Originally Posted by LS-57
A 406 is a very common build, it is a 400 bored over with a ton of options. I believe it was John Lingenfelter (could be wrong) who built the "first" one in the '80's & they took off from there. The early ones used 350 rods (longer) with custom pistons. Today it is still a common way to go but the options are endless. Scat and others now have stroker kits to bring it to a 427 and 434.
The factory 400 has 5.5" rods, a 350 has 5.75" rods which where the most common way to go till recently when the 6" rods became available. It is easy to push over 400hp with over 400 torque reliably on pump gas on a proper modern 406 combination.
Rod length has absolutely nothing to do with making a 406, and boring a 400 isn't what a "stroker" 406 is all about, it was made to increase the size and power potential of a 350, just as the 383 setup was designed to do.
Stroking a motor is all about changing crank journal throw, rod length is only a matter of preference and determines what compression height piston is required.
Boring a 400 .030 to 406 is chump change, isn't going to make any appreciable gain, and won't be a "stroker". I'm not saying a GM 400 can't be made to make power, just clarifying things for some who may not know the difference.