Hi, I'm running a mephisto .12 on a large 1:5 scale track. What pipe/manifold combo do you reccomend?

If you are really talking about long straights then you can go 2 ways....

1) advised pipe with short manifold. Brings up the RPM high.
2) advised pipe, long manifold, larger pinions. Lowers the RPM a tiny bit but will boost some torque that you can use with larger pinions (or smaller gears).

Thank you