I have an OS .28 with about 2.5 gallons on it that would be a beast on a buggy or truggy if you are bashing but to much for the track. Would sell with jp-4 pipe for $225. PM if interested

i owned a argus... 8 gallons before i needed a new rear bearing after it ate dirt...
same with my alpha but its still going...

for bashing............any engine will be fun!!!

What are your thoughts on a RB Concept MT11, I figure I'll bash more than race so I will buy a big engine for bashing. If I later on want to race I'll buy a smaller engine.

Bigger isn't always better. The 21's will rev higher. The 28 will have more torque, which will accomplish little more than destroying your drivetrain faster. Get an Argus A52 or the new B52 which is supposedly even more powerful.., Werks, OS, Novarossi, Go GX II, RB Fire 11, etc...

If it has to be bigger and overpowered, than an OS 25XZ. But you really might as well spend now on something you can at least race later if you want, but that will still be really fast...

My whole drivetrain is steel and titanium so far, would a .21 get me going as fast as the .28 would, but with less torque?

Depends if you are talking racing or bashing. If bashing, then go mad with the .28 engine and let er rip. If racing, stick with the .21. The .28 will be overkill for a buggy and you'll actually spin out too easily, giving yourself slower lap times than if you were using the .21. The .28 will also be a pig on fuel, making more frequent pitstops a necessity. For buggies, the general consensus seems to be to go with a .21 engine and get a mid-high range pipe. If you find that you just aren't getting enough bottom end take-off, then you can look at either getting a bottom-end pipe or go with a light clutch setup for snappier take-off. That setup is usually more commonly used on race truggies though.

I will bash more then race so I'm going with the .28 Novarossi 7 port for some serious quick power.