So I refuse to run a test pipe. But with my aquamist and FPred, my cat is starting to really rob power.

I have a Mil Spec 100cell that’s going in the car next week.

At BEST, I suspect it will still take 5%. At 500whp, that’s 25whp.

Assuming I can make it fit, I think I’m going to attempt a dual cat setup, see MS paint drawing below :



Thoughts?

 

Test pipe with CEL fix, they make test pipes that look like a cat if your afraid of inspection.

 

You could also gut the stock cat, and bolt the shell up around the test pipe. That way you get straight, unrestricted flow, with a stock cat appearance.

 

You will not gain or loose any power providing the inner diameters are the same and the cell count is the same. In the end you are still forcing the same amount of air through the same space and creating possibly more turbulence as well.

 

My goal is to not pollute as much. I know could run a test pipe and probably never even get caught or make a cat looking test pipe.

My goal is to make cleaner power.



The inner diameter would go from 3inch to 6inch overall. There would be the same amount of air with more space for it to flow. Think about if the cat restricts/takes up 66% of the 3 inch pipe, that gives the air 33% or 1inch of an area to flow through. Multiple that by two and that same air now has a 2 inch opening.....

Thanks for everyone's initial thoughts.

 

you remind me of an old friend from my vw days. and man do i miss it. check out his smog friendly build, def worth reading through.

http://forums.vwvortex.com/zerothread?id=4490090

 

I have always wanted to do the same thing, since I don't run a test pipe either (both for smell/pollution as well as sound). I run the stock cat back with a high flow cat and I have an e-cutout, but I barely ever use it. Keep us posted if you ever do it.

One of my concerns would be the space available to fit it. If you do it, post up some pics and maybe some before and after logs or dyno runs.

 

I was considering doing this very same thing instead of using a muffler. I was going to use twin 2.5 100cell cats though to keep it compact. the cells would be staggered instead of side by side.. the cats are very light. should work very well. the 2.5 cats have same cat as 3.0 does. twin 2.5 is like one 4 inch tube. plenty of flow..

 

The y-pipes, especially the one that splits the flow, will need to be a good design to keep from robbing power.

 

Haha, that's an awesome thread! CA emissions prob would make for some creative stuff.

Yeah, space will be the only factor. I'm thinking about welding the two cats two each other just to minimize space.



I can't imagine the Y-pipe doing much damage at all. It wouldn't be any worse than a bend and considering the overall diameter doubles, it may be better.

 

you are forgetting that while your two cats are each 3" in diameter, you still have the same single 3" bottleneck if you will at each end. Because the airflow through the cat section will be increased by the doubled cat area, you will reduce some backpressure, but the point that I'm making is your gains will not be worth it. Not too mention you now have a huge cat to fit under the car.

 

Get and 3.25" cat and pipe a 3" threw the middle of it

 

your better off either getting a 100 cell 3" cat or getting a larger single 4"-5" cat.

 

This.

Or this.

 

I understand your point, I just don't understand why you feel that way?

If you consider the entire post turbo exhaust system (or even in some respects, the entire intake to exhaust system) the cat is doing some major restricting. If you double the capacity of that restriction, how can it not free up flow?

If two 3inch 100cell mil spec cats can flow more air than a single 3" test pipe, the restriction (minus the Y bend -which again i don't think will be even measurable) will vanish, freeing up 5% in hp...


As i mentioned, I have a 100 cell 3" cat ready to be welded into a test pipe, but these cats still restrict hp...



Does anyone have any under-the-car pics so i can brain storm at work today?