A 400 is just a 383 w/ bigger pistons & lower compression. This was because of the down grading of gas at that time, & changing emissions requirements. Also, the 400 has an EGR valve that the 383 did not have. All it takes to wake up a 400 is a little more compression, & a little more timing. Emissions requirements mandated lower timing in most all motors to meet hydrocarbon emissions standards. 400's are actually preferable when building a stroker motor, because it has the biggest bore of any stock Chrysler engine.
