C U IN REARVEIW

Looking to change my 2 1/2 bassani exhaust out for full 3" Z06 npp system. Will i need to retune?

Boomer111

If it is just the cat back, no. Gases have cooled down at this point flow is not affected, waste of $$.

If you have a tune already you have all the gains anyway available with your existing mods. The mufflers will do nothing other than sound.

Dano523

Yep, the back pressure/ lack of exhaust scavenging is at the OEM exhaust manifolds and factory cats, and anything down line of them changed, it pretty much down for exhaust note sound instead.

So no re-tune needed for just cat back systems.

Bill Curlee

100% on the mark! Your good to go!

C U IN REARVEIW

My car has 1 3/4 lt's, no cats and ecs mail order tune. Seems a. Little rich as i get smoke sometimes on an aggressive deceleration (and lots of gurgle).....so i was just wondering if going to a 3" exhaust would cause it to lean out more/to much? I am only doing the swap to reduce sound...but if i got some gain from it then great.

lbzraptor

I think the gurgle can be tuned out by a good tuner.

Bill Curlee

Yep! Significantly reduced if not eliminated.

Unless your engine is significantly modded and your stock exhaust is a restriction to flow, anything that you do to AFTER THE CATS, should not degrade or change the tune. Ive seen the OEM ZO6 Ti support in excess of 500 HP without any issues.

Heres why. Its basically a straight through chambered exhaust:

CUT OPEN Ti Muffler:



Bill

Most after the cat change, only change the exhaust note and loudness. Going from a completely stock LS1 base muffler system to a higher flow exhaust usually nets approx 5-7 HP. On a good day, maybe 10.

Entaille

I've wondered if this applies for catback systems on .. 2012+? vettes that have the two additional cats. my borla atak catback eliminated the two additional cats, and I think my MPG has gone down slightly - something I've noticed over the past few months.

car is performing fine, no CELs or anything, mostly just curious how the tune may be impacted by the additional cats being eliminated.

C U IN REARVEIW

This will be a headers/collector back install as I'm not running cats...?

C U IN REARVEIW

Also....would the smoke on the aggressive deceleration be due to that gurgle/tune? Back of the car gets a ton of carbon on it after running it? Is that just a bi-product of not having cats?

Bill Curlee

Smoke on deceleration is usually a sign of bad valve guide seals.

BC

C U IN REARVEIW

Car only has 25k miles on it. ....how could i test this?

C U IN REARVEIW

^^^^^ this^^^^^

Seadawg

If you have bad valve seals, it means you are leaking oil past them, and it shows as black smoke out the exhaust.

You should be able to "smell" it it too, it would be a burning oil smell, if you sniff near your exhaust once it is warmed up. Don't go crazy and do it for too long, but your nose is a good test.

If your car is warmed up and tuned properly (meaning, not burning or leaking any oil past seals), and if all emission parts are working properly, the exhaust should be virtually odorless.

You would be having to add oil between changes, if your valve seals were leaking any appreciable amounts of oil too.

C U IN REARVEIW

thanks for the reply. I only notice it occasionally on hard decelerations after spirited driving. I don't see the oil level going down at all (normal ls motor consumption). exhaust tips are always black with lots of carbon on them/rear of car. assume it is due to the off road x-pipe. smoke is not real dark though...although hard to tell as it disapates quickly

Boomer111

Sounds like your running rich.

I have a custom tune and I see no soot whatsoever on the tips.

The rear area is the direst area of the car though. It the exhaust tips are always clean.

C U IN REARVEIW

I have a mail order tune from ecs,obviously not optimal as it is probably tuned very conservatively. ... i was try to get by with it until i figure what i want to do with the car (h/c or fi) as there are no good tuners real close to me. Any concerns with running rich for awhile?

Boomer111

Better than too lean!

Seadawg

Just about all factory (stock tuned) vettes run a little rich it seems.

Seadawg

Some of the dirt on the rear will be brake dust particles, if you have the factory (non-ceramic) brakes too.

If you're burning/leaking internal oil (having it get past the valve seals, etc.), your inside of the pipes will almost be wet/oily, not the "sooty" look of too rich fuel.