Quick question.
Is there a cat on the 2004's and does it help removing it, and where exactly is it?
Has anyone tried cutting out the front of the air box for better air flow?


2004 chevy DD, no mods exept AFE filter

do some reading.

Quick question.
Is there a cat on the 2004's and does it help removing it, and where exactly is it?
Has anyone tried cutting out the front of the air box for better air flow?
2004 chevy DD, no mods exept AFE filter

tdess welcome to the Diesel Place. For the air box info use the search funtion and look for "swiss cheese". There will be pics in some of the posts for you to reference. Also search for "catalytic" and you will find info for that.

I swiss cheesed my stock box while I was still using it and my model year didn't come with a cat in my area. Also if you want more info on air filters do a search on that and you'll find a study that some members worked on and is very informational.

Quick question.
Is there a cat on the 2004's and does it help removing it, and where exactly is it?
Has anyone tried cutting out the front of the air box for better air flow?


2004 chevy DD, no mods exept AFE filter

My 04 doesn't have a cat. LB7 engine. Depends on if truck was california emissions or canadian about the cat.

Thanks for the info, just new to the site and the search areas.

To help us help you, fill out your sig with your truck model, engine type, any mods to the truck and any power enhancements, as well as where the truck is from and yourself too.

That way if you aske a question about something that pertains to your truck, we can look at a glance in your sig and give you an answer that will help you.

Welcome to the forums!

By the way, smart A** answers are always free, good answers will cost a little more.

There is plenty to help you with your truck here and don't be afraid to ask!

Now, on to your question. As the others have said, "It Depends". Up until about mid Jan, 2004, the 2004 MY trucks came with LB7's that had no Cat unless they were destined to specific areas like California or Canada, or the North East. When the LLY's came out, they all have Cat's and EGR's.

Unless your running some big performance additions, the stock air box is fine. If you believe you must try to increase breathing you can swiss cheese the air box, however your gains will be minimal if any. Many guys here on the board have tried just about every conceivable combination of intake and exhaust out there and the results are that the stock intake is fine. To drop EGT's, you can add a 4" exhaust and that will get you about a 200°F reduction. Going to a 5" exhaust will do nothing to help your performance but if you wallet is too heavy, it will take care of that problem.

Hope that helps.

If you don't know what type of Dmax you have, I believe the 8th digit of the VIN code will tell you. If it's a 1 than it's an LB7, if it's a 2 then it's an LLY.