Penultimate LT1, Part 1: Aiming for 600-Plus HP with a 396 Gen II
Building a street-driven 396-cid LT1 with high compression, solid roller, and CNC-ported heads
Scott ParkerWriter
This may not be the last Gen II LT1 that Super Chevy ever builds, but we certainly aimed to make it the most impressive. The original concept was to take every trick we’ve learned over the years, and apply them to a 600-plus-horsepower street-going engine. Of course, just because it is “street-going” doesn’t mean we won’t be pushing the envelope of what many would consider streetable. Yes sir, this was to be a high-revving engine that would scare the bejesus out of common folk from an idle. Eventually the LT1 would find a home in Greg Lovell’s ’96 Chevy Impala SS with an EFI Connection 58x system, Flex Fuel compatibility, and 6L80E six-speed automatic transmission. But to get there, first we’d need to start at the bottom.
For those that aren’t familiar with the Gen II LT1 (not to be confused with the Gen I LT-1 from 1970-’72 that was so cool it got a hyphen at no extra charge), the second-generation small-block Chevy bares a striking resemblance to any other 350-cid small-block when stripped of its intake manifold and electronics. Its reverse-flow cooling was the one notable deviation, which cooled the cylinder heads first to better resist detonation and allow for higher compression. Cooling was facilitated by a gear-driven water pump, bolted to the block just above the flat distributor (mounted flush to the timing cover) known as the Optispark. Therefore, this also made the timing set as well as the hydraulic roller camshaft unique to the Gen II. The intake was also substantially different than even the previous Tuned Port Injection manifold. Shorter runners and a lower profile plenum made the engine compact, yet LT1s were still known for their torque. With a little port work and opening up the twin 48mm throttle body opening, this intake proved quite capable over the years. And the introduction of the OBD I/II flash-based PCMs helped open the doors to EFI tuning on highly modified vehicles.
The LT1 was the standard issue bullet in the ’92-’96 Corvette, ’93-’97 Camaro (Z28, B4C, SS), and ’94-’96 B-body (Impala SS, Caprice) as well as other GM brands. Both two- and four-bolt main caps came on LT1s depending upon the application, though every LT4 came with four-bolt mains. Aluminum cylinder heads were standard on all models except B-bodies. However, on this build we planned to exceed the limits of virtually all of these components, starting with the main caps. Spinning high rpm puts the main bearings at risk, even with the four-bolt main blocks. So Greg Lovell picked up a set of Cipco splayed main caps and ARP studs for the ultimate in bottom-end stability. Since the plan was to drive this on the street, filling the block wasn’t an option nor did it seem necessary naturally aspirated. Thankfully the LT1 block itself is fairly sturdy. So we’d be relying on precision machining and meticulous assembly from the LT1 experts at Golen Engine Service, along with a forged rotating assembly from Scat Enterprises to keep this thing together. A 4340 forged steel crankshaft would provide 3.875-inches of stroke to the 4.030-inch cylinders for a total of 396 cubic inches. Scat’s 4340 forged 6-inch H-beam rods and high-compression forged pistons would help us put the squeeze on this E85-sipping LT1.
Once the Golen short-block arrived at AntiVenom’s facilities, Greg Lovell would mate it to a set of Air Flow Research 227cc CNC-ported cylinder heads. These are pretty much the best heads you can get without converting a set of SBC heads. The standard version flows a whopping 312 cfm at 0.600-inch lift. However, when we consulted with the folks at Lunati for our valvetrain needs, it became apparent that lift would be a healthy 0.688/0.688-inch with a custom-ground solid roller camshaft and 1.6 ratio rockers. Lunati spec’d the cam to carry 257/265-duration at 0.050, cut on a 110 LSA with a reduced base circle to clear the stroker crank. We had hoped to use an LS1 engine’s firing order or even a swap of the No. 4 and 7 cylinders for additional gains, however, Lunati did not offer a cam small enough to accommodate us (that’s big-boy stuff). However, Lunati was able to provide the solid roller link-bar lifters and heavy-duty pushrods needed to round out the combination.
