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post #5 of (permalink) Old 08-29-2008
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Originally Posted by jgard07 View Post
This is not correct. With a longer stroke in the same block, you would need a shorter rod or a higher piston pin location to account for the increase in piston travel. With an increase in stroke, the piston travel increases equally in both directions.
I'm not trying to argue but you are 90% incorrect. I noticed you said "you would need a..." which I took to mean that you've never built a stroker motor before... The reason I said longer rods are used is because I've built a handful of strokers, including my current daily driver and in every single case, a longer connecting rod was used. Here's the differences between a stock (left side of picture) and stroked motor (right side of picture)

A stroker motor utilizes:
Increased Crank Throw (distance between C and D)
Increased Rod Length (distance between B and C)
Decreased Piston Compression Height (distance between A and B)

The rod length does not affect the displacement of the engine. One way to build a stroker is to use an increased crank throw, decreased piston compression height, and stock rod length to achieve additional stroke. The big drawback to this method is reduced crankshaft strength. The best way involves calculating the Rod to Stroke Ratio to adjust the rod angle. This is achieved by dividing a motor's rod length by its' stroke. This is an important calculation to understand since it informs the builder about a motor's rod angularity which for this purpose is translated to cylinder wall stress. A low Rod Ratio yields a high rod angle. For example, a motor with a 5.400" rod length and a 3.000" stroke yields a rod ratio of 1.8:1. If we maintain the same stroke and shorten the rod length to 5.000" we get a 1.7:1 rod ratio. The rod angle has increased. A high rod angle or low Rod Ratio creates a greater potential for accelerated wear to cylinder walls, pistons, and piston rings. You were correct about one thing, by lengthening the rod, as stroke is increased, we can offset the increased rod angle. This makes it necessary to use shorter pistons but the shorter pistons prevent the premature wear caused by high rod angles.
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1984 Mustang 331 stroker
1990 Mustang 5.0L convertible

Last edited by stlwagon; 08-30-2008 at 07:43 AM.
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