Howdy all. As stated, my engineers and I are going round and round together about the necessity or actual performance of high-flow cats. I have equal number of guys saying they are helpful, and those that say no. I'm tempted to, instead of purchasing expensive aftermarket cats, modify a set of stock cats that Mr. Schwing has lying around (*hint hint* Steve). Whether it'd be punching them out, or building my own filter screen, I don't know.

The other debate is whether or not to do a Y-junction behind the cat at all. There are a few of my racing peeps who feel it would save weight and be equally as efficient to run one single pipe all the way, then split it into two at the muffler-exit to retain the dual-exhuast look we have now (which I prefer). Any thoughts on this?

Any thoughts or preferences on what brand or company of muffler to use as well? If I go with an after-cat Y-split (like we have stock), I will probably install 2 mufflers in line with each exhaust pipe.

I will eventually perform the downpipe swap, but I just don't have the money now, and 99% of this project will be custom fabbed by me and a couple buddies at their race/performance shop locally and my home. Until then, the stock downpipe will be there, but the exhaust diameter is negotiable right now to set up for future DP modding. I'm assuming 3-3.5" pipe will be appropriate, but would there be any benefit to 4"? This is presupposing it'll fit of course.

I might have some more questions, but they are eluding me at this hour, so I'll chime in more if anyone responds to this book I just wrote.

Thanks everyone, I'm looking forward to your input on my next project for the TIE FTR!

 

I have no clue but I want to see what you guys come up with... keep us informed

 

Basically you're only going to flow as hard as your downpipe will allow you to. Since you're going to keep the factory DP, you won't see any benefits, just a change in the exhaust note.

I plan on switching to the Milltek cats here in a few weeks, behind them I have a 2.75" custom system. Basically the only restriction I'll have left is the factory downpipe. Ideally I'd love to go with the 42DD, but as you said, the cash is a factor.

My thoughts on your system would be to obtain a set of OEM cats, cut out the cats, save the Y-pipe and the flanges. Find something ala Magnaflow cats and mount them on the y-pipe with flanges. This way you'll be OEM compatible and at the same time have hi-flow cats in the process. Check out the spun catalytic converters at Magnaflow, they're new, and it's supposedly what's coming on the 42DD. The nice part is that they make one (59906) that's offset so you can theoretically go side by side to fit your y-pipe.

<img src="http://www.car-sound.com/02product/parts/59906.jpg"><ul><li><a href="http://www.car-sound.com/02product/universal/599spun.asp">http://www.car-sound.com/02product/universal/599spun.asp</a></li></ul>

 

Increasing pipe diameter decreases velocity of the exhaust gas, additionally, a lower flow of exhaust gas also decreases the pressure drop, or back pressure on the engine. What I do not know is whether or not the engine requires a certain amount of back pressure.

I am certain that whoever makes catalytic converters knows for a given set of flow rates what the pressure drop through the unit is.

I just don't think you can make a knowledgeable decision without better engineering data.

 

back pressure is quasi irrelevent on FI cars... Dp's provide will still be most restrictive

 

The most I'd EVER do for the catback is 3".

I ran 3" DP, 2.5" cat, then a 2.3" straight pipe on my 1.8T GTI and IMO it was perfect.

FYI...3" will be quite loud.

 

Getting by the haldex/rear subframe area is already a pain when i was under there, since the car is lowered that is one of the points that scrapes a lot and its a tight area. I'm going to bet getting two smaller pipes through there could be harder.

Your call

My advice, get a small 14" or 12" muffler and copy the borla exhaust setup. Good, clean, simple idea and it works.

Goodluck