If your car is screaming for big-block power but your wallet is crying for small-block mercy, then a budget 383 might be just the silencer you're looking for. The first 383 strokers were based on 350 blocks and utilised a 400 small-block crankshaft to increase cubic inches. That was back when 400 blocks were fairly common and manufacturers hadn't yet figured out that a 3.75-inch crankshaft costs about the same to cast as a 3.48-inch unit. If you're rebuilding your 350, then you might as well spec out a 383 kit for an instant 10 per cent increase in horsepower and torque from idle to redline.
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Things you need
- Basic hand tools (screwdrivers, pliers, Vise-Grip, hammers, plastic mallet)
- Standard sockets, full set
- Torque wrench and sockets
- Measuring tools (machinist's ruler, dial calipers, snap gauge)
- Die grinder and head porting kit
Start with any small-block 350 engine, preferably four-bolt main. You can use an LT-series engine, but the ancillaries will cost more. Have the block bored 0.030 over to 4.030 inches. Have the main bores align-bored and honed, have the deck surfaces milled flat (decked) and have the lifter bores checked and honed. All told, you should have about £455 into the block in purchase price.
Purchase any one of the several 383 stroker crankshaft/rod/piston kits on the market. You could try to find a factory 400 crankshaft, rods and pistons, but they're hard to find as a set and you'll need to have the main journals cut down from 2.65 inches to 2.45 inches. Better to buy new parts so that you can spec the exact rods and pistons you desire. Speaking of pistons, order a set of forged units designed to yield about 9.5-to-1 compression with a 64-cc combustion chamber.
Acquire a set of new or used, fully assembled L31 GM Vortec cylinder heads. These fist-generation Vortec heads flow about 239/147 cubic feet per minute of air at 0.50 inch lift, which will support about 490 horsepower in completely stock form, and are a direct bolt-on for any small-block. You can find L31 heads in 1996-1999 GM full-sized trucks, 1996-2003 Chevrolet Expresses and Tahoes, 1996-2003 GMC Savannas and Yukons and the 1999-2000 Cadillac Escalade.
Purchase an intake manifold designed to fit a carburettor to Vortec heads; the Edelbrock Performer RPM is a good choice, but Weiand and Professional Products both make competitive offerings. If you're looking for something different, take a look at a high-rise dual-plane intake designed for 1996-2007 Indmar marine engines.
Install a hydraulic, flat-tappet camshaft with about 222 degrees intake and 229 degrees duration at 0.050, 0.500 inch lift intake and 0.510 inch lift exhaust (with 1.6-to-1 rocker arms) with about a 112-degree lobe separation angle. This camshaft will be fairly tame in a 383, and the L31 head's flow begins to fall off over 0.500 inch lift anyway.
Coat the tops of the pistons, the combustion chamber roof, the insides of the intake and exhaust ports and the inside and outside of your tubular exhaust headers (any used 1 5/8-inch headers will work) with thermally insulating ceramic powder coating. This will help to keep heat and pressure inside the engine where it can make power instead of leaking into your cooling system and engine bay.
Top the engine off with 1.6-to-1 roller-tipped rocker arms, a 700-cfm carburettor, a GM HEI (high-energy ignition, coil in cap) distributor, a multi-spark ignition box, wide-gapped spark plugs, a standard oil pump and some synthetic race oil.
Tips and warnings
- An engine built to these specs should make about 425 horsepower at a low-as-can-be 5,300rpm and a torque peak at 450 pound-feet at 4,500rpm with a wide and stable power band all the way through the rpm range. The engine should run fairly cool, idle like a kitten, tolerate 91-octane gas (provided that you retard timing) and will probably get decent fuel economy to boot.
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