Horsepower Gains

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Low/no-cost starter mods

Remove air silencer & MAF mesh screen +5rwhp
Short belt AC/smog pump bypass & ASP underdrive crank pulley +8rwhp
Advance ignition timing +3rwhp

Simple bolt-ons

C&L 76mm MAF/CAI kit +5rwhp (over air silencer/MAF mesh screen delete)
Larger bore throttle body +0rwhp (but sharper throttle response)

With the intake side uncorked, the engine will respond better to exhaust upgrades:

High-flow mufflers +5rwhp
Offroad X-pipe +11rwhp
Long tube headers +7rwhp

Higher ratio roller rocker arms reduce valvetrain friction, increase valve lift, and increase 0.050" lift valve opening duration without changing the stock camshaft. While there's only a modest HP gain if the stock cylinder heads are still in place, the gain is greater when higher-flowing aftermarket heads are installed.

1.7 ratio roller rockers +4rwhp

With this simple package of mods, the output from a '94-'95 Mustang 5.0 GT with a T5 manual transmission can be increased from the stock average of 192rwhp (168rwhp with AODE or 220hp flywheel) to about 240rwhp (210rwhp with AODE or 275hp flywheel) for an easy 25% gain.
At the 275hp level, the stock 87lph fuel pump and stock 19lb/hr injectors will be performing very close to their limit so a higher-flowing fuel pump, injectors, and an adjustable fuel pressure regulator will be required before proceeding with the next stage of performance mods (heads, camshaft, intake manifold or H/C/I).

H/C/I combinations

GT40 heads/stock cam/GT40 intake/1.7 rockers/65mm TB:

310hp/360lbft (270rwhp/315rwtq T5, 240rwhp/280rwtq AODE)

GT40P heads/stock cam/GT40 intake/1.7 rockers/65mm TB:

330hp/375lbft (285rwhp/325rwtq T5, 255rwhp/290rwtq AODE)

GT40X heads/E303 cam/GT40 intake/1.6 rockers/65mm TB:

340hp/370lbft (295rwhp/320rwtq T5, 265rwhp/285rwtq AODE)

Edelbrock 60379 heads/E303 cam/Performer intake/1.6 rockers/70mm TB:

360hp/375lbft (310rwhp/325rwtq T5, 275rwhp/290rwtq AODE)

Holley 300-575 heads/Lunati 51027 cam/Holley intake/1.6 rockers/75mm TB:

370hp/375lbft (320rwhp/325rwtq T5, 285rwhp/290rwtq AODE)

AFR 165 heads/CompCams XE270HR-12 cam/Performer RPM intake/1.7 rockers/70mm TB:

370hp/390lbft (320rwhp/340rwtq T5, 285rwhp/300rwtq AODE)

TFS Twisted Wedge heads/TFS 1 cam/TFS Track Heat intake/1.6 rockers/75mm TB:

375hp/385lbft (325rwhp/335rwtq T5, 290rwhp/295rwtq AODE)