when is it ok to change to 24# injectors?

Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

304 HP x .85 = 258 HP
385 HP x .85 = 326 HP
480 HP x .85 = 408 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See http://users.erols.com/srweiss/ to get the calculators used in these examples.

let me put it this way...it shouldnt hurt you to change to 24's...but you dont like NEED them unless you have, say, a 347 or bigger

347 or bigger? No, a healthy 302 will need 24lb injecors, which is why the 93 Cobra came with them. Not saying the 19lb'ers wouldn't work, but more air means more fuel....and you're getting more air. Get some 24's.

It sounds to me like his 306 (10:1, windsor jr heads) is probably putting out more than the 258hp jrichker recommended for 19lb'ers.

As long as he's already buying a new MAF, I would say go with the 24lb injectors.

Also, get rid of those 2.73's in the sig, unless you did already...