Fitting A Cast Intake To A Tall-Deck Block
As if the build wasn’t interesting enough up to this point, the team realized that in its intended environment (an airboat), the vibrations would more than likely crack the welds on a sheetmetal intake manifold, which are the norm for an 11.1-inch deck application.
Instead, Prestige decided to adapt one of AFR’s cast aluminum Magnum single-plane intake manifolds (designed for a 10.2-inch deck height) to the engine. First, they machined the flanges to accept O-rings, eliminating the need for traditional intake gaskets.
Then, Prestige machines a set of intake spacers, along with a set of custom china wall spacers for the front and rear of the block to properly support the intake manifold. Not finished with the custom work, the customer also wanted to run a traditional distributor, which most places would call impossible in this application. However, with some careful measuring, cutting, and welding, they were able to pull it off.
To fuel the fire, A 1475cfm
Holley Gen-3 Ultra Dominator race carburetor was bolted to the intake manifold, along with a one-inch thick four-hole carb spacer. A Moroso vacuum pump system was also fitted to ensure a more-than-adequate vacuum supply for the engine.
Since a fabricated sheetmetal intake manifold was a no-go, the team at prestige build spacers for both the runners and the front and rear china walls to adapt an intake designed for a 10.200-inch deck block, to the 11.100-inch deck of the Brodix block.
Making Power
Putting this bad boy on the engine dyno, Prestige knew it was going to make a ton of power, but wanted to do a little testing as well. In addition to the normal BBC dyno headers, the team also wanted to dyno test several variants of the actual custom airboat headers that will be run on the engine, as well.
The first thing Prestige did was set a relatively conservative RPM limit on the tests, due to the long stroke. If you read the
Bore Vs. Stroke article we recently published, the method for calculating piston speed (the main concern when limiting RPM in a long-stroke application) tells us that for this combo, 6,200 rpm is pushing the piston speed pretty hard. However, in the airboat application, the most the engine should see is mid-5,000 rpm.
The customer also wanted to run a traditional distributor instead of an individual coil pack setup, so with the custom spacing, there were custom modifications necessary to make it happen.
In the first pull with the dyno headers, the engine made 730 lb-ft of torque at the start of the test, at 3,500 rpm. Peak torque was 910.7 lb-ft at 5,000 rpm. Peak horsepower was 984.5 at 6,200 rpm, and still climbing.