Calling all v6ers who have gone from 2.5" to 3" exhaust...

[shenanigans]

post if you showed any gains...

we are trying to see what seems to be working best on our 3.8L v6s...

a 2.5' catback or a 3 in" catback...

http://web.camaross.com/forums/showt...2&page=1&pp=15

(thread got knocked off topic)

[Predator Bird]

i went from a 2.75'' flowmaster catback to a 3'' rumbler. i went from a 16.8 to 16.3 at osw. not too shabby if you ask me. i think you were there that night i ran that time.

[jessica2112]

Wow, that post got intresting.....I have a 3" to the muffler, but no track times yet. I put on 3" because I have an SC, and she runs and sounds good.

[Chris Camaro]

if it was free i would like to try the 2.75, but i love my 3 inch, make sure u go with high flow cat at the same time, no track times, but definatly more top end when i did it

[WickEdSix9838]

I went from a 2.5" flowmaster and a custout to the 3" rumbler. I never got any good ET comparisons because of crap track prep but my MPH picked up about 1 over the other setup.

[99davenport]

all I did was go from 3" flowmaster to a 3" borla and saw about .2 seconds of gain but it was about 94 during the day when I ran w/ the borla and it was only about 60 at night when I ran with the flowmaster

[HBHRacing]

Going from one company to another isn't a good comparison. Thats why I said in the other thread to compare the same company. going from a bad flowmaster to a better cat back like a borla ect is not suprising that there was a gain. Remember, best to compare apples to apples when trying to win an argument. Eric can't do that and I suspect no one else can either.


Cheers [img]smile.gif[/img]

[99davenport]

In that thread it says if 3" does work for our cars why dont all v8's get a 4" catback? Correct me if I'm wrong but don't most v8's go to a true dual system of 2 2.5" pipes which = 5" of exhaust flow?

[HBHRacing]

It doesn't work that way. Actualy a lot of them seem to think that 3 inch duels is a good thing. In fact it's very much overkill. But no. 2.5" duals =/= 5" single flow pipe.

it's "recomended" that cars running 350 CI and putting out "about" 350 HP should run 2.25" true duels. So for the V8 guys thats about right.

[99v6cam]

v8s dont get 4" because its really difficult to get it to fit. I know of alot of people who get 2.5" and 3" true duals though.

[99davenport]

I don't understand why he is arguing about why don't all v8s run 4" cat-backs saying they won't gain from them

[HBHRacing]

There are 4 inch cat backs, and they do fit fine. Thats not the point. It's severe overkill for a V8. They would need to be pushing at least 400 HP to even come close to needing 3.5" let alone 4inches. 4 inch is a deisel size. thats massive.

[toast]

Well here is the best i can do. When i had my car i started off with just a Ravin muffler on stock 2.25 exhaust and went a 15.3. Then i ran the car again with a cutout right before the axle on the same stock 2.25inch pipeing and stock cat. That time i ran a 15.1. Then i redid the whole exahust system with a highflow cat and an American Thunder 3inch system. After the install of the cat back alone i ran a 14.8 at the track. Now I believe it makes NO SENSE whatsoever if i went to a 2.5inch system from the stock 2.25inch system, to only gain .25inch in the diamter of the pipe that is just loney. Now if i had true dual exhaust then that would be a different story. It makes perfect sense if you have lets say a Mustang GT with stock dual 2.25inch pipeing to an aftermarket 2.5inch dual pipeing. The reason why is because the exahust is able to flow through two pies instead of just one big one, thus resulting in better flow, but not not always better sound. As an expert in exhaust and exhaust systems i know what works and what doesn't. Not only is an important to have an exahust system that yeild a nice power increase but you also want one that produces a great sound.

[HBHRacing]

I would love to make sence of your post toast. But honestly I can't. You had me up untill the mustang part. you gained by attacking restrictions. The cat that you changed helped a ton for this reason. Thats the key. you want as little restriction as possible while maintining velocity.

Remember. the bigger the pipe the more atmosphere in it that you need to overcome. this in itself will cause a restriction.

[mjparme]

The only thing you are going to get by asking people what their gains were, are seat of the pant guesses. Guesses that are influenced by someone who has just forked over a few hundred dollars for an exhuast and are desperate to see a gain.

The only way to put the 2.5" vs 3" debate to rest is for someone to measure backpressure AND exhaust gas velocity throughout the ENTIRE rpm range with a 2.5" system, repeat the test with a 3" exhaust system, and then compare the results.

Absent those numbers people on both sides of the debate are just guessing.

BTW, does anyone know what the optimal exhaust gas velocity is considered to be? (or does it vary from car to car)? I have read 300 ft/sec but not sure as to the reliability of my source.

[ August 08, 2005, 10:44 PM: Message edited by: mjparme ]