I'm another one that has been very lucky with TRX engines, they always run pretty good for me. I find that sealing them is the trick to getting good power out of them without the high temps.
I have seen the Novarossi 2.5 run against 3.3's and they are close in power, the 2.5 seemed a little stronger on the bottom with the 3.3's having the edge on the top end. The Novarossi also uses turbo plugs at twice the price of regular plugs.
That OS 21 on the other hand will toss that Revo around like a rag doll, it is a beast in a Maxx or Revo! If your getting into that price range the OS is the way to go IMO.
only problem i see with the novarossi 2.5 is for 20$ more i could have an o.s .21.http://www.ebay.com/itm/Novarossi-2-5-Super-Charged-Engine-Kit-Traxxas-Revo-NVRN25SCRT-R-/290874890557?pt=US_Radio_Control_Control_Line&hash=item43b97e993d#ht_2447wt_984
I have seen the Novarossi 2.5 run against 3.3's and they are close in power, the 2.5 seemed a little stronger on the bottom with the 3.3's having the edge on the top end. The Novarossi also uses turbo plugs at twice the price of regular plugs.
That OS 21 on the other hand will toss that Revo around like a rag doll, it is a beast in a Maxx or Revo! If your getting into that price range the OS is the way to go IMO.