I have seen thsese engines run at my track and the idm .21 will have a little more bottomend, the 359 tuned will be the better all around engine in terms of performance and reliabilty. However the siro is a great engine and has a ton of top end speed thats what they are none for there revs. Just make sure that you dont over heat the sirio because it has an AAc piston&sleeve which can be ruined if they are overheated. But if you want sirio top end and novarossi durabilty get the jp r9. But the siro is a great buy you wont lack any power.