Grandmaster Engineering: 351 - 450
351 - 370: Most of the stuff that you would be making now would be used right away to skill up. Make Handful of Cobalt Bolts till you have 50 of them.
Note: When you craft Handful of Cobalt Bolts you can get 1 or 3 bolts because of its random nature.
371 - 377: Keep making Volatile Blasting Trigger till you have atleast 18 of them. Keep a check on your inventory.
Tip: You can use you "Engineering-Skinning" ability to scavenge any mechanical mob in Northrend to get some of these. Try Library Guardians in Storm Peaks.
378 - 385: Make 10 Overcharged Capacitor. Save all the above items along with this to make the next couple of stuff.
386 - 390: Get to 390 by making Explosive Decoy using some of the Volatile Blasting Trigger along with Frostweave Cloth. You would probably have to make around 8 of these.
391 - 400: Make 15 Froststeel Tube. If you happen to reach 400 then stop making them and only make more if you need it later on.
401 - 405: 5 of Diamond-cut Refractor Scope. Sells well on the AH since most hunters will be using them.
406 - 410: Make 5 Box of Bombs to get to 410.
Now comes the real money making part of this profession.
411 - 415: 15 of Mammoth Cutters. These things are used by almost all hunters that are into hardcore raiding. So you will definitely sell these for a lot of profit.
416 - 425: Craft some Saronite Razorheads. Will need to make around 25 to get to 425 skill level. Same as above will sell for a fortune.
Tip: Try to make good money by selling Mammoth Cutters and Saronite Razorheads asap. It is rumored that the whole ammunition system of hunters might be revamped soon in the coming few patches. So make good use of it while you can.
426 - 430: Make around 7 of Mechanized Snow Goggles. If you happen to be a Goblin Engineer you can skip this and make Goblin Thermal Sapper Charge upto 435. If not proceed down to the next part.
431 - 435: 5 of these - Noise Machine. A very nice and useful trinket that can be used by yourself if you happen to play a caster or can be sold to other fellow Engineers.
436 - 450: This last part is a little bit tricky. You can keep making Gnomish Army Knife all the way to 450. Although at 440 you can make your epic Engineering Helm. So if you want to get to 450 anyhow I'd suggest waiting on making that epic helm until you reach 445. Reason being there are ony green recipes at that point while the Epic Goggles are still orange to you.
Goodluck on your journey to 450 in Engineering. Hope you liked this guide and could pick up some useful tips from it. So long then...