After an hour or so of using the search button, it still doesn't seem too clear. I figured I'd make a thread for my application.

I am going to go duals with a x/sweet thunders. With the mods I will have in the spring (below)....

Mods...
Pace Setter LT's (1 3/4 primary - 3" merge)
No cats, AIR, EGR
LS6 Intake
Ported TB
TSP Lid
ASP Pulley
4.10's
Mikey @ Rapid tune

I don't want to lose low end or torque. In a year or so I plan on having a G5X3 (114 LSA) as well, so keep that in mind. I'd like to run better than 12.50's at 115 on the stock cam while making at least 350-360rwhp. My goal with the cam is consistent high 11's at 120 while making over 400rwhp.

One of my friends is running just about the same setup (minus the pulley and LS6) and he has ran a best of 12.2 @ 117 while putting down 370rwhp and 355rwtq before the TB. He is running 3" duals with Edelbrock mufflers. 3" seems to work for him, though I'm thinking the Sweet Thunders might flow better than the Edelbrocks which would possibly negate the advantage of the 3" in my case.

With all of this info in mind, would 2.5" or 3" work best for my application?
Now, I've seen users like Noseup say 2.5" is all you'll need for a n/a 346. OTOH, I've talked to people like Big Bronco who say just go with 3". TSP also uses 3" for their system. So who knows.

I'm not buying the stuff for a couple months, so i've got some time to think about this. Please help me out though!

*EDIT*I've just read on Sweet Thunder's website...
So even if I went with 3", would the effect be negated because the mufflers inside diameter itself is only 2.5"?

 

Id just go for the 3in if you plan on H/C in the future. I am still waiting to install my 3in true duals. Im a little paranoid because im still not sure how much ground clearence I will have because im lowered.

 

I'd stick w/ 3". It will be find for your power goals. But beware if you get lowering springs with a 3" TD system.

 

Just planning on a cam. I won't needs heads to run 11's.

I drive the car every day rain or shine, so I don't need to be out of control. 11's will fend off 99% of all cars around this area.

I only plan on lowering maybe an inch, that's if I even bother lowering it.

 

I read that 2.5" piping was good for up to 450-500hp, based on that, I 'd say go with 3".

 

I went with the 3" and I saw/felt no loss of low end. In fact I felt a noticable SOTP gain and then I got it dynoed and the power was there too. I just thought if your coming out of a 3" collector it should be constant. I would have went with 2.5" if lowered but I don't have any intentions of dropping it. Cheers!

 

I do believe you're the guy that made my buddy decide with the Edelbrocks and with the 3" system.

So I guess 3" might be the best way for me then. What should I do about the Sweet Thunder inner diameter though?

 

I'd say 3" too if you are planning on running those times in the future. If you are worried about ground clearence get 2.5". I had 3" duals and lowered 1" and couldn't go over speed-bumps. Now I'm back to y-pipe

 

I'm not too worried about clearance. My buddy doesn't seem to have any problems with his.

 

That's what made me decide against the Sweet Chambers, but saidly I "think" the inside of the Edlebrocks reduce down to 2.5 as well. I can't remember and I wish I would have taken a shot of the inside. If anything, it helps with some backpressure and with my system (dumps) the bottleneck would occur at the end, so I don't think it will matter, with either muffler you choose. If you don't have you heart set on the Thunders, I do know that the Magnaflow 4x9s are exactly 3" all the way through because I have them on my truck. Pics of those can be seen on the second page of my site. Good Luck!

 

You're probably right. When I saw inside the Edelbrock's, they really looked like they bottle necked. I am dead set on the Sweet Thunders because I've heard them and I think they sound excellent, not to mention I'm not going to run cats and I know they won't pop. I won't do the Edelbrock's because my buddy has them and I don't want to sound exactly like him. Thanks for your replies!