Thanks for the input. Jun 18, 4. My engine is a stroker bored. If I had it to do over again I would think twice about using that block as a starting point. However the engine runs strong and no problems after a couple thousand miles. Jun 18, 5. Jun 19, 6. Jun 19, 7. Messages: 9, Likes Received: 2. Sonic test the block first. I wouldn't run any less than. I've found that precious few blocks that I would run at. Jun 19, 8. Jun 19, 9. Messages: 11, Likes Received: Jun 19, Rather than minimally offset grinding the journal down to the next standard bearing undersize which yields only a small stroke change , performance offset grinding typically reduces the final journal diameter to a smaller size used by a different but still commonly available connecting rod.
For example, when a 2. In theory, going from a 2. However, in the real world this much of an increase isn't practical: p Pi, the math operator used to define the boundaries of a circle is an infinite figure, so trying to exactly intersect the tangent point of two different diameter circles is impractical; there is tool-chatter to overcome; and usually you're starting with a used crank that requires normal undergrinding to make up for wear.
For these reasons, crank grinders typically allow a 0. The small-block Chevy guys are fortunate that their favorite engine design has two different rod journal sizes available. That's not the case for many other engines. In fact, the vast majority of engines built with offset stroker cranks use rods from a different model engine or aftermarket specialty rods. This may require the use of pistons with a different than stock for the original engine pin diameter.
Welding Engines with large rod journals such as Buicks, Oldsmobiles, and Ford Windsors can achieve fairly decent stroke increases via offset grinding and nonstock rods.
But in most cases, really radical stroke increases require other solutions. Welding is a traditional procedure for obtaining big stroke increases. This process involves adding material to the top side of the rod journal, then regrinding to the original rod journal size but with the journal centerline moved outward in relation to the main-bearing centerline, thereby increasing the stroke.
Forged cranks are more suitable welding candidates than cast cranks, but in any case, traditional welding induces tremendous heat which adversely affects the crank's metallurgical strength.
In recent years sophisticated submerged arc-welding and reheat-treating processes have been developed that address these issues, but the cost of a welded stroker has correspondingly increased to the point that for popular engines like the small-block Chevy, a custom-ground stroker crank made from a universal raw forging is actually cheaper in many cases.
Still, welding remains a viable alternative on those off-brand engines for which universal raw forgings aren't available.
Universal "econo" raw forgings are available for the more popular engine families. Their quality and metallurgy are acceptable for most uses. Typically, a universal raw forging is made with an elliptical rod journal so almost any stroke can be ground into it. The drawback is that grinding an elliptical journal into a finished round journal interrupts the continuity of the forging's grain structure, effectively negating its supposed advantage over a billet crank. Assuming you can afford it, you big-arm boys may as well buy a custom billet crank.
Limiting Factors So many possibilities, so little room. With all the stroker options these days, you'd think the sky's the limit when it comes to building giant engines. But real-world stroke increases are limited by the physical constraints of the cylinder block.
We've already discussed the problems with reciprocating assembly stack-up, but there are also other clearance issues: Big stroker cranks may hit the oil pan rails, and the rails can sometimes be trimmed, but there's danger of breaking into an oil passage or water jacket. Clearance problems with the bottom of the cylinder bores or with the camshaft are also common. There's also the problem of the overlap between the main and rod journals. To find overlap O :. As stroke increases, the overlap in the areas of circles defined by the main and rod journal diameters decreases.
Less overlap reduces crank strength and rigidity. The amount of acceptable overlap is determined by the strength of the crank material, the engine's power output, and its intended use.
When regrinding a finished crank into a stroker, care must be taken not to run into the internal oil passages. Attempts at welding the original passage shut and drilling a new passage usually prove unsuccessful; eventually the crank cracks in the fillet area. Piston Problems As we've seen, increasing the stroke and making no other changes usually causes the piston to stick out the top of the block. Shorter connecting rods are usually not the best solution; rather, pistons with raised pin heights help move the top of the piston back down below the deck.
The pistons can be made shorter but only to a point-there must be room for the ring package above the piston pin. Various devices allow running the oil ring through the pinhole area, and there are even two-ring pistons; while acceptable for regularly torn-down race engines, these solutions aren't recommended for long-term street use.
You could also go to a smaller diameter pin and bush the rod-but "a smaller stick breaks easier.
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