So I am about to start putting together custom exhaust for my 99 d2. Has anyone tries ising High flow cats? If so how did it go?

 

I had a 3" hiflo on my Audi wagon back on the day, certainly helped the turbo breathe along with high rpm pulls on the fwy. It did cause a CEL but i'm sure tuning has come a long way in the last 15ish years so i doubt that would be a concern anymore.

For a stock 4.0, 3" is probably a little over kill but a nice 2.5 or 2.75" system can help the engine breathe better while not losing low end torque.

 

Im sure you know how picky rovers can be, I'm really looking for someone Who has done this on a d2

 

I doubt anyone has really done high flow cats on these trucks -- certainly replacement cats but not high flow. There isn't really any point with the massive 188hp these engines are putting out.

 

I'm sure you are right but no harm in asking. It would help it breath easier, the only thing is will the light come on lol

 

I did high flow cats, long tube headers, 2.5" dual into a single 3" with a borla muffler. I'll be honest, it's not worth it if you're going for more power. You'll notice zero difference until you do long tube headers, and even then it's not really worth the cost, not to mention trying to keep them from leaking.

And "high flow" cats don't matter in today's time. All modern cats are "high flow", as that terminology is in reference to the old style cats used mostly thru the 80s which were actually a big drain on power.

In today's time, even with stock cats, as long as the pipe diameter is large enough you won't notice a power difference with cats till you're getting into the 800+ horsepower range.

 

Did you have any check engine light issues with the cats

 

No, no check engine lights. I've used Magnaflows, Flowmasters, and Chinese cheapos of Amazon all three with equal luck.