Any tips for casting and making relatively heat-resistant/strong molds?

[noahyamen]

I'm trying to make an intake kit for a bike I own, and I'd like to try to cast and mold from my 3D printed prototype.

I've originally tried casting it in a flexible silicone. That worked pretty nice. And tried my hand at doing cold casting; mixing 1:1 ration of metal powder with resin+catalyst. And I was kinda surprised by how brittle and delicate the product felt after setting. Not sure how heat resistant it would have been either, but thats out of a lack of knowing.

Any tips for me? It sits directly on top of the carbs, and the carbs sit a few inches above the motor.