Alright guys, before I get flamed into eternal damnation I gotta ask. Which size plumbing. I see half say 2.5 while others say 2.25 and I've seen a few say 2.0. Downey sells a system catback that's 2.5 (no cat). I am planning on buying a set of Downey Ceramics this week (at least ordering them) and I am considering their catback, but I need some advice first. This is primarily a daily driver with some hauling and play involved too. Mostly daily driving however. Opinions before I dump a grand on an exhaust that I am unsure of would be super.

Additionally for those of you who have done the Downey Headers. Is ceramic worth the extra $100? I would think so, but I am curious as to what others have to say.

Thanks in advance

 

The theory is that you want to keep the exhaust velocity high but also keep the pipe large enough to eliminate as much back pressure as possible. Yeah yeah I know "back pressure" is the most abused phrase associated with exhaust on most message forums.

Instead of writing a novel here I wil just point and you can read for yourself.
-------------> http://www.geocities.com/MotorCity/7...usttheory.html

read and learn young Jedi.

 

If you want to make your life much easier you can just plan on a 1-2" body lift as well. I just bought bulk UHMW and made my own at 1.5"

Its a very tight run down the passanger side floor board against the brake lines. After reading the link in the above post you may also realize that downey in thier infinite wisdom basically put a huge expansion chamber on the end of thier headers when that made that collector. I cut the end section of the header down to half of what it was in stock form and then welded a good quality 3/8" thick 3 bolt flange onto them. I used the downey crossover as well but also welded 2 more of those thick 3 bolt flanges onto them. If you plan on having a shop do the plumbing after the install I would have the flanges welded to the headers before you put them on. Since thay wont be able to get all the way around them after your done installing. Even if you camp everything together initially like I did you will want to get it all welded solid when your done. The difference between clamped and welded was quiet significant in terms of noise and sound quality.

 

Awesome article. It explains a ton. I went ahead and ordered an entire system from Downey this afternoon. I bought the Ceramic Headers, Crossover pipe, and Full exhaust. I hear all the nightmare stories, but I am looking forward to the challenge of the install. Got my SawzAll ready (hehe). I won't be doing a body lift any time soon so I am just gonna have to rough it. Any other tips would be hugely appreciated.

 

I decided on 2" when I got my Flowmaster 40 and catco put on. Cheap and OK.

Most of the restriction in in the manifolds and the crossover, not the tail pipe. If you had headers, go bigger though, 2.5"

Lamm

 

I have 1 3/4" for my 2.4L. I think 2" should be perfect for the 3.0.

 

I think the downey kit is a good solution.
2.5" is the way to go on a 3.0 personally. I plumbed my headers and xover into my stock system for a day or two and it was very depressing. Once I bought my welder and fabbed my new exhaust on I went from a motor that went limp at 4500 to one that pulled strong clear to the redline. The downey head pipes are 2" from the header collector to the y pipe. using a single 2" tail pipe in this situation would be pointless.

 

I just got 2.25'' put on my 2.4L with a 50 series FLOWMASTER. I would of gotten the 40 series cause the sound the best but I got the 50 for free. But I think for the size of our engines the 4 cyl. and the V6 anything above 2'' is real good.