I have a 5.0 with the mods listed in my signature, and I wanted to get a little more power out of it. Should I put a bigger Mass Air Meter and bigger injectors on my car? If so, what size should I get? And what size do I already have?
A bigger MAF won't do too much until you increase the airflow through the engine. Items like a ported lower manifold (search on Tmoss), Explorer upper & lower manifold, bigger throttle body, etc will be needed to make the MAF worth while.
On a budget? do the junkyard upgrade...
Gears - 87-88 T-Bird Turbo Coupe rear axle - disc brakes and 3.55 or 3.73 gears in one package for $125-$300. Add another $100-$200 or so to complete the brake upgrade.
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a $25-$35 flange adapter from Pro-M to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1
95-97 Ford Explorer intake manifold & throttle body $150-$300. The intake manifold flows 220 CFM +, much better than stock. Throttle body is 65 MM, bigger than the 60 MM on stock stangs. I got a 96 with EGR passages that match the stock setup, so my smog gear works just like factory. You’ll need a 65 MM EGR spacer & new gaskets for $65-$90 so you have a place to mount the EGR & throttle linkage.
3G alternator from 94-95 Mustangs or other Ford. $20-$120. A must have to make the electrical system work like it should. You’ll need a 4 gauge power wire and a 125-135 amp fuse to go with it about $15- $30.
Lincoln MK VIII electric fan -$40-$160. Free up some HP by not having to drive the stock fan. The 3G alternator upgrade is a must have prerequisite before you do the MK VIII fan. You won’t have enough electrical power if you don’t do the 3G upgrade.
*1.) Pro-M has revised their website lately, but here's what I found for the MAF adapter flange.