Has anyone sawed off their cats and had a shop weld on straight pipe? I did this on my Viper and it was probably the best bang for your buck upgrade ever. I never dyne's it afterwards but I'm almost sure I gained 15hp and it cost $200.

Im curious:

1) How does it sound?
2) Does it improve throttle response?
3) Hows the smell?
4) What can I expect the HP gain will be?

I hear the cats we have are quite restrictive so just want to see if anyone has done this with positive results.

Thanks!!!!

 

not that I have heard of. There are some on the board who replaced out the restrictive cats with 200 cell high flow cats with very positive results. Responses with the 200 cell cats:

1) Deeper and louder. Some have exhausts as well (mine Quicksilver) and its almost too loud. I would imagine straight pipes would be almost too loud.
2) Noticeable improvement in throttle response just with cats.
3) Smells a little more like unburnt fuel at times. Not bad though.
4) See attached for before/after dyno. Believe 18RWBHP gain and solid gains across range.

Most importantly IMO it leaned out the AFR. Car originally was very rich before exhaust, filters and power pack (10), now running a much leaner 12 at WOT high in revs.

 

Do not just weld in straight pipe, replace with 200 cell race cats.

 

I imagine cost is a part of the question you're asking but my concern would be what would you do when you needed to take the car for emissions testing (long term) and (short term) am guessing that removal of the O2 sensors would throw continual engine codes at you. Not sure if any would push the car into limp mode, if so that would be untenable.

Consider the cost of having to remove the pipes and refashion the flanges for reattaching the stock cats for emissions testing and resale into your equation.

 

The sound is A LOT louder. If that's what you're going for along with a bit more bhp, then it's a good mod.

 

Thanks guys, I think Im gonna do it, Ill post some vids after I do. Thats pretty impressive dyno results from something as easy and inexpensive as this. Im sort of surprised more guys aren't doing this. Does the volume bother people that much? It seems the pros far outweigh the cons and it would be pretty easy to reverse if need be. Am I missing something?

 

Most ppl aren't doing this cause they have emissions, they can't be bothered with swapping them out each time..and on a V8, it just stinks, sure, had cat deleted on my car and you can get used to the smell but chicks don't dig it(had to keep my A/C on recirc)..and really whats the point of owning a sexy car if you can't get a chick anywhere near the thing when it's running!! ..at least on the V12 you have 4 upstream cats that are o2 monitored and 2 dowsnstream un-monitored, but the V8 there is only the 2 cats which are O2 monitored

 

As long as you are willing to attach the rear O2 sensors into the straight pipe, there are at least 2 solutions that will keep you OBD emissions safe. If you have a visual inspection, you'll need to have the appearance of a Cat.

 

By installing the downstream sensors into a straight pipe will give you P0420/P0430, simply because the downstream will now be mirroring the upstream reading..thus codes are flagged and engine light comes on. To get around this you will have to find a simulator for the downstream sensors. Then even by making the straight pipes look like cats(or just simply hollowing out the cats)..you will fail the Nox gas test for they will be to high. If you have no emissions in your area..this is possible, but for a emissions area, not worth the hassle

 

What car & MY do you have?

 

The gains with the 200 cell cats are very good. I believe the fact that the really lean out the rich AFR has a lot to do with it.

Cons may be cost or noise?

 

The difference between high flow 200 cell cats and straight pipes is only 1-2 HP max, and it's not worth all the negatives you have to deal with. Just buy high flow cats, it's worth the little bit extra cash I can assure you.

 

2006 v8v

 

That a good point, i wasn't aware the difference was only 1-2 HP, cost difference however is a different story.

 

I have used the following 2 solutions on my aston martin.
1) Add mini-Cats from bigdaddiesgarage.com to the rear O2 sensors. This will bring an Index ratio of .7 or .8 down to .1 or .2
2) Change the Index Ratio in the PCM from .396 to .999 and you will have no more P0420/0430 codes. Both Index ratios are side by side and easy to find as long as you have access to the binary and know where/how to look. RSC knows.

You way fail a sniffer test and a visual inspection but OBD2 will be as happy as a clam.