the 23,500 RPM (NOS) Motor from the fast and furious kit is the fastest a ZZ can run with until you start tweaking it. it can use a 2.6 but it's really slow and you have to push it to get it moving.
Once you've done dual battery and other mods it should run with a 2.6 and probably the 3.0 and 3.8 if you work on it enough.
Depending on the battery size you may be able to get two batteries inside a Zip. Just WATCH THE STEERING WIRES!!! Another popular way to do it is to hack out the rear window and put it in there. That puts more weight towards the back for possible HOT HOT wheelie action.
As far as the mod itself is concerned, check my sig <shameless plug>
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I drive an Auldey, because it shouldnt cost you your first born for a 55MPH R/C car.