You can fit the turbax in it I did it several years back, with the turbax and K&B 7.5 it took off with more gusto but it wasn,t that much faster than the kress jets with the .25 about 10 to 15 mph since the fuse cheater hole and side blowin doors can only pass so much air, I to just purchased another one from E-bay as well as a new K&B 3.5 and a fan unit also new there are a lot of these still out there, total cost was $350, just keep in mind that the kress fan unit is all self contained eng. fan and fuel tank, the .46 will be much more hungy for fuel and you can only get a small pair or tanks in it' flights will be short these are great flying jets with a top speed of about 110 mph, a little more if you are building the newer retract model so dont' give up on it, they build real easy, Fastlash- Eatonvlle Washington