the 5 and 7 port may have a hair more top end for big tracks, i had a 3 port in a hyper tuggy and it moved it around nicely. right now i am running Caster Grenades and they are about all i can handle bottom through top. whenever i tune this motor i always end up at flush and flush with about 1mm gap and cold plugs. about 9 minutes with 7mm venturi in a tuggy too, temps in the 230's. after a race i can let it sit and it will idle through the rest of the tank if i let it, just purrs.