Normally Aspirated C7 Z06 Build


Horsepower Research in McKinney, Texas has made quite a name for itself building large displacement late model LS and LT based  Chevrolet engines for drag racing, road racing and all around hot street cars. One of their newest builds is a 468 cubic inch C7 Z06 LT engine for a local customer who was dissatisfied with the performance of his Corvette. While fast, the supercharged car created excessive heat when run hard at the track. He didn't like that and asked the Horsepower guys to find a solution.

After investigating various cooling upgrades they decided to pursue a different path by completely replacing the supercharged engine with a big cubic inch normally aspirated engine capable of meeting or exceeding the output of the factory powerplant. The existing engine was removed and saved for another project and the team proceeded to engineer a normally aspirated 468 cubic inch engine designed to exceed the power of the supercharged engine while handily removing weight from the front of the car.

The core structure of this engine is a new GM Gen V LT1/LT4 cylinder block both of which share the same part number. As seen here, the new LT block is immediately machined to accept large bore Darton sleeves which permit a larger 4.185-inch bore and longer cylinders to accommodate the increased stroke.

The longer Darton sleeves are necessary to accommodate the desired bore size. They also prevent piston damage with the longer stroke. If the piston dips out of the bore further than the manufacturer's checking point, it can rock  over at BDC causing the cylinder wall to gouge the piston skirt when the piston reverses direction. These are significant details that top engine builders like Horsepower Research take into account when building these high horsepower long stroke engines. After the sleeves are installed, the cylinder bores are torque plate honed to the final finish at 4.185-inch. LS bearing machine work, rod clearance for the bigger stroke, and final deck surface squaring is performed along with final block deburring. The block is then washed, air dried and the cylinders are hand cleaned and wiped down so that main bearing clearance checking can be performed. Block plugs are also installed at this point.
Once bearing clearances are properly established the bearings are lubricated with Horsepower Research's preferred Motul 10-40 break-in lube and the crankshaft is laid in place. Main bearings are set at .0025-.0027-inch depending on the block material and application. They typically set them a little tighter with aluminum engines because of the growth factor. They also base it on the type and weight of oil the customer will run.
The Callies crankshaft is a robust piece that provides very good reliability for these engines.  Like all engines, the GEN V LT engine requires the thrust clearance to be checked and set any time the thrust cap is installed. This application uses an LS bearing set it has a full thrust face instead of the 1/2 thrust that GM uses in the stock engine. Once the thrust is set, the #3 cap is torqued in place, side bolts installed and the thrust is re-verified. Thrust clearance is particularly important on any track car or road race car as there are so many gear changes and thrust applications over time compared to short term drag racing use.
Forged H-beam rods connecting rods have ARP 2000 7/16" bolts and a slender profile  to provide cam tunnel clearance while remaining robust enough to endure heavy track abuse.  Wiseco custom 2618 forged pistons are made to spec for Horsepower Engineering.  The pins feature a tool steel dual taper design for added strength without the weight penalty of a thick wall pin typically used in power adder applications. 
The rods and pistons are assembled and equipped with file fit Total Seal rings that include a .9mm steel top ring, a .9mm Napier second ring and a 2mm oil ring with standard tension. The rod bearing clearance is set at 2.4-2.7 thousands. When the short block is fully assembled they check rotational torque values, verify side clearances on the rods, rod to block clearance and apply final lube between the parts.
At this point we have a "normal" 468 cid GenV LT short block.  This will accept any drop in LT camshaft, hyd lifters, and all of the normal functions could be retained as you would in the production car.   But they had other plans.
The GEN V world suffers from a lack of good performance cylinder heads. LT1 and LT4 heads have huge ports that flow a lot of air if required. But they also diminish performance in the low and mid RPM ranges where most of these cars live on the street.  However, the Competition Induction Design (CID) LT casting provides very small ports so a head porter can design and tweak everything from valve size to port design and location. HPR works closely with cylinder head porter Greg Good who has developed one of, if not the very best set of ports for direct injection heads. 
