It's actually overlap that is the critical number in determining streetability (vacuum). You can have large 0.050" duration numbers but with a wide lobe center you can actually have decent idle vacuum numbers. 18 - 19 deg (at 0.050") of overlap for a 455 will be around 10-11" of idle vacuum (assuming enough initial timing, tuning, etc.). For a 400 ci, you prob need to be around 13-14 deg of 0.050 overlap. These vac numbers will be on the edge for needing a vac can.
|