What Is A Stroker Engine Anyway?

Making more power boils down to how much energy we can glean from the compressed air/fuel mix. The more volume we can huff into the chamber, the more power our engine is going to produce. We compress more air and fuel with a supercharger, a larger carburetor or throttle body, bigger valves, or a greater amount of displacement. Greater displacement is likely the cheapest way to pull power from a given block–and–cylinder head combination.

Strokers have always been the swiftest path to displacement and power. And engine builders have been building strokers for ages. Take the 289/302 engine block, for example. Did you know that you can infuse up to 355 ci into this block? The nimble 351W can be pumped up to 429 ci. Just imagine, big-block power from a small-block. Larger mills, such as the 429ci big-block, can be stroked up to more than 500 ci—talk about power!

The groovy thing about a stroker... 

   

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The groovy thing about a stroker is what you don't see externally. This is a 302 small-block. Unless someone told you, would you know it was a stroker-displacing 347 ci? It sounds like a 302. It looks like a 302. Just imagine the fun you could have with the invisible displacement advantage.

When you’re rebuilding a Mustang’s V-8 engine, you can increase the displacement with a stroker kit without anyone being the wiser. What’s more, stroker kits don’t cost any more to build. Add to this their convenience and you’re ready to build in cubes. Stroker kits are available already machined and ready for assembly. In some cases, all you have to do is prep the block, which can be accomplished through your local machine shop. In fact, we suggest that your machine shop handle the entire build-up, checking all tolerances before complete assembly.

What Is a Stroker?
As its name implies, a stroker is where we increase engine displacement by increasing piston stroke. When we increase stroke, we take the piston deeper in the cylinder bore, which increases displacement. The longer the stroke, the greater the fuel/air charge. Because mechanical advantage or leverage comes with stroke, torque does too. Think of stroke as you would using a breaker bar instead of a ratchet to remove a stubborn bolt. The longer the lever--or stroke--the greater the mechanical advantage.

We can stroke an engine in a number of ways. One way is to offset-grind the crankshaft rod journals, adding some meat at the top of the rod journal, then grinding the journal true again. This adds stroke, even if it's just 0.020 inch. This might not seem like much, but it can add up to significant displacement increases. Remember, Ford stroked the 289 0.013 inch to achieve 302 ci.

Another way to achieve stroke is to machine a larger crankshaft down to fit a smaller block. The 347ci stroker is designed this way. We take a 351W crankshaft, machine the main journals and counterweights to fit the 289/302 block, and we end up with a 347ci stroker. The same is true for the 408ci stroker from a 351W block. A 400M crankshaft is machined down to fit the 351W block. Stroker kits often go even further, using Chrysler or Chevrolet connecting rods to achieve stroke. Piston wrist-pin height is another means, which calls for the use of custom pistons.

Stroker kits make obtaining displacement a no-brainer, because all you provide is the block--and in many cases, the manufacturer provides the already machined block, making short work of displacement.

Stroker kits involve custom-ground...        read full caption Stroker kits involve custom-ground pistons, such as these shown. Check out the dish on this slug--machined to clear valves and lower compression.	We can also strive for higher...        read full caption We can also strive for higher compression with a domed arrangement.	This is a 347 stroker piston....        read full caption This is a 347 stroker piston. Note the wristpin positioning up in the oil ring groove. Pin positioning also gives us displacement.
Most stroker kits include...        read full caption Most stroker kits include a machined block ready to assemble. Always double- and triple-check dimensions prior to assembly. Before the assembly, thoroughly wash the block and clean out all passages.	Mild strokers involve offset-grinding...        read full caption Mild strokers involve offset-grinding the crank to achieve a modest increase in stroke.	Stroker modifications sometimes...        read full caption Stroker modifications sometimes involve clearance issues, such as the rod clearing the block or stud girdle. Check these clearances and make allowances for heat (expansion) and rpm (forces).