Typically, a healthy 396-cid LT1 is capable of over 515 horsepower with a hydraulic roller, pump-gas friendly compression, and a decent set of heads. Since we planned to run a mix of race gas or E85, this engine spec’d out at around 13:1 compression. Factor in the high-flowing heads and solid roller, and it stood to reason that this combination should exceed 600 hp. With the intent on spinning past 7,000 rpm, the real question would be the intake manifold. We’ll cover that next time, but for now let’s take a look at the long-block preparation.
1Golen Engine Service in Hudson, New Hampshire, got to work on the bottom-end of our 396-cid LT1. Each block is baked, blasted, and Magnafluxed before the cylinders are bored. The final bore will be 4.030-inch after honing with progressively higher grit stones to achieve an ideal crosshatch. This is key to getting the rings to seat. Golen uses a deck plate to simulate bore distortion with the heads in place.
2Greg Lovell purchased these Cipco billet, splayed main caps to stabilize the crank at high rpm. In any performance application, four-bolt mains are recommended, however, it is time to step up to splayed main caps with high rpm or boost. The Cipco caps have a 10-degree angle on the outside bolts to lock the caps in place and grab a stronger section of the block.
3Paul Rindaldi line-honed the splayed caps after torqueing the ARP studs down to 75 ft-lb. Even with factory two- and four-bolt caps this is essential on any LT1 rebuild. For those not familiar, LT1s use a 350 main and a one-piece rear seal like many late-model SBCs.
4The main bearing clearances are set to 0.00025-inch using a calibrated dial bore gauge. The bearings came with our Scat rotating assembly, which we had sent to Jet-Hot to be coated. Jet-Hot’s Slick Coat is a fluoropolymer coating that provides anti-friction protection for improved oil management and lubrication. We’ll be using this coating on the pistons and a few other surfaces in contact with oil.
5The Scat forged pistons and rods are assembled with the supplied 0.927-inch floating wristpins and locks. The pistons measure 4.030-inches and were treated to Slick Coat to prevent galling. There is risk for galling whenever metal surfaces are sliding against each other, but even more so with aluminum. The connecting rods are 6.00 inches in length and weigh 616 grams. 4340 forged steal H-beam rods are a must with high rpm.
6The caps and ARP 8740 7/16 bolts were then removed and carefully laid out so as not to mix them up, prior to dropping them into the cylinder and bolting to the crank. You can see that the rod bearings are also coated, sitting inside the 2.100-inch rod journal. Bearing clearances are set at 0.0028-inch. Also note: on this build, the ring gaps were set at 0.018-inch on the top ring and 0.020-inch on the second ring.
7Golen resurfaced the block during the machining process and verified during assembly that it is set to zero deck. This is important to note before selecting the head gaskets. Greg picked up a set of Cometic 0.040-inch MLS gaskets (PN 1-12429) to keep quench within the recommended 0.035-0.045-inch range. This flat part of the piston and corresponding part of the head is the quench area, which pushes the air/fuel mixture into the chamber and towards the flame.
8Here is a good look at the installed Scat rotating assembly (PN 1-41839BIE). The 4340 forged crankshaft provides 3.875 inches of stroke to the 4.030-inch cylinder, for a grand total of 396 cubic inches. With Scat’s kit you get everything you need with one part number. It is just up to you to provide the block and machine work.
9Golen even treated the block to some black engine enamel and new freeze plugs.
10When the short-block made its way to AntiVenom in Florida, Greg got right to work by installing a custom Lunati solid roller camshaft (PN 40089909). An iron distributor gear was a must with the EFI Connection kit, and thankfully it came on the cam. Meanwhile, this cam also had to be ground with a smaller base circle to clear the extra-long stroke.