Greg Good's high velocity ports and corresponding combustion chambers are a work of art that offers the best possible performance from a direct injection engine.
This application uses the OE LT4 valves given their light weight. The Ti intake valves and the OEM exhaust valves are strong enough to use in this application. Good's high-velocity ports and the reliability of GM's power adder friendly valves make this a robust combination well suited for this application.
Pac 1209x springs are a proven dual spring setup that works well with this camshaft. It is small enough to fit into the spring pockets of the LT head and it provides a low enough bind height for the lift of the camshaft. This application is not using an OE phaser style gear. An LS2 single bolt gear removes any chance of timing changes. Since we will not be using the OE phaser style gear this is very critical. It requires the use of a Katech front cover because the cam sensor needs to move closer to the gear.
Exceeding the operating range of the original equipment rocker arm required use of steel-bodied T&D Machine LT drop-in rocker arms. They have a smaller body to reduce weight and provide a roller tip to allow for the larger lift. HPR determined that the T&D rocker has slightly more ratio (most rockers will) and actually measures out to a 1.86:1 ratio which yielded 0.763 lift before deflection in the system when checking with the solid lifter.
Their final choice of lifters on any hydraulic lifter LS and LT engines has been Johnson Lifters which have performed flawlessly for them in every application they have built so far. Here they are using the standard travel link bar style, non-axle oiling. On this fully assembled head you can see a better view of the PAC springs and also the DOD delete valley cover from Katech.
 Great view of the robust T&D rocker system.  They do NOT clear the OE valve covers, so a quick order to Katech produced the clearance they needed with Katech's cast Gen V valve covers.
The  LT4 high pressure fuel pump, OE rails, lines, fitting and LT4 injectors  are all adequate to feed this big inch beast. With the fuel rails and injectors installed, the injector wiring harness is connected. The system appears clean and neat against the backdrop of the Katech valley cover. The high pressure fuel pump is necessary for direct injection applications. It is a pulse width modulation capable fuel pump that delivers 72 psi at 45 gallons per hour. It mounts on the rear of the engine under the manifold and is driven by a 3-lobe cam on the camshaft. Pressure is regulated by an internal solenoid valve controlled by the ECM.
While the C7Z06 did come stock with a dry sump oil system HPR wanted to improve oil control and provide a crankcase vacuum source. ARE offers a number of systems including this 4 stage package that, at least for the C7 Corvette, even allows the retaining of the A/C system which is nice to have in Texas.Now you can see the Katech billet front cover as well as the new ARE pan and scavenge ports to pull the oil out of the engine which will be pumped back to a ARE oil tank as well.
The stock C7Z06 runs a blower pulley on the front side of the balancer thus leaving room to put the dry sump drive on the front here as well. The fit is tight but everything tucks in around the steering rack without moving the engine or the rack. To complete the package, the engine is topped off with a MSD Atomic Air Force  intake manifold and NW 103mm drive by wire throttle body to clear the low hood line of the Corvette. While this limits max power, the ability to keep the engine under the hood for aerodynamic reasons was considered more important.
Here's the engine sitting on the factory engine cradle before installing it into the car.  The dry sump system scavenges from three pickup points on the ARE pan. An Earl's billet filter mount holds the filter down low next to the pan rail.
This view shows the whole oiling system except for the tank and oil cooler which are mounted forward under the fender. Although tight, the undercarriage provides some space for the scavenge lines to cross over to the tank and cooler. Beautiful plumbing job by the crew at GSpeed.
Engine installation and prep was performed at GSpeed, a specialty track prep shop specializing in high performance road race Corvettes, Camaros, Mustangs, and exotic sports car preparation.
Track car ready to rock with big power from a normally aspirated 468-cubic inch LT4 V8.


Horsepower Research, HPR
401 Power House St, Suite 104
McKinney, TX 75071
972 597-4367



215 Performance Ct
Cresson, TX 76035