I have a 6.0 stage 2 summit cam and a next gen vs7875 turbo. What size should the exhaust be? I already made a 4" downpipe but cant figure out what size pipe to run the rest of the exhaust, Single 4" or dual 3" or bigger ? I plan on putting a manual cutout on it for track use.

 

If your going to run a cutout, a single 4" should be plenty. I would think the muffler choice if your going to run one, would be more important.

 

Depends on boost and muffler choice. A single 3.5 inch exhaust is fine if you plan to run a cutout. But make it electric, so much nicer.

 

Run single 2.25" crush bent junk installed by the closest muffler shop. Cheaper, light weight, and can be at factory like noise levels on the highway. You'll want that at one point, trust me! Then the 4" cutout for when you want to wake up the neighbors or race. I never understood why people would run a cut out AND obnoxious performance exhaust. You already have the performance exhaust with the cut out open. Why spend 5x the money and effort?

 

I decided to run the cutout and dual 3" exhaust with a straight thru mufflers. I was not sure if this was going to be big enough, if you look at the calculators on the internet it shows 3" or4 " inch wont support much hp. I didnt want to totally make it a turd with the exhaust shut.

 

Nothing against a nice full exh system, just thinking about the added weight/cost. Also, what's the point of a cutout if you have a nice duel 3" exhaust with a straight through muffler? I run the vacuum operated cutouts, so they are normally open and close with vacuum at idle and cruise. I can also flip a switch and block the vac signal if I want to cruise around and be loud. Or flip on a tiny vac pump and run them fully closed all the time.

 

lol, I have a single 3" ran all the way out the back with a borla muffler and a vibrant resonator. Can you say Choked!

 

If you're running an electric or boost actuated cutout, anything behind the cutout is completely irrelevant. You could run stock exhaust on the car. I'd get the absolute cheapest crap that fits. Boost actuated cutouts FTW.

 

Agreed. I have a small 3" downpipe, with a cutout down by the starter...From there, a Jeg's $250 catback, which actually sounds really good, IMO. The power difference between open & closed cutout, is VERY noticeable.

I'd like to end up with a 4" fender exit, or close to fender exit, but still retain the catback, but with my heavy car already having went 9.70's @ over 140, I'm not even going to bother with that expense/effort.

With it closed up, the car is super quiet, as opposed to being super annoying after about 10 minutes of being ran open...lol.

 

I understand the cutout makes it ok to use whatever size exhaust you want , but going by the online calculators 3" doesnt support much hp. I figure the turbo is good for 850hp or more and the dual 3" exhaust cam only support roughly only 680 capped up. Thats why i asked the question to see what everybodys experances are . i was looking at this chart.https://m.roadkillcustoms.com/determ...t-tubing-size/ I also picked flowmaster fx series muffler that is staright threw but seems to be a milder tone to keep the noise level down.

 

A full single 3" exhaust doesn't support much, that's the point of the cutout. When you want to make full power you open it and none of the exhaust matters. When you're just cruising around at idle/part throttle you're not making alot of power so you don't need the big exhaust.

 

so food for thought. Single 3”, borla muffler, vibrant resonator all the way out the back. Back when I had the stock engine I trapped 128. That’s full weight, 4000lbs with me in it. There were factors involved on that outed that were holding me back, but this is just Data to think on. Online calc says 646hp. That was on 10lbs. There’s a guy on the gto forum that dynoed like 630 at the tire and he trapped a couple mph less than me. I know it’s not cold hard data, it’s just simple comparisons and you can form your own conclusions. Now I have the same exhaust but a built 5.3. I’m currently on 20psi, while it’s a lot faster than it was, I feel like it’s definitely being choked as I cant tell much of (some) a difference from 14-20lbs. Cutout was going on it probably this Sunday.

 

I have to wonder if back pressure playing a role in your 5.7 giving up the ghost.

 

could be. But I think the larger factor was high compression, pump gas, and me being quite inexperienced at tuning. I’ve learned a **** ton since. Youve contributed to my knowledge. I’m still learning.

 

I do know my LS6 will knock on straight pump on anything over 10 psi at 14 degrees.

 

Could be what got my L77 too lol. I had a 3.5 dp down to the stock exhaust and mufflers. Took a lot of wg spring to make 9#'s.

 

told you.....

 

Cut out should be here this week!

 

I ran a 3" downpipe with a cutout about five feet south of the turbo and made almost 700whp at 13ish lbs.
3" will be easier to package and cost less than 4" for sure and if you have an electric cutout then who cares lol.

 

Cheapest/lightest after the cutout FTW. Don't try and run cutout tune with cutout closed. It will be a recipe for detonation and disaster.