Technical Write-Ups

High Flow Cat vs Test Pipe vs Stock

Magnaflow High Flow Catalytic Converter

It’s been argued for years. What are the gains, and how considerable are they, of using a test pipe or high flow cat on your car?

Thanks to Import Tuner (hit up the source link to find the article), we now have raw data and numbers to test the results and differences of the multiple configurations.

The article shows a test between these four:

  1. Stock Cat
  2. Magnaflow Ceramic Core High Flow Catalytic Converter
  3. Magnaflow Metallic Core High Flow Catalytic Converter
  4. Test Pipe

Basically, they put a slightly modified Civic (it had Intake, Headers, and a Cat-Back exhaust) on the dyno and get “147hp and 105 lb-ft to the front wheels.”

Here’s the results

  1. Stock Cat Benchmark
    • 147 whp
    • 105 lb-ft
  2. Ceramic Core
    • 150 whp (+3 whp over stock)
    • 107 lb-ft (+2 lb-ft over stock)
  3. Metallic Core
    • 151 whp (+4 whp over stock) (+1 whp over ceramic)
    • 107 lb-ft (+2 lb-ft over stock)
  4. Test Pipe
    • 152 whp (+5 whp over stock) (+1 whp over metallic)
    • 108 lb-ft (+3 lb-ft over stock) (+1 lb-ft over metallic)

Keep in mind that this test pipe is a stainless steel straight pipe (with flanges and O2 hole, of course). The eBay “test pipes” are mostly resonated, so they will actually flow a little less.

Anyway, this has been discussed before and many people have giving their ideas/insight, but now we have some dyno numbers to back it up.

  • gewinnste

    I said it elsewhere before and I’ll say it again here: This is the situation on a mid-performance setup. My mech.-eng. gut feeling tells me that there is non-linear behavior when the exhaust flow is largely increased like in a highly modded performance car (especially with a turbo) – in which case one could not just extrapolate the numbers given in this test and they might very well look like this: e.g.

    1. Stock: 400 hp

    2. Ceramic high-flow: 420 hp

    3. Metallic high-flow: 425 hp

    4. Straight pipe: 450 hp

    Somebody PLEEEASE do this test!!

    • Rican7

      Oh yea, I absolutely agree that its not linear. Almost all engine-performance/HP/torque improving mods will increase power based on a percentage. Its not like a high flow exhaust is going to increase 2hp on both a Ford Pinto and a Formula 1 race car. :P

      But yea, I’d love to see what happens when a turbo is strapped to the same car and the tests are run again. Things could get verrry interesting, I’m sure.