bob53

Has anyone just taken out the pre-cats without doing a long-tube header install just to see what kind of HP is lost? The options are take the car to someone good at welding or purchase the Z06 plumbing distal to the headers as it lacks the pre-cats. Thanks for the info and advice.

-Bob

Tiger Shark

FWIW, I have the 2002 Z06 plumbing starting from after the manifold to where my Corsas bolt on. With only the Z06 plumbing, a Blackwing, high-flow air coupler (replaces accordian coupler) and Corsa Indy exhaust, my "after" dyno showed a solid 20 rwhp gain over my completely stock numbers. I don't think I would have gotten any actual rwhp increase out of the Corsas or the air coupler, so I attribute the 20 rwhp increase to the Blackwing and the Z06 components. This is just my guesstimation of the breakdown, but I probably got 17-18 rwhp from the Blackwing and 2-3 rwhp from the 2002 Z06 main cats.

stock: 307.5 rwhp SAE corrected
after above mentioned mods: 327.9 rwhp

Hope this helps!

:cheers:

01C5fan

Bob,

There is very little (if anything) to be gained eliminating the pre-cats on a stock engine. It will get a little louder, but performance gains are marginal at best. More trouble than it's worth imho.

Gordon

bob53

Gordon,

Are you sure? I am on the fence and here's why...

1. C5 Engineers attribute the change from 385 HP Z06 to the 405 Hp variant in part due to the removal of the pre-cats... They were unable to do this on the 2001 Z06 for emissions reasons. They cited these cats as a source of power.

2. The few cases like the one listed above where install of a blackwing + Z06 exhaust plumbing gives some noticeable gains... The problem with these installs is that "we" like to install a few things at one, and then we have a hard time knowing where the power gains came from... 20 HP gain is really high for a 2001+ LS1 from an intake... I suspect that the Z06 exhaust gains may be in the range from 5-10 HP, but this is a guess nothing more.

I hope this did not come off as rude, but I just want to spark some friendly and constructive conversation! :)

Thanks,

Bob

01C5fan

Bob,

First of all, you're absolutely right to question opinions you see posted here. They are widely varied and from time to time incorrect. My slant on this is the following. When I first had my 427 installed, it was my intention to keep the stock cats to avoid a potential problem with emissions inspection. The results on the dyno were disappointing so several attempts were made to improve the numbers. One of the first things that was done was to remove the pre-cats. The hp gain was less than five. Significant gains were attained only by adding long tube headers (without the pre-cats). With long tube headers installed, the difference between cats and straight pipes was also quite small. I believe that much of the difference between a Z06 and stock LS1 is in the heads and cam. This is just one in what will surely be a long line of opinions. Good luck with your mods!

Gordon

bob53

Gordon,

Thanks for your input! Given your experiences, I think that if i can find a competent welder for cheap (like some beer... :) ) then this "mod" would be worthwhile.

I am 1 to 1.5 years behind on mods as I kinda fell off the C5 planet for 1.5 years and didn't even think about mods... I used to be on top of these things. :)
-Bob

Mike Mercury

Bob, I did just that and noticed a slight deepening in the exhause tone and I swear the engine runs a little cooler. It costs's nothing to do this mod... plus you "give-the-finger" to the AlGore types that force this crapola onto us.

DIY here:
mikemercury.home.att.net/precats.htm

SpinMonster

:iagree: as if our clean running cars needed it in the first place.

bob53

Mike Mercury,

Thanks for the link!!! I thought it would involve welding but not so!!! Your solution is straightforward and very clever. This weekend is booked with preping the car for driving - wax, etc. I sense a mod weekend coming on in the next few weeks!!! :) Sorry, this sort of stuff is therapy for me!

BTW When you painted your engine covers and airbox, what sort of primer did you use? You sanded the "ripple" down first?

