^^^I'm sure that the larger 3" y-pipe will make a noticeable difference.

I expected that I'd lose something down low when I installed my StainlessWorks LT's and catted y-pipe but was surprised to find that I didn't. The primaries are 1 3/4 which is definitely overkill for my mild setup, but the collectors and y-pipe are 2.5 which I'm sure helps the situation.

 

I never noticed a loss of lower end after headers and Y-pipe, and I've had several different setups ranging from 1 5/8" primaries up to my current 1 7/8" primaries, and Y pipes varying from 2.5" to 3" both catted and non-catted.

I'm not going to sit here and tell you that you won't lose low end with larger primaries and Y pipe simply based on the various setups I've had, because physics will ultimately dictate that with each individual setup. However, of all the setups I've had, I like the 1 7/8" catted the best, mind you that's on a moderately modified 6.0L. That being said, I really liked the OBX headers too, which are much smaller in comparison, but were probably better suited to a stock motor.

 

So if you had no plans of doing anything else to your motor, would LT's even be worth your time? I"m talking stock *** motor with just a cat back and Hot air intake? Or would they be, IF you bought the appropriate size primaries, which brings up that can of worms too, which size?
I'm not positive but I remember reading somewhere that the stock manifolds flowed pretty swell.

 

Yes, there is a massive increase in power on a stock motor with LTs, above 3000 rpms or so. The first time you mat it, you will say "holy ****." A gain of approximately 25 rwhp is very noticeable.

 

You will feel gains from LT's, even stock, and especially if tuned. On a stock setup, I'd go with either some tri-y's or 1 5/8 primaries, or a smaller 2.5" collector if going with 1 3/4" primaries.

 

I put LT's on my truck a couple weeks ago. All I've got right now is a performance hypertech tune right now but I've got a 6.0, 33's, and 3.73's. I done this with a 2 second power brake with similar conditions.

Before headers(still hypertech tune)


After headers(same tune)

 

Haha btw don't mind the tractor, it's a buddy that stopped to see if those were mine.. He knows me all too well 

 

The problem with going to the 2.5 collector for me would be that I have a 2500hd and the exhaust is all 3" to the muffler.