Hi Agen yes it is a very old novarossi engine and i think its a short stroke one but i'm not up to date on the older models. That boost bottal Some one corect me if i am wrong is not a standard novarossi option. A few years ago it was all the rage to have a boost bottal or boost chamber I think yours is a home job. The fad has now faded and rarely do they make engines useing the boost type of backplate or bottal. If the engine is not in very good nick things like a frosted piston top or low compreshion. I honastly don't think its worth rebuilding. Apart from the expence you may find it very hard to get parts and less you find some old stock as it would most defenatly be a discontiued engine line. Parts may still be able to be found But I think the cheaper and better option is a new engine. There are plenty of good engines out there at all price ranges and for exprenced tuners and new ones. Here are my segestions If you want a high paformance engine thats ezy to tune and is well priced you could try an os vzb-v-spec. The os I feel is a great starting engine for some one new to micro nitro engines there cheap they may not last as long as some of the higher priced brands. But they paform great for the money. If you want somthing that will last and have high paformance go for a novarossi 21 plus 5 or 21 plus 5t. Info can be found at
www.novarossi.com. But don't rush into anthing do some looking at prices and how ezy parts are to find. I would also sugest going down to your local rc gas off-road club and haveing a chat to some racers. Most rc clubs and rc club members world wide will happly give you sugestions or advice and help. I Hope this helps you. Best regards Jeremy.