I just got my mugen mbx-5 and I need to buy an engine that will give it the most power on a short track. I would like to keep the price under 300. my buddy said lamberto collari b3 or b7. any suggestions or advice?

Get an rb s7 or a rossi 421b[&:]

If its a short tight track then maybe a OS21RG is what you need. Only a hundred dollar engine, but well worth it. They have GREAT bottom end, and it will leave you with 200 to buy upgrades for the buggy. They are very reliable and hold a tune. On a tight short track they can hold there own no doubt. I run one and i keep up with some great engines if not beat them....Its just not a top end demon, but on low-end grunt its got you covered... Do a search and see for yourself..

For a short track a Novarossi RX21P5 will be the best and if you buy the turbo you get a bit of extra top end, it keeps its tune well and is one of the smoothest and reliable engines built. Not just cause I've got one but i hear it from most people with them. If you have a short track you want bottom end which is also a long stroke engine.

I think either the Novarossi/Top/Rex/Crono/JP P5/B5 is a solid decision. Very reliable, durable and long lasting. The Lamberto COllari B3 and B7 are also great motors for the money- but there durability and longevity still have yet to be seen. BUT, from what I hear from other racers that have quite a few gallons through them they are great engines that put out alot of performance regardless of the price.