i got 1:45:45 3 laps and 33:85 1 lap for luigi's. then i found some stuff on the internet. havent been able to do it yet, didnt try much either but:
After coming out of the tunnel in Luigi Raceway, head toward the part where the gray wall meets the brick wall off to your left. Look for the fourth brick from the left, and use a mushroom to blast toward it (right behind a tree). Now jump with the R button as soon as you hit the wall. If all goes well, you'll jump over the wall and skip the final curve of the course, saving you some precious seconds.
for those of you doubting the shortcut on luigi raceway, check out the attachment (save target as, it's a keeper ). obviously, that isn't me. I have allot of clips like that but I don't remember where I got them. I'll post the link if I find the site again.