I’ve been a reader and subscriber for many years and have worked on Chevy engines in cars, trucks, boats, and even generator sets. My current engine project is for my Sea Ray boat. It has a ’78 Chevy four-bolt main engine with a COMP Cams 252 flat-tappet cam. I’ve become disturbed over the years with the loss of zinc from modern oils and the cam going flat. To enhance the issue, the boat will sometimes sit there for weeks without being run. I’ve come across a Vortec 350 complete with the roller cam I would like to build. The price was right (free), although it has a lightly spun No. 2 main bearing that will clean up with an oversize bearing. Since it needs line bore anyway, I figured a set of Milodon splayed caps would be a good upgrade. I’ll feel better running at 4,000 rpm for a couple hours with the extra beef on the bottom end. I’m not looking for a powerhouse as I am limited to about 300 hp, due to the driveline limits. I’d like a clean-burning engine, and the Vortec heads are advertised to create a swirl (vortex) in the combustion chamber. I was looking at an 0.030 overbore and the use of Keith Black 12cc D-dish pistons. The pistons would yield roughly a 9:1 compression (in the ballpark of what I want). How would this affect the air/fuel flow in the chamber? Will they enhance or disturb the vortex? Thanks for the great magazine.
The Vortec truck engine will be a great base engine to build for your maritime adventure. Making 300 hp out of this package will be very easy. Let’s check out a couple of parts you’ll be needing.
The Milodon four-bolt caps will be a great upgrade to the standard two-bolt bottom end. While you’re there, make sure you continue with main studs to round out the package. The three center four-bolt Milodon caps are sold under PN 11150 for the 4.490-inch narrow register, and PN 11160 for the 6.200-inch-wide register. Check out the registration width of your Vortec and order the appropriate caps. Also, we’d go with the Milodon replacement two-bolt front main. In a marine application with continuous operation at torque peak, the front main can take a beating. The front main cap is sold under PN 11153. Last but not least, pick up a set of Milodon’s main studs, PN 81125. This will give you the most bulletproof bottom end for crankshaft stability in a production block.
The Vortec heads were a major improvement over other factory production iron heads. These heads were modeled after the LT1 aluminum heads that came out in 1992. When the engineers went back to the drawing board to build the LT1 engine for the Impala with iron heads, they applied everything they’d learned and then some. The iron LT1s were a stepping stone to the Vortec truck heads. The iron Vortecs are the best production Gen I small-block head ever produced. Yes, it does create a good deal of mixture motion, but most of the gains come from good old-fashioned airflow increase. The intake valve area and bowl of the port introduce the fuel and air into the combustion space in a very efficient manner that keeps the mixture well homogenized. The kidney-shaped combustion chamber promotes good mixture motion in the combustion chamber when the piston comes to top dead center. The KB D-shaped dished piston retains a good deal of quench area on the top side of the piston. This will match nicely with the deck of the Vortec head.