[Z06] removed catts do i need new tune?
#1
Instructor
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Location: fayetteville nc
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removed catts do i need new tune?
my mods are kooks longtubes cam and bullet exhaust. removed my catts, now i smell a strong gas odor. my friend told me i would loss tq and hp. anyone know if thats true. and do i need a new tune? thanks for your input. car is ls7.
Last edited by lynnb; 10-23-2011 at 05:40 PM. Reason: change
#2
Melting Slicks
Some cars need the additional back pressure that having cats brings and can lose power and torque w/o them.
Lots of guys say other wise but I have seen it back to back on a dyno.
#6
Le Mans Master
You don't "need" a retune, the computer will modify itself to correct the air/fuel mixture. but you will need to turn off your rear 02 sensors or you will shortly get a "check engine" light.
As far as the HP/Torque, you will actually see an overall increase in both, but at a higher rpm's. Folks are correct about backpressure, but that is usually for lower displacement motors, not the LS7. Some cars will loose a small amount of low end torque when removing their cats, but for what they loose at the bottom, they gain it up top. Most people drive their cars at the lower RPM range vs. racers who live at or close to redline.
I had a 280z back in the day with removeable cats and you could feel the bottom end loss, but it pulled harder at redline. My last 2 cars (LS6 and LS7) did not have cats and they both made more power on the dyno. The larger displacement motors do not rely on backpressure to make torque like an import 4 or 6.
As far as the HP/Torque, you will actually see an overall increase in both, but at a higher rpm's. Folks are correct about backpressure, but that is usually for lower displacement motors, not the LS7. Some cars will loose a small amount of low end torque when removing their cats, but for what they loose at the bottom, they gain it up top. Most people drive their cars at the lower RPM range vs. racers who live at or close to redline.
I had a 280z back in the day with removeable cats and you could feel the bottom end loss, but it pulled harder at redline. My last 2 cars (LS6 and LS7) did not have cats and they both made more power on the dyno. The larger displacement motors do not rely on backpressure to make torque like an import 4 or 6.
#9
Safety Car
back pressure is the enemy of power, period. the only motor that uses/need "back pressure" is a two stroke with an expension champer.
The smell is normal...if you remember pre 75 cars, they all smelled like that with some lead in it too, like aviation gas smells...has nothing to do with the tune, if anything, with more scavanging, the car will run a tad leaner at WOT in open loop, but during closed loop, the O2 will re-adjust the mix to 14.7:1
The smell is normal...if you remember pre 75 cars, they all smelled like that with some lead in it too, like aviation gas smells...has nothing to do with the tune, if anything, with more scavanging, the car will run a tad leaner at WOT in open loop, but during closed loop, the O2 will re-adjust the mix to 14.7:1
#10
Le Mans Master
after a nice cruise, you and your clothing will smell like those fumes. I would have left the cats on
#11
Racer
I just removed the stock cats and left the stock headers on. No big increase in fumes to me, I have not even got a CEL yet. So far 100 miles with no cats..sounds sweet!
#12
Melting Slicks
No cats are great until the a traffic cop or highway patrol pulls you over and cites you for the smog equipment violation. In CA you have to have the car inspected every year after that citation and it is not a sign off but a mandatory court appearance and proof of correction by the state. But the caveat is if the cop is a car guy and you are not an Adam Henry, that is the hammer for street racers that we like to use