I have a 20' deep V planing hull project boat that I'm planning to repower soon. I'm thinking of having custom built marine engine based on the 292 chevy 6 installed in it. Given that a marine engine has to operate in a continuous duty environment, it has to be built differently to stand up to the challenge. Getting rid of the heat and detonation are the main enemies here so you can't build anything wild and expect it to last. I'm not interested in racing. I want an engine that's happy to run reliably at 3000 RPM all day long on mid-grade gasoline. The goal is to produce as much torque as possible at a cruising RPM of 3000-3200 without burning mountains of fuel in the process.

In my view there's lots of good reasons to use the 292 inline 6 for this application which I'm sure many of you might already be aware of:

-7 main bearings instead of 5
-the undersquare bore x stroke produces lots of torque at low and mid-range RPM's
-cast iron cylinder head instead of aluminum which can be really troublesome in a marine environment
-simple gear driven camshaft
-lots of readily available marinization parts suchs as manifolds, carbs, vapour proof starters, vapour proof alternators, vapour proof distributors

I haven't yet read Leo Santucci's inline 6 manual but I plan to at some point soon. I want to be sure that any modifications to the block/head required to eliminate any possibility of hot spots and oil starvation are carried out.

I think I've done my homework so here's what I propose to have assembled:

-precision machined block and head
-forged steel crankshaft
-forged connecting rods
-forged or cast pistons (suggestions here anyone)
-clevite bearing shells

-I want to burn midgrade fuel without any possiblity of detonation under load so I believe compression should be 8.8 to 1 or slightly more or less

-fully balanced rotating assembly

-roller lifter and roller rocker valve train assembly
-stiffer valve springs
-hardened larger than stock intake/exhaust valves
-hardened valve seats
-mild port and polish of cylinder head (finished ports dimensions must match marine spec intake/exhaust manifold)
-polished and cc'd combustion chambers
-stainless steel headgasket and manifold gasket
-marine profile camshaft for maximum torque at 3000-3200 RPM with a smooth idle and proper cylinder scavenging/heat removal (is this all possible at once?)

No scrimping on vapour proof marinized parts that could result in a FATAL explosion! I believe that crusader marine still sells parts for the 250 CU. IN. chevy 6 that should bolt right up including:

-vapour proof starter
-vapour proof alternator
-crusader intake/exhaust manifold and riser
-crusader fresh water cooling system (might need a larger heat exchanger)
-oil cooler
-centrifugal advance distributor with correct advance curves and a pointless HEI
-450 CFM marine 4 bbl carb with fitted with flame arrestor (Mercruiser had this on the only marine 292 they offered for sale in 1974)

I want everything kept as simple as possible for reliability, so I'll stay away from any fuel injection and electronic engine management systems.

I'm thinking that the finished engine should produce 225 HP at 4800 RPM and about 275 ft/lbs of torque at 3000 RPM and with proper operation and maintenance should last for 2500 operating hours before needing a teardown and rebuild. Fuel consumption should be in the order of 5-6 GPH at cruising.

Excluding the marine accessories, what will it cost to build my engine at a specialty engine shop?

Have I missed or overlooked anything? Your suggestions/comments/advise/feedback are welcome.

Thanks in advance.