Cat before turbo?

[MissingMyBuick]

I was told by a friend that his sister in laws boyfriend has a Subaru WRX. He told my friend that it has 3 catalytic converters, 1 before the turbo and then 2 after. This doesn't make sense to me. Wouldn't a cat before the turbo rob the turbo of a lot of heat and energy that it could use for more boost and faster spool times? I am no expert on this, but I am sure some of you guys are. Please enlighten me. I was also told that the WRX's are 0 emission cars because of this. TIA

 

[fitz3820]

Cats before the turbo provide a shorter "light off" time to get the cats hot so they can do their thing. Cold cats do not do the converting and thus cars produce the most pollution the first few minutes after start up.

A turbo converts this energy (aka. heat) into rotary motion and thus absorbs some of the heat needed to get the cats working.

Yes they are restrictions but cars are making more power than ever and are much cleaner than ever too.

The scooby wrx isn't a 0 emmisions car, no car is - even electrics have emissions, they are just from a power plant someplace else...

Mark F. 87 GN 11.9 @ 115

 

[MissingMyBuick]

So the WRX could definitely benefit from a straight pipe instead of a cat before the turbo? Those cars would be quick if you got rid of all the cats. I was wondering about the 0 emissions thing. I didn't see how that was possible. Maybe that is just what they are considered since they run so clean. My friend who told me this works for Ford as a mechanic, so I know he is no dummy. He is smog certified among many other certifications. Also thanks for a quick response. I just learned something new today.

 

[bruce]

Originally posted by MissingMyBuick
So the WRX could definitely benefit from a straight pipe instead of a cat before the turbo? Those cars would be quick if you got rid of all the cats. I was wondering about the 0 emissions thing. I didn't see how that was possible. Maybe that is just what they are considered since they run so clean. My friend who told me this works for Ford as a mechanic, so I know he is no dummy. He is smog certified among many other certifications. Also thanks for a quick response. I just learned something new today.

The old quick answers sometimes aren't the answer anymore.

With the advent of OBDII, the ecms/pcms are MUCH MUCH more elaborate in self diagnostics. that large of change in backpressure, and effects on the O2 reading might trigger a malfunction code. And without some tweaking of the calibration, I'd wonder what the real gain might be.

Often 0 emissions, just means they are just generated at a remote location. It's the EPA of misleading people into thinking they're doing something good when in fact they might not be. It takes X HP to move a vehicle so far. If you use coal or gas to make the electricity, there is little difference in emissions from just using gasoline to make the same amount of HP.

 

[monte_383]

I can confirm that the WRX does indeed have 3 cats, having removed all of mine. The first one before the turbo, the second in the downpipe right after the turbo, and the 3rd just downstream of the d/p (more conventional location). De catting is usually the first and cheapest mod on these cars. The car responds well to swapping an up pipe (which houses the 1st cat on these) and a down pipe. And on the zero emissions thing, I think its just "low" emissions or LEV status, for the US market anyways. HTH's -Chuck

 

[monte_383]

bruce,
The primary fueling trims are taken care of by a quasi- WB o2 (reads down to ~12.5) in the manifold, before the "up pipe".
Some folks have had MIL come on with removal of one cat, others have had no MIL with removal of all cats. There's a plethora of MIL eliminator kits available (pony express is common and like $15) for the second o2 sensor. I haven't had a problem with mine as far as a MIL goes, but I took a mechanical approach to "slow" the response time of the second o2 sensor, rather than an electronic fix. I have a piece of 1.25" pipe about 6" long that makes an elbow (kinda an L shape, short leg welded to the exhaust, with the o2 bung in the longer end). Been that way for 10,000 miles now with no MIL. Also have engine management to take advantage of the better flow characteristics of freeer exhaust.
Prolly gonna do the same trick on my brothers '96 SS Impala when he decides to put different pipes on. -Chuck

 

[MissingMyBuick]

Monte-383, Yeah, my friend told me that they replace the "up pipe", I just forgot what it was called. I remember thinking Up pipe, with a cat? In my experience with cars, an up pipe is usually an intake pipe ( intercooler to tb on GN's ). About the power gains, how noticible was it when you replaced the up pipe, and then the other two? Did you do them all at one time. What other mods do you have done it? Also do you have any times? Sorry about all the questions, I love those cars and I am just curious about them and how well they respond to bolt ons.

 

[monte_383]

MMB- I knew if I said "up pipe" on this forum w/o explaining I'd cornfuse a few. The same terminology is on completely different ends of the turbo in this case. When I did mine, on the stock turbo, I actually changed the downpipe first, which made a rather nice difference. Also made the turbo whistle more pronounced. That prompted me to drop the up pipe, but it didn't feel like it gained as much, course I still had the 3rd cat in place at the time. Took it to a muffler shop and had them build 2.5" exhaust from the downpipe back, and that seemed to help quite a bit. I couldn't justify spending (at the time) $1300 for a cat back exhaust system when the guy local to me could do it for $150 installed. No it's not fully polished mandrel bent stainless titanium plated with a fat 4 1/2" carbon fiber lighted tip, but it's very functional and I'm happy with the gains.
For mods as of now, have a small Garrett T3/T4 to replace the tiny stock Mitsu TD04, custom up/down piping (made by me), 2.5" exhaust from the turbo back, Turbo XS UTEC piggy back controller (allows programming of boost, fuel, timing values in open loop), and DIY water injection (triggered by the UTEC) for the 18-20 psi runs I like to make now and then. The rest is stock, I change the oil and filters and thats it. HTH's -Chuck

 

[MissingMyBuick]

Monte, That's Sweeeeet!!!

Your car must fly. No times? I know not everybody is into drag racing, but I'm just curious. I have seen some at the track running anywhere between low 14's to low 12's. One other thing, how is the cost of a regular WRX like yours including the mods you have done compared to a WRX STI? I'm sure yours is putting out the same numbers as the STI. And you have water injection also. By the way I think it was a great idea for Subaru to install factory water injection on the STI. But the cost of the STI is probably not worth it.

 

[monte_383]

No track times, and here's why : A. taking it easy on the trans (5MT, not known to be durable with higher than stock power), B. The closest track is about 100 miles away, C. no truck and trailer if I break something, D. scared to see that it's not really as fast as it feels, cause I know it ain't.
The STI has a factory water sprayer for the intercooler (shoots water on the outside of the IC, mine sprays inside). It would be great if it was making the same Hp as an STI, but I'm in the middle of nowhere, road tuning by myself, working on the cheap. Total costs for what I've added is prolly around $1500. Looked at an STI at a dealer in Columbia MO for $39K (that's with a $10K markup, they are nazi's down there) , I paid $25K for my WRX, I'd trade if they were $29K. I do most of the work myself, called in a favor or two from vendors here at work, and studied a lot before I changed stuff. I'm still learning in the tuning game, be interesting to get it dynoed to see how I did on my first attempt. This is my first car with fuel injection, all the ones before have been carburators. Even with the limited amount of stuff I can change, I really like EFI. -Chuck

 

[MissingMyBuick]

Oh your just trying to be humble on the part about it not being as fast as you think. I bet it can run at least low 13's. Are there modifications you can make to the tranny and the rest of the driveline? That sucks about the STI water sprayer, I thought it was actual water injection like yours. That makes yours better. Hey you could mix in a little Alcohol and it might be even better. Also sounds to me like your doing a pretty good job with your car considering it's your first EFI car. Good Stuff!!!!