i picked up a set of 990s at a swap meet. i have a 402 with a up graded cam.the heads on the engine now are truck heads and a world intake with a 750 holley. does anybody know how significant the change will be

those heads are open chamber, so you'll lose some compression if your truck heads are peanut ports.

You have the # off the heads you have on there now?

# 3986133

You'll have a motor that's lazy/soggy on the bottom-end and midrange if you use those heads. Try and stick with ovals if you can.

the guy who built my last motor runs them on a std bore,std stroke 454 with a solid roller. 10.0 dial in a 65 chevelle drag car.

Sounds like an overkill !! The heads will be "too much" for your engine & create all new problems. (Been there, done that)! Best bet is to put 'em on eBay, make a profit, then go out & but some nice headers to improve what you already have.

i picked up a set of 990s at a swap meet. i have a 402 with a up graded cam.the heads on the engine now are truck heads and a world intake with a 750 holley. does anybody know how significant the change will be

They have really large intake runners, so you will lose bottom end with them, but if you're racing the car and want good high end performance, use them. I use a set of 291's on the street, they similar to the 990's but small chambers...I have no complaints, but I have about 100 cubes more than your combo, so that will make a difference. Unless it's strictly a drag car, you would be better off with a set of oval ports, or aftermarket rect. ports with smaller runners.