bolting on our stock GM L92 heads, we made sure to check our piston-to-valve clearance with some lightweight springs. Once that was done, we finished installing the Lunati Voodoo dual valvesprings (PN 73925K1, $250) and 4140 chrome-moly retainers. The spring kit also included steel 7-degree valve locks and Viton synthetic rubber, steel-reinforced valvestem seals. Before dropping the heads on we installed a set of FelPro MLS head gaskets (PN 26192PT, $67) and torqued the heads down with ARP head bolts (PN 134-3610, $123).
14. For rockers, it's really hard to beat the GM design, but they can be made better. We've seen trunnion kits on the market to help make the rockers more stable, but they are sort of a pain to install. Well, Lunati made things easier by offering the L92 1.7 ratio GM rockers with the captured roller trunnion bearings already installed (PN 85428-16, $417). Once paired up with Lunati's 7.400-inch hardened pushrods (PN 5048-16, $110) our valvetrain was complete.
15. When we pulled Betty's engine, we found that the stock rubber engine mounts were toast. To replace them, we grabbed a set of poly replacements from Energy Suspensions (PN 1151R, $32 each).
16. The rest merely involved bolting on the parts, like the Holley 90mm throttle body and F-body accessory drive from our old LS3. The beauty of added displacement is that it's invisible to the eye.
17. We also dropped in six quarts of Driven Racing Oil BR-30 LS break in oil. This 5w-30 oil has the highest levels of zinc and phosphorus to ensure proper ring seal and protection to the cam and lifters during break-in.
18. We headed over to Westech Performance for some time on their chassis dyno. Technician Eric Rhee spent some quality time banging away on his keyboard and getting the tune-up dialed in. At this point we were really looking forward to seeing what the stroker could do.
19. Unfortunately, the stock (and old) fuel pump wasn't able to supply ample fuel volume and started falling off hard at about 4,200 rpm (pink line), so as you can see in the dyno graph, we aborted the pull at 5,000 rpm to avoid going lean and causing major damage. With that said, the engine showed good promise as it made 450 hp and 481 lb-ft of torque up to that point. We'll address the fuel pump issue and head back to Westech and finish what we started in the next issue.