Jump to content
LegacyGT.com

Why not just replace stock Up pipe and third Cat?


sashadg1

Recommended Posts

Really here why not just replace the Stock UP Pipe with a STI Catless pipe, run a Catless Crucial Midpipe or run 3" Exhaust all the way out from the Stock Catted Downpipe, Run Stage 2 Software leaving the Stock Catted down pipe in place. I understand a HFC will flow more, however I can't see getting a neck snapping night and day difference by using a HF Down or using a stock down while getting rid of the two other Cats. I can't see getting more than 5 to 8 HP between the two. Am I way off here guys. Both are going to restrict, one just a little more than the other right? Here is my thought On a budget ,Replace the Stock Up with a STI Up, leave the Stock Down, do a full 3" Exhaust back from the Stock Down Pipe then run a TDC Stage 2 Program.

Help me understand why this wouldn't work?

 

Thanks Scott

Link to comment
Share on other sites

  • Replies 62
  • Created
  • Last Reply

It would make more sense to just get a sti uppipe or invidia and get a dp (crucial shorty etc..), thats a little over $400. The full exhaust back from the stock dp would not yield you much if any hp. Theres much more power to be had if u replace the stock dp and up. Forget about the rest of the exhaust especially for cost benefit.

 

 

I keep restricting myself from going stage 2 :( only 400 dollars.

Link to comment
Share on other sites

So you are telling me the third Cat is not very restrictive?? If it's a real cat then it has the honeycomb crap and will cause a decrease in flow and turbulence to say the least. The work involved changing the Downpipe and the $400.00 extra dollars seems like a waste when a whopping 5-8 Hp is all to be achieved. Also by leaving the Stock Down in place you also will pass most any Spot check for us in California especially if you got some noise.

Somebody give me some real numbers that could sway me. If I was told 20 HP could be achieved by swapping the Stock Catted down with a HF catted Downpipe then I would probably go for it.

 

Thanks Scott

Link to comment
Share on other sites

Why don't you PM Cobb, PDX, or TDC and they can tell if and why that won't work. They are tuners and now more about this stuff then you, I and most people on this site. I Just ordered a AP and TDC map from TDC. I trust them to know the best way to go to stage 2. I already have a UP and will get a shorty DP in January. I will keep the third catt to cut down on the smell.
Racer X FMIC for '05-'09 LGTs, '08+ WRX and '10+ LGT,'14+ FXT, and '15+ WRX TMIC Racerxengineering.com
Link to comment
Share on other sites

Is the third cat a true full operating Cat? These cars have O2 sensors before the 2nd cat and after it not after the third cat which tells me it's not measured, more like icing on the cake for emissions. The First and Second Cat seem like ones that do the most work burning the unspent fuel not the third Cat. This will surely throw CEL's removing the Up and Down Cat's and leaving the third Cat. Leaving the Second Cat in place which is measured before and after will get very normal levels of gas fumes opposed to the third Cat doing all the work. I would imagine you may have to replace it a lot sooner than normal because of the heat lost between the Turbo and Third Cat and it's ability to reach temps to burn properly and then to ask it to burn everything? Tell me I got thinking.....

 

Scott

Link to comment
Share on other sites

One thing I did forget about all this is the fact the stock down pipe or second cat is bolted right to the Turbo which is very bad because of all the turbulence it causes and the Turbo can'the be very efficient fighting to flow slamming headon into honey comb wall. My fabricator always told me have a catless Downpipe and move the cat farther down to allow the turbo to spool up first and gain velocity before smacking the honey comb wall. He said that's were the power is and the gains are more substanial. itsme may have something by keeping the third Cat, only my concerns are still what will happen with CEL's and the 3rd cat getting overwhellmed trying to burn everything by itself.

Scott

Link to comment
Share on other sites

You know you want to spend the money VTGT. I will help you do the install.

 

hehe so tempting. you need an AP!

 

On another note, If you want the cheapest way a lot of people on here have had success gutting all the cats. I'm pretty sure your leaving 5-10 hp on the table by not buying a crucial or some other aftermarket dp.

Link to comment
Share on other sites

This is good to know, Can anybody speak on the other issues?

 

1.(I would imagine you may have to replace it a lot sooner than normal because of the heat lost between the Turbo and Third Cat and it's ability to reach temps to burn properly and then to ask it to burn everything?)

 

2. Using a 3" Catless DP joined to the stock 2.25" pipe (or whatever it is) then into the third Cat then back into 3" all the way out would be defeating the purpose of keeping a smooth flow and probably would look like crapola.

 

I guess I will have to make that decision...

Money always stands in the way. Best bang for my buck is what I'm looking for.

I have 5 Kids!!!!!

Link to comment
Share on other sites

If you want bang for the buck either get the sti up or an invidia (anywhere from 100-150) and a crucial shorty (320). I think Invidia just came out with a full length dp(pre-order some where on the site) for 320 so u might be able to jump on that.
Link to comment
Share on other sites

I'm with Hoggers, though I'd "splurge" ;) on an already gutted WRX pipe ($50 or so). I'm quite happy with my budget exhaust. Stock looking and cheap, with only a little HP left on the table (3rd cat in place).
Link to comment
Share on other sites

What about selling the vehicle later down the line, will I have to buy new cats. My Passat needed a new one and it was $1400.00, thank god it was under warranty. Would anybody ever figure it out? What kind of trouble could I get into if they linked back to me?
Link to comment
Share on other sites

Is the third cat a true full operating Cat? These cars have O2 sensors before the 2nd cat and after it not after the third cat which tells me it's not measured, more like icing on the cake for emissions.

Scott

 

I am an idiot, see my later post...

 

Err, the third cat is the one with the O2 sensors before and after it, not the 2nd.

Link to comment
Share on other sites

you can buy a stock DP for $135 shipped. I got mine for that. It's good to keep stockers, just in case.

 

Oh I think you could get one for $50. Plenty of people don't believe in keeping the stockers around and are just looking to clear material out of their garage. At the $135 price point, you might as well go used aftermarket.

Link to comment
Share on other sites

huh?

 

1st cat = Uppipe (O2 sensor)

2nd cat = Downpipe (O2 sensor)

3rd cat = Midpipe

 

 

 

Yah that 's what I remember when nI was looking under the car. I made a mental note of that.

I figure I will but a STI Uppipe and gut the DP Cat and do 3" all the way out from there...

So No Cat's for me!!!

If the Stage 2 Cancels out the CELS then why not?

Oh wait a minute, what if I need to take my car in for any type of engine issues, I would have to put AP back to stock which would allow for CELs...

 

CRAP!!!

Link to comment
Share on other sites

Yah that 's what I remember when nI was looking under the car. I made a mental note of that.

I figure I will but a STI Uppipe and gut the DP Cat and do 3" all the way out from there...

So No Cat's for me!!!

If the Stage 2 Cancels out the CELS then why not?

Oh wait a minute, what if I need to take my car in for any type of engine issues, I would have to put AP back to stock which would allow for CELs...

 

CRAP!!!

You dont have to revert to stock. They cant really tell u have the flash. and you shouldnt have any engine issues, these motors go forever.

 

But you do live in Cali and you wont pass emissions if you are catless.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.




×
×
  • Create New...

Important Information

Terms of Use