for most bolts on the car they dont have to be on so so hard. if u feel its tight and when ur turning ur ratchet its giving resistnace stop..unscrew and screw it in more time. chances are it went in just a little crooked, or the bolt is old and cant take the torque. if it feels hard and u keep turning it, it will snap. remember that.

Yes...ive never broken a bolt in my life so i cant help...But i cant imagine how you broke 2 unless they are crossthreaded or just the wrong bolts for the holes or something. Did you try oiling the bolts first? get that 3 in 1 crap from the dollar store, Its great for bolts.

WTF are you using for a ratchet? A breaker bar?
Intake manifold bolts are very light torque, as you're threading into aluminum. I have no idea how you're not stripping the fuck out of the manifold, but breaking bolts instead.
Use a 1/4" drive ratchet next time. You can't really overtighten with a 1/4" drive, and if you are, you know it because you're trying.

Just snug it up, and give it a little pull. That's all you need...