Thanks again!
-Bob

JWD01

Take Mikes advice - just gut those babies. I did mine and added Z06 Ti exhaust. The result was exactly what I wanted. :yesnod:

Mike Mercury

the primer I used is in the picture showing the paint spray cans; at this URL:
mikemercury.home.att.net/mods.htm
I didn't necessarily sand "down" the ripple; instead I filled them in using multiple coats of primer... sanding each coat inbetween. Mine aren't perfect, the camera makes the surface look more mirror like than they really are.


[Modified by Mike Mercury, 4:38 PM 4/23/2003]

Tiger Shark

Bob, one last thing to consider before you decide on a route to take.
The 2002 Z06 main cats flow more freely than the main cats that are on the non-Z06 plumbing from what I've read. So you're still going to get a better performance gain (although I'm still not exactly sure how much) with going to the 2002 Z06 plumbing over just deleting your pre-cats.

One last thing, I don't recommend buying a new 2002 Z06 section. They're way too expensive for what you gain. Maybe if you found a used one... a take-off, you could get a good deal. You might ask some of your local tuners/Corvette aftermarket shops to see if they have it. Make sure you get the 2002 over the 2001 parts.

The only reason I have it on my 2002 Coupe is that the dealership botched an X-pipe install when I took delivery, and when I literally demanded they put it back to stock (<- it was their fault... bad installation... long story... search archives back to around October 2001 with my user-id if you want the story), they had to order the part since the 2002s had just come out and they didn't keep any of the new stuff in stock yet. They messed up and ordered the Z06 version, and that's what they installed. I didn't realize their mistake until later. However, I'm not complaining. :D

2001 Red Coupe Bandit

I had my exhaust off for my TC and Gears install and they gutted my "Pup" Cats. I see no harm in doing so and it can only make the car better. if nothing else, it will sound slightly better and have less restriction, although slightly less restriction, it is still less restriction and it is a free mod.

I think they just used a drill and drilled out the material.

kewlbrz

Soemthing to note: the power increase on the 02 LS6 came from a combination of things.

beefier cam
lighter sodium filled valves
higher flowing more efficient main cats / allowing precat deletion
freer flowing air box
no maf screen
updated pcm programming

To me the cam accounts for the majority of the power increase.

-----------



- 2001 Yellow/Black/Black MN6/Z51 Ragtop - some mods
- Times : Blackwing & B&B PRT's 13.31 @ 107.26 (2.28 60ft on runflats - forum cruizein - bad track prep)
- 2000 Silver/Black/Black MN6 Ragtop ) Gone
- Times : Stock 13.39 @ 104.78 (2.07 60ft on runflats) - Vortex & B&B PRT's 12.90 @ 109.84 (2.08 60ft on runflats)
- 1979 White/Red L82 377ci Destroked 400 Drag Motor, 4speed, 4.10:1 Gear

MODS - w/How To's - Including some low level PCM/Control System Stuff

-shawn
Museum Member #8870


"The early bird gets the worm, but the second mouse gets the cheese."


[Modified by kewlbrz, 3:54 PM 4/24/2003]

BQuicksilver

Good question, but I had to laugh since I knew exactly what you did once you used the word "distal" to describe your exhaust. :lol:

Closer_2001

My old 01 Coupe MN6:

Dyno w/ Donaldson: 328 RWHP/343 RWTQ

Dyno w/ Donaldson, Thermostat, Z06 Ti, hollowed-out Pre-Cats: 326/348 RWTQ

Not really much difference, but I loved the change in sound!!!

BQuicksilver

Just curious, has anyone done the opposite? Left the pups in and taken out the mains? Or would that just be the same as using an X-pipe?

Leadfoot77

some people say that taking out the pre cats causes turbulence and other minor problems...is this true?

JWD01

I don't see how this could be true. All you're doing is removing a large obstruction from the flow of the exhaust. I noticed that it was a little throatier and it seems to pull harder above 3000rpm. Just my $.02.

Mike Mercury

they're guessing... or trying to make facts out of generalized common-sense thinking. And that's OK, as long as it is labled as such.