Pushrod length...
From what I've seen if you are too long you could possibly cause coil bind and most likely break a rocker bolt amoung other things. So yeah they need to be right, that's why they sell the length checkers.
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
With OEM non adjustable valvetrain, pushrod length mainly dictates preload on lifters.
Valvetrain geometry (center wipe on valves) is done via shimming of rocker stand.
Preload range is argued amongst enthusiasts. Some like it light, some midrange+
Plunger travel on LS1/LS6 lifters is .150>.200 (depending on lifters).
I prefer using ~ .080 or nearest of preload, but I've used as much as .100 on certain lobes.
The "ideal" situation would be custom length pushrods, which is not hard to do or that much more expensive but a PIA.
Hydraulic lifters being "all forgiving
" we normaly just get to the nearest preload range desired and call it a day.
Valvetrain geometry (center wipe on valves) is done via shimming of rocker stand.
Preload range is argued amongst enthusiasts. Some like it light, some midrange+
Plunger travel on LS1/LS6 lifters is .150>.200 (depending on lifters).
I prefer using ~ .080 or nearest of preload, but I've used as much as .100 on certain lobes.
The "ideal" situation would be custom length pushrods, which is not hard to do or that much more expensive but a PIA.
Hydraulic lifters being "all forgiving
" we normaly just get to the nearest preload range desired and call it a day. 
