Do big 500 cubic inch mountain motors, or 400 cubic inch small blocks, make more horsepower than the foundational engines of their beginnings? Not necessarily. As a matter of fact, raw horsepower is not always the answer for lightning quick acceleration. In most street or bracket applications, pure gut-wrenching torque is tremendously more important than outright horsepower for 99 percent of us. And torque is the exact reason for building a long arm engine.
Why build a stroker motor? It's an engine's torque, multiplied by gear ratios, that slingshot a vehicle from a dead stop. The advantages of more torque converter stall speed helps both street and strip vehicles. On the street, low-speed torque makes an engine tractable and easy to live with. A few hundred rpm more converter flash from the long arm engine sure works well with those standard rearend gears-whether for the street or strip. As any experienced racer will attest, a drag race is won at the starting line. The added low-end torque of a stroker slips an existing converter to a greater degree so more stall speed occurs and a vehicle will launch harder. A few hundred rpm more converter slip trackside will show up in lower elapsed time.
Straight-line racing and street performance aren't the only beneficiaries of low rpm engine torque. Short track, half-mile, and dirt racers also reap benefits from bottom-end power when coming out of slow speed turns. Low rpm power is torque in action. Additionally, power at the bottom of the rpm range means less wear on the engine and greater longevity.
If we think back to the musclecar era, the one thing Mopar engines were noted for was thundering amounts of torque. When you think of those high-winding late '60s/early '70s 302 buzz bombs offered by brands X and Y, do you think of torque? Hardly! Those engines needed high numerical rear gears, close ratio transmissions, and stratospheric rpm to propel away from a starting line. The lack of torque was the reason Z28s came standard with 3.73 gears (up to 4.88 factory available), not to mention the fact that 302 Z28s and Boss 302s couldn't be had with an automatic trans. Without the deep gears, those cars would have needed Jet Assist Take-Off bottles to get out of their own way. By comparison, the standard gear for most high-performance Chrysler engines (big or small blocks) was a 3.23. The 727 was both ubiquitous and legendary among Mopar followers. It was available with anything Mopar had to offer, street or race.
Of all the American V-8s ever made, the Chrysler engine is unquestionably the best nominee for the long arm treatment. Those outstanding OEM rod ratios, voluminous crankcases, and generous crank center-to-deck dimensions provide Mopar engines with an unfair advantage over the competition. Let's run down a list of the what-nots and where-fors that'll help guide potential long arm Mopar engine builders with the how-tos.
The Connecting Rod
The connecting rod is at its greatest angle when it swings up from bottom dead center to the halfway point of the stroke (90 degrees from bottom dead center). The angle, and/or what engine builders refer to as the rod ratio, gives a general idea of how much pre-load is placed on the center of the cylinder wall (the weakest part of the cylinders) and the piston skirts. As the rod tilts toward generating its lowest numerical ratio, frictional drag increases in the engine. More friction equals less potential horsepower, especially at higher rpm. Keep the rod as parallel to the bore as possible (higher numerical ratio) and you'll build a better mouse (or rat) trap. Pun intended.
To calculate the rod ratio, simply divide the center-to-center length of the rod by the engine's stroke.