Engine Stroking

The information presented below is based on experience in building Chevy 383s from 350 blocks. Much of it will also apply to most any other stroker motor, however.

You can spend a little or a lot on a stroker. You can make stock parts work or you can go all out on nearly indestructible hardware. In this guide, we'll focus on a more budget-oriented stroker.

On the surface, it looks like the cheapest route to a 383 would be to buy all the parts separately and make them work together. But my recommendation for the first time stroker builder is to go with a kit from a supplier such as Speed-O-Motive www.speedomotive.com. You get a lot more than just the parts. You also often get parts that are pre-clearanced and balanced. But you need to compare exactly what you get when pricing kits from various businesses. Some don't balance the assembly, some don't mock up the assembly and take care of any clearance issues, etc.

Speaking of clearance issues, no matter where you get the parts, you'll want to check out certain areas to be sure the longer stroke isn't creating problems. You need to investigate the rod bolt-to-block/pan rail clearance, the rod-to-cam clearance, the piston-to-crank clearance at BDC, and the rod-to-block clearance in the cam area. Different rods will require different amounts of clearancing. Usually a production 5.7" rod will need the shoulder of the rod bolt nearest the cam ground for clearance, as well as some work to the block under the pan rail to clear the rod bolt nuts. Larger/thicker rods, such as an H-beam rod will require a significant amount of material to be removed from under the pan rail and at the bottom of the cylinders near the cam. Production 400 rods won't require nearly as much clearancing, but I don't recommend them unless you are on a very tight budget. They aren't as strong and place higher loads on the cylinder walls since they are somewhat short. Lots of people still run them in 400s, but for the money, I'd rather use something like a GM X, pink or powdered metal rod.

Most machine shops will clearance the block for you for a price, but I was able to do mine myself using a carbide burr. The carbide bits are a little pricey, but you'll save money if you buy one to begin with and skip the standard tool steel cutters. They're not worth your time. Just cut a little at a time and check your work often. Be sure not spin your assembly with metal shavings and grit on the parts or the bearings, or you will likely scratch up a crank very quickly. You'll be doing lots of cutting, cleaning the block, dropping in a the crank, piston and rod, checking, removing parts, cutting some more, cleaning again, etc. It takes time, but to me, it was worth the money saved.

Big rods and lots of lift can create interference with the cam if using a block with the stock cam location. If going with a roller cam, strongly consider a small base circle cam to avoid this issue. Aftermarket blocks often raise the cam bore to accommodate larger strokes, but that is beyond the focus of this guide.

Definitely balance the rotating assembly when you get all the clearancing done. External balancing is cheaper and will be fine for most street/strip motors that won't see a ton of rpm. This will require you to use an externally balanced harmonic damper and flexplate/flywheel. When building a 383, you can use dampers and flexplates/flywheels from a 400 SBC. Internal balancing is usually more expensive, especially when using light weight cranks, because the use of heavy and expensive Mallory metal is required. The balance is better, however, and it allows you to spin more rpm with better durability.

One aspect of stroking that is often overlooked is compression ratio. Adding more stroke increases the displacement of the engine, but all that air is still compressed into the same space at TDC. So the C/R is increased significantly. While one should not be afraid of compression; it should be thoroughly investigated and taken into consideration when building and engine (stroker or otherwise).

Most of the piston manufacturers sell pistons for 383 SBCs as well as other strokers that will work with varying rod lengths. Different pistons are required when stroking a 350 except when using 400 rods with a 3.75" crank. The 400 rods are 5.565" long, which makes up for the extra stroke when compared to a 5.7" rod. See my earlier comments on these rods. Long rods and stroker cranks can put the wrist pin up in the oil ring grooves, which isn't necessarily bad, but you can't necessarily get too carried away with long rods. Plus a short piston tends to rock a lot in its bore. Most 383s are built with 5.7" or 6" rods and both perform very well.

The stroker motor builder no longer has to find a good 400 crank and have the main journals turned down to 2.45" to fit a 350 block since there is an abundance of aftermarket cranks on the market that are ready to drop in. For a budget stroker, I like a cast ductile iron crank. It has the strength of steel but is much less brittle than cast steel. There are also some good buys out there on 4340 forged steel cranks. While not cheap, they could be a lot worse. I am not a fan of 5140 forged cranks though. The price difference is small and they aren't nearly as tough and hard as a 4340 crank.

A 383 is a definite improvement over a 350; a lot more torque and a lot more fun. In my opinion, they are worth the effort and expense, not to mention the satisfaction of building something that is not "off-the-shelf".

If you have any questions or comments please click the "Contact Craig" link and let him know.

Copyright 2009 Bruce Johnson and Craig Watson