ThunderV12, LLC has overcome many obstacles to bring these engines to market. Besides the rarity of the engines and the lack of over-the-counter parts, ThunderV12 also pushed through numerous design and engineering issues to make the engines operate and perform in their new role as a modern mobile powerplant. Such issues as insufficient oil supply, no available bell housings, outdated point ignition, 1960's induction, and limited RPM range of the original 702 engine had to be addressed.
Our first engine was one of three located for purchase. One was a locked-up engine ruined from water ingestion. The other was similar but presented as in "good condition". The borescope showed it wasn't. The last was a standard bore, the standard crank engine that was not stuck and had no measurable bore wear. What a find! We bought that engine and tore it down for inspection. Turns out it had a 6" crack in the crank, two bad rods, and two cracked heads! It took three core engines to build one truly good one. We realized other people are going through the same thing and there needed to be a way to buy a good engine without the "box of chocolates" surprise. We realized from the get-go, that the only way to build these engines right was to have a huge inventory of core engines. And we do..
A year and a half was spent locating, purchasing, and bringing back to the plant over 100 core engines. The freight alone on these endeavors was substantial.
The majority of these core engines have been torn down and graded with only the best parts available to become a ThunderV12.
As shown in the photos to the right, ThunderV12, LLC has manufactured adapters for attaching Chevy transmissions. This setup also allows the use of modern hi-performance aftermarket Chevy flywheels and permanent magnet gear reduction starters. These modern starters are a real benefit to the 702.
Two different cylinder heads were produced for the V12. A ThunderV12 comes only with the industrial casting that was not offered in fire or over-the-road trucks. Besides the better water flow of these heads, they also feature an internal PCV system that negates the six-hole valve cover and external hoses of its truck version. All heads are pressure tested for cracks.
Also shown are the holley style carbs to work with our custom cut Hot-rod Cam profiles and higher compression ratio. This cam, carb, and compression combination change the nature of the engine from a slow revving industrial engine to a free-revving hot-rod engine providing a peak torque curve between 2,000 and 3,000 rpm and peak horsepower at 4,000 rpm.
Valve train modifications are required anytime an engine's RPM range is doubled and lift is increased. The heads on a ThunderV12 engine have been machined for custom valve guides, springs, retainers, and locks to assure trouble-free operation.
ThunderV12, LLC has contracted with ARP for custom fasteners to allow these big engines to survive at the RPM's a hot-rodder expects. Rods are resized and checked for straightness and dimension.
A custom oil system bumps oil pressure from 35psi at 2,400 rpm stock to 60-70psi at 4,000 rpm.
The photos also show the stock V12 distributor has been tossed in favor of a modern crank triggered/coil pack ignition setup. The stock distributor becomes a huge firewall interference issue for most installations. ThunderV12's DIS unit provides dials for timing adjustments as well as a dial rev limiter. We have used the services of a dyno to verify carb tuning and to nail down the ignition timing requirements. Our dyno runs were made up to 5,000 rpm and we consider that speed an absolute redline. We recommend our engines be kept under 4,000 rpm.
Endless custom bracketry and machining have been tackled to make all these parts work together in harmony. Small touches are easy to overlook when they simply look "right".
For example, in 1960, this engine would have had a generator sitting on a bracket low and well off to the side of the engine. When the generators failed, they were eventually replaced with alternators. Usually, brackets were cobbled together to fit the alternator where the generator was. In a hot-rod, this would be about where the front tire is. We have custom-made a bracket that not only places the alternator in line with the valve cover (like a modern engine) but is also adjustable to allow for a variety of alternator pulley offsets. This is just an example of a detail that would be easily overlooked when walking around one of our engines simply because it looks "right".
Other custom items include the mandrel drive for the oil system, beefy and adjustable pump brackets, aluminum mount for ignition pickup, ignition trigger wheel, balancer machining for trigger wheel, oil pan supply taps, oil return plates, coil brackets, higher compression, and the custom distributor hole plug which is critical to prevent rear cam lobe failure.
Machining of the engines for rebuilding produces its challenges. Crankshafts and camshafts that are over 4 feet long and monster V12 blocks cannot be machined with standard "automotive" equipment. This leaves a challenge locating shops and equipment able to do the quality work required. We ship parts from Oklahoma to North Carolina to get the level of quality machine and balance work we require. For crankshaft grinding, we sent 4 cranks each to 3 different grinders. Upon return of the cranks, we evaluated each company on quality and selected the one that does the best work. This is a process that a person rebuilding 1 or 2 V12's simply cannot do. They are stuck with what they get. This is the kind of stuff that makes the ThunderV12 the best.
Although not a full list of what had to be done to bring these engines to market, we hope you can see the level of commitment and dedication.
The images above show the ThunderV12 dressed up with a 5spoverdrive transmission, valve cover art, and our test stand/dyno exhaust (not for sale).