Going to a 3" downpipe and eliminating the cat and keeping the stock catback or switching to a custom 2.5" catback with the stock downpipe? Which will yield more horsepower and torque?

I'm thinking the DP will yield more because the stocker is a POS

 

Catless DP

 

id say dp.
the stocker is an abomination.

 

I say the downpipe and 3 inch exhaust will give you more hp gain.. But instead of getting any old exhaust.. I'd say do a 3 inch custom like you were going to with the 2.5.. Or if your worried about loudness go 2.5 custom with catless dp.. Cuz 3 inch catless will be loud

 

3 inch custom will also lose to much low end power unless your pushing ALOT more hp than stock.

 

Go with the DP. The stocker has that horrible dimple in it.

 

3.0 is wayyyy to bigg for ss/sc hp dude

 

Unless he runs a turbo!!!

 

this is something i don't get. why would you recommend this? by starting with a 3" and then going to a 2.5" you're creating restriction. the entire point of changing your exhaust is to eliminate restriction. so by intentionally creating restrictions, that defeats the point.

 

3" is suitable for 270whp. I'm not going to be shooting for that much till i finish the exhaust work and get the ported head

 

since when?

i vote for cat back.

 

Suprisingly, as the exhaust flows further down the pipe it cools. As it cools it becomes more dense and the flow slows. A way to help keep velocity up is to reduce the pipe diameter further down the exhaust pipe.

Do a Google search exhaust flow David Vizard. You'll learn a lot. I did.

Actually, I took the liberty of finding a good read for all of you.

http://www.geocities.com/motorcity/t...92/vizard.html

Enjoy.

EDIT: Dang nabbit .... only the first two pages of that link work.

Well, do a search on Google and I'm sure you'll find what I'm talking about.

 

actually by starting at 3 inch you allow the exhaust to exit the header with less restriction, and then by going down to the 2.5, you increase the exhaust velocity again leaving the downpipe and moving through the catback.

its better to have big to smaller, than the other way around.



and 3 inch has been to big for this car since very very few people actually move enough exhaust to keep the velocitys up.
most peoples ss/sc are under 280hp. above that, you may be pushing enough exhaust volume to pull it off. but not below.
hence why 90% of people with 3 inch experience a noticable loss in power, and a shift of the powerband a little to high in the RPMs

 

I have 3" catless downpipe. It isn't too loud. I stayed with stock exhaust. I believe too that it is best to get flow away from the header quickly, but keep the pressure further out. I still see 250 torque and pull great at low RPM. Stock exhaust otherwise is holding up well so far. Haven't even felt the need to mess with it.

 

thats why you wrap your exhaust up so it will keep the heat inside the pipe and flow faster. thats why i dont get when people only wrap their header and not the rest of the exhaust. wrapping from the header to the muffler is very beneficial.

 

my thought would be price.
wrapping a header will take alot less wrap than 10 feet of exhaust piping, and unless im mistaken that stuff isnt really cheap is it?

but i understand your point.

 

We don't lose that much power in the bottom end from going with 3"....With the issues that we have getting out the hole, I would say that 3" is a good idea to help with our 60' times and traction issues. A full 3" exhaust actually gives some pretty respectable gains as well. Check out Moderneco's posts about the Vibrant Header & DP combo with the Vibrant cat-back. Some damn good numbers posted up, and not much if any loss down low.

 

downpipe for sure stocker is so restrictive im hoping to get one soon 2

 

Although I dont have a aftermarket DP, I would think that the DP would see a better gain than switching the cat-back. A DP or a header is most likely my next purchase!

 

Thanks guys. I ordered the Catless DP

 

Picture courtesy of www.zzperformance.com

which i can say from personal experience, makes a great downpipe!

 

Congrats!! Make sure to let me know how you like it! I am stuck between buying a DP or a Header.

 

I had my stock cat replaced by a straight pipe on the stock DP and the sound was sooooo shitty. Plus the fact I was not running HPTuners so there was some sensation of performance loss. I got it re-installed for now (all stock dp).

 

Catless Downpipe , and replace your muffler and your set until you want to make ridiculous power

 

Will do

Staying with the stock exhaust for now. Want ZZP's shorty header next and then onto the ported head