does it make a dramatic difference to say go from a 1 7/8 header with 2.5 inch piping to the same exact header in 3.0 inch piping?

i wanna do headers in the future and love the idea of bi modal exhaust however my 05 c6 currently has the 2.5 in bullet catbacks on it that i dont necessarily wanna get rid of just yet. to add to the equation i just bought a blower so im really trying to figure out how i wanna work the exhaust side of things now.

how much power are we really talking with the 3 in exhaust vs the 2.5?

 

Dump the 2.5 inch! We didn't see alot from 1 7/8 to 1 3/4! But I had nice gain from 1 3/4 by 2 1/2 to1 7/8 by 3 inch.

 

the npp mufflers have a 2.5 inlet,, the z06 bi-mode are 3.. of course the npp cost more though.

 

Rockin Blue's back to back test with the swap to headers with the bigger pipes proved that beyond any doubt.

 

With this being said unless I misunderstood, dosen't the Z06 bi-mode neck down to 2 1/2" right in front of the cans the same as the stock and NPP C6. Curious if GM had a reason for this as it would have been just as easy to make it 3" alll the way thru or did they do some testing and found it provided just enough back pressure on the stock motor to keep the torque up with out any or marginal HP loss. No facts here just questions if anybody knows or has a reasonable answer. Thanks

 

Yes the Z cans are 2.5, but the over axle pipes are 3 inch, so that helps a bunch. BTW, backpressure is NEVER a good thing in an exhaust system. It is, however a fact of life in production automobiles, so the production camshaft timing, ignition, and fuel delivery is designed to make the best of a bad situation. The ULTIMATE exhaust system would pull a vacuum...

 

seems like the obvious decision is the full 3 in exhaust.

now even though i have an ls2 would i be looking for exhaust that would fit the ls7/z06?

i remember reading something about the d port of the z06 exhaust being different from the circle port on the ls2....

 

I have just done the full LS7 or Z06 exhaust on my 05 LS2 MN6, in the past 2 weeks, perfect choice for me as I did not want the full length headers along with the difference in price, giving up a few ponys and retaining the factory look. I have to date thrown no codes, will pass emmisions (so far my state does not have inspections but you never know, they may need the tax money) have a definite SOTP mid range increase and estimate 15- 20 HP increase, which may be conservative, maybe not. Hope to dyno at the Cruise in at Bowling green next month after chuck COW checks the tune (he tuned it last year at the bash in Bowling Green) and will have some results as this was dynoed at effingham last year and have no other changes since. Many have dyno results to show in this range + some are claiming more. While the arguments will go on how much HP is being given up with the LS7 manifold over the LT headers, I may have sacrificed a few but have under $850 in this complete system including new gaskets and the NPP in a box. I used new d ring exhaust gaskets off the heads for the LS7 as recommended by many on here and love the NPP in a box. I do understand however if you are running the Auto there may be some clearance problems on the tranny pan with the 3" pipe clearing and some modifications may be in order. The rest was simply swap out the old and in with the new, a little finnagling but not bad, I do recommend dropping the rear sway in order to get the old cans off and the new ones on, it can be done but is much easier.

 

definitely helpful information in this thread keep it coming

 

Good info.