My experience just does not jive with it. Maybe the 6.0 requires more flow.

Like I said, with the cutout on my stock exhaust there was a huge gain in power. Very noticeable down low. Parish demonstrated 15rwhp gain with a cutout on a stock LQ4. Again, with the longtubes and cutout it's the same thing. With the cutout capped my lowend goes to ****. The best way I can describe it is like with the cutout open it feels like I have my 30" tires back on. Cutout closed feels like the 31.5" tires.

 

I say don't go bigger than 3", but if you want to go to a 3.5" go ahead, but at least hit the dyno and see the numbers.

 

not every truck is the same, neither is the exhaust...the horsepower gain is very believable...sickredsierra gained like 21hp i think...but where did they gain it? 1200 rpms? doubt it...more like 5500-6500...i would have to agree that my 4.8 is a lot different than a 6.0, plus mine being and ecsb with full stereo and 20s and being a 5 speed...just stating my opinion buddy and my experiences...

 

This was also with my 4.8, not the 6.0

John

 

Yeah, the smaller engine no doubt has a large play in it. Like I said, it's all about matching your exhaust to your engine. You can't make blanket statements like "you lose lowend with LTs." You lose low end because the pipe is too big and thus the velocity of flow goes down. The lower the velocity the higher the pressure and resistance to flow. A 1 5/8" header would probably be best for a setup like yours.

 

Exactly. I think 3.5 is Too big even on a 6.0. Feel free to prove me wrong with a dyno run, but you asked for opinions and that was mine. If you knew it was the right size you never would have asked what other people did.

Not trying to stir anything up, but don't call BS and Myth on opinions that you ASKED for.
There's a reason why almost everyone on here is running dual 2.5 or single 3" and it's because anything larger hasn't proven to work well without F/I.

Just my opinion.

I'd go 3" with your current muffler and a turn down. Does your current exhaust go out the back?

 

this turned into a pissing match btw.

 

I stated results may vary earlier. I said going too large will have an effect, not just slappin on LTs.
Yes, a 6.0L has different requirements. Thats why the pipe setup is different. Check out a stock 5.3 & 6.0 exhaust layout.

Perhaps a better thing to say is ditch a stock catback. It's nice @ the scrapheap or for stock.

 

Under certain areas you do though, just as you said, on a mixed matched set up.. So for a everyday joe, that wants to put them on his 4.8. 5.3, more then likely they will exp a low end loss, like a lot of the guys here have.. I see exactly what your saying, I shouldev been a lil more clear..

John

 

The catback is so far back I don't think it will make a difference whether it's 3" or 3.5". The only thing that matters now is the fact that I'm running a 3" Y into a single 2.75" pipe. If I'm not mistaken Mangled03 said his truck was faster with his truck running the open Y pipe. I gain power everywhere with my cutout after the Y. So I'm thinking the least resistance to flow will give me what I'm looking for. That's why I asked about the (custom) 3.5" catback. I also thought about just removing the catback and putting a turndown off the Y pipe