Greetings,
I've learned much from reading posts on this forum, but I'm wondering what changing the catalytic converter will do for my car. Will the sound change? Will the gas mileage decrease further? Will it be quicker/faster? Will it pass inspection?

I feel my car is special now and it sounds like many here change to freer flowing cats to make it even better. I'd appreciate any comments--including why NOT to do this.

Thanks--

 

Changing to 200 cell, probably nothing noticeable + your post indicates that you already have the X51. For better info than our opinions go to http://www.randomtechnology.com/technical.html or contact one of our sponsors - Alex at Fabspeed Alex@fabspeed.com.

 

change to 200 cell cats together with flashing ECU with aftermarket software essentially allows for more agressive usage of increased air flow so it raises engine power and torque by means of pushng engine a bit higher temperature wise and emissions wise. non of that is dangerous.

on a stock ECU 200 cell cats will also improve ai flow obviously and it will improve hi revs power as well but not as much as if combined with ECU flash.

 

I agree with Utkinpol but also you should be aware that the exhaust sound will definitely become noticeably louder (by around 50% i'd say) but still retains good sound qualities, IMO.

I did the mod in the middle of winter (in combo with a bunch of others) and have been happy with it. Yesterday, though was the first day with spring-like temperature in many months (62 degrees), and I noticed that the oil temp hit 225 much quicker than it usually does in spirited driving.

I'm a bit concerned that when we get into real summer temperatures, I will have an overheating issue, so I'd like to hear from the guys with these mods whether that is a legitimate issue.

 

I had a 2007 T4S with PSE, X51 headers, and 200 cell cats, and never had any heating issues, even here in warm So Cal. I absolutely loved the sound. The cats are apparently the only add-on exhaust part that can actually add power. Can't say I felt it, but loved the sound, especially with PSE versatility.

 

i posted this graph before - what matters most is not how many actual horses you gain as it is a very questionable topic but how this changes stock curve shape - on a stock car, both c2 and c2s you have a nasty drop of 'torque' and power starting from about 6K rpm so essentially car does not pull properly after 6K. after cats and flash it changes and you get steady equal 'pull' in whole hi revs area from 4.5K to 7K.
in practical reality it makes a world of difference if you have to upshift at 6K or at 7K rpm.

 

I have ordered FVD headers, cats, and a ECU software upgrade cable. From your post, I'm heading to the right direction, right?

 

I'm in Texas (100 degree summers) with 100 cell cats (EP2) - never a problem with overheating.

 

Davidkuola, I'm considering the same upgrade. I'd like to hear about your results.

 

Partly right. Alex would probably know that this answer leaves something to be desired in the fact department.

 

When you change out exhaust components your not really "making power". In essence your freeing up power that is already there. The engine actually has to work to force exhaust gases through your headers, cats, and mufflers. Reducing this back pressure actually reduces the amount of effort the engine is exerting just to move gases. Furthermore, because you are reducing back pressure you are actually making the engine more efficient and thus, in most cases your fuel efficiency will improve.

Jason

 

Except that modern engines are carefully tuned to work best with the right amount of back pressure. It's not like old hot rods where you want the exhaust as free as possible. A lot of people who do exhaust mods actually wind up with less torque, you have to be careful about it.

BTW I understand the DFI engines are particularly sensitive to back pressure; that's part of why they used the 4 cat system.

 

Actually all engines are sensitive to back pressure. Your not actually reducing overall torque, your actually adjusting the curve. What your talking about is the associated loss of low end torque at low revs/engine speeds when you reduce back pressure on these engines or really any engine. At low engine speeds the intake and exit for the combustion gases requires a smaller opening/exit to be efficient... to get going.... the engine is sorta wheezing. Think about trying to suck up soda through a super big straw, to get going you need a lot of sucking force that simply does not exist. But due to the loss of back pressure overall peak output is improved, especially at the top of the rev band. That is why just about all Porsche race cars, that thrive at the top of the rev range, (GT1, M96, 9A1) tend to have straight pipes. This argument brings on the question of the practicality of a variable geometry exhaust system. I am sure the idea has been tried.

Jason