Cat vs Test Pipes & Power

[DrBrown]

Okay boostheads I need some experienced advice. I currently have a 2.5" turbo back w/ test pipe exhaust making around 300whp 310trq. I do intend on trying to make as much as 340whp and my ### state requires emission testing. Theres a nice $500 fine for driving w/out a catalytic converter so I want to build a real street legal exhaust. My plan is to go with a 3" high flow cat like a magnaflow or catco and build a 3" mandrel catback to free up the backpressure from adding the cat. Have you guys had any good/bad experience using high flow converters with turbos? Ive heard from some folks that the rich conditions can burn out the ceramic core. I dont want to waste $100 on a cat but I do need to get a legal exhaust so I can pass emissions. I dont want to loose too much power from the cat so I thought the larger dia catback would at least reduce the power loss. Im also curious what it will do to the lag issue even if its a large 3" cat. If anyone can share some expertise on the subject I would appreciate input. Thanks in advance!

 

[blackGSX2g]

I used to run a 3" high flow cat with my RNR exhaust, then swapped to a different RNR 3" without one and didn't notice a difference at all in performance, spool-up, etc.

Yes, running rich can cause the converter to overheat as will running leaded fuel (race fuels).

 

[turboglenn]

run your test pipe with leaded gas or if you're pig rich adn need to tune it down a bit ( or you can just stink like sulfer from teh cat with an overly rich situation)

but anyway, we did this ona friends car in VA because they "inspect" the vehicle. We ended up gettting a 4'' highflow cat ( it was summit or jegs we ordered from) and welded that inline on his car. It was a turbo 2.3 ford mustang SVO, but with teh large 4 incher we didn't noticve hardly any power or spool; change.. now when we put the stock one back on just to see, we about died laughing with how weak teh car was.... Get a good cat, as long as you have over 55k miles on your car, you are allowed to change the cat by federal law

And for 500 dollar fine for driving wihtout a cat where you live...believe me , if the federal law catches you it's a MUCH bigger fine.. i think it was 2500 for car owner and i know it's 25,000 dollar fine for a shop to remove it and get caught. That's why i give people there test pipes and have them put them on them selves and i right up a receipt for "misc part: off road use only" that covers my a$$ as far as my business goes..

I know( or should say knew) a shop here in omaha that went out of business for building "cat-less" exhausts for people, the EPA got them and fined them 25,000 dollars and they were forced to close up shop from going broke.

 

[crimsondragon]

I thought it was a federal violation to change cats unless it was approved there was something wrong with the old one? I always figured I shoved a pipe into mine, bring it to a shop, and have them issue me a new high flow one.

 

[Avionixx]

Anyone read here read Import Tuner? In one of the latest issues they had a 240SX with a SR20DET swap and were trying on some basic bolt on mods to see how much more power they could get. In the very last part they swapped in a test pipe in place of the catalytic converter and picked up 7WHP. Don't know if the butt dyno would notice it, but definitely not worth it for a daily driven street car.

 

[1992awdlaser]

I thought it was a federal violation to change cats unless it was approved there was something wrong with the old one? I always figured I shoved a pipe into mine, bring it to a shop, and have them issue me a new high flow one.

That is the law for shops. A person can legally change their cat at their house without getting in trouble. A shop like you mentioned needs to determine the cat has a problem in order to change it. A test pipe being put in place is obviously illegal as I am sure you know.

A test pipe in place of a cat will typically yield a 5-8hp gain. So, it would depend on if you think it is worth it or not. I have a test pipe and will never have a cat on any of my cars that I want to go fast. My truck on the other hand still has all 3 cats.

 

[crimsondragon]

Ah sweet deal. I'm gonna fab up a custom exhaust soon and this is good to know.

 

[daren_p]

I have only ran mine with a 3" HF cat, so I don't know what difference a test pipe would make but I don't think the typical gains would be huge compared to a good, high flowing cat (but yes I do agree there will probably be some nice gains vs the very restrictive stock cats).

One of my buddies had a straight downpipe & ran that for a summer or so then swapped in a 3" high flow cat. I'm not sure if he did any before/after logs but he told me that the car felt faster after adding the cat, so.....?

 

[talonalex92]

Personally, the only difference ive seen in all my cars, is sound. If you dont have the cat, your going to sound like a dumptruck. If you do, you wont. This is all based on my experience with dsms, and all 3'' TBE with no resonators, just a can style muffler.

 

[1992awdlaser]

Personally, the only difference ive seen in all my cars, is sound. If you dont have the cat, your going to sound like a dumptruck. If you do, you wont. This is all based on my experience with dsms, and all 3'' TBE with no resonators, just a can style muffler.

My car doesn't sound like a dump truck with my 3" Buschur turbo back and test pipe. It did once I was running open down pipe though.

 

[turboglenn]

If i knew the ONLY thing i would lose by putting a cat on would be 7hp and not loose ANY spool, or any other back pressure related issues, then i'd have one on order tomorrow!

 

[fourreGsixty3]

Super ZStreet, or Modified did a test with a stock cat, test-pipe, and high flow cat. The test pipe only made +1hp vs the cats. If you face a fine I'd grab a hi-flow one, and you will never notice a difference, besides in your wallet that one time you get fined.

 

[hereitcomes]

I was just going to post that...the test was on a 2000 Si and yes, they only gained 1 HP. Might be slightly different on different cars...but theory is the same for everything. I dont use a cat, but lots of people do - so just install one. Then you wont have to worry.

 

[1992awdlaser]

Was the si turbocharged? Probably not. And as you probably know turbo 4 cylinders gain more power from an exhaust than a n/a 4 cylinder.

 

[hereitcomes]

No it wasnt turbo, and yes I know the gains. I got about 30 from my stock to full 3" Turbo back SS custom exhaust. Greatest feeling ever.

EDIT: well..not really 30 : ) but close

 

[1992awdlaser]

I know what you mean with how it feels. Once I put my 3" Buschur turbo back on it was nuts. This is the first turbo car I have owned and I was like how does this gain so much just from an exhaust? I now know why though. It felt as fast if not slightly faster at 70% throttle or so with the exhaust then it did with the stock exhaust at 100% throttle. I couldn't push it anymore then that with the exhaust because of boost creep.

 

[dalatinromeo]

My car doesn't sound like a dump truck. And at idle the car sounds fairly quite. The only time it sounds super loud is at WOT.

I order my exhaust from Extreme Motor Sports. Its a down pipe that just slides into the cat back. No cat no test pipe. Love the sound