As for installing an aluminum block in your Airboat, I think it's going to come down to cost. A production 350 iron block weighs around 170 pounds, and aluminum blocks on the market come in between 90 and 100 pounds. Dart Machinery, GM Performance Parts, and World Products all offer very nice aluminum blocks that you could use for your engine buildup; however, for the cost of an aluminum block, you could build a really nice 383, which would have a bunch of torque right in the rpm range you need. Also, most of the aluminum blocks out there are set up for racing, with very large cubic inches. The camshafts have been raised and the pan rails are spread to clear stroker crankshafts. All of this causes you to use specialized components, equaling dollars.
Before you start your build, find out the peak rpm your Airboat's prop will handle. It's very important that you do not overspeed the prop. The prop's limiting speed is determined by the diameter. When you overspeed a prop, the tips of the blades go sonic (the speed of sound) which will cause the blade to break over time. When this happens, you definitely don't want to be in that boat. Once you have this limiting speed, build your combination around this number for maximum torque. Also, we'd recommend installing a rev limiter several hundred rpm below this threshold just to be safe. Happy boating!
Sources: dartheads.com, gmperformanceparts.com, orldcastings.com
Bracket G-Body
Q I purchased a '78 Malibu bracket car from an estate sale, and according to the e.t. slips I found, it ran 12.40s at 107 mph. I need some help in a couple of areas: identifying whether it has forged or cast pistons, selecting a solid flat tappet cam, and determining what slick size to run. I'm guessing the car weighs 3,300 to 3,400 pounds (it has been stripped for racing). It has a 0.040-inch-over 427 BBC (435 cid); a cast GM crank (3904815), pistons (2385P), and closed-chamber factory heads (3904390); a Weiand 7544 single-plane intake; a 1-inch carb spacer; and a too-small 650 Holley double-pumper. The rest of the drivetrain is a TH400 trans, a 3,000-stall B&M Holeshot, and a Ford 9-inch rear with 4.11:1 gears. The engine had a Crane Cams CCH-304-2 NC hydraulic cam, which specs out at 234/244 at 0.050-inch tappet lift and 0.553/0.576-inch max lift, and is ground on 114 centers. One lobe on the cam has me concerned so I don't plan on using it again. Currently, the car has a set of worn-out Goodyear 30x9.0x15 slicks on it. According to my research, with help from my good friend Google, it seems the pistons are Speed-Pro/Federal Mogul, but I can't find out if they are cast or forged. I have looked at cams from Comp Cams, Crane Cams, and Herbert Cams, and will also install the cam manufacturer's valvesprings. Lastly, I'm thinking of running 28x9.0x15 slicks but am unsure what rpm the engine will be pulling though the traps. What do you recommend?Gene Reedy
Via e-mail
A It appears your engine was built around an L36 390hp 427 from 1967. From the factory, all 390- and 400hp 427s came with cast 10.25:1 compression pistons. However, the Speed-Pro piston number you gave us was one of the approved performance replacement pistons for the IHRA Stock Eliminator engines. The Speed-Pro number was in good company with CP, JE, TRW, and Venolia forged replacements. Could I find a direct listing to confirm that your pistons are forged? No, I couldn't. However, if you inspect your pistons and look for a flat steel plate cast into the piston to reinforce the wrist-pin area between the skirts, they are cast. If your pistons are a nicely smooth, molded piston without any noticeable cast patterns and steel reinforcements, that's definitely forged. Also, check your piston-to-wall clearance with a feeler gauge. If it's around 0.002-0.003 inch, they're cast; if it's 0.006-0.007 inch, they're forged. Sorry, but this is the best we can do.