[KingLT1]

The bottle neck in the exhaust is the primary cat pipes. There is more then 5hp by deleting those. They free up 10-12whp(With tuning) on a bolt-on car...blower car would be a bit more. They neck down under 2" at the inlet connection side between the factory Tri-y header. Remove those and you have a exhaust that will flow fine all the way up to 700whp. CA performance made a nice bolt-on set, but they appear to be down for the count. The next option is New ERA, which requires cutting and they remove all 4 cats.


At this point your best option is a set of Texas Speed catted headers.


I believe the reason why there is a different part number for the cats on a ZL1 vs SS is: The driver side slip connection is larger diameter on the ZL1. Reason I know this is because I initially bought a set of Bullet performance cat deletes that came off a ZL1 from a Vendor(claimed they worked for all 6th gens). They bolted right up at 3 of the 4 connection points except the bullet delete pipe on the driver side would not slide into the stock cat back(slip connection)...it was too large diameter, so I had to modify it to make it work. I ended up selling them and going back to stock for a short awhile, then found a used set of CA delete pipes for a SS and they bolted up fine other then I ended up buying a 2.5" 2 bolt preformed band clamp to use instead of the stock style clamp to keep it from leaking.

[squish72]

Good to know!

[oldman]

The OP question was not HP / flow gain between no front cats but was between the two setups SS and ZL1, and it is probably zero.

To me they are nearly identical systems. with the same or nearly the same components, yes admittedly to my surprise the ZL1 does NOT come with a better exhaust system. The car seems to perfume well enough stock, so, IMO a base supercharger kit on a SS would be OK with the stock exhaust.


Obviously if more money is to be spent on a base supercharged SS, it should go into the front:
Stage 1: CA front cat deletes 650 to 700 engine HP

Stage 2: LT with high flow cats I'd prefer a 1 and 7/8 fit and heat 700 to 800 engine HP


Stage 3: LT 2" coated full no cat 3" exhaust 800+ till you run out of money


Note that they are not really stages as one can't really build on the other. More like build targets that you should know what you are going for.

[KingLT1]

a discussion came up about why there is a different part numbers for the cats. I was just pointing out what that difference more then likely is.

I am also surprised that the ZL1 doesn't have a more capable exhaust, but perhaps the factory NPP is more capable then most give it credit for being Laynlo went over 700whp and 10.0 @ 139 on the stock exhaust down to the cats. I believe Mike(toohighpsi) went 9's on the stock exhaust system.

[oldman]

https://wildhammermotorsports.com/ca...borla-exhaust/

says these 2nd cat deletes work for SS and ZL1, it would indicate that the primary cats have similar exit dimension.