Downpipe

[newJhoser]

I have searched a ton and can not find my answer. I am putting in a 4" custom exhaust. I live in CA so the cat is staying. I Do not want to lose ANY low end torque which I understand 4" DP does. My question is this. Is it worth going from a stock 3" to a 3.5" downpipe? My motor will be kept at stock horse power. My truck is an 05 6.0 Thanks in advance.

[smokersteve]

A 3.5" down pipe will fit better than the 4" down pipe. There is little benefit to be noticed or felt between a 3.5" dp to a 4"dp. If you had a 3.5"dp and purchased a 4" dp, it would be a waist of money IMO. You will see a benefit going from a stock system to better flowing and bigger components.

Another option is that you can get a 4" cat back system and get a cat delete pipe. Getting a cat delete pipe will allow you to have the ability to remove the cat and put it on when ever you want.

[colo_dually]

Understand your concern with the 4"DP. My opinion you may not see a performance difference in the 3" vs the 3.5"DP, you will see the difference in the EGT's. I've seen this on two 6.0's, and will be doing a 4" turbo-back from MBRP with CAT and 3.5" DP to my 6.0 when I get the chance this spring.

[dhanna6powerstroke]

I didn't lose any low end with the 4" downpipe.

[newJhoser]

There are a lot of threads on 3.5" VS 4". I have ruled out a 4". If 3.5 will lower my egt's 200 I'll do it. But if not I'll just keep the stick downpipe.

[dhanna6powerstroke]

Originally Posted by newJhoser

There are a lot of threads on 3.5" VS 4". I have ruled out a 4". If 3.5 will lower my egt's 200 I'll do it. But if not I'll just keep the stick downpipe.

Every truck reacts differently to some extent and to each his own, but you will not notice a loss in low end with the bigger downpipe.

[newJhoser]

Originally Posted by dhanna6powerstroke

Every truck reacts differently to some extent and to each his own, but you will not notice a loss in low end with the bigger downpipe.

That's what origionally thought. But after reading through 20+ threads on downpipes, the common theme on this forum is that there are figment issues and you lose low end torque with a 4" DP.
Many of those threads turned into physics debates. I learned it's not a back pressure issue but a velocity issue.

[dhanna6powerstroke]

Originally Posted by newJhoser

That's what origionally thought. But after reading through 20+ threads on downpipes, the common theme on this forum is that there are figment issues and you lose low end torque with a 4" DP.
Many of those threads turned into physics debates. I learned it's not a back pressure issue but a velocity issue.

Noted I'll stick with the 4", fits great.

Don't want you to think I'm arguing or being a smarta** either. I'm just reporting about my truck.

[mike 6.0]

4 inch turbo back diamond eye comes with reducers to add cat. I would think with cat on truck 4inch back would be less restrictive. My 05 is just as slow as it was when it was stock, just lower temps.

[newJhoser]

Thank you everyone for your responses. I think I'm going to go with a 4" cat back for now and if I don't like it then I'll get a 3.5" downpipe. I love forums like this. Your experiences have saved me 1000's over the years