11Greg lubed up the cam before inserting it into the block. Here you can get a little better look at those substantial lobes: 257/265-degree duration at 0.050, 0.688/0.688-inch lift (with 1.6:1 rockers), 110 LSA, and 104-degree centerline. This thing was built for top-end power, so it’s a good thing we’ve got an intake manifold that can support it.
12This double roller timing set came in the EFI Connection 58x kit. It was another essential component to high rpm living. Greg also noted that there was no slack or slop in the chain, a testament to Golen’s engine building.
13Here you can see the EFI Connection 58x reluctor wheel—a piece built to replicate the reluctor wheel on the crank snout of a Gen IV such as the LS3. This piece will allow the LT1 to run an LS3/LS7 or LSA/LS9 computer to control the EFI. This allows for Flex Fuel, six-speed automatic transmission control, and enhanced tuning capabilities not present with the 24x/Gen III kit.
14The proprietary EFI Connection timing cover houses the sensor to read the 58x signal. It is essential to operation and looks awesome with its anodized finish, too.
15ARP fasteners were used throughout this build. There are complete LT1 kits, however, for these heads you’ll want part number 234-4301. These are a standard 12-point small-block Chevy part, which is made from heat-treated 8740 chromoly and rated to 200,000 psi. Even in a naturally aspirated combination, you’ll want a re-useable set of fasteners with ample tensile strength. Remember, high compression means high cylinder pressure as well.
16Greg found that it is easier to put the Cometic head gaskets on first, before the head studs. Just like a Gen I SBC, the head studs go into the water jacket, so Permatex thread sealant is a must. Look at the crosshatch on the No. 2 and 4 cylinder.
17Since we’ll be using an SBC intake manifold, Greg used a gasket as a template to drill new boltholes in the Air Flow Research cylinder heads. The factory LT1 intake is quite capable, but definitely rpm limited. And since there are almost no aftermarket intake options, the SBC intake is the way to go for this application. Some aftermarket LT1 heads can even be ordered with the SBC intake bolt pattern for this reason.
18Here is a close look at the finished product. The 227cc CNC-ported intake runners on the Air Flow Research heads flow 315 cfm at 0.650-inch lift. That’s a lot of flow for that runner size, so we are expecting excellent velocity on the 396-cid mill. We also opted for the ARP 7/16-inch rocker studs, 5/16-inch guideplates, and PAC Racing 1.550-inch OD solid roller dual valvesprings. AFR says these are good for up to 0.710-inch lift with 220 psi of seat pressure and a max rpm of 7,200-7,400. Many other options exist, including a competition version, which would have taken flow up to 327 cfm.
19The exhaust runners are also CNC ported, measure 80cc and flow 233 cfm at 0.650-inch lift.
20We went with a 58cc chamber, though AFR will cut the heads all the way down to 55 cc. In a race application we probably would have opted for angle milling to get every last ounce out of it, however, we elected for flat milling to keep things simple. AFR uses massive 2.10-inch intake and 1.60-inch exhaust valves with a 23-degree angle (yet offset) to generate the 227cc head’s massive flow. The 60/40 valve spacing requires careful consideration of piston-to-valve clearance.
21Greg slides the heads onto the head studs. Eventually he’ll torque these down, with moly lube, to 65-70 ft-lb. However, with so many trick components on this engine it is even more essential to test-fit everything first.
22And we’ve discovered the first problem. The massive PAC springs needed for the solid roller have encroached on the area in which we need to fit a washer for the head studs. We may be able to remove one of the springs to bolt the heads down, or machine the washer.
23To accompany our big solid roller cam, Lunati sent us its Solid Vertical Bar Roller Lifters (PN 72403-16). The lifter bore is maximized with this design to provide more surface area and less wear. Material has also been removed from non-critical areas to reduce weight.
24Unlike the factory hydraulic roller lifters, no spider tray is needed and each lifter is connected via a tie-bar.
25Before we wrap up our progress for the day, Greg measures for pushrod length. We’ll need a very sturdy set of pushrods in the neighborhood of 8.15 inches. Stay tuned for next time when we wrap up this build and head to the dyno.