# How do spark plugs affect catalytic converters **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [November 25, 2019, 3:12pm UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511 "2019-11-25T15:12:53Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![nickjordan1414\_160227](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nickjordan1414_160227/32/18458_2.png) [@nickjordan1414\_160227](https://community.cartalk.com/u/nickjordan1414_160227)\ **Post date:** [November 25, 2019, 3:12pm UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/1 "2019-11-25T15:12:54Z")
Hey, i have a 2004 Subaru Impreza and had the catalytic converters removed. i was after new spark plugs and in the owners manual, it has an option of different spark plugs to use if you have no catalytic converters. I was wondering what is the difference it has to the engine and would it cause it to run differently. ---
**Author:** ![It\_s-Me](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/it_s-me/32/12660_2.png) [@It\_s-Me](https://community.cartalk.com/u/It_s-Me)\ **Post date:** [November 25, 2019, 3:59pm UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/2 "2019-11-25T15:59:17Z")
> [@nickjordan1414\_160227](#): > > i was after new spark plugs and in the owners manual, it has an option of different spark plugs to use if you have no catalytic converters. The only options I see are for Turbo vs non turbo ![Capture](https://global.discourse-cdn.com/cartalk/original/3X/4/8/48e0ab76cebb868fdd5f042bb26f1010c3b6ee28.jpeg) ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [November 25, 2019, 4:13pm UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/3 "2019-11-25T16:13:27Z")
Cats provide a small amount of back pressure and hold heat in the exhaust between the spark plug and the cat so it works more effectively. I’d guess the plug might be a heat range step hotter without cats. The hotter range burns off contaminents a bit more. A cooler plug is normally used on a performance engine because the combustion process builds more heat. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [November 25, 2019, 7:06pm UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/4 "2019-11-25T19:06:11Z")
NGKs work the best but I do question why you removed the converters and how you figure the owners manual specifies no converters. You say you “had” the converters removed. Who removed them? ---
**Author:** ![ledhed75](https://avatars.discourse-cdn.com/v4/letter/l/f6c823/32.png) [@ledhed75](https://community.cartalk.com/u/ledhed75)\ **Post date:** [November 25, 2019, 8:09pm UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/5 "2019-11-25T20:09:52Z")
I was wondering the same thing, as I was under the impression removing the catalytic converters on pretty much any vehicle made in the past 45-odd years is illegal. ---
**Author:** ![kurtwm1](https://avatars.discourse-cdn.com/v4/letter/k/13edae/32.png) [@kurtwm1](https://community.cartalk.com/u/kurtwm1)\ **Post date:** [November 26, 2019, 1:56am UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/6 "2019-11-26T01:56:18Z")
Federal laws make it illegal to remove a catalytic converter if the vehicle was manufactured with one. Fines are as high as $10K for the individual who removed it. Interesting enough, it is NOT illegal to be caught without a catalytic converted, but likely will fail emission testing. ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [November 26, 2019, 2:31am UTC](https://community.cartalk.com/t/how-do-spark-plugs-affect-catalytic-converters/153511/7 "2019-11-26T02:31:52Z")
I think the enforcement would be difficult if you are not subject to emission tests. Not saying it is right.