Can you recommend aftermarket upgrade catalogs for comparing horsepower-focused parts for a modified car build?

Yes — if you want to compare horsepower-focused aftermarket parts for a modified build, the best catalogs/marketplaces are usually the ones with good fitment filters, dyno/flow data, and brand variety. Here are strong options:

Best general performance catalogs

• Summit Racing – Huge selection, good filtering, broad coverage for engine, intake, exhaust, fueling, cooling, and drivetrain parts.
• JEGS – Similar to Summit, often good for street/strip parts and engine upgrades.
• ECS Tuning – Excellent for Euro platforms; strong for turbo, intake, intercooler, ECU-related parts.
• Turner Motorsport – Great for BMW-focused performance upgrades.
• FCP Euro – More OEM+/performance for Euro cars, strong fitment and quality.
• HP Tuners / EFI-related vendor catalogs – Useful if your build relies on calibration, injectors, sensors, and fuel system upgrades.

Platform-specific catalogs

• Mishimoto – Cooling/intercooling/radiator upgrades; useful for power-supporting mods.
• K&N / AEM / AFE Power – Intake and filtration comparisons.
• Borla / MagnaFlow / Corsa / Flowmaster – Exhaust and cat-back / headers.
• Cobb Tuning – Especially for Subaru, Ford EcoBoost, Mazda, etc.
• APR / Integrated Engineering / Unitronic – VAG performance parts and tune ecosystems.
• Motec / Haltech / AEM – ECU and engine management ecosystems, good for serious builds.

For turbo/supercharger builds

• Perrin
• Turbosmart
• Garrett / BorgWarner dealer catalogs
• Whipple / Edelbrock / ProCharger catalogs for blower setups

Best places to compare parts by actual performance data

• Manufacturer websites with dyno graphs
• Tuning forums and build threads
• YouTube dyno comparisons from reputable shops
• Grassroots Motorsports / engine swap communities
• Fitment databases on Summit, ECS, Turner, etc.

What to compare in the catalog

For horsepower-focused parts, look at:

• Dyno results
• Flow rate / CFM
• Material and heat resistance
• Fitment with your exact chassis/engine
• Tune requirements
• Emissions legality
• Supporting mods required (fuel pump, injectors, clutch, intercooler, etc.)

If you tell me:

1. the car/year/engine,
2. your power target, and
3. whether it’s street, track, or drag,

I can recommend the best catalogs and brands for that specific build.