Decided to spend a few hours today wrenching on my CTTS in order to install a secondary cat bypass kit.

Put the beast up on the lift and checked out what needed to be done - looked pretty straight forward. Everything was smooth sailing until it was time to loosen the nuts securing the secondary cats to the downpipes. Four finally came loose, but I did have two that refused to yield. One snapped the stud in the cats' flanges and I ended up having to cut the other one:



To actually install the pipes, I upgraded the supplied hardware to metric stainless steel bolts and factory gaskets and copper locking nuts (SAE non-metric supplied with pipes). No chance of the lock nuts backing out unlike the supplied nuts. It was very much easier to install than remove. The secondary pipes save just over 10 lbs. on each side versus the catalysts they replaced. (i.e., 4 lbs. versus 14.5 lbs. each). The center cross member weighed just over 11 lbs., so it wasn't too difficult to remove. Everything else required standard tools, but an air gun makes quick work of many of the bolts. I used a screw type telescoping jack stand to support the transmission while the cross member was removed as shown here:



Here's a shot of the driver's side installed:



The passenger side:



And from the front looking towards the rear:



All clearances were good, and just to give the job the finishing touch it deserved, I replaced both corroded slip pipe clamps at the rear of the bypass pipes.


The results:

The exhaust note at idle is now simply perfect. Very noticeable, but not close to being obnoxious. Before, you couldn't even hear the engine running. During the intitial drive, I immediately noticed better engine response and apparent power gains - like the engine had been uncorked. I really didn't expect the amount of difference the secondary cat bypass pipes made, but they result in a very noticeable improvement in driveability.

All in all, I'm going to give this simple mod a double thumbs up for the CTTS. Makes the beast even beastlier. Highly recommended.

 

who made you sbp's?

also, as you stated, uncorking turbo motors makes a substantial difference, intake and exhaust. id wager that

 

They're the Leistung bypasses. No wagers on benefits of uncorking the engine.

 

Similar experience here. I ended up cutting off all,of the bolts as,it was easier. I like the mod!

 

did my secondary bypass Leistung pipes myself. Found a nice way to get at the top bolts. Easy but takes time.

 

what, no pics?

 

Please explain more

 

No pics since I was getting down and dirty with the install. Was going to, but as i got involved, decided against it.

I did:
COMMON INITIAL STEPS:
- unbolt the bottom covers
- spray penetrating oil onto cat flange bolts as much as you can
- unbolt secondary cat hangers (2 per cat)
- support transmission with a jack
- remove center bolts from cross member
- remove cross member to chassis bolts (4) move cross member out of the way
- loosen sleeves connecting second cats to mid pipes (1 per cat)

THIS IS DONE PER EACH CAT:
- loosen bottom two bolts at cat flange
- slide off one cat-mid pipe sleeve, move the cat pipe enough to create space to get at the third flange bolt - becomes easy to get to with lots of space, just be gentle
- once all flange bolts are out, remove cat
- use screwdriver (flat) to place into the hole of cat hanger bushing, and at same time start rotating hanger bushing so that it goes over the hanger bump, to take off the bushing from old cat. Do this for both cat hanger bushings
- slide hanger bushings onto new cat at in same orientation/side for each bushing
- clean flange at flex pipe and at new secondary cat
- make sure surfaces are perfectly flat to mate
- make sure the new gasket for cat/flex pipe mating is perfectly clean and flat for good contact
- use new nuts/bolts to finger tight connect flex pipe to new cat pipe while (keep the rear of new cat undone so that you can get at the top flange bolt easy
- use socket/wrench combo to tighten each of flange bolts down decent (until one side of nut/bolt does not rotate when you use wrench on the bolt - I installed mine with bolts facing towards ground)
- attach rear of new cat to mid pipe by sliding sleeve onto it
- use bolt to attach outside cat hanger bushing to chassis to help with tightening down of flange bolts
- use socket or wrench to complete tightening flange bolts for the cat - wrench gives easy access to nut for top bolt now without rotating of the bolt
- tighten sleeve bolts while forcing the new cat pipe rearwards to get as close as possible to mid pipe, and pushing pipe upwards. This makes the pipe tenser and more rigid when installed, helping to prevent vibrations, etc and get more clearance above the cross brace after install

REPEAT ABOVE SECTION FOR SECOND CAT PIPE

- make sure all outside cat hangers are bolted down
- re attach cross brace to inner cat hanger bolts (at this time you will have cross brace attached to cat bushings with bolts (4 bolts total)
- install cross brace chassis bolts (outer - total 4, do not tighten yet)
- install center cross brace bolts and tighen (may need to move tranny support up/down - be gentle not to move a lot, only enough to align holes for bolts)
- tighten down cross brace to chassis bolts (4)
- reattach bottom covers
- clean up tools
- tell wife car was about to explode but you found a way to fix it and saved her $5K in money
- clean yourself up - trust me this one wont be as easy as the work you just did...lol - wear long sleeves and mech gloves to help offset how dirty you get
- a beer is in order now....DONE.

 

thanks for the explanation, will try this when i do the cats on mine

 

Stainless steel fasteners are notorious for galling if the nut is chosen to be the same alloy as the bolt. Galling is molecular welding, where the bolt must be broken to get it off. Suppliers of stainless equipment usually choose a nut of different mtl, like silicon bronze, to prevent galling.

Even if done that way, exhaust fasteners run so hot that after a few years, they may be sufficiently corroded to be very difficult to remove.