600 HP 468 Big Block
JMac Performance is building a 600 Horsepower street 468 Big Block Chevy engine. As the build progresses I will cover all the details that goes into building a high quality street engine.
As our foundation we’ll be using a Gen V four bolt main 7.4L block
Pictured below are all the parts that will go into our 468 build
SRP Pistons on Scat 6.385″ connecting rods with ARP bolts
At the heart of the engine is an Isky hydraulic roller cam and Cloyes double roller timing chain
A pair of Profiler 290cc aluminum cylinder heads will take care of the intake and exhaust flow
600 HP 468 Big Block “The beginning”
We start our build with a Gen V – 4 bolt main 7.4L (454) block. The block gets fully machined; Hot tanked, magged for cracks, line honed, bored .030 over, and decked to zero deck height
The extra casting (flash) is removed and all the threads are individually cleaned with a thread chaser.
New cam bearings are installed
After boring and honing the cylinders they are chamfered on the top and bottom. (The top to help with the piston and ring installation, the bottom to reduce internal friction and eliminate scuffing of the piston skirts)
600 HP 468 Big Block “Checking bottom end clearances”
To insure our 468 will live a long and happy life we need to check all the clearances of the bottom end. We started out by cleaning and deburring all the bearings. This is a step most engine builders delete. I like to verify the quality of the bearing finish and insure they are burr free before installation.
I installed the main caps and the bearings then torque them to spec. In this case 100 ft-lb. (Note: For added insurance we replaced the stock main bolts with ARP bolts.)
I used the micrometer to verify the crank main journals (2.748″) then I used the bore gauge on the main bearings (2.751″) to get our (.003″) bearing clearance.
I did the same with the rod journals (2.194″), torqued the ARP rod bolts to 63 ft-lb, I used the bore gauge to verify the connecting rod bearings (2.219″) to get our (.0025″) bearing clearance. (Note: The use of the rod vise when torquring down the rod bolts)
The first set of rod bearings yielded a (.003″) clearance, a little too wide for our application. The wider rod bearing clearnace would have resulted in lower oil pressure. After installing a slightly under sized bearing we got our (.0025″) clearance.
THIS IS WHY YOU HAVE TO CHECK EVERYTHING! Leave nothing to chance.
Once the bearing clearances were verifyed I installed the crank and checked the end play. It was a little tight (.003″) with a few taps of the rubber mallet got me (.006″) end play.
600 HP 468 Big Block “Bottom end installed”
I used the micrometer to check the Forged SRP piston diameter (4.277″)
then I checked the cylinder diameter with a bore gauge (4.281″) subtracting the two and we get (.004″) piston to cylinder wall clearance.
To insure proper cylinder sealing and minimize oil consumption the ring end gap needs to be set. I used a set of Total Seal file fit rings which are (.005″) larger than the bore diameter. This allows the builder to cut the rings to the exact size for each cylinder. The ring manufacturer calls for a (.019″) top ring and (.016″) second ring end gap. Each ring is hand filed and fitted to its specific cylinder.
The pistons are installed and I check the deck height (.000″)
After the pistons and rods are torqued down the rod side clearance is checked (.023″ – .024″)
600 HP 468 Big Block “Camshaft and oiling system installed”
I buttom up the lower end with the installation and degreeing of the camshaft. I’m using Isky hydraulic roller cam 396282/294. After adjusting the crank sprocket the final resting position for the camshaft is +3 degrees advanced
Unlike flat tappet camshafts roller cams rely on backing plates or cam buttons to limit camshaft movment. I installed a timing chain with a Torrington bearing to help minimize the internal friction between the timing chain and the block. Because after market Gen V Big Block timing chain covers are hard to come by I modified the existing timing chain cover. I welded on an additional plate to stiffen up the cover. By doing so I was able to get the proper camshaft end play of (.005″)
Oil control is key to freeing up extra Horsepower so I installed a Moroso 7 Qt. pan and a oil scraper.
The oil pump pickup to the bottom of the oil pan clearance was checked (3/8″) and the oil pump pickup was tack welded to the pump for added protection.
600 HP 468 Big Block “Heads, valve train, and induction system installed”
Before bolting on the heads and valve train I needed to verify the valve to piston clearance. I placed small chunks of modelling clay in the valve reliefs.
The head gaskets were installed and the heads bolted in place
The rocker arms, lifters, and push rods were installed (Note: because the push rod length was not known at this time I used two adjustable push rods) The engine was rotated two full cycles, the heads were removed, and the clay was inspected.
Piston to valve clearance on the intake (.220″) and exhaust (.200″). More than enough for our application
The valve train geometry and push rod length was verified. I marked the valve tip with a sharpie pen, install the valve train and rotated the engine one full cycle. This process was repeated until I got the witness marks in the middle of the valve tip.
The push rods lengths ended up at (7.650″ and 8.650″) and a set of Manley push rods were ordered
The heads were bolted on, the Isky hydraulic roller lifters, Manley push rods, and Crane rocker arms were installed.
The build was finished off with the installation of an Edelbrock Performer RPM Air-Gap intake manifold, Speed Demon 850 CFM double pumper carburetor, and MSD billet distributor
600 HP 468 Big Block “Dyno Testing – Judgement Day”
To insure we got all the performance out of our 468 build it was run on a DTS Powermark engine dyno at Saddleback Community College in Mission Viejo Calif.
I did an intial 15 minute break-in then a few short pulls to verfy timing and set the air/fuel ratio. After a quick cold down period we let the 468 go pulling it to 6500 RPM
624 Horsepower – 590 lb-ft Torque, on 91 Octane pump gas.
Click here to view the JMac Performance built 468 on the dyno
This engine is a great example of what can be done when the proper parts are used, the proper engine building techniques are implemented, and nothing is left to chance.
Contact John@JMacPerformance.com if you’d like more details on this engine build.