My 2.5 Tmaxx engine is giving me so much problem that I want to change the motor. What motor besides the sirio will fit in the new tmaxx with no or slight modification?

That engine(2.5) should be more than adequate, what's it doing???
Matt

Hsn is at 4 turns out and lsn is flush with inner ring per traxxas. after 2-3 minute of running temp is 320. then its running rich because it load up and starts to cut off on after i let off the throttle and idle screw is set. Ten years of on road and I have not seen a .12 motor act like this (novarossi, o.s., RB, etc.) ny suggestions

Sounds similar to the problem I had with mine. It would either idle & not pull second gear, or pull second & not idle. I sent the motor to Traxxas(under warranty) and they replaced the piston & sleeve. Apparently, it had worn excessively & prematurely, a manufacture defect. I think you should send your motor to them & let them fix it for free. It'll save you from buying a new motor. I was baffled too about my truck, as I've got much experience with these little engines. Good luck, let me know how it works out for you.
Matt

Matt
Thanks for your info I called Traxxas and sent my motor out today!

Cool. When a company cranks out as many products as Traxxas does, there's bound to be a few screw ups, and fortunately they will take good care of their customers, as I found out. Good luck to you, and happy truckin'!!
Matt

i personnally do not like the 2.5 the thing really sucks to get it tuned.which i never could do it always overheated no matter what

Check for any cracks in the plastic on the carb, A major problem.