It's not my duty to make sure the car goes the number...that's on the racer. If the car sucks, or is sub par...not my problem. I can't hold everyone's hand. I do offer advice to our customers, again maybe they follow it...maybe they don't.
Converters seem to be the biggest problem with cars not running good #'s with a known HP engine. See this way too much! A buddy of mine running a Ford had me do his heads and intake, car slowed down...I kept telling him to check rpm at trap...never would. But I somehow got the blame for it slowing down...until he changed engines (more power) and it went even slower! That's when he wised up and changed converter/trans and car came to life...it is what